• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Table of Contents
 Introduction
 Symptoms and effects of melano...
 The cause of melanose
 Control of melanose
 Wettable sulfurs and copper sprays...
 Control of insects following melanose...
 Discussion and conclusions
 Spray schedules
 Acknowledgement
 Literature cited






Group Title: Bulletin - University of Florida. Agricultural Experiment Station - no. 349
Title: Melanose of citrus and its commercial control
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027741/00001
 Material Information
Title: Melanose of citrus and its commercial control
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 54 p. : ill. ; 23 cm.
Language: English
Creator: Ruehle, George D
Kuntz, Wm. A
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1940
 Subjects
Subject: Citrus -- Diseases and pests -- Florida   ( lcsh )
Fungal diseases of plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 53-54.
Statement of Responsibility: Geo. D. Ruehle and Wm. A. Kuntz.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027741
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000924580
oclc - 18218056
notis - AEN5207

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page 1
        Page 2
    Table of Contents
        Page 3
    Introduction
        Page 3
    Symptoms and effects of melanose
        Page 3
        Page 4
        Page 5
        Page 6
    The cause of melanose
        Page 7
        Page 8
        The imperfect or phomopsis stage
            Page 9
            Page 10
            Page 11
        The perfect or diaporthe stage
            Page 12
        Contributing conditions
            Page 13
    Control of melanose
        Page 14
        Previous melanose
            Page 15
        Experiments of 1932 to 1937
            Page 15
            Page 16
            Page 17
        Pre-growth sprays
            Page 18
            Page 19
            Page 20
            Page 21
        Pruning
            Page 22
            Page 23
            Page 24
            Page 25
            Page 26
        Bordeaux mixture 3-3-100
            Page 27
            Page 28
            Page 29
        Proprietary copper sprays
            Page 30
            Page 31
            Page 32
        Sulfur sprays
            Page 33
            Page 34
            Page 35
            Page 36
            Page 37
        Mercury-oil emulsions
            Page 38
        Zinc sulfate
            Page 38
            Page 39
    Wettable sulfurs and copper sprays combined for controlling melanose and rust mites
        Page 40
    Control of insects following melanose sprays
        Page 41
        Page 42
        Page 43
        Page 44
    Discussion and conclusions
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    Spray schedules
        Page 50
        Page 51
        Page 52
    Acknowledgement
        Page 53
    Literature cited
        Page 53
        Page 54
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida







UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
WILMON NEWELL, Director
GAINESVILLE, FLORIDA

MELlNOSE OF CITRUS
lAND ITS
COMMERCIAL CONTROL
GEo. D. RUEHLE AND WM. A. KUNTz-


Fig. 1.-Typical severe melanose blemish on mature grapefruit.

Single copies free to Florida residents upon application to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


Bulletin 349


September, 1940




EXECUTIVE STAFF BOARD OF CONTROL


John J. Tigert, M. A., LL.D., President
of the University"
Wilmon Newell, D.Sc., Director"
Harold Mowry, M. S. A., Asst. Dir.,
Research
V. V. Bowman, M.S.A., Asst. to the
Director
J. Francis Cooper, M.S.A., Editor8
Jefferson Thomas, Assistant Editor3
Clyde Beale, A.B.J., Assistant Editors
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Managers
K. H. Graham, Business Managers
Rachel McQuarrie, Accountants
MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist'
W. A. Leukel, Ph.D., Agronomist3
Fred. H Hull, Ph.D., Agronomist
G. E. Ritchey, M.S., Associate2
W. A. Carver, PH.D., Associate
John P. Camp, M.S., Assistant
Roy E. Blaser, M.S., Assistant
ANIMAL INDUSTRY
A. L. Shealy, D.V.M., Animal Indus-
tralist3
R. B. Becker, Ph.D., Dairy Husbandman3
E. L. Fouts, Ph.D., Dairy Technologists
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian3
N. R. Mehrhof, M.Agr., Poultry Hus-
bandman3
W. G. Kirk, Ph.D., Asso. An. Husband-
man3
R. M. Crown, M.S.A., Asst. An. Husbs
P. T. Dix Arnold, M.S.A., Asst. Dairy
Husbandman3
L. L. Rusoff, Ph. D., Asst. in An.
Nutrition
O. W. Anderson, M.S., Asst. Poultry
Husbandmans
SOILS
R. V. Allison, Ph.D., Chemists 3
Gaylord M. Volk, M.S., Chemist
F. B. Smith, Ph.D., Microbiologist8
C. E. Bell, Ph.D., Associate Chemist
H. W. Winsor, B.S.A., Assistant Chemist
J. Russell Henderson, M.S.A., Associate8
L. H. Rogers, M.S., Asso. Biochemist
Richard A. Carrigan, B.S., Asst. Chemist
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural
Economist'1
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
ECONOMICS, HOME
Ouida D. Abbott, Ph.D., Home Econ-
omist'
Ruth Overstreet, R.N., Assistant
R. B. French, Ph.D., Asso. Chemist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist'
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticul-
turist8
R. J. Wilmot, M.S.A., Fumigation
Specialist
R. D. Dickey, M.S.A., Asst. Horticulturist
J. Carlton Cain, B.S.A., Assistant
Horticulturist
Victor F. Nettles, M.S.A., Assistant
Horticulturist
F. S. Lagasse, Ph.D., Horticulturists2
H. M. Sell, Ph.D., Asso. Horticulturist2 3
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist' a
George F. Weber, Ph.D., Plant Path-
ologists
L. O. Gratz, Ph.D., Plant Pathologist
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Asst. Botanist


H. P. Adair, Chairman, Jacksonville
W. M. Palmer, Ocala
Chas. P. Helfenstein, Live Oak
R. H. Gore, Fort Lauderdale
N. B. Jordan, Quincy
J. T. Diamond, Secretary, Tallahassee

BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
J. D. Warner, M.S., Agron. Acting in
Charge
R. R. Kincaid, Ph.D., Associate Plant
Pathologist
Elliott Whitehurst, B.S.A., Assistant An.
Husbandman
Jesse Reeves, Asst. Agron., Tobacco
CITRUS, STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in
Charge.
John H. Jefferies, Asst. in Cit. Breeding
Michael Peech, Ph.D., Soils Chemist
L. H. Greathouse, Ph.D., Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Associate
Entomoolgist
W. W. Lawless, B. S., Asst. Horticulturist
R. K. Voorhees, M.S., Asst. Plant Path.
F. F. Cowart, Ph.D., Asso. Horticulturist
EVERGLADES STATION, BELL GLADE
J. R. Neller, Ph.D., Biochemist in
Charge
J. W. Wilson, Sc.D., Entomologist
F. D. Stevens, B.S., Sugarcane Agron.
Thomas Bregger, Ph.D,. Sugarcane
Physiologist
Frederick Boyd, Ph.D., Asst. Agronomist
G. R. Townsend, Ph.D., Plant Pathologist
R. W. Kidder, B.S., Asst. An. Husbandman
W. T. Forsee, Ph.D., Asso. Chemist
B S. Clayton, B.S.C.E., Drainage En-
gineer2
F. S. Andrews, Ph.D., Asso. Truck Hort.
SUB-TROPICAL STA., HOMESTEAD
W. M. Fifield, M.S., Horticulturist Act-
ing in Charge
S. J. Lynch, B.S.A., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist
W. CENTRAL FLA. STA.,
BROOKSVILLE
W F. Ward, M.S., Asst. An. Husband-
man in Charge2

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist
in Charge
K. W. Loucks, M.S., Assistant Plant
Pathologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist.
E. N. McCubbin, Ph.D., Asso. Truck
Horticulturist
Monticello
Samuel O. Hill, B.S., Asst. Entomologist2
Bradenton
Jos. R. Beckenbach, Ph.D., Truck Horti-
culturist in Charge
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in
Charge, Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant
Pathologist
Lakeland
E. S. Ellison, Meteorologist2
B. H. Moore, A.B., Asst. Meteorologist2

THead of Department
I2n cooperation with U.S.D.A.
sCooperative, other divisions, U. of F.









MELANOSE OF CITRUS AND ITS COMMERCIAL CONTROL
GEO. D. RUEHLE AND WM. A. KuNTZ1

CONTENTS
Page Page
Symptoms and Effects of Melanose_ 3 Proprietary Copper Sprays -..---_ 30
Sulfur Sprays _.._._.. 33
The Cause of Melanose _........._ 7 Mercury-Oil Emulsions 38
The Imperfect or Phomopsis Zinc Sulfate -.....--- ..-.-..--.-- 38
S ta g e ........ ....... ... .. ... 9
The Perfect or Diaporthe Stage----- 12 Wettable Sulfurs and Copper Sprays
Contributing Conditions 13 Combined for Controlling Melan-
ose and Rust M ites ....... ............. 40
Control of Melanose...------------- 15 Control of Insects Following Mel-
Previous Methods 15 anose Sprays ___._.-__. __ 41
Experiments of 1932 to 1937 --- Discussion and Conclusions ---- 43
Pre-Growth Sprays 18........
Pruning .- -----..---- _---- 22 Spray Schedules .---.- ___.._.. 50
Bordeaux Mixture 3-3-100 .-_. 27 Literature Cited ._ _.--... .._ ___. 53

INTRODUCTION
Melanose is one of the most important fungous diseases occur-
ring in the citrus groves of Florida.
A study was begun in 1931 at the Citrus Experiment Station at
Lake Alfred to obtain more information pertaining to the life his-
tory of the fungus responsible for the disease, and to develop'
more practical methods for its control in commercial citrus plant-
ings.
The purpose of this bulletin is to present the known facts re-
garding the etiology of melanose, and the results obtained from
extensive tests for its control. Recommendations are given for
avoiding losses from the disease in commercial groves.

SYMPTOMS AND EFFECTS OF MELANOSE
Melanose is characterized by small, superficial, light to dark
brown or black eruptions on the surface of leaves, shoots, fruit
pedicels or fruits of various plants belonging to the genus Citrus.
The leaf spot phase of the disease begins soon after the leaves
emerge from the bud if conditions are favorable for infection.
The young infections appear first as minute, scarcely visible,
round, water-soaked spots, which gradually become dark sunken
depressions. As the leaves become older the spots become dis-
tinctly raised, with more or less irregular margins, and vary in
size from mere dots to one millimeter in diameter. The lesions
may occur on either surface of the leaf and may be arranged in
various patterns. They may occur as widely separated spots
(Fig. 2), or they may appear in more or less circular patterns
from one to several centimeters in diameter, or sometimes as
solid scar tissue of various shapes (Fig. 3). In early spring, when

1Formerly Associate Plant Pathologist, Citrus Experiment Station.









MELANOSE OF CITRUS AND ITS COMMERCIAL CONTROL
GEO. D. RUEHLE AND WM. A. KuNTZ1

CONTENTS
Page Page
Symptoms and Effects of Melanose_ 3 Proprietary Copper Sprays -..---_ 30
Sulfur Sprays _.._._.. 33
The Cause of Melanose _........._ 7 Mercury-Oil Emulsions 38
The Imperfect or Phomopsis Zinc Sulfate -.....--- ..-.-..--.-- 38
S ta g e ........ ....... ... .. ... 9
The Perfect or Diaporthe Stage----- 12 Wettable Sulfurs and Copper Sprays
Contributing Conditions 13 Combined for Controlling Melan-
ose and Rust M ites ....... ............. 40
Control of Melanose...------------- 15 Control of Insects Following Mel-
Previous Methods 15 anose Sprays ___._.-__. __ 41
Experiments of 1932 to 1937 --- Discussion and Conclusions ---- 43
Pre-Growth Sprays 18........
Pruning .- -----..---- _---- 22 Spray Schedules .---.- ___.._.. 50
Bordeaux Mixture 3-3-100 .-_. 27 Literature Cited ._ _.--... .._ ___. 53

INTRODUCTION
Melanose is one of the most important fungous diseases occur-
ring in the citrus groves of Florida.
A study was begun in 1931 at the Citrus Experiment Station at
Lake Alfred to obtain more information pertaining to the life his-
tory of the fungus responsible for the disease, and to develop'
more practical methods for its control in commercial citrus plant-
ings.
The purpose of this bulletin is to present the known facts re-
garding the etiology of melanose, and the results obtained from
extensive tests for its control. Recommendations are given for
avoiding losses from the disease in commercial groves.

SYMPTOMS AND EFFECTS OF MELANOSE
Melanose is characterized by small, superficial, light to dark
brown or black eruptions on the surface of leaves, shoots, fruit
pedicels or fruits of various plants belonging to the genus Citrus.
The leaf spot phase of the disease begins soon after the leaves
emerge from the bud if conditions are favorable for infection.
The young infections appear first as minute, scarcely visible,
round, water-soaked spots, which gradually become dark sunken
depressions. As the leaves become older the spots become dis-
tinctly raised, with more or less irregular margins, and vary in
size from mere dots to one millimeter in diameter. The lesions
may occur on either surface of the leaf and may be arranged in
various patterns. They may occur as widely separated spots
(Fig. 2), or they may appear in more or less circular patterns
from one to several centimeters in diameter, or sometimes as
solid scar tissue of various shapes (Fig. 3). In early spring, when

1Formerly Associate Plant Pathologist, Citrus Experiment Station.









MELANOSE OF CITRUS AND ITS COMMERCIAL CONTROL
GEO. D. RUEHLE AND WM. A. KuNTZ1

CONTENTS
Page Page
Symptoms and Effects of Melanose_ 3 Proprietary Copper Sprays -..---_ 30
Sulfur Sprays _.._._.. 33
The Cause of Melanose _........._ 7 Mercury-Oil Emulsions 38
The Imperfect or Phomopsis Zinc Sulfate -.....--- ..-.-..--.-- 38
S ta g e ........ ....... ... .. ... 9
The Perfect or Diaporthe Stage----- 12 Wettable Sulfurs and Copper Sprays
Contributing Conditions 13 Combined for Controlling Melan-
ose and Rust M ites ....... ............. 40
Control of Melanose...------------- 15 Control of Insects Following Mel-
Previous Methods 15 anose Sprays ___._.-__. __ 41
Experiments of 1932 to 1937 --- Discussion and Conclusions ---- 43
Pre-Growth Sprays 18........
Pruning .- -----..---- _---- 22 Spray Schedules .---.- ___.._.. 50
Bordeaux Mixture 3-3-100 .-_. 27 Literature Cited ._ _.--... .._ ___. 53

INTRODUCTION
Melanose is one of the most important fungous diseases occur-
ring in the citrus groves of Florida.
A study was begun in 1931 at the Citrus Experiment Station at
Lake Alfred to obtain more information pertaining to the life his-
tory of the fungus responsible for the disease, and to develop'
more practical methods for its control in commercial citrus plant-
ings.
The purpose of this bulletin is to present the known facts re-
garding the etiology of melanose, and the results obtained from
extensive tests for its control. Recommendations are given for
avoiding losses from the disease in commercial groves.

SYMPTOMS AND EFFECTS OF MELANOSE
Melanose is characterized by small, superficial, light to dark
brown or black eruptions on the surface of leaves, shoots, fruit
pedicels or fruits of various plants belonging to the genus Citrus.
The leaf spot phase of the disease begins soon after the leaves
emerge from the bud if conditions are favorable for infection.
The young infections appear first as minute, scarcely visible,
round, water-soaked spots, which gradually become dark sunken
depressions. As the leaves become older the spots become dis-
tinctly raised, with more or less irregular margins, and vary in
size from mere dots to one millimeter in diameter. The lesions
may occur on either surface of the leaf and may be arranged in
various patterns. They may occur as widely separated spots
(Fig. 2), or they may appear in more or less circular patterns
from one to several centimeters in diameter, or sometimes as
solid scar tissue of various shapes (Fig. 3). In early spring, when

1Formerly Associate Plant Pathologist, Citrus Experiment Station.







Florida Agricultural Experiment Station


Fig. 2.-Severe melanose infection on leaves and twigs of grapefruit,
resulting in distortion and shedding of leaves.

but one to several scattered infections appear on rapidly expand-
ing grapefruit leaves, the growth of the leaf blade sometimes be-
comes elevated at the points of infection to form raised conical







Melanose of Citrus


Fig. 3.-Distortion of mature grapefruit leaves from severe melanose
infection.
pimples with the melanose spot at the apex inside the depres-
sion. The, condition may be confused with certain outgrowths
caused by the cjitLs scalJ fmugus. In cases of severe infection the
leaves may become crinkled and distorted (Fig. 2), lose their
green color and drop prematurely from the tree.







6 Florida Agricultural Experiment Station
Melanose spots on the fruit are at first light brown, circular,
and sunken, later becoming dark brown to almost black with a
wax-like appearance and distinctly raised, so that the surface of
an affected area possesses a roughness suggestive of coarse sand-
paper. This roughness, which is persistent, serves to distinguish
melanose from surface stains caused by anthracnose or from the
smoother russetting produced by rust mites. The spots may be-
come arranged in various patterns (Fig. 1) similar to those de-
scribed for foliar infections. Tear-streaked patterns are some-
times brought about by drops of spore-laden water flowing down
over the fruit surfaces during light showers or heavy dews (Fig.
4). Infections may be so numerous as to cause the development of
solid, raised and roughened scar tissue that may cover a large
part, or even all, of the fruit. Where shallow cracks develop in
this dead scar tissue (Fig. 5) as a result of enlargement of the
fruit, a type of blemish is produced that has been described as


Fig. 4.-Tearstreak patterns on mature grapefruit.







Melanose of Citrus


"mud-cake" melanose by Winston, Bowman, and Bach (33)2. A
flaky appearance infrequently develops due to a partial slough-
ing of scar tissue from the mud-cake areas (Fig. 6). According to
Fawcett and Lee (9), fruits severely infected while quite young
are likely to be stunted and weakened and may be the first to
drop if the tree encounters adverse conditions.
Melanose on the bark of young twigs is similar in appearance
in early stages to foliar infections. Later, if the spots are few in
number they usually become much more raised than on leaves
and fruits. Twigs severely infected may die as a result of the
bark becoming more or less completely covered by the corky
tissue.
Melanose infections frequently occur on the fruit pedicels and
on the floral parts, especially the calyx lobes. The spots formed
on these parts are similar to those produced on leaves and fruits.
The fungus that causes melanose is also responsible for other
disease effects which are of considerable importance to the citrus
industry. As early as 1911 it was shown to be the cause of a /
stem-end rot (5). Later it has been shown to play a part in the
development of the shell-bark disease of lemons in California
(8, 10), and of a serious bark disease of the Persian lime and the
Perrine lemon in Florida (31). These effects are not discussed in
this bulletin.

THE CAUSE OF MELANOSE
The first published account of melanose was made by Swingle
and Webber in 1896 (26), but it was not until 1912 that the causal
fungus was definitely determined.
In 1911 Fawcett (5) showed that a species of Phomopsis caused -
a stem-end decay of citrus fruits, and in 1912 -(6) described the
fungus as a new species, Phomopsis citri. In the same year Floyd
and Stevens (12) demonstrated by means of inocultions that
melanoise is caused by P. citri, which sporulates in dead citrus
wood, but they were unable to recover the fungus from he
melanose spots.
In 1926 Wolf (34) found the perfect, or ascospores stage grow-
ing saprophytically on decaying citrus twigs in contact with the
soil, and named it Diaporthe citri. The genetical relationship of

2Italic figures in parentheses refer to "Literature Cited" in the back
of this bulletin.







8 Florida Agricultural Experiment Station
the two stages was established by cultural studies and by patho-
genicity of Phomopsis spores produced in cultures obtained from
the Diaporthe stage.
In 1928 the isolation of D. citri (Fawc.)\Wolf from melanose
lesions was reported for the first time (1), tht~ making it pos-
sible to follow strictly the standard procedure for proof of path-
ogenicity. In 1933 (21) the writers reported the development of
typical melanose spots from inoculations of citrus leaves with
ascospores of D. citri. ,
q ,( Melanose, therefore, is caused by either the imperfect or per-
fect spore type of D. citri. (Fawc.) Wolf lodging upon susceptible
parts and germinating there in the presence of moisture. In-
fection may be accomplished within 36 hours after inoculation,
Sbut is not visible to the unaided eye until four to seven days have
elapsed)


(* *n


Fig. 5.-Mudcake type of melanose on mature grapefruit.







Melanose of Citrus 9
According to Bach and Wolf (1) the fungus is able to penetrate i
the cell walls by means of pectic enzymes which digest the host
cells. The collapse of these cells produces a slight depression in
the early stages, but later the injured cells and cuticle become
raised by the development of corky tissue beneath. The cuticle
finally becomes ruptured by the tension produced, and the mass
of gum-like substance resulting from the digestion process be-
comes brown and dry upon exposure to the air, giving the char-
acteristic color to the spots.

THE IMPERFECT OR PHOMOPSIS STAGE

Observations made over a period of eight years in bearing
groves in various sections of Florida indicate that the spores of/ '
the Phomopsis stage produced on the dead wood in the tree are
the chief source of infection. The minute pustule-like fruiting1'
bodies of this spore stage can be found at any time of the year


Fig. 6.-Mudcake type of melanose showing flaking effect on mature
grapefruit.







10 Florida Agricultural Experiment Station
on dead wood in citrus trees, although they are seldom found dis-
charging spores in midwinter or during extended drought per-
iods.
t These fruiting bodies are scattered and embedded in the bark
of infected parts which usually become grayish white in color.
When they are very young a small dark-colored pimple in the
w bark is all that is visible. When fully mature they begin exuding
masses of spores through an opening, or osiole, at the tip. When
this exudation occurs during a rain the spores appear as a light
or cream-colored mass at the tip of the fruiting body. When ex-
Spelled during a period following a rain, or in moist situatienst1he
spore mass appears as a stringy tendril, soft and sticky at first
but becoming hard and brittle and somewhat darker in color
when dry.
The individual spores are microscopic in size and usually are
accompanied by functionless, slender, curved bodies called stylo-
Sspores. The functional spores and stylospores are embedded in a
mucilaginous material which swells when wet, and is thus forced
from the fruiting body carrying the spores with it. From this
point they are spread chiefly by free water, dripping, spattering
or washing from the fruiting areas, as the result of rains, fogs or
heavy dews. When strong winds accompany rains, spore-laden
water may be blown for distances of 20 t9 30 feet fromthe spqru-
lating area.
SInsects are capable of transporting the spores from place to
place. It has been observed occasionally that portions of the
bark infected by D. citri have been eaten away by insects but this
is not of common enough occurrence to consider spore dissemi-
nation by this means as important.
Under average growing conditions in older groves some wood
is dying continually from such factors as shading effects, the at-
tacks of scale insects, and from cases of malnutrition resulting
from insufficient or improper fertilization. Under these condi-
N tions the fungus is usually found fruiting in small scattered
patches in the bark of deadwood, intermingled with patches in-
fected by various other saprophytic fungi which are grove in-
habitants in Florida. Since enormous numbers of spores may be
produced from a very small area of infected wood the infection
resulting from spores produced in such small patches frequently
may be very severe in the aggregate.
S Under conditions where frosts or freezes, storms, droughts, or
other unfavorable conditions lower the vitality of the tree and







Melanose of Citrus 11
lead to the sudden death of large portions of the top, D. citri
may infect large areas of the killed wood. Dead patches in the
bark of larger limbs may become infected as well as the smaller
twigs and branches. Following the freeze of 1934-35, in a test
grove of grapefruit trees four to five years of age in Pinellas
County, large portions of the tops were killed back by the cold.
Early in the spring the melanose fungus fruited so abundant
on the wood killed in this manner that large patches of the -
fected bark assumed a furry appearance from the innumer le
spore tendrils produced. When such an abundance of iaulum.
occurs the recovery of the trees will be greatly retarded unless
measures are taken to check infection on the new growth.
As a general rule D. citri is more apt to be found actively fruit-
ing on wood that had died within two or three months than on
parts that had died many months before. However, the writers
have demonstrated experimentally that dead wood infected with
the fungus will continue to serve as a source of infection for more
than one year.
At the Citrus Experiment Station just before the spring growth
started in 1932, prunings infected with D. citri were suspended in
wire racks over young grapefruit trees and left there for several
years. Observations were made on the development of melanose
on fruit and foliage during this period. At the beginning of the
experiment the trees were practically free of melanose and the
dead wood which developed in them during the course of the
experiment was carefully pruned out periodically, so that practi-
cally all the infection which appeared must have come from the
prunings in the racks. Other trees in the same planting were
pruned in the same manner to serve as controls.
Foliage and fruit which developed on the trees under the racks
became, severely blemished with melanose during the first season,
whereas the check trees remained practically free of the disease.
During the second year the disease was again more severe in the
trees under the racks than in the check trees, but the difference
in infection was much less. During the third year little or no
difference could be observed. It was concluded that the dead
wood may still harbor the fungus in an active state well into i
the second year after it is killed, but the amount of inoculum
becomes progressively less with increasing age.
The production of spores of the Phomopsis type may be induced
in immature citrusafruits artificially inoculated, but spore pro- A/
duction has not been observed in mature citrus fruits under nat-




VF


12 Florida Agricultural Experiment Station
Sural conditions. The fungusnever produces spores ithe .mela-
nose sots produced on living parts of the tree. It is difficult to
detect the mycelium of the fungus in these blemishes, and isola-
tions can be accomplished only with a fair measure of success
"from the young lesions in early stages of development.
THE PERFECT OR DIAPORTHE STAGE
SThe Diaporthe stage of the melanose fungus is produced on
decaying citrus wood in contact with the soil. It may be found
at practically any time of the year where the dead wood is al-
lowed to disintegrate on the ground. It is probable that the ma-
Sturing of the spores depends largely on the length of time the-
wood has been in contact with the soil, rather than on the time
or season of the year.
,r The fruiting bodies are single or in groups of several, immersed
Sin black stromata which are covered more or less completely by
the bark, and possess long slender curved beaks which ordin-
arily extend less than one millimeter above the bark. In some
instances, where the dead wood is more or less buried under
-leaves, the beaks may attain a length of 2 to 3 millimeters. These
beaks are rounded at the apex and are entirely black except at
the tip, which is dark brown in color. The stromata extend some
distance into the woody cylinder of the stem. .
-The spores, which are produced in sacs, are microscopic
in size and are forcibly ejected into the air from the fruiting
bodies. This is readily demonstrated by the inversion of harden-
ed agar plates over twigs placed on moistened blotting paper in
the tops of petri dishes. They are probably carried for con-
siderable distances by air currents.
The writers have demonstrated, by means of artificial inocula-
tions, that ascospores of D. citri can produce infections resulting
in typical melanose spots on citrus foliage. Ascospore production
is very difficult to induce on culture media, so that inoculations
were made with suspensions of ascospores obtained from fruit-
ing bodies produced under natural conditions. Melanose spots
produced by ascospores were indistinguishable from those which
developed on leaves artificially inoculated at the same time with
Phomopsis spores of D. citri from pure cultures.
Inoculations of mature oranges with ascospores resulted in the
SdevelIopment of a plia leleathery rot typical of Phomopsis stem-
end rot, and re-isolations from the decayed tissue resulted in the
development of typical colonies which produced the Phomopsis
stage on culture media.







Melanose of Citrus 13
Judging from the relative abundance of the two spore stages
produced by the fungus, it is probable that comparatively little
of the melanose on fruit and foliage results from ascospore in-
fection. At no time havelarge numbers of ascospores been found.
Their chief importance in the life cycle appears to be the wide-
spread dissemination of the fungus through the agency of air
currents. Observations on the occurrence of melanose in very
young groves planted in more or less isolated situations bear out
this hypothesis. Foliage infection in such young trees consists
for the most part of widely scattered melanose spots. It is dif-
ficult to account for this light scattered infection in any other
way than to suppose that it resulted from air-borne ascospores.

CONTRIBUTING CONDITIONS

In Florida melanose is likely to occur at any season of the
year, provided infected dead wood is present in the tree and
rainy periods coincide with the time when leaves, twigs, or fruits
are in a susceptible condition. Temperature within certain limits
is also probably an important factor.
Citrus tissues are susceptible to melanose infection only when
they are young and growing rapidly (2, 10, 33, 20). From exten-
sive inoculation experiments, Winston, Bowman, and Bach (33)
found that citrus leaves and shoots are extremely susceptible
short after emergence from the bud, but as they expand become
progressively resistant. Leaves develop immune to infection
before they assume the deep-green color of maturity which us-
ually takes place witin a period of two o ee weeks under
average conditions. The fruits are susceptible for a longer period,
usually from five to eight weeks after the petals fall. Winston,
Bowman and Bach (33) found that young fruits also are very
susceptible at first and gradually become more resistant as they
increase in size. They give the approximate diameter at which
oranges and grapfruit develop immunity as 1/2 inches and
21 inches, respectively. The present writers found that the
diameter size at which grapefruit may be considered immune
should be increased to 3 inches.
Moisture in some form must be present during the susceptible /7
period for infection to take place. The connection between severe
outbreaks of melanose and the occurrence of rainy periods has
been reported by earlier workers (33, 20, 10). Some infection
also may take place during heavy fogs and dews. In certain lo-
calities, even when the causal fungus is present, melanose is not J







14 Florida Agricultural Experiment Station
important because of lack of rain during the susceptible period.
Melanose is reported as severe in the coastal moist areas of Aus-
tralia where rains occur when the fruit is small, but it is not
reported in South Australia where a dry period of several months
occurs when the fruit is susceptible (10).
-V<
Fawcett worked out the temperature relations of the fungus
itself on certain media, and considers that temperature within
certain limits is probably an important factor along with suscep-
tible tissue and moisture (7). He found that an increase in tem-
perature has a marked effect on increased rate of growth of the
fungus up to 75 to 81 degrees F. (24 to 27 degrees C.), but a furth-
er rise retards the growth and at about 95 degrees F. (35 degrees
C.) growth ceases entirely.
As a general rule melanose increases in severity with the ad-
vancing age of the trees. The damage occurring in trees of non-
bearing age is of slight importance, unless freezes or scale attacks
occur of sufficient severity to cause an accumulation of dead
wood, or dead pruning stubs are left to become sources of infec-
tion. In bearing trees less than 10 years of age the disease is not
likely to become serious if the trees have been kept thrifty, com-
paratively free of scale insects, and relatively free of dead wood.
In older trees the disease increases in severity, because even
Switch the best of care dead wood tends to become more abundant
through natural causes. The dying of fruit spurs and the death
of small twigs through shading effects offer situations for the
fungus to grow. Prolonged drouths, inadequate or improper
fertilization, mineral deficiencies, root pruning by deep cultiva-
tion, scale attacks, the occurrence of wasting trunk and root dis-
eases, and unfavorable rootstock combinations all may favor the
development of melanose. In general, all factors which reduce
tree vigor and cause an accumulation of dead wood tend to in-
tensify the severity of melanose infection.


CONTROL OF MELANOSE
PREVIOUS METHODS
Although the experiments of Swingle and Webber (26) in 1896
showed that melanose could be controlled by the use of copper
sprays, few growers availed themselves of this method until
after the introduction of bordeaux-oil emulsion about 1920. The
use of copper sprays, and especially bordeaux mixture at the








Melanose of Citrus 15
recommended strengths, generally caused a considerable increase
in scale insects. Winston, Bowman, and Bach (33) stated that
the injurious effects from the increase of scale insects following
applications of copper sprays were usually more damaging to
the tree and fruit than the severest outbreak of melanose.
The discovery that oil emulsion could be combined with bor-
deaux mixture for use on citrus largely removed the former ob-
jections to the use of this fungicide. Experiments by Winston
and Bowman (32), Grossenbacher (13), and Burger, DeBusk,
and Briggs (2) demonstrated the effectiveness of the combination
sprayfor the control of melanose.
n 1912 Floyd (11) noted that where melanose had been severe,
pruning out the dead wood lessened the disease. Stevens (23, 24,
25) concluded from pruning experiments carried out from 1913
to 1916 that very careful pruning reduced the disease decidedly
and that ordinary commercial pruning gave moderately good
control.
In 1927 Winston, Bowman, and Bach (33) concluded from ex-
tensive pruning, dusting and spraying experiments, that pruning" ;
for control is impractical, that copper dusts and weak copper or
sulfur sprays were ineffective, but that good control would be
obtained by applying 6-6-100 bordeaux mixture,_plus 1 percent
;-T- efriiii6'fi--ijistnadvance of the May rains. This recom-
mendation has been followed by later writers on citrus diseases
(9, 10, 20).
EXPERIMENTS OF 1932 TO 1937

Although the single application of bordeaux-oil emulsion ap-
plied shortly before the May rains set in gave excellent control of
melanose as a rule, several objections to the combination spray
developed with extension of its use. Small fruits were occasion-
ally burned or blotched and tender foliage was frequently scorch-
ed by the spray. Unless the scale infestation was very light when
the spray was applied it was usually necessary and always ad-
visable to follow the bordeaux-oil combination with an oil emul-
sion later in the season to assist in control of the scales. This was
especially true in groves infested by the Florida red scale (Chry-
somphalus aonidum Linn.). The increase in cost of the spray from
adding oil emulsion to the fungicide was becoming an item of








Melanose of Citrus 15
recommended strengths, generally caused a considerable increase
in scale insects. Winston, Bowman, and Bach (33) stated that
the injurious effects from the increase of scale insects following
applications of copper sprays were usually more damaging to
the tree and fruit than the severest outbreak of melanose.
The discovery that oil emulsion could be combined with bor-
deaux mixture for use on citrus largely removed the former ob-
jections to the use of this fungicide. Experiments by Winston
and Bowman (32), Grossenbacher (13), and Burger, DeBusk,
and Briggs (2) demonstrated the effectiveness of the combination
sprayfor the control of melanose.
n 1912 Floyd (11) noted that where melanose had been severe,
pruning out the dead wood lessened the disease. Stevens (23, 24,
25) concluded from pruning experiments carried out from 1913
to 1916 that very careful pruning reduced the disease decidedly
and that ordinary commercial pruning gave moderately good
control.
In 1927 Winston, Bowman, and Bach (33) concluded from ex-
tensive pruning, dusting and spraying experiments, that pruning" ;
for control is impractical, that copper dusts and weak copper or
sulfur sprays were ineffective, but that good control would be
obtained by applying 6-6-100 bordeaux mixture,_plus 1 percent
;-T- efriiii6'fi--ijistnadvance of the May rains. This recom-
mendation has been followed by later writers on citrus diseases
(9, 10, 20).
EXPERIMENTS OF 1932 TO 1937

Although the single application of bordeaux-oil emulsion ap-
plied shortly before the May rains set in gave excellent control of
melanose as a rule, several objections to the combination spray
developed with extension of its use. Small fruits were occasion-
ally burned or blotched and tender foliage was frequently scorch-
ed by the spray. Unless the scale infestation was very light when
the spray was applied it was usually necessary and always ad-
visable to follow the bordeaux-oil combination with an oil emul-
sion later in the season to assist in control of the scales. This was
especially true in groves infested by the Florida red scale (Chry-
somphalus aonidum Linn.). The increase in cost of the spray from
adding oil emulsion to the fungicide was becoming an item of







16 Florida Agricultural Experiment Station
increasing importance in view of the tendency in recent years for
the spread between costs and gross returns to the grower to be-
come less. A coarsening and delay of maturity of the fruit was
also attributed by some growers to the use of 6-6-100 bordeaux
mixture with or without oil added.
With melanose increasing in severity as the groves became
older, and with the lack of satisfaction with the standard recom-
mendations, it was advisable to attempt to modify control prac-
tices so that they would be more practical or more efficient. With
this object in view experiments for the control of melanose were
started in 1932 and continued through the season of 1937.
The tests were conducted in commercial bearing grapefruit
and orange groves situated in various localities in Central Florida
where the disease is of annual occurrence and of major import-
ance. In part, they were carried out cooperatively with commer-
cial growers and in part in the groves of the Citrus Experiment
Station. Groves were selected for the tests that had the required
number of trees of the same age, variety, and rootstock and of
approximate uniformity of vigor. Test plots in individual groves
were of nearly equal size but were varied in size in different
groves according to their expectancy of bearing. In each case
they were made sufficiently large that a representative number
of fruits (usually 1,000 or more) could be readily and convenient-
ly examined from each treatment, provided an average crop
would be produced.
The tests included a comparison of pruning and spraying
methods and a combination of both treatments for control.
The fungicides tested included several proprietary copper, mer-
cury, and sulfur preparations, liquid and dry lime-sulfurs, bor-
deaux mixtures, and compatible combinations of many of these
fungicides with insecticides.
Many of the proprietary products were new or little known at
the time and the recommendation of the manufacturer or his
field representative was followed in mixing and applying such
sprays. Bordeaux mixtures used in the experiments of 1932 to
1934 were made with either equal amounts df bluestone and rock
lime or with one-third more hydrated lime than bluestone. Re-
sults of these tests showed that rock lime was no better than
hydrated lime and that it was unnecessary to increase the amount
of lime in the formula. In later experiments, therefore, bordeaux
mixtures were made with equal amounts of bluestone and hy-
drated lime. The materials for making bordeaux mixture were
always of the best obtainable commercial grade.







Melanose of Citrus 17
The sprays were all applied with power machinery at 300 or
more pounds pressure, and various types of spray guns supplying
a mist type of spray were used during the course of the tests.
An attempt was made to thoroughly cover the foliage, fruit and
branches without unnecessary loss of spray material from ex-
cessive drip. When pre-growth sprays were applied special at-
tention was directed to thoroughly covering the bark of the
twigs, branches and trunk of the trees to prevent development
of the fungus on tissue of these parts which might die subsequent
to spraying. When post-bloom sprays were applied the aim was
to cover thoroughly the fruits and immature foliage.

Several types of spreaders were used. Unless special spreaders
were recommended, or were already incorporated with the pro-
prietary preparations, either calcium caseinate or a non-casein
colloidal dry spreader was used and gave satisfactory results.
Combinations of oil emulsion with bordeaux mixture or other
copper compounds, and of wettable sulfur or bentonite sulfur
with lime-sulfur or copper sprays, gave very satisfactory cover-
age without the addition of other spreaders.

In the pruning experiments only dead and weakened parts were
removed. Although the work was done with more thoroughness
than is the case in average commercial pruning, no attempt was
made to remove all of the small dead terminal twigs and fruit
stems, as this was considered impractical. The larger prunings
were removed from the grove.
In securing the comparative records of control a representative
number of fruits from each plot were examined and the degree
of blemish was determined by counting the number of melanose
spots occurring in one square inch field of surface, selected at
random from the upper half of each fruit. The counts were made
with the aid of a metal ring which circumscribed an area of one
square inch. The examinations were generally made when the
fruit was beginning to assume the color of maturity, at which
time the spots or lesions were more readily discernible than on
green fruit. Whenever feasible, only the fruits from the lower
branches of the tree were examined, in order that the data would
be from specimens which had a good chance to become infected.
Whenever the size of the crop permitted at least 1,000 fruits were
examined from each replication and some were examined from
every tree in the plots. The fruits were then grouped into four
classes of infection, as follows: very slight, none to 10 spots per






18 Florida Agricultural Experiment Station
square inch; slight, 11 to 25 spots per square inch; moderate 26
to 50 spots per square inch; and severe, more than 50 spots per
square inch (Fig. 7).
Examinations of graded fruits in commercial packinghouses at
various times to determine how much melanose blemish was
being included in the first grade showed that the tolerance varied
somewhat in the different houses and at different times during
the packing season. In a typical packinghouse 70 percent of the
grapefruit included in the U. S. No. 1 grade showed from none
to 10 spots per square inch and approximately 15 percent showed
11 to 15 spots per square inch, with the remainder more severely
blemished. In the orange pack the U. S. No. 1 Bright grade
included 84 percent with none to 10 spots per square inch and
13 percent with 11 to 15 spots per square inch.
In comparing the results from the experiments fruits showing
very slight infection were considered to be first grade fruit, al-
though this is a slightly higher grade with regard to melanose
blemish than is commonly used in packinghouses.
The data are presented by subjects rather than by seasons, for
ease in comparing various spray formulas with 6-6-100 bordeaux
mixture, which was taken as the standard fungicide, and for com-
paring spraying with pruning for the control of melanose. Some
of these data have appeared in early progress reports by the
writers (15, 16, 17).
Melanose varies in intensity from one season to another de-
pending upon weather conditions and upon the general state of
health or vigor of the trees, as well as other factors. Furthermore,
during a single season its intensity varies from one grove to an-
other, from one part of a grove to another, or even from tree to
tree. Because of this lack of uniformity in melanose outbreaks
the control results must vary considerably, and in drawing con-
clusions from control experiments the results over several years
must be considered collectively. To take the results in any one
plot or one grove as a standard for comparison may prove mis-
leading.
PRE-GROWTH SPRAYS
In sections of Florida where citrus scab is of annual occurrence
on grapefruit, and copper sprays have been regularly applied
for its control, melanose has not been a very serious problem.
Early recommendations for the control of scab (20, 10) called for
a pre-growth or dormant application of 6-6-100 bordeaux or bor-
deaux-oil which was to be repeated in the last of the bloom. Re-








Melanose of Citrus


..^'''"
i n

All




fc q


C
40,


Cc


ad


,


~~
1
-
:b


Fig. 7.-Typical examples of the various classes of infection used in
grading fruits from experimental plots. Lower left, very slight; lower
right, slight; upper left, moderate; upper right, severe.


:
- r







20 Florida Agricultural Experiment Station
cent experiments by Ruehle and Thompson (22) show that once
the trees are relatively free of scab the disease can be controlled
in grapefruit groves by a single application of this spray just
before the spring flush of growth appears. Although a partial
control of melanose was obtained from the pre-growth spray, it
gave little reduction of infection in years favorable for melanose
development. Good commercial control of melanose was ob-
tained when the pre-growth spray was followed in the last of the
bloom by a 3-3-100 bordeaux mixture or its equivalent in other
copper sprays. Delaying the second application until three weeks
after the petals were shed increased the freedom from melanose
fruit blemish still further. It was considered that two sprayings
with copper fungicides are necessary for effective control of both
scab and melanose, and that the timing of the second spray should
depend upon the relative importance of the two diseases in the
grove to be protected.
Additional tests were made to compare the effectiveness of
pre-growth with post-bloom applications of bordeaux mixture for
the control of melanose. These included spraying experiments in
conjunction with pruning tests in seedling grapefruit trees more
than 25 years of age, and spraying experiments in old and young
grapefruit trees where pruning was not practiced.
The location of the tests, age of trees, spray schedules, and
severity of melanose blemish on the mature fruits, are shown in
Table 1.
The results show that a pre-growth or dormant application of
fungicide is less effective than timing the spray after the petals
have shed. In the old seedling grapefruit grove near Largo in
both 1933 and 1934 most of the dead wood was removed from the
trees in the spray plots by pruning just prior to the pre-growth
application of fungicide, and the control of melanose blemish on
the fruit was fairly effective. It may be noted from Table 1,
however, that in 1933 a 3-4-100 bordeaux application made on
April 18 after the petals were off was more effective than a 6-8-
100 application of bordeaux-oil made on February 10. In un-
pruned trees at Babson Park in 1934 somewhat similar results
were obtained, but the difference in control was still more pro-
nounced in favor of the post-bloom application.
It was concluded that on varieties not susceptible to scab in-
fection, or in groves of susceptible varieties located in situations
where scab is generally not troublesome, it is inadvisable to ap-
ply a pre-growth spray for control of melanose fruit blemish.







TABLE 1.-COMPARATIVE RESULTS OBTAINED IN THE CON TROL OF MELANOSE FRUIT BLEMISH WITH BORDEAUX MIX-
TURE APPLIED AS PRE-GROWTH AND POST-BLOOM SPRAYS


SPRAYING PROGRAM

Materials and Concentrations


Locality
and
Year


Largo
1933




Largo
1934




Babson
Park
1934


Variety
and Age
of Trees

Seedling
grapefruit

24 years
of age
Seedling
grapefruit
25 years
of age



Seeded
grapefruit

19 years
of age




Marsh
grapefruit

10 years
of age


Dates
Applied


Melanose on Mature Fruit
None to
Very Slight Mod'rte Severe
Slight I


Feb. 1

Apr. 5
(bloom)


37.1
26.4

9.7


5.7
1.5

0.3


Trees
Pruned
Com'cially

No

Yes

Yes
No

Yes

Yes


Vero
Beach
1935


percent percent percent percent
20.1 34.7 38.2 7.0

Feb. 10 | 81.5 13.4 4.3 0.8

Apr. 18 84.8 13.0 1.8 0.4
1 0.4 9.8 37.2 52.6

Jan. 26 73.2 22.2 4.1 0.5

Apr. 12 95.0 4.4 0.6 0.0
6.4 22.6 44.3 26.7

Feb. 6 21.4 40.8 25.8 12.0

Feb. 6
Apr. 24 26.4 35.9 27.3 10.4
May 7

Apr. 9 63.0 27.9 7.1 2.0

Apr. 9 77.2 20.9 1.6 0.3


No

No

No


---------- ----;---


check

bordeaux 6-8-100, oil as emulsion 1%

bordeaux 3-4-100, calcium caseinate
check

bordeaux 6-8-100, oil as emulsion 1%

bordeaux 6-8-100, calcium caseinate


No check

No bordeaux 6-8-100, oil as emulsion 1%
bordeaux 6-8-100, oil as emulsion 1%
No liquid lime sulfur 21-100
liquid lime sulfur 21/-100

No bordeaux 3-4-100, calcium caseinate

No bordeaux 6-8-100, calcium caseinate


check

bordeaux 6-6-100, oil as emulsion /2%

bordeaux 6-6-100, non-casein colloidal
spreader


o







Florida Agricultural Experiment Station


PRUNING
Theoretically, melanose might be effectively controlled by
pruning, since the chief source of infection is the dead wood in
the tree. Such a practice would doubtless give good results if a
perfect job of pruning were done and all dead wood removed
as fast as it accumulated. However, to prune with the necessary
degree of thoroughness in old bearing trees, and especially in
large groves, would be an endless and exceedingly expensive un-
dertaking.
Pruning to remove most of the dead wood in one operation, in
accordance with ordinary commercial practice, was tested as a
means of preventing melanose in bearing grapefruit and orange
groves. Pruning was compared with spraying, and its effect
when combined with spraying was also determined.
The experiments were conducted for four consecutive years in
a grapefruit grove at the Citrus Experiment Station, planted
equally to four commercial varieties. The trees were in their
ninth to twelfth years, dating from the time they were planted
in the grove. For the first two seasons the pruning was done
early in the spring as the new foliage began to appear. Low
temperatures during the winter of 1934-35 killed back a portion
of the top of many of the trees, making it necessary to delay the
pruning the third season until the latter part of March when the
extent of the killing could be fully determined. In the fourth
season pruning was again done during March because the results
during the previous season appeared to justify delaying the re-
moval of the dead wood until shortly before the spray was ap-
plied.
Similar tests were made in 1934 in a block of old seedling
grapefruit trees near Largo where dead wood had been allowed
to accumulate for several years, and in 1935 in a grove of orange
trees 10 years of age near Vero Beach, where dead wood was
abundant and melanose was becoming a serious problem.
The location, variety and age of the trees, dates of pruning and
spraying and the results in control of melanose fruit blemish, are
recorded in Table 2.
The results obtained at the Citrus Experiment Station show
that pruning by itself is unreliable for the control of melanose.
From Table 2 it may be noted that, considering the age of the
trees, melanose infection was rather severe in the control plots
in 1934 and in 1936, and in these years pruning failed to give





TABLE 2.-COMPARATIVE RESULTS OBTAINED IN THE CONTROL OF MELANOSE FRUIT BLEMISH BY PRUNING, SPRAYING
WITH BORDEAUX MIXTURE, AND THE COMBINATION OF PRUNING AND SPRAYING


Locality Variety
and and Age
Year of Trees


Duncan, Ex-
Lake celsior, Marsh
Alfred and Walters
1933 grapefruit

9 years of age


Lake
Alfred
1934


Lake
Alfred
1935



Lake
Alfred
1936


Duncan, Ex-
2elsior, Marsh
and Walters
grapefruit

10 yrs. of age


Duncan, Ex-
celsior, Marsh
and Walters
grapefruit

11 yrs. of age


Duncan, Ex-
celsior, Marsh
and Walters
grapefruit

12 yrs. of age


Condition Trees
With Regard to
Dead Wood


Not pruned

Not pruned

Pruned Jan. 20-
Feb. 3
Pruned Jan. 20-
Feb. 3
Not pruned

Not pruned

Pruned
Feb. 13, 14
Pruned
Feb. 13, 14
Not pruned

Not pruned
Pruned Mar. 20-
April 6
Pruned Mar. 20-
April 6


Not pruned

Not pruned
Pruned
March 12-27
Pruned
March 12-27


SPRAYING PROGRA1VI


Materials and Concentrations


SMelanose on Mature Fruit


Date None to
A- ae l Very Slight Mod'rte
Slight


Severe


percent percent percent percent

no spray-check 76.1 15.4 6.3 2.2

bordeaux mixture 3-4-100 Apr. 24 92.0 6.1 1.5 0.4

no spray 91.5 6.9 1.3 0.3

bordeaux mixture 3-4-100 Apr. 24 98.8 1.1 0.1 0.0

no spray-check 22.1 34.1 24.3 19.5

bordeaux mixture 6-8-100 Apr. 17 92.5 6.9 0.5 0.1

no spray 46.8 44.3 7.3 1.6

bordeaux mixture 6-8-100 Apr. 17 96.9 1.9 0.1 0.1


no spray-check

bordeaux mixture 3-3-100

no spray
bordeaux mixture 3-3-100


no spray-check

bordeaux mixture

no spray

bordeaux mixture


3-3-100


3-3-100


Apr. 16


Apr. 16


25.8

14.9

14.2

1.7


I ~I _______- --


Apr. 6


I Apr. 6


10.9
1.2

0.4

0.0


15.1

0.4

3.4

0.0


- I









TABLE 2 (Concluded).-COMPARATIVE RESULTS OBTAINED IN THE CONTROL OF MELANOSE FRUIT BLEMISH BY PRUN-
ING, SPRAYING WITH BORDEAUX MIXTURE, AND THE COMBINATION OF PRUNING AND SPRAYING


Variety
and Age
of Trees


Seedling
grapefruit
25 yrs. of age







Valencia
oranges
10 yrs. of age


Condition Trees
With Regard to
Dead Wood


INot pruned

Not pruned

Not pruned


Pruned Janu'y

Pruned Janu'y
Not pruned

Not pruned

Pruned March

Pruned March


SPRAYING PROGRAM


Materials and Concentrations


no spray-check

bordeaux mixture

bordeaux mixture
bordeaux mixture

no spray


6-8-100

3-4-100
3-4-100


bordeaux mixture 6-8-100


no spray-check

bordeaux mixture 3-3-100
dry-lime sulfur 5-100,
bentonite sulfur 2-100

no spray

bordeaux mixture 3-3-100
dry-lime sulfur 5-100,
bentonite sulfur 2-100


I Melanose on Mature Fruit


Dat Noneto
Date Very Slight Mod'rte
Applied Slight
0.4 9.8 37.2


Apr. 12

Apr. 13
May 4


Apr. 12


Apr.

May


Apr. 19

May 21


7.9 27.5 39.4

95.0 4.4 0.6


Severe

26fi


1.6 .

1.1


25.2

0.0
8.3

1.4


7.8

0.1


Locality
and
Year


Largo
1934







Vero
Beach
1935


~


---







Melanose of Citrus 25
good control while spraying was quite effective. In 1933 pruning
gave nearly as good protection from melanose blemish as spray-
ing, but this was in a season when very little infection occurred
in the control plots. In 1935, however, following cold injury to
the trees during the previous winter, when large quantities of
recently killed wood were present in the trees, the removal of
this wood by pruning just prior to the period when greatest in-
fection of the fruits takes place, was slightly more effective than
spraying for control. In all seasons control of melanose was most
effective where pruning was followed by a post-bloom applica-
tion of bordeaux mixture. Even a weak bordeaux mixture (3-3-
100 formula) following pruning gave nearly absolute commercial
control of melanose blemish.
In the old grapefruit trees near Largo pruning out the bulk of
the dead wood was of considerable benefit in reducing melanose
fruit infection when followed by a post-bloom spray, and was of
obvious benefit to the trees in that it promoted a vigorous growth
and was conducive to the renewal of bearing wood in the top.
However, it is apparent from Table 2 that pruning in old trees is
not likely to reduce melanose infection to such an extent that this
method alone can be relied upon to give commercial control of
the disease.
In the test with orange trees at Vero Beach in 1935 pruning
was also relatively ineffective for control. In these trees the
tops were very dense and the dead wood consisted mostly of very
small sprigs or branches which were difficult to remove with
the same degree of completeness that can be accomplished with
the same labor applied in grapefruit trees of equal size. From
the results obtained it appears that pruning of orange trees for
control of melanose is a doubtful practice from the practical
standpoint.
From these experiments it was concluded that pruning out
the larger dead and dying branches regularly is good grove
practice from the standpoint of maintaining vigor of the trees,
but it is not practical to attempt to control melanose solely by
this method. Pruning will give some control, both directly and
indirectly, but must be supplemented by spraying in order to
insure a crop of fruit commercially free of melanose. Generally,
this desired control may be accomplished by the use of fungicides
weaker than the 6-6-100 bordeaux mixture where pruning is
practiced regularly. After severe injury to the wood by low
temperatures or other factors pruning is especially desirable and







26 Florida Agricultural Experiment Station
may assist greatly in reducing melanose infection on both the
fruit and foliage. Protecting the foliage from infection in trees
so damaged will be an aid to their recovery. Few data are avail-
able concerning the effects of pruning citrus trees at different
times of the year. From the standpoint of melanose control
probably the best time is during the late winter and early spring.
The time will depend somewhat on the variety and the extent to
which pruning will interfere with other grove operations. In
late varieties it is probably best to delay pruning until the crop
has been removed in order to avoid injury to the fruit.
Spraying for melanose control is more reliable and effective
and costs somewhat less than pruning. In large trees where
the regular removal of dead wood has not been practiced
for many years, the first pruning is apt to be very costly.
In the old grapefruit trees included in these tests the cost of the
first pruning, with the subsequent removal of the prunings from
the grove, amounted to approximately $2.00 per tree. The same
trees were pruned again the following season at an average cost
of only $0.44 per tree. The Valencia trees 10 years of age at Vero
Beach in 1935 were pruned for the first time for approximately
$0.20 per tree. In the grove at the Experiment Station the cost
of pruning varied from approximately $0.08 per tree to nearly
$0.20 following the low temperature injury during the winter of
1934-35. In general, if trees with an accumulation of dead wood
are pruned thoroughly at first and then given a regular annual
pruning subsequent pruning operations become less costly under
average conditions. This is in accord with the findings in Cali-
fornia where it has been shown that the amount of pruning re-
quired to keep a bearing citrus tree in good condition is reduced
to the minimum by regularity of treatment with consequent sav-
ing in expense (14).
In removing the dead wood it is advisable to cut back into the
living wood. The tools should be sharp, so that clean, smooth
cuts are made and no projecting stubs should be left. The prun-
ing tools need not be disinfected. Where large cuts over two
inches in diameter are made it is advisable to coat the exposed
surface with an antiseptic or waterproof dressing. Well mixed
paint of white lead and raw linseed oil, applied after the wounds
have dried, is a standard dressing but should be renewed year
after year on very large cuts. Avenarius carbolineum, pine tar
preparations, and asphaltum preparations also may be used for
this purpose.







Melanose of Citrus


The small prunings less than one inch in diameter may be left
beneath the trees with little danger of increased infection, pro-
vided they do not interfere with other grove operations. The
practice of piling these prunings close to the trunk of the tree
should probably not be followed, since their presence may pro-
mote the development of certain crown diseases. The larger
prunings interfere more or less with other grove practices, such
as spraying and picking the fruit, and since the ascospores of
D. citri are more apt to develop in this type of wood than in
smaller twigs, it is advisable to remove them from the grove.

BORDEAUX MIXTURE 3-3-100

In connection with the first spraying experiments the oiX t
of various fungicides to the spores of D. citri was tested in the
laboratory. Clean glass slides were sprayed in a uniform man-
ner with the formula to be tested, and were then exposed to
weathering in a grove environment. The toxicity of the spray
film was determined at intervals by bringing slides to the lab-
oratory, placing drops of a spore suspension of D. citri on the
sprayed surface, and observing the spore germination by means
of the technique described by McCallan (18). After 22 days of
weathering a film of 3-4-100 bordeaux with calcium caseinate
spreader was still sufficiently toxic to inhibit all spore germina-
tion. Approximately three inches of rain fell during the weath-
ering period.
Results obtained from the toxicity studies and from spray tests
with 3-4-100 bordeaux mixture in 1933 indicated that this for-
mula might be substituted advantageously for the 6-6-100 for-
mula in the spray schedule. During 1934, 1935, and 1936, 6-6-100
bordeaux was compared with the half-strength formula in a
number of groves and under varied conditions of infection.
The location, variety and age of trees, and results obtained
for control of melanose fruit blemish are recorded in Table 3.
The results show that the weaker formula may, in many in-
stances, give nearly as good protection from melanose infection
as the 6-6-100 formula. In pruned trees especially a 3-3-100
formula may be substituted for 6-6-100 bordeaux with approxi-
mately equal results. It may be noted from Table 3 that in
pruned Pineapple orange trees and pruned grapefruit trees in
1935 and 1936 at Lake Alfred, and in pruned grapefruit trees at
Largo in 1936, approximately equal results were obtained with








TABLE 3.--COMPARATIVE RESULTS OBTAINED IN MELANOSE FRUIT BLEMISH CONTROL WITH 6-6-100 AND 3-3-100
FORMULAS OF BORDEAUX MIXTURE
Condition of SPRAYING PROGRAM ~ Melanose on Mature Fruit
Locality Variety Trees With one to
and and Age Regard to Materials and Concentrations Date Very Slight Mod'rte Severe
Year of Trees Dead Wood _Applied Slight
cent p percent percent percent
check 0.4 9.8 37.2 52.6
Seedling
Largo grapefruit bordeaux 6-8-100 Apr. 12 73.4 21.3 3.7 1.6
1934 25 years Not pruned
of age bordeaux 3-4-100 Apr. 13 47.9 33.1 13.7 5.3

bordeaux 3-4-100 Apr. 13
bordeaux 3-4-100 May 4 79.9 15.4 3.6 1.1
check 6.4 22.6 44.3 26.7
Babson Seeded
Park grapefruit Not pruned bordeaux 6-8-100 Apr. 9 77.2 20.9 1.6 0.3
1934 19 years
of age bordeaux 3-4-100 Apr. 9 63.0 27.9 7.1 2.0
check 59.2 28.3 9.3 3.2
Lake Pineapple bordeaux 6-6-100, wettable
Alfred oranges Pruned sulfur 10-100 Apr. 23 98.3 1.4 0.2 0.1
1935 12 years bordeaux 3-3-100, wettable
of age sulfur 10-100 Apr. 23 97.4 2.2 0.3 0.1


Valencia
oranges
10 years
of age


Not pruned
Not pruned

Not pruned

Not pruned


Pruned


check


bordeaux 6-6-100

bordeaux 3-3-100
bordeaux 3-3-100
bordeaux 3-3-100
bordeaux 3-3-100


r. 19

r. 19
ir. 19
ly 22
ir. 19


Vero
Beach
1935












Lake
Alfred
1936


Mar. 31

June 5


Mar. 31

May 26


Seeded
grapefruit
13 years
of age


26.4 11.3



2.5 0.5



5.3 1.2


Pruned


check

bordeaux 6-6-100, wettable
sulfur 10-100
lime sulfur 2-100, wettable
sulfur 5-100

bordeaux 3-3-100, wettable
sulfur 10-100
lime sulfur 2-100, wettable
sulfur 5-100
check

bordeaux 6-6-100

bordeaux 3-3-100

bordeaux 3-3-100
bordeaux 3-3-100
check

bordeaux 6-6-100
lime sulfur 1/4-100, wettable
sulfur 4-100
bordeaux 3-3-100
lime sulfur 2-100, bentonite
sulfur 3-100

bordeaux 3-3-100
sulfur dust

bordeaux 3-3-100
bordeaux 3-3-100


65.5


48.8


75.5


86.7


20.7


24.1


37.0


19.4


11.3


23.6

2.0

1.9


0.4


0.2


97.0



93.3


Largo
1936


Babson
Park
1936


2.4 5.0 30.2 62.4

Apr. 9 57.0 21.1 114.2 7.7

Apr. 9 59.4 28.4 11.2 1.0

Apr. 9
May 7 85.0 14.1 0.8 0.1


Seedling
grapefruit
27 years
of age


Seeded
grapefruit
21 years
of age


Apr.
Apr.

Apr.
Apr.


Apr.
Apr.

Apr.
Apr.


Pruned


Not pruned


8.2



0.0



0.2


F
xt
s"


CIl
0







30 Florida Agricultural Experiment Station
both formulas. However, in unpruned old grapefruit trees at
Largo in 1934, under conditions of extremely severe infection,
control with the half-strength formula was decidedly inferior
to results obtained with the stronger spray. Two applications of
the weaker spray, spaced three to four weeks apart, usually gave
better control than a single application of the stronger spray.
This was particularly so in 1936 in both the Largo and Babson
Park experiments.
Conclusions which may be drawn from the experiments are
that in both orange and grapefruit trees which have been pruned
With regularity, 3-3-100 bordeaux mixture may be substituted for
the 6-6-100 formula in the spray schedule with good results. In
old unpruned trees where infection is likely to be severe, how-
ever, the stronger spray should be retained in the schedule, or
the weaker spray should be followed in three to four weeks with
a second application of the same spray. The latter practice will
prove particularly effective in seasons when the bloom is inter-
mittent or is drawn out over a long period and in seasons when
heavy rains occur immediately following the first application.
The weaker bordeaux has certain advantages over 6-6-100 bor-
deaux other than the reduced cost of materials. It deposits less
spray residue on the sprayed parts and consequently insect con-
trol is somewhat easier of accomplishment and re-establishment
of entomogenous fungi in the grove is faster following its use.
There is also less danger of injuring fruit and foliage and of
checking growth by using the weaker spray.

PROPRIETARY COPPER SPRAYS
At the time the experiments were started in 1932 home-made
bordeaux mixture was the only copper spray used extensively in
Florida citrus groves. A proprietary copper-oil emulsion and
commercially prepared bordeaux powders were used in a limited
way, but other copper sprays were practically unknown. It was
desirable to find a spray material which possessed fungicidal
properties as good as bordeaux mixture and which would be
easier to employ and less objectionable in promoting scale in-
creases.
A number of proprietary copper spray materials of the so-called
"insoluble" type have appeared on the market since 1932, and
growers quickly became interested in the possibilities of using
them as substitutes for bordeaux mixture. An effective bor-
deaux mixture requires careful mixing which involves consider-







Melanose of Citrus 31
able labor and time. In general, these newer copper materials
are easier to employ than bordeaux, since they do not require
mixing with lime for neutralization. Since lime is not required
less residue is deposited on the sprayed parts, which probably
accounts for the fact that scale infestations are less difficult to
control following this type of spray than following bordeaux
mixture (22). Thompson (27, 30) demonstrated that lime resi-
dues on citrus foliage distinctly favor scale increases.
A number of the "insoluble" copper sprays were compared with
bordeaux mixture for control of melanose. They included copper
ammonium silicate in both paste and powder forms, tri-basic
copper sulfate (53% copper as metallic), red cuprous oxide, cop-
per zeolite, and a basic copper sold as copper hydroxide (26%
copper as metallic). In addition, a proprietary copper-oil emul-
sion (said to contain copper oleate) was compared with bordeaux
mixture in 1934.
The location, variety and age of the trees, the spray formulas,
and the results in melanose fruit blemish control are shown in
Table 4.
Results of these tests show that bordeaux mixture 6-6-100 con-
sistently gave more effective control of melanose than any of
the proprietary copper sprays compared with it. Two of the new
sprays controlled infection as well as, or slightly better than,
3-3-100 bordeaux mixture. These were red cuprous oxide and
tri-basic copper sulfate.
The red cuprous oxide was originally manufactured and sold
as a seed disinfectant, but in recent years has found considerable
use as a spray for vegetables, tobacco, and other crops where
bordeaux mixture has proved undesirable for one cause or an-
other. The form used in these tests contained approximately
85% metallic copper, was comparatively heavy for its bulk, and
settled rapidly in the spray tank unless constantly agitated. It
was applied with a special spreader of emulsified cottonseed oil,
which was objectionable in that it was time-consuming to prepare
in the spray tank, before adding the copper material. The fin-
ished spray, however, possessed good spreading and wetting
qualities, left little visible residue on the sprayed parts, and
injury to foliage and fruits was not observed following its use.
The control of melanose was consistently good with this material
(Table 4, 1935-37).
Recently, red cuprous oxide has been greatly improved for
spray purposes. It may now be purchased in package form with







32 Florida Agricultural Experiment Station
spreader already added, and needs only to be mixed with water
to make the finished spray. This new form contains less metallic
copper and should be used at greater concentrations than the
original form. The senior writer has obtained excellent results
with this spray for the control of diseases of avocado and vege-
tables, and it appears to be worthy of trial as a fungicide for
control of citrus diseases.
Tri-basic copper sulfate at 3 pounds to 100 gallons gave fairly
consistent control which was about equal to that obtained with
3-3-100 bordeaux mixture. The results were somewhat better
with this spray when oil emulsion (1-200 to 1-400) was added as
spreader, rather than calcium caseinate or a non-casein colloidal
spreader. A minor form of copper injury, known as stellatee
melanose," sometimes developed on the foliage following the use
of this spray. Tri-basic copper sulfate also has been improved
for spray purposes in recent years, chiefly in that the particle
size has been reduced and the material remains in suspension bet-
ter than formerly. Particle dispersion on citrus foliage has been
improved by increasing the fineness of the material.
The basic copper sold as copper hydroxide, and containing 26%
metallic copper, gave less effective control at the recommended
strength of 4 pounds to 100 gallons than 3-3-100 bordeaux mix-
ture or red cuprous oxide, with which it was compared (Table 4,
1937). No injury was observed following its use.
Copper ammonium silicate was first obtained as a paste, which
possessed no special advantages over bordeaux and gave less
effective control of melanose at the recommended concentrations.
In 1935 this material was obtained as a powder and was consider-
ably easier to handle. The powdered form contained 22 percent
metallic copper, and at the recommended concentration of 3
pounds to 100 gallons, was less effective than bordeaux mixture
3-3-100 in the 1935-36 experiments. The concentration of copper
in the finished spray was lower than with the other copper sprays
it was compared with, and this may account for its failure to
control infection more effectively (Table 4, 1935, 1936). Injury
to foliage and fruits was not observed following its use.
The proprietary copper-oil emulsion and copper zeolite showed
little promise as substitutes for bordeaux mixture for control of
melanose in tests carried out for one season.
Insecticides compatible with bordeaux mixture may be com-
bined safely also with tri-basic copper sulfate, red cuprous oxide,








Melanose of Citrus 33

and copper ammonium silicate. When oil emulsions or wettable
and bentonite sulfurs are combined with these copper materials,
the addition of special spreaders is unnecessary for good cover-
age. The advantages of such materials in the saving of time and
labor for preparation of the finished spray, and the gain in uni-
formity and stability of the spray mixture over home-made
bordeaux mixture is evident. In general, there is less tendency
for the "insoluble" copper spray to burn immature citrus foliage
than is the case with bordeaux mixture.

SULFUR SPRAYS

Germination studies with spores of D. citri on glass slides
sprayed with sulfur sprays showed that liquid lime-sulfur 2/2-100
inhibited spore germination when it was first applied, but rap-
idly lost its fungicidal effectiveness from weathering. Adding
bentonite sulfur increased the effectiveness of the spray and
retarded the loss of toxicity from weathering. Thus, on glass
slides sprayed with lime-sulfur 2%-100, 64 percent of the spores
germinated in drops of water placed on the sprayed surfaces
after 8 days of exposure to weathering, and 83 percent germin-
ated after 22 days of exposure. When bentonite sulfur 3 pounds
to 100 gallons was added to the lime-sulfur spray, germination
was reduced to 15 percent after 8 days and 26 percent after 22
days of exposure. The germination was approximately 99 per-
cent on unsprayed slides. Other sulfur sprays tested were less
effective in inhibiting germination than lime-sulfur with ben-
tonite sulfur.
These studies indicated that a single application of lime-sulfur-
bentonite sulfur could be expected to give only slight control
of infection. There was a possibility, however, that repeated
applications of this spray during the period when the fruits are
most susceptible to infection might give fairly effective control
of melanose and at the same time inhibit the development of
insects inimical to citrus.
Experiments to test the possibilities of using lime-sulfur sprays
for the control of melanose were made under varied conditions
of infection. The data are recorded in Table 5.
The results obtained in these experiments show conclusively
that it is impractical to attempt to control melanose with lime-
sulfur sprays. At Babson Park in 1933 and 1934 three applica-
tions of lime-sulfur-bentonite sulfur timed at intervals of two
weeks during April and May reduced infection considerably less




TABLE 4.-COMPARISON OF BORDEAUX MIXTURE WITH OTHER COPPER SPRAYS FOR THE CONTROL OF MELANOSE
FRUIT BLEMISH IN COMMERCIAL GROVES


Locality
and
Year



Babson
Park
1933






Babson
Park
1934



Lake
Alfred
1934







Flor'nce
Villa
1935


Seeded
grapefruit
19 years
of age

Valencia and
Pineapple
oranges
12 years
of age






Seeded
grapefruit
20 years
of age


Variety
and Age
of Trees



Seeded
grapefruit
18 years
of age


Pruned


SPRAYING PROGRAM


Condition
of Trees
With Regard
to Dead Wood





Not pruned







Not pruned




Pruned


check

bordeaux 6-8-100
copper ammonium silicate
(paste) 4-100
check

bordeaux 3-3-100
dry lime-sulfur 5-100,
bentonite sulfur 3-100
red cuprous oxide (85%), 1-100
dry lime-sulfur 5-100
bentonite sulfur 3-100
copper ammonium silicate
(22%) 3-100
dry lime-sulfur 5-100
bentonite sulfur 3-100
basic copper sulfate (53%) 3-100
dry lime-sulfur 5-100
bentonite sulfur 3-100


None to Slight Mod'rte Severe
Date Very
Applied Slight


Materials and Concentrations


check

bordeaux 3-4-100
ilquid lime-sulfur 2%-100
liquid lime-sulfur 2-100

copper ammonium silicate
(paste) 22-100
liquid lime-sulfur 21/2-100
liquid lime-sulfur 2-100
check

bordeaux 6-8-100
proprietary copper-oil
emulsion 2-100
basic copper sulfate (53%)
3-100 + 1% oil


percent percent percent
34.0 9.7 3.6


percent
52.7

Apr. 7
Apr. 20 90.7
May 4

Apr. 7
Apr. 20 84.4
Vlay 4
| 6.4

Apr. 9 77.2

Apr. 9 34.0

Apr. 9 65.0
37.6

Apr. 19 94.6

Apr. 19 89.4
16.9

Apr. 17
May 14 95.6

Apr. 17
May 14 94.8


Apr. 17
May 14 85.3

Apr. 17
May 14 90.3


8.4



13.4

22.6

20.9

45.9

30.9
42.9

5.1

9.7
22.0

3.4

4.0



10.3

8.4


0.7 0.2



1.4 0.8

44.3 1 26.7

1.6 0.3

15.9 4.2

3.3 0.8
14.9 4.6

0.3 0.0

0.8 0.1
30.1 31.0

0.8 0.2

1.1 0.1



3.3 1.1

1.1 0.2





Vero
Beach
1935






Lake
Alfred
1935



Lake
Alfred
1936



Lake
Alfred
1936



Lake
Alfred
1937


Valencia
oranges
10 years
of age





Seeded
grapefruit
12 years
of age

Valencia and
Pineapple
oranges
14 years
of age


Seeded
grapefruit
13 years
of age


Valencia and
Pineapple
oranges
15 years
of age


Seeded
grapefruit
14 years
of age


Pruned


Pruned


Pruned


Pruned


Not pruned


check
bordeaux 6-6-100

bordeaux 3-3-100
dry lime-sulfur 5-100,
bentonite sulfur 2-100
basic copper sulfate (53%) 3-100
dry lime-sulfur 5-100,
bentonite sulfur 2-100
copper ammonium silicate
(22%) 3-100
dry lime-sulfur 5-100,
bentonite sulfur 2-100
check
bordeaux 3-3-100, bentonite
sulfur 6-100
basic copper sulfate (53%)
3-100, bentonite sulfur 6-100
check

bordeaux 3-3-100

red cuprous oxide (85%) 1-100
copper ammonium silicate
(22%) 3-100
check
bordeaux 3-3-100, wettable
sulfur 10-100
basic copper sulfate 3-100 (53%),
wettable sulfur 10-100
check
bordeaux 3-3-100

red cuprous oxide (85%) 1-100

copper hydroxide (26%) 4-100


Apr. 19

Apr. 19
May 21


60.7 21.7 10.5 7.1
Apr. 25 95.5 3.3 0.8 0.4

Apr. 25 96.2 2.8 0.9 0.1

45.1 32.6 16.1 6.2

Apr. 7 97.9 1.5 0.4 0.2

Apr. 7 93.1 5.1 1.3 0.5

Apr. 7 88.1 10.0 1.7 0.2


Mar. 31

Mar. 31

Apr. 21

Apr. 21

Apr. 21


copper zeolite (25%) 4-100 Apr. 21
check

bordeaux 3-3-100 Apr. 21

red cuprous oxide (85%) 1-100 Apr. 22

copper hydroxide (26%) 4-100 Apr. 21


54.1

97.3

96.3
23.2
72.1

75.0

63.7

59.9
49.1

89.8

94.0

80.8


26.4

2.4

2.8
53.5
19.6

19.3

29.6

32.9
22.7

6.0

4.4

8.7


Pruned


Lake
Alfred
1937


34.6
5.3

18.6


18.2


30.5


.


,


24.3
0.8

2.7


2.6


13.6






TABLE 5.-SULFUR SPRAYS COMPARED WITH BORDEAUX MIXTURE FOR CONTROL OF MELANOSE FRUIT BLEMISH
Locality Variety and Condition SPRAYING PROGRAM Melanose on Mature Fruit
and Approxime With Regard Materials and Concentrations Date Very light Moder-Severe
Year Age of Trees to Dead Wood Applied Slight rate

Percent percent percent percent
check 52.7 34.0 9.7 3.6
bordeaux mixture 3-4-100 Apr. 7
lime-sulfur 21/2-100 Apr. 20 90.7 8.4 0.7 0.2
Babson Seeded lime-sulfur 2-100 May 4 Q
Park grapefruit lime-sulfur 21/2-100,
1933 18 years Not pruned bentonite sulfur 4-100 Apr. 7
of age lime-sulfur 2%1-100,
bentonite sulfur 4-100 Apr. 20 79.4 17.4 2.3 0.9
lime sulfur 2-100, bentonite
sulfur 4-100 May 4
colloidal sulfur 1-100 Apr. 7
colloidal sulfur 1-100 Apr 20 62.4 26.9 8,2 2.5
colloidal sulfur 1-100 May 4
check 20.1 34.7 38.2 7.0
Seedling
Largo grapefruit Not pruned bordeaux 3-4-100 Apr. 17 54.7 20.1 18.0 7.2
1933 24 years
of age lime-sulfur 21/2-100,
wettable sulfur 5-100 Apr. 17 38.0 33.8 23.3 4.9
check 6.4 22.6 44.3 26.7 a
bordeaux 6-8-100 Apr. 9 77.2 20.9 1.6 0.3
lime-sulfur 2%-100
Babson Seeded bentonite sulfur 4-100 Apr. 9
Park grapefruit lime-sulfur 2%-100
1934 19 years Not pruned bentonite sulfur 4-100 Apr. 24 26.1 35.2 28.1 106
of age lime-sulfur 2%-100,
bentonite sulfur 4-100 May 7
lime-sulfur 2%-100, Apr. 9
lime-sulfur 2%-100, Apr. 24 19.6 43.3 29.1 8.0
lime-sulfur 2%-100, May 7





check 17.6 54.0 20.4 8.0
Lake Pineapple
Alfred oranges Pruned bordeaux 6-8-100 Apr. 20 91.8 7.9 0.3 0.0
1934 12 years lime-sulfur 2%-100,
of age bentonite sulfur 4-100 Apr. 20 45.4 40.6 9.5 4.5
check 31.1 46.6 18.6 3.7
Lake Valencia
Alfred oranges Pruned bordeaux 6-8-100 Apr. 20 95.1 4.7 0.2 0.0
1934 12 years lime-sulfur 2y-100,
of age bentonite sulfur 4-100 Apr. 20 | 33.5 40.7 20.6 5.2
check 27.2 53.4 16.0 3.4
Lake Seeded
Alfred grapefruit Pruned bordeaux 6-8-100 Apr. 20 93.4 5.4 0.8 0.4
1934 12 years lime-sulfur 22-100,
of age bentonite sulfur 4-100 Apr. 20 35.2 43.8 17.4 3.6
check 16.9 22.0 30.1 31.0

Flor- Seeded bordeaux mixture 3-3-100 Apr. 17
ence grapefruit dry lime-sulfur 5-100,
Villa 20 years Pruned bentonite sulfur 3-100 May 14 95.6 3.4 0.8 0.2
1935 of age dry lime-sulfur 5-100,
bentonite sulfur 3-100 Apr. 17
dry lime-sulfur 5-100,
bentonite sulfur 2-100 May 14 73.5 14.2 7.1 5.1
check 28.9 38.1 24.7 8.3
Valencia
Vero oranges bordeaux mixture 6-6-100 Apr. 19 93.9 5.3 0.8 0.0
Beach 10 years Not pruned dry lime-sulfur 5-100,
1935 of age bentonite sulfur 3-100 Apr. 18
dry lime-sulfur 5-100,
bentonite sulfur 2-100 May 21 31.6 39.5 23.4 6.0
check 45.1 32.6 16.1 6.2
Lake Valencia
Alfred oranges Pruned bordeaux 3-3-100 Apr. 7 97.9 1.5 0.4 0.2
1936 14 years lime-sulfur 2Y-100,
of age bentonite sulfur 4-100 Apr. 8 49.9 32.3 12.8 5.0







38 Florida Agricultural Experiment Station
than one application of bordeaux mixture (Table 5). In one
grove at Florence Villa in 1935 dry lime-sulfur-bentonite sulfur
applied on April 17 and repeated on May 14 was fairly effective
on pruned grapefruit trees, but the fruit sprayed in the same
manner from unpruned orange trees at Vero Beach showed nearly
as much infection as fruit from the control plots (Table 5, 1935)
In practically every test fruits from plots sprayed only once with
lime-sulfur-bentonite sulfur showed nearly as severe melanose
blemish as the fruit from unsprayed trees. A paste form of col-
loidal sulfur used at Babson Park in 1935 proved to be practical-
ly worthless for control.
MERCURY-OIL EMULSIONS
An oil emulsion containing ethyl mercury oleate as fungicide
was introduced into Florida about 1932 and offered for sale as a
substitute for bordeaux-oil emulsion. Samples of the spray
material were furnished by the manufacturer and it was includ-
ed in some of the tests for comparison with bordeaux mixture-
At recommended concentrations the oil emulsion in the spray
was expected to suppress citrus insects that were controlled by
ordinary commercial oil emulsions.
The comparative results in melanose fruit blemish control with
the mercury-oil preparation and with bordeaux mixtures are
recorded in Table 6. The organic mercury-oil emulsion is inef-
fective for the control of melanose. The oil in the spray was not
superior to ordinary cheaper oil emulsions for insect control, so
the preparation has nothing to recommend it for use as a citrus
spray.
ZINC SULFATE
Growers became interested in the application of zinc sulfate
to citrus trees as a means of correcting "frenching" in 1934 and
1935, following the experiments with zinc on bronzing of tung
trees by Mowry and Camp (19) and on frenching of citrus by
Camp (3). Zinc sprays are widely used at present on citrus in
Florida (4).
With the increased use of zinc sprays the question arose as to
whether these sprays would reduce melanose if applied at the
critical time for infection. The toxicity of a spray film of 10-8-
100 zinc sulfate-lime to spores of D. citri, was very slight com-
pared with 3-4-100 bordeaux mixture in laboratory tests.
In a grove of Valencia orange trees in full bearing near Lake Al-
fred an experiment was carried out to determine the effect on
control of melanose of combining bordeaux mixture with zinc sul-







38 Florida Agricultural Experiment Station
than one application of bordeaux mixture (Table 5). In one
grove at Florence Villa in 1935 dry lime-sulfur-bentonite sulfur
applied on April 17 and repeated on May 14 was fairly effective
on pruned grapefruit trees, but the fruit sprayed in the same
manner from unpruned orange trees at Vero Beach showed nearly
as much infection as fruit from the control plots (Table 5, 1935)
In practically every test fruits from plots sprayed only once with
lime-sulfur-bentonite sulfur showed nearly as severe melanose
blemish as the fruit from unsprayed trees. A paste form of col-
loidal sulfur used at Babson Park in 1935 proved to be practical-
ly worthless for control.
MERCURY-OIL EMULSIONS
An oil emulsion containing ethyl mercury oleate as fungicide
was introduced into Florida about 1932 and offered for sale as a
substitute for bordeaux-oil emulsion. Samples of the spray
material were furnished by the manufacturer and it was includ-
ed in some of the tests for comparison with bordeaux mixture-
At recommended concentrations the oil emulsion in the spray
was expected to suppress citrus insects that were controlled by
ordinary commercial oil emulsions.
The comparative results in melanose fruit blemish control with
the mercury-oil preparation and with bordeaux mixtures are
recorded in Table 6. The organic mercury-oil emulsion is inef-
fective for the control of melanose. The oil in the spray was not
superior to ordinary cheaper oil emulsions for insect control, so
the preparation has nothing to recommend it for use as a citrus
spray.
ZINC SULFATE
Growers became interested in the application of zinc sulfate
to citrus trees as a means of correcting "frenching" in 1934 and
1935, following the experiments with zinc on bronzing of tung
trees by Mowry and Camp (19) and on frenching of citrus by
Camp (3). Zinc sprays are widely used at present on citrus in
Florida (4).
With the increased use of zinc sprays the question arose as to
whether these sprays would reduce melanose if applied at the
critical time for infection. The toxicity of a spray film of 10-8-
100 zinc sulfate-lime to spores of D. citri, was very slight com-
pared with 3-4-100 bordeaux mixture in laboratory tests.
In a grove of Valencia orange trees in full bearing near Lake Al-
fred an experiment was carried out to determine the effect on
control of melanose of combining bordeaux mixture with zinc sul-




COMPARED WITH BORDEAUX MIXTURES FOR THE CONTROL OF MELANOSE.


SPRAYING PROGRAM


Materials and Concentrations


Locality
and
Year



Largo
1934





Babson
Park
1934


Lake
Alfred
1934

Lake
Alfred
1934

Lake
Alfred
1935

Lake
Alfred
1936

Lake
Alfred
1937


check
bordeaux 6-8-100
mercury-oil emulsion 1 2/3-100


Date
Applied


Variety
andc-Age-
of Trees



Seedling
grapefruit
25 years
of age


Condition of
Trees With
Regard to
Dead Wood




Not pruned


check
bordeaux mixture 6-8-100+1% oil
bordeaux mixture 6-8-100
bordeaux mixture 6-8-100
mercury-oil emulsion 1 2/3-100
mercury-oil emulsion 1 2/3-100
check
bordeaux mixture 6-8-100
mercury-oil emulsion 1 2/3-100
mercury-oil emulsion 1 2/3-100


Apr.21
Apr. 21
Apr. 21


Melanose on Mature Fruit
None to
Very Moder-
Slight Slight ate Severe


percent
0.4

83.4
73.4

0.6


6.4
77.2


17.6
91.8
53.6


percent percent
9.8 37.2

12.9 2.9
21.3 3.7


percent
52.6

0.8
1.6

44.8


0.3

15.5
8.0
0.0
1.2 -


C.


check 31.1 46.6 18.6 3.7
bordeaux 6-8-100 Apr. 21 55.1 4.7 0.2 0.0
mercury-oil emulsion 1 2/3-100 Apr. 21 50.5 35.4 10.8 3.3
check 32.4 35.4 19.2 13.0
bordeaux 3-3-100 Apr. 17 66.3 16.7 11.1 5.9
mercury-oil emulsion 1 2/3-100 Apr. 17 33.1 37.2 20.5 9.2


Seeded
grapefruit
19 years
of age

Pineapple
oranges
12 years
of age
Valencia
oranges
12 years
of age
Budded
oranges
13 years
of age
Budded
oranges
14 years
of age
Budded
oranges
15 years
of age


Apr. 7
Apr. 8


Apr. 21
Apr. 22


Apr. 9
Feb. 6
Apr. 9


I -


check
bordeaux 3-3-100
mercury-oil emulsion 1 2/3-100
check
bordeaux 3-3-100
mercury-oil mulsion 1 2/3-100


Jan.
Apr.
Apr.
Jan.
Apr.


Not pruned




Pruned


Pruned



Pruned



Pruned



Pruned


---I-'L-


,


I -


TABLE 6.-MERCURY-OIL EMULSION







40 Florida Agricultural Experiment Station
fate in both acid and basic forms. A mild form of frenching was
general in the trees. The following sprays were tested compara-
tively in replicated plots: 3-3-100 bordeaux mixture, 3-3-100 bor-
deaux mixture combined with 5-2V2-100 zinc sulfate-lime, 3-3-100
bordeaux mixture combined with 7-100 basic zinc sulfate, 5-2/2-100
zinc sulfate-lime, and 7-100 basic zinc sulfate.
The addition of either form of zinc to bordeaux mixture gave
slightly increased control of melanose on the fruit over control
obtained by plain bordeaux. Either form also gave a slight re-
duction of infection when used alone.j The frenched condition
of the foliage was improved in every plot where zinc was applied.
uhe use of the zinc sulfate-lime spray caused an increase in
umbers of purple scale over control plots in every case, but the
data on scale increases following basic zinc sulfate alone were
conflicting/ In one replication a large increase in purple scale
followed its use while in others it apparently had no effect in
increasing these insects.
Although the tests were for only one season they showed
rather conclusively that zinc sulfate as used for correction of
frenching is practically worthless for direct control of melanose
infection. It is possible that some reduction of melanose infec-
tion may result from its use indirectly through stimulation to
the trees.
WETTABLE SULFURS AND COPPER SPRAYS COMBINED
FOR CONTROLLING MELANOSE AND RUST MITES
The possibility of adding wettable sulfur to bordeaux mixture
for combined control of citrus insects and diseases in Florida was
first reported by Yothers (35) in 1935. He found that when the
combination spray was applied at the peak of the crawler and
first larval stage purple scales were held in check, but he did not
report on its effect on melanose control.
Tests were made in 1935 and 1936 for melanose and rust mite
control, in which combinations of bordeaux mixture and wet-
table or bentonite sulfurs were compared with combinations of
bordeaux mixture with oil emulsion or a non-casein colloidal
spreader. Tri-basic copper sulfate was also combined with ben-
tonite or wettable sulfur to determine whether an insoluble pro-
prietary copper would give results comparable with bordeaux
mixture in combinations of this kind. The tests were made co-
operatively with W. L. Thompson of the Citrus Experiment
Station, who studied the effect of the melanose sprays and varia-
tions in the follow-up applications on insect and mite infestations.








Melanose of Citrus 41
The spray materials applied during the period of melanose in-
fection, dates of application, and results obtained for the control
of melanose, are given in Table 7.
The control of melanose was most effective where wettable or
bentonite sulfur was added to bordeaux mixture in three of the
tests (Table 7), and in the fourth (Pineapple oranges) control
was as good with bordeaux-wettable sulfur as with bordeaux-
oil. The tests also showed that basic copper sulfate and wettable
sulfurs are compatible and that the combination of the two will
control melanose equally as well as the combination of bordeaux
mixture and wettable sulfurs.

CONTROL OF INSECTS FOLLOWING MELANOSE SPRAYS
The investment in time and money for control of melanose will
be largely wasted if damage to the fruit or trees from rust mites
or scale insects is not prevented during the growing season. In
a spray schedule for the control of melanose provision must be
made for checking these pests, since they usually increase more
rapidly following the use of effective fungicides, which in this
case are the copper sprays, than when such fungicides are not
applied.
Experiments to develop improved methods for control of in-
sect pests and mites which attack citrus were being made by W.
L. Thompson during the period when the writers were making
the experimental tests for control of melanose. The melanose
test plots were utilized by Thompson to secure information on
the relative scale build-up and ease of control with scalecides
following many of the fungicides under test, as well as to secure
other pertinent data regarding pest control in connection with
spraying for melanose. Many of the data relating to insect con-
trol from these plots and from other experimental tests in con-
nection with spraying for disease control have been reported
by Thompson (27, 28, 29) and by Ruehle and Thompson (22).
The percent increase of scale insects is generally greater fol-
lowing an application of 6-6-100 bordeaux mixture than when
following 3-3-100 bordeaux. The percent increase of these insects
is also generally greater following an application of bordeaux
mixture than when following basic copper sulfate, red cuprous
oxide, or copper ammonium silicate, when comparable amounts
of metallic copper are used in the spray formulas. As a corol-
lary, scalecides are somewhat more effective when they follow
3-3-100 bordeaux than when 6-6-100 is the fungicide, and are












TABLE 7.-COMPARISON OF COPPER SPRAYS COMBINED WITH WETTABLE SULFURS AND OIL EMULSIONS FOR CONTROL
OF MELANOSE.


Condition
of Trees
With Regard
to Dead Wood




Not pruned


Pruned


SPRAYING PROGRAM

Materials and Concentrations


Melanose on Mature Fruit
None to
Date Very


Applied I Slight Slight ]Mod'rtel Severe
percent percent percent percent
check 28.9 38.1 24.7 8.3
bordeaux 3-3-100, wettable
sulfur 5-100 Apr. 19
dry lime-sulfur 5-100, May 21 83.2 14.8 1.7 0.3
bentonite sulfur 2-100
bordeaux 3-3-100, non-casein
colloidal spreader Apr. 19
dry lime-sulfur 5-100, May 21 77.3 18.6 2.7 1.4
bentonite sulfur 2-100


cnecK
bordeaux 3-3 100, wettable
sulfur 10-100
bordeaux 3-3-100, wettable
sulfur 5-100
lime-sulfur 2-100, wettable
sulfur 5-100
bordeaux 3-3-100, oil as
emulsion V2 %
lime-sulfur 2-100, selocide 1-800


Apr. 23

Apr. 23
May 28


Apr. 23
May 23


1.3


1.5


Locality
and
Year




Vero
Beach
1935


Lake
Alfred
1935


Variety
and Age
of Trees



Valencia
oranges

10 years
of age


Pineapple
oranges

12 years
of age


I I ___ ______





check-dusted with sulfur dust ) 60.7 21.7 10.5 7.1
bordeaux 3-3-100, wettable
sulfur 5-100 Apr. 25
liquid lime sulfur 1-100, June 4 95.7 3.6 0.5 0.2
wettable sulfur 6-100
bordeaux 3-3-100, bentonite
Seeded sulfur 6-100 Apr. 25
Lake grapefruit liquid lime sulfur 14-100, June 4 95.5 3.3 0.8 0.4
Alfred Pruned bentonite sulfur 6-100
1935 12 years bordeaux 3-3-100, oil as
of age emulsion Y2% Apr. 25
lime sulfur 1%-100 May 15 91.4 6.8 1.3 0.5
bordeaux 3-3-100, non-casein
colloidal spreader %-100 Apr. 25
lime sulfur 1%-100 May 15 85.8 10.7 2.5 1.0
basic copper sulfate 3-100,
bentonite sulfur 6-100 Apr. 25
dry lime-sulfur 5-100, June 4 96.2 2.8 0.9 0.1
bentonite sulfur 6-100
check-lime sulfur 2-100,
wettable sulfur 6-100 Apr. 27 54.1 26.4 11.3 8.2
bordeaux 3-3-100, wettable
sulfur 10-100
lime-sulfur 1%-100, wettable Mar. 31
sulfur 5-100 May 26 93.3 5.3 1.2 0.2
bordeaux 3-3-100, non-casein
Seeded colloidal spreader Mar. 31
Lake grapefruit lime-sulfur 2-100, wettable Mar. 31
Alfred Pruned sulfur 6-100 Apr. 27 92.9 6.0 0.8 0.3
1936 13 years basic copper sulfate 3-100,
of age wettable sulfur 10-100 Mar. 31
lime-sulfur 2-100, wettable June 5 96.4 2.8 0.6 0.2
sulfur 6-100
bordeaux 3-3-100, bentonite
sulfur 10-100 Mar. 31
dry lime-sulfur 5-100, June 5 98.1 1.7 0.2 0.0
bentonite sulfur 6-100








44 Florida Agricultural Experiment Station
still more effective when they follow proprietary copper sprays.

Oil emulsions proved to be the most satisfactory scalecides in
most cases. In extensive experiments oil emulsions at concen-
trations of 1% to 1 2/3 percent of oil have proved more satisfac-
tory for the control of red scale than weaker concentrations, but
emulsions containing 14 to 1% percent oil have given good
control of purple scale. Infestations of both insects vary con-
siderably in different localities and in different seasons. The
results of experiments indicate that red scale are more abundant
and more difficult to control in groves along the East Coast of
Florida than along the West Coast, and in the central part of the
state are seldom a serious problem. Purple scale have been less
common and more readily controlled along the East Coast than
along the West Coast and in central Florida, but in recent years
this pest has become almost as serious as red scale in some situa-
tion along the East Coast. Therefore, the concentration of oil
best adapted to a particular grove should be used.
Results to date indicate that for the control of scale insects the
most opportune time for applying the oil spray is between the
latter part of May and the first of July, especially if the fruit is
to be kept free from serious red scale infestation. Regardless of
the date of spraying one of the most important factors in scale
control is thoroughness of application. Good coverage is abso-
lutely necessary for good control.
Three well timed lime-sulfur sprays following a single copper
spray for the control of melanose may be used to check purple
scale if these pests are scarce and red scale are not present. An
application of lime-sulfur 2%-100, made about three weeks after
the copper spray has been applied, will be quite effective in re-
ducing the population of scale insects, whitefly and mites in
average years. Rust mites usually do not appear in damaging
numbers before the middle of June or later if this application has
been thorough. If the lime-sulfur schedule is followed, however,
a second application of lime-sulfur 1l2-100 should be made in
June for the purpose of checking purple scale, even though there
are not enough rust mites present to warrant spraying. The third
application of lime-sulfur may be made when needed for rust
mite control. If the first two applications gave rust mite pro-
tection well into the summer a sulfur dust may be substituted
for the third spray, especially if the fruit is of an early variety
and scale insects are not increasing. The effectiveness of either







Melanose of Citrus 45
liquid or dry lime-sulfur against purple scale and rust mite is
increased by the addition of either wettable or bentonite sulfur.
It has been observed that a rather heavy leaf drop often occurs
when lime-sulfur follows within several weeks after an applica-
tion of bordeaux mixture, which is a serious objection to the lime-
sulfur schedule for control of purple scale following the melanose
application. There has also been observed, in recent years, an
increasing tendency for lime-sulfur sprays to cause a burn of the
fruit, especially on oranges. The lime-sulfur schedule is not so
practical as formerly because wettable sulfurs may be combined
with the copper sprays for rust mite control.
The results from adding bentonite or wettable sulfurs to the
copper sprays were very satisfactory from the standpoint of rust
mite control. It was necessary, in the grapefruit tests at Lake
Alfred (Table 7), to apply a sulfur spray for control of mites 3
to 4 weeks after the melanose spray in those plots where wet-
table sulfurs were not added to the copper spray. This applica-
tion of sulfur after the melanose spray was unnecessary in plots
where the copper-wettable sulfur combination sprays were ap-
plied for melanose control, thus effecting the saving of one spray
application in the schedule. The addition of 10 pounds of wet-
table sulfur to each 100 gallons of spray gave better protection
from rust mites than one-half this amount.
The results show rather conclusively that the addition of wet-
table sulfur to the copper spray is highly practical. Some control
of scale crawlers is accomplished, early rust mite damage to the
fruit is eliminated, and the use of other spreaders is unnecessary
when the combination is used. Spray injury was not observed
as a result of its use.
DISCUSSION AND CONCLUSIONS
The consumer's preference for fruit of attractive appearance
and his willingness to pay a premium for it is the primary reason
for the growers' endeavor to produce bright fruit.
Conditions beyond the control of the grower are responsible for
some of the lowering of grade but a great many of the factors
that affect the appearance of Florida citrus fruit, and conse-
quently its grade and sale price, are controllable blemishes caused
by insects and diseases, of which melanose is the most important.
A program for the control of melanose should be practical if
it is to be justified. --That is, the grower should realize some pro-
fit, over a period of years, from his investment in labor and cost







46 Florida Agricultural Experiment Station

of materials necessary to carry out the program. \Absolute com-
mercial control of melanose fruit blemish may be accomplished
by repeated applications of strong bordeaux mixture during the
period when infection takes place, but such a practice under
Florida conditions would be undesirable from the standpoint of
efficiency as well as economy. Not only the cost of control of
melanose would be high, but the cost of subsequent necessary
control measures for scale insects and mites would become ex-
cessive because these pests increase, and often with amazing
rapidity, when spray residues non-toxic to insects are deposited
on citrus trees.
The most practical program for control, therefore, may be the
one which falls somewhat short of giving complete commercial
control of melanose but does not make the subsequent control
of insects excessive. From the results obtained from these ex-
periments and from observations of spraying results in com-
mercial groves it is apparent that most of the melanose infPetion
ui abe vented by theplication of an efficient
co er fungicide two to three weeks after the petals are off in
tr s whic yve sh-eta normal bloom.
As a general rule the petals are shed some time from the mid-
dle of March until the first of April. From the middle of March
until the middle of Aprilis.uslual ly adry period and unfavorable
to infection, although there have been some notable exceptions to
this_.Most of thp fruit infection occurs during rainy periods from
tri latter p-rt of April until the first of June. in average years.
t ears.
It is best not t dey raving longer than three weeks after
most of the petals are off however, regardless of the time when
this shedding takes place. Abundant infection occurring shortly
after the bloom results in the production of severely blemished
fruits which are graded out at packing time. Infection that -
c on frts which are approaching ractica immunity results
in- the production of a minute type of melanose which does not
affect the grade seriously.
Homemade bordeaux mixture, made with equal amounts of
bluestone and hydrated lime, has consistently given effective
control of melanose. Single applications of the 6-6-100 formula
have given better control than single applications of lesser con-
centrations, especially under conditions of severe infection. A
3-3-100 bordeaux mixture has given control nearly equal-to that
obtained with the 6-6-100 formula where these sprays were com-
pared in young bearing trees, or in older trees with little dead-







Melanose of Citrus 47
wood or where the deadwood had been removed by pruning.
w post-bloom applications of 3-3-100 bordeaux mixture with
anintrl f three or four weeks between sprayings will give
better control than a single application of the 6-6-100 formula.
The double application should be made only where infection is
expected to h -,-y PserP such as usually occurs in old un-
pruned grapefruit trees, or in groves where drouth or other
unfavorable growth conditions cause a delayed bloom or a suc-
cession of light blooms, so that a large percentage of the fruits
are still susceptible to infection when the summer rains begin.
A pre-growth applicati of cppp fi icide has consistently
given partial control of melanose blemish on the fruit and good
control of infection on the early spring foliage, but in general
this application is impractical unless citrus scab is present. Us-
ually melanose on the spring foliage is not of sufficient import-
ance to warrant control measures, and even though a pre-growth
copper spray has been applied for scab control it is necessary to
apply a post-bloom application of 3-3-100 bordeaux, or its equiva-
lent in some other form of copper, to secure good protection from
melanose on the fruit.
Several of the proprietary copper materials of the so-called
"insoluble" or "neutral" type may be substituted for bordeaux
mixture in the spray schedule with nearly equal control of mel-
anose. Many of these new forms of copper have been developed
since the spraying experiments started and real progress has
been made in recent years toward improving these materials for
spray purposes. A wider use of such sprays may be expected
in the future, since they possess certain advantages over home-
made bordeaux, chief of which are their greater uniformity and
stability, the saving in time and labor in preparation of the spray
mixture, and the.fact that citrus insects do not increase so rapidly
following their use. Although scale infestations are less pro-
nouhced and less' difficult to control following their use, it is
never advisable to disregard scale control whatever the form
of copper used as fungicide. Scale increases may be marked
following any copper sprays unless scalecides are applied.
ITsecticides co patihle with hnrderlx mixture may also be
combined s y th ins ble copper materials. Wettable
or bentonite ulfurs appear to be th st pratial readers to
usewith post-bloom cnpper fungiides. These forms of sulfur
control rust mites and kill many scale crawlers, when added at
the rate of 5 to 10pounds to the 100 gallons of spray. Fungicidal







48 Florida Agricultural Experiment Station
efficiency of the copper is reduced little if any by their addition
to the spray and the combination possesses good spreading qual-
ities. When bentonite sulfur is used, a form with a relatively
high sulfur and low bentonite content is preferred to one which
has low sulfur and high bentonite content, because of lower cost
per unit of sulfur in the former type.
t he addition of 1 percent oil, as emulsion, instead of wettable
sulfur to the post-bloom copper spray, is not practical unless
scale insects or whiteflies are abundant in the trees and are
liable to cause injury before a summer oil emulsion can be ap-
plied. The addition of oil at this concentration increases the
danger of burning or blotching the young fruits and does not
obviate the necessity of applying an oil emulsion later in the
season for scale control. Smaller amounts of oil (% to '/2 per-
cent) may be added to copper sprays to serve as wetting or
spreading agents. A concentration of oil of /2 percent in the
spray will kill rust mites that are hit, but the copper-wettable
sulfur combination will give a more effective kill and longer
protection from these pests.
Other spreaders may be used with the copper sprays that will
have good spreading and wetting qualities, but those tested were
less practical to use than wettable sulfur since they did not
possess insecticidal properties.
Sulfur sprays as a class are relatively ineffective for the con-
trol of melanose and are not practical to use for this purpose. An
organic mercury-oil emulsion likewise proved unreliable for
control.
Whenever efficient copper sprays are applied for melanose
control some extra spraying for scale control will be necessary.
In most cases oil emulsions will prove to be the most satisfactory
scalecides. Thompson (27) has shown that where a light infesta-
tion of purple scale is present and only a single application of
copper spray is made these insects, together with rust mites, may
be controlled by three well timed lime-sulfur sprays, without the
necessity of applying an oil emulsion. However, where Florida
red scales are present or purple scales are abundant, and in all
cases where two applications of a copper spray have been made
for disease control, an oil emulsion of high efficiency should be
thoroughly applied to the trees between the latter part of May and
the early part of July. The spray should be timed, if possible,
when the majority of the scales are in immature stages. It is
essential that thorough coverage be made at this application, not







Melanose of Citrus 49
only of fruits and foliage but also of the limbs and branches.
Scale insects must be hit by the spray to be killed and if a high
mortality is not obtained with this spraying a fall application of
oil emulsion may be necessary. It is advisable to use a high
grade emulsion suitable for summer use and to follow the recom-
mendation of the manufacturer for dilution.
If wettable sulfur is not added to the copper spray it is fre-
quently necessary to dust or spray with sulfur during the interval
between the melanose application and the summer oil spray for
the control of rust mite. The oil emulsion will kill all mites hit
by the spray. During the summer rainy season rust mites are
generally kept in check through natural causes, especially in
groves where a dense cover crop is maintained. It is usually not
necessary, therefore, to apply further control measures for these
pests until some time in the fall, but the grower should be on
the lookout for them and be prepared to dust or spray with
sulfur whenever necessary.
Certai-pecautions should be observed in applying the dif-
ferent spravs used in the schedules, if spray injuries are to be
avoided. Application of lime-slf says should notbeclser
than three weeks to the copper spray, and any application of
sulfur should not be closer than three weeks to an oil application.
It- iabestnot oapplplyan sprays when the trees are wilted and
oil or lime-sulfur sprays should not be applied when the tempera-
ture is above 90 degrees F.
A form ofsrayinjux _known as stellate melanose sometimes
develops entrees sprayed with bordeauxmixtue, triasic copper
sulfate or a roritar vcopper-oil spray. The spots take the
form of raised dark brown excrescences with irregular margins
with from two to six more or less distinct points. They are
larger and more conspicuous than the true melanose spots and
occur more frequently on the leaves than on the fruits. The use
of oil emulsion with, or closely following, the copper sprays ap-
parently favors the formation of these spots. This type of blem-
ish is rarely abundant enough to cause appreciable damage to
the leaves and fruit, but is frequently mistaken for true melan-
ose.
Succulent shoots, up to six or eight inches long, on either
grapefruit or orange trees are often burned severely by copper
or li sprays. T id this of nur pray
should b played whenthe trees arebeinning to flush vigor-
ously. Spraying this kind of growth is seldom necessary for







50 Florida Agricultural Experiment Sta n
melanose control because the timing of spray or control of fruit
infection does not coincide with the time when the trees are
flushing vigorously. It is sometimes desirable to protect suc-
culent growth from melanose infection after low temperature
injury to the trees. Experiments showed that an insoluble cop-
per spray, such as copper ammonium silicate, is safer to use for
this purpose than bordeaux mixtures.
(The practice of keeping the trees reasonably free of dead wood
by pruning is a valuable supplement to spraying for the control
of melanose. Pruning without spraying is not an effective means
of melanose control, but when pruning is regularly practiced the
results from spraying are much more effective than where prun-
ing does not supplement spraying. Generally, good commer-
Scial control of melanose fruit blemish may be accomplished by
the use of weaker spray concentrations where pruning is practic-
ed regularly. This is desirable from the standpoint of insect
control)
Pruning must be done in accordance with sound principles if
it is to accomplish beneficial results. Pruning may, if carelessly
done, actually increase disease or render the tree less resistant.
As a general rule, in pruning citrus trees the cuts should be made
so as to leave no projecting stubs and the tools should be sharp
so as to avoid rough and jagged cuts. Cuts will heal more readily
if branches are cut back to a fork.
The logical time to rune, from the standpoint of melanose
control, is in early or mid-spring, in order to remove much of the
Swood which died during the previous fall and winter months.
The causal fungus is most active in recently killed wood and the
removal of a portion of this wnna hefnre the sprays are applied
eliminates some of the source of infection. Summerpruning
parent as little effect toward reducing melanose infetion.

SPRAY SCHEDULES
Based on experimental data, spray schedules for the control of
melanose and the principal insects inimical to citrus in commer-
cial groves are presented in Table 8. The schedules_ are varied
to cp with different conditions of infectionand t infesta-
tion and the grower should adopt the schedule best suited to his
particular conditions. The success of the spray schedule adopted
will be proportional to the thoroughness with which the sprays
are applied. Good coverage is absolutely essential 'for good
control.










TABLE 8.-SPRAY SCHEDULES.
A. Young bearing trees with little dead wood or B. Old trees with considerable dead wood not
bearing trees of all ages commercially pruned, pruned
Oranges, grapefruit and tangelos Grapefruit and Oranges, grapefruit and tangelos Grapefruit and
SCAB absent or negligible tangelos SCAB absent or negligible tangelos
SCAB present SCAB present
No pre-growth spray Pre-growth spray No pre-growth spray Pre-growth spray
Pre-bloom of 6-6-100 bor- of 6-6-100 bor-
condition deaux or its deaux or its equiv-
equivalent in alent in other
other forms of forms of copper+
copper+oil emul- oil emulsion or
sion or wettable wettable sulfur
sulfur
3-3-100 bordeaux
or its equivalent
In the last in other forms of
of the copper, with wet-
bloom table sulfur 5-10
lbs. to 100 gals.


3-3-100 bordeaux or its equiva-
lent in other forms of copper
with wettable sulfur2 5-10 lbs.
to 100 gals.


6-6-100 bor-
deaux or its
equivalent in
other forms of
copper with
wettable sulfur
5-10 lbs. to 100
gals.


3-3-100 bor-
deaux or its
equivalent in
other forms of
copper with
wettable sulfur
5-10 lbs. to 100
gals.


3-3-100 bordeaux
or its equivalent
in other forms of
copper, with wet-
table sulfur 5-10
lbs. to 100 gals.


I
2-3 weeks
after most
of the
petals are
off









Red scale pres- Red scale ab- 3-3-100 bor-
ent or purple sent and pur- deaux or its
II scale abundant ple scale scarce equivalent in
3-4 weeks other forms of
after I Lime-sulfur copper with
2Vz-100+ wet- wettable sulfur
table sulfur 5 5-10 lbs. to 100
lbs. to 100 aals_ gals.


For rust mites,
if inspection
shows infesta-
tion Sulfur
spray or dust.
This applica-
tion is seldom
necessary.


Summer oil
emulsion 14-
1 2/3 percent
actual oil, the
concentration
depending up-
iu


July I oni severity o
scale infesta-
tion'


Lime-sulfur
11%-100 + wet-
table sulfur 5
lbs. to 100 gals.


For rust mites, if
inspection shows
infestation Sul-
fur spray or dust.
This application is
seldom necessary


Summer oil emul-
sion 1-1 2/3 per-
cent actual oil,
the concentration
depending upon
severity of scale
infestation


For rust mites,
if inspection
shows infesta-
tion Sulfur
spray or dust.
This applica-
tion is seldom
necessary.


Summer oil emulsion 1i4-12%
percent actual oil, the concen-
tration depending upon the
severity of scale infestation.


F or rust miles, Hi
inspection shows
infestation Sul-
fur spray or dust.
This application is
seldom necessary.


Summer oil emul-
sion 1Y4-1% per-
cent actual oil,
the concentration
depending upon
severity of scale
infestation


V For mites and scale- For mites and For mites and scale- For mites and
As Lime-sulfur spray or sulfur dusts scale- Lime-sulfur spray or sulfur dusts scale-
needed Lime-sulfur spray Lime-sulfur spray
or sulfur dusts or sulfur dusts
iCopper sprays-Tri-basic copper sulfate 3-100, copper ammonium silicate 4-100, red cuprous oxide (88%) 1-100, and
basic copper sulfate (26%) 4-100 are about equal in effectiveness to 3-3-100 bordeaux mixture.
2Bentonite sulfurs are also wettable sulfurs. Other spreaders are not needed when wettable sulfurs are added to
copper sprays.
3For best results the oil emulsion should be timed when most of the scale insects are in immature stages. Oil sprays
should be applied thoroughly to limbs and branches as well as foliage and fruit, using high pressures. This spray will
also kill white flies and rust mites that are hit. Red scale are more difficult to control than other scales and if present
in small numbers are potentially dangerous. Greater concentrations of oil are necessary to control this insect than
other citrus scales.


III
6-8 weeks
after I


IV
Last of
May to
T---I_- 1


I I -


'-----








Melanose of Citrus


ACKNOWLEDGMENTS

The writers acknowledge their indebtedness to the several
citrus growers who cooperated in permitting experiments to be
conducted in their groves, and to the insecticide manufacturers
who furnished some of the spray materials used in the experi-
ments. Grateful acknowledgment is made also to Dr. W. B.
Tisdale, Dr. A. F. Camp, and W. L. MThompson for reading the
manuscript and offering helpful suggestions and advice.


LITERATURE OCTED

BACH, WALTER J., and F. A. WOLF. The isolation of the fungus that causes
citrus melanose and the pathological anatomy of the host. Jour. Agric.
Res. 37: 243-252. 1928.
2. BURGER, O. F., E. F. DEBUSK and W. R. BRIGGS. Preliminary report on con-
trolling melanose and preparing bordeaux-oil. Florida Agric.. Exp. Sta.
Bul. 167: 123-140. 1923.
3. CAMP, A. F. The use of zinc sulfate on citrus. Citrus Industry 15 (10): 16, 18.
1934.
4. CAMP, A. F., and B. R. FUDGE. Some symptoms of citrus malnutrition in
SFlorida. Florida Agric. Exy. Sta. Bul. 335: 1-55. 1939.
5. FAWCETT, H. S. Stem-end rot of citrus fruits, (Phomopsis sp.). Florida Agric.
Exp. Sta. Bul. 107: 1-23. 1911.
6. FAWCETT, H. S. The cause of stem-end rot of citrus fruits, Phomsopsis citri
n. sp., Phytopath. 2: 109-113. 1912.
7. FAWCETT, H. S. Temperature relations of growth in certain parasitic fungi.
Univ. Calif. Publ. Agr. Sci., Ser. 4: 183-232. 1921.
8. FAWCETT, H. S. A new Phomopsis of citrus in California. Phytopath. 12:
419-424. 1922.
SFAWCETT, H. S., and H. A. LEE. Citrus diseases and their control. 1st Ed.
-0 McGraw-Hill Book Co. 1926.
S10) FAWCETT, H. S. Citrus diseases and their control 2nd Ed. McGraw-Hill
Book Co. 193
11. FLOYD, B. F. Melanose. Florida Agric. Exp. Sta Ann. Rept. 1910-11; 73-81.
12. FLOYD, B. F., and H. E. STEVENS. Melanose and stem-end rot. Florida Agric.
Exp. Sta. Bul. 111: 1-16. 1912.
13. GROSSENBACHER, J. G. Preventing melanose. Florida Grower 25 (17): 19, 20.
1922.
14. HODGSON, ROBERT W. The pruning of citrus trees in California. California
Agric. Exp. Sta. Bul. 363: 489-532. 1923.
15. KUNTz, WM. A., and GEO. D. RUE LE. Some field experiments for the control
of melanose and stem-end rot of citrus. Proc. Fla. State Hort. Soc. 48:
79-84. 1935.
-16. KUNTZ, WM. A., and GEO. D. RUEHLE. Spraying and pruning for melanose
control. Proc. Fla. State Hort. Soc. 51: 89-102. 1938.
17. KUNTz, W A., and GEo. D. RUE~LE. Control of melanose on citrus. Citrus
Industry 19 (8): 3, 6-7, 15, 18-19, 22 and 19 (9): 11, 12. 1938.
18. McCALLEN, S. E. A. Studies on fungicides II. Testing protective fungicides in
the laboratory. Cornell Univ. Memoir. 128: 8-24. 1930.








Melanose of Citrus


ACKNOWLEDGMENTS

The writers acknowledge their indebtedness to the several
citrus growers who cooperated in permitting experiments to be
conducted in their groves, and to the insecticide manufacturers
who furnished some of the spray materials used in the experi-
ments. Grateful acknowledgment is made also to Dr. W. B.
Tisdale, Dr. A. F. Camp, and W. L. MThompson for reading the
manuscript and offering helpful suggestions and advice.


LITERATURE OCTED

BACH, WALTER J., and F. A. WOLF. The isolation of the fungus that causes
citrus melanose and the pathological anatomy of the host. Jour. Agric.
Res. 37: 243-252. 1928.
2. BURGER, O. F., E. F. DEBUSK and W. R. BRIGGS. Preliminary report on con-
trolling melanose and preparing bordeaux-oil. Florida Agric.. Exp. Sta.
Bul. 167: 123-140. 1923.
3. CAMP, A. F. The use of zinc sulfate on citrus. Citrus Industry 15 (10): 16, 18.
1934.
4. CAMP, A. F., and B. R. FUDGE. Some symptoms of citrus malnutrition in
SFlorida. Florida Agric. Exy. Sta. Bul. 335: 1-55. 1939.
5. FAWCETT, H. S. Stem-end rot of citrus fruits, (Phomopsis sp.). Florida Agric.
Exp. Sta. Bul. 107: 1-23. 1911.
6. FAWCETT, H. S. The cause of stem-end rot of citrus fruits, Phomsopsis citri
n. sp., Phytopath. 2: 109-113. 1912.
7. FAWCETT, H. S. Temperature relations of growth in certain parasitic fungi.
Univ. Calif. Publ. Agr. Sci., Ser. 4: 183-232. 1921.
8. FAWCETT, H. S. A new Phomopsis of citrus in California. Phytopath. 12:
419-424. 1922.
SFAWCETT, H. S., and H. A. LEE. Citrus diseases and their control. 1st Ed.
-0 McGraw-Hill Book Co. 1926.
S10) FAWCETT, H. S. Citrus diseases and their control 2nd Ed. McGraw-Hill
Book Co. 193
11. FLOYD, B. F. Melanose. Florida Agric. Exp. Sta Ann. Rept. 1910-11; 73-81.
12. FLOYD, B. F., and H. E. STEVENS. Melanose and stem-end rot. Florida Agric.
Exp. Sta. Bul. 111: 1-16. 1912.
13. GROSSENBACHER, J. G. Preventing melanose. Florida Grower 25 (17): 19, 20.
1922.
14. HODGSON, ROBERT W. The pruning of citrus trees in California. California
Agric. Exp. Sta. Bul. 363: 489-532. 1923.
15. KUNTz, WM. A., and GEO. D. RUE LE. Some field experiments for the control
of melanose and stem-end rot of citrus. Proc. Fla. State Hort. Soc. 48:
79-84. 1935.
-16. KUNTZ, WM. A., and GEO. D. RUEHLE. Spraying and pruning for melanose
control. Proc. Fla. State Hort. Soc. 51: 89-102. 1938.
17. KUNTz, W A., and GEo. D. RUE~LE. Control of melanose on citrus. Citrus
Industry 19 (8): 3, 6-7, 15, 18-19, 22 and 19 (9): 11, 12. 1938.
18. McCALLEN, S. E. A. Studies on fungicides II. Testing protective fungicides in
the laboratory. Cornell Univ. Memoir. 128: 8-24. 1930.









54 Florida Agricultural Experiment Station

19. MOWRY, HAROLD, and A. F. CAMP. A preliminary report on zinc sulfate as a
corrective for bronzing of tung trees. Florida Agric. Exp. Sta. Bul. 273:
1-34. 1934.
S20.' RHOADS, ARTHUR S., and E. F. DEBUSK. Diseases of citrus in Florida. Florida
Agric. Exp. Sta. Bul 229: 1-213. 1931.
21. RUEHLE, GEO. D., and WM. A. KUNTz. Melanose and stem-rot of citrus. Florida
Agric. Exp. Sta. Ann. Rept. 1933: 139-140.
22. RUEHLE, GEO. D., and W. L. THOMPSON. Commercial control of citrus scab in
Florida. Florida Agric. Exp. Sta. Bul. 337: 1-47. 1939.
23. STEVENS, H. E. Pruning for Melanose. Proc. Fla. State Hort. Soc. 28: 122-
123. 1915.
24. STEVENS, H. E. Melanose II. Florida Agric. Exp. Sta. Bul. 145: 105-116. 1918.
25. STEVENS, H. E., Florida citrus diseases. Florida Agric. Exp. Sta. Bul. 150: 1-
110. 1918.
26. SWINGLE, WALTER T., and HERBERT J. WEBBER. The principal diseases of citrus
fruits in Florida. U. S. Dept. Agric. Div. Veg. Phys. and Path. Bul. 8:
1-42. 1896.
27. THOMPSON, W. L. Lime-sulfur sprays for the combined control of purple scale
and rust mites. Florida Agric. Exp. Sta. Bul. 282: 1-38. 1935.
28. THOMPSON, W. L. Control of purple scale and white flies with lime sulfur.
Florida Agric. Exp. Sta. Ann. Repts. 1935, 1936 and 1937.
29. THOMPSON, W. L. Wettable sulfur as a supplement for lime-sulfur, copper, and
zinc sprays. Citrus Industry 18 (3): 5-7, 18-19. 1937.
30. THOMPSON, W. L. Some possible reasons for the increase of purple scale in-
festations. Citrus Industry 19 (12): 6-7, 17, 20. 1938.
31. TISDALE, W. B. Diseases of lime trees. Proc. Fla. State Hort. Soc. 15: 123-127.
1934.
32. WINSTON, J. R., and J .J. BOWMAN. Commercial control of citrus melanose.
U. S. Dept. Agric. Circ. 259: 1-8. 1923.
33. WINSTON, J. R., J. J. BOWMAN and W. J. BACH. Citrus melanose and its con-
trol. U. S. Dept. Agric. Bul. 1474: 1-62. 1927.
34. WOLF, F. A. The pefect stage of the fungus which causes melanose of citrus.
Jour. Agric. Res. 33: 621-625. 1926.
35. YOTHERS, W. W. Miscellaneous results obtained by the Fruit Insect Investiga-
tions Division of the Bureau of Entomology and Plant Quarantine, Orlando,
Florida. Proc. Fla. State Hort. Soc. 48: 96-97. 1935.




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