• TABLE OF CONTENTS
HIDE
 Title Page
 Credits
 Introduction
 Hosts
 Geographical distribution
 Economic importance
 Symptoms
 Causal organism
 Physiology
 Factors influencing infection
 Studies and results
 Inoculation experiments
 Spore production
 Source of infection
 Modes of over-wintering
 Modes of dissemination
 Time of natural infection
 Period of incubation
 Effects on the physiology of the...
 Susceptibility and resistance in...
 Climatic relations
 Summary
 Literature cited














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 181
Title: Pecan scab
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027267/00001
 Material Information
Title: Pecan scab
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 249-276 : ill., charts ; 23 cm.
Language: English
Creator: Nolen, R. E ( Robert E )
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1926
 Subjects
Subject: Pecan -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 276.
Statement of Responsibility: by R.E. Nolen.
General Note: Cover title.
General Note: Originally presented as: Thesis (M.A.)--University of Florida, 1925.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027267
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000923482
oclc - 18172674
notis - AEN4033

Table of Contents
    Title Page
        Page 249
    Credits
        Page 250
    Introduction
        Page 251
    Hosts
        Page 251
    Geographical distribution
        Page 252
    Economic importance
        Page 252
    Symptoms
        Page 253
        Page 254
        Page 255
        Page 256
    Causal organism
        Page 257
        Page 258
        Page 259
    Physiology
        Page 260
    Factors influencing infection
        Page 261
        Page 262
    Studies and results
        Page 263
    Inoculation experiments
        Page 264
    Spore production
        Page 264
    Source of infection
        Page 265
    Modes of over-wintering
        Page 266
    Modes of dissemination
        Page 266
    Time of natural infection
        Page 267
    Period of incubation
        Page 268
    Effects on the physiology of the host
        Page 269
    Susceptibility and resistance in varieties of the host
        Page 270
        Page 271
        Page 272
    Climatic relations
        Page 273
    Summary
        Page 274
        Page 275
    Literature cited
        Page 276
Full Text


Bulletin 181


UNIVERSITY OF FLORIDA
Agricultural Experiment Station



PECAN SCAB

By
R. E. NOLEN


Fig. 118.-Scab on the under side of a young pecan leaf.


Bulletins will be sent free upon application to the Experiment Station,
GAINESVILLE, FLORIDA


May, 1926






BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN, Citra
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee

STATION STAFF
WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT, B. S., Vice Director and Animal Industrialist
SAM T. FLEMING, A. B., Assistant to Director
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entomologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUPRECHT, Ph. D., Chemist
R. M. BARNETTE, Ph. D., Assistant Chemist
C. E. BELL, M. S. Assistant Chemist
E. W. COWAN, A. M., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
O. F. BURGER, D. Sc., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKS, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Grass and Forage Crops Specialist
W. A. LEUKEL, Ph. D., Assistant Grass and Forage Crops Specialist
A. F. CAMP, Ph. D., Plant Physiologist, Cotton Investigations
W. A. CARVER, Ph. D., Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
C. V. NOBLE, Ph. D., Agricultural Economist
BRUCE McKINLEY, B. S. A., Assistant in Agricultural Economics
H. G. HAMILTON, M. S., Assistant Agricultural Economist
OUIDA DAVIS ABBOTT, Ph. D., Head, Home Economics Research
GEORGIA WESTOVER, Assistant in Home Economics
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S. A., Pecan Culturist
IDA KEELING CRESAP, Librarian
J. FRANCIS COOPER, B. S. A., Editor
RUBY NEWHALL, Secretary
HENRY ZEIGLER, Farm Foreman
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
J. G. KELLEY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
A. N. BROOKS, Ph. D., Assistant Plant Pathologist (Plant City)
STACY O. HAWKINS, Field Asst. in Plant Pathology (Miami)
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)


K. H. GRAHAM, Auditor
RACHEL MCQUARRIE, Assistant Auditor








PECAN SCAB
By R. E. NOLEN1

INTRODUCTION
The pecan industry in Florida dates from the beginning of
the 20th century, altho a few commercial groves were planted
prior to this time. The number of plantings increased during
the last 20 years until there were 138,000 bearing trees in 1923,
producing 1,215,000 pounds of pecans valued at $340,000. New
orchards are being planted each year, and the production of
pecans is considered as one of the leading horticultural indus-
tries of western Florida.
Shortly after the first commercial plantings came into bear-
ing a fungous disease, known as pecan scab, became so severe
on certain varieties that it became necessary to discard them.
The spread of this disease and the number of varieties suscepti-
ble to it have so increased during the last 20 years that at present
it is considered the most important disease of the pecan. Be-
cause of these conditions considerable control work has been
done and the writer has spent the last two years making a study
of the fungus causing the disease. Control work has not been
conducted by the writer, and this bulletin is not intended to
give the method of control. However, the information con-
tained should be helpful in working out and applying control
methods, and in choosing varieties to set.

HOSTS
Fusicladium effusium Wint., the fungus causing pecan scab,
has been found on practically all of the varieties of the pecan
(Hicoria pecan). It was reported on the Mockernut (Carya
alba) in 1882 (10)*, Carya amara in 1889 (4), and on Pignut
(Carya cordiformis) in 1922 (1). It was found by the writer in
the fall of 1923 on Water hickory (Hicoria aquatica Nutt.) on
the shores of the St. Johns River near Sanford. Fusicladium
carygenum Ell. & Lang., which is considered as identical with
Fusicladium effusum Wint. by Davis (1) and Rand (8) was re-
ported on Carya olivaeformis in 1888 (3). Smith in his transla-

1 This work was done under the supervision of the Plant Pathologist of
the Florida Agricultural Experiment Station, and was presented to the
faculty of the University of Florida in partial fulfillment of requirements
for a master's degree in June, 1925.
*Numbers in parentheses refer to literature cited on page 276.








PECAN SCAB
By R. E. NOLEN1

INTRODUCTION
The pecan industry in Florida dates from the beginning of
the 20th century, altho a few commercial groves were planted
prior to this time. The number of plantings increased during
the last 20 years until there were 138,000 bearing trees in 1923,
producing 1,215,000 pounds of pecans valued at $340,000. New
orchards are being planted each year, and the production of
pecans is considered as one of the leading horticultural indus-
tries of western Florida.
Shortly after the first commercial plantings came into bear-
ing a fungous disease, known as pecan scab, became so severe
on certain varieties that it became necessary to discard them.
The spread of this disease and the number of varieties suscepti-
ble to it have so increased during the last 20 years that at present
it is considered the most important disease of the pecan. Be-
cause of these conditions considerable control work has been
done and the writer has spent the last two years making a study
of the fungus causing the disease. Control work has not been
conducted by the writer, and this bulletin is not intended to
give the method of control. However, the information con-
tained should be helpful in working out and applying control
methods, and in choosing varieties to set.

HOSTS
Fusicladium effusium Wint., the fungus causing pecan scab,
has been found on practically all of the varieties of the pecan
(Hicoria pecan). It was reported on the Mockernut (Carya
alba) in 1882 (10)*, Carya amara in 1889 (4), and on Pignut
(Carya cordiformis) in 1922 (1). It was found by the writer in
the fall of 1923 on Water hickory (Hicoria aquatica Nutt.) on
the shores of the St. Johns River near Sanford. Fusicladium
carygenum Ell. & Lang., which is considered as identical with
Fusicladium effusum Wint. by Davis (1) and Rand (8) was re-
ported on Carya olivaeformis in 1888 (3). Smith in his transla-

1 This work was done under the supervision of the Plant Pathologist of
the Florida Agricultural Experiment Station, and was presented to the
faculty of the University of Florida in partial fulfillment of requirements
for a master's degree in June, 1925.
*Numbers in parentheses refer to literature cited on page 276.





Florida Agricultural Experiment Station


tion of Tubeuf's "Diseases of Plants," reports Fusicladium effu-
sum Wint. as having been found on the Hornbeam (Carpinus
Americana), while Ellis and Everhart reported finding Fusicla-
dium effusum Wint. var. carpinieum on the Hornbeam (Carpinus
Americana).
The disease caused by Fusicladium effusum Wint. is of little
economic importance on any of the species mentioned above ex-
cept on the pecan, where it causes the disease known as pecan
scab, which is responsible for losses of thousands of dollars
annually.
GEOGRAPHICAL DISTRIBUTION
Pecan scab was first described by Winter in 1885 from a
specimen on the Mockernut (Carya alba) received from Illinois
in 1882. At the present time it is distributed over the larger
part of the pecan belt of the Southeast and has been found in the
following states: Alabama, Arkansas, Florida, Georgia, Louis-
iana, Mississippi, North Carolina, Oklahoma, South Carolina and
Texas on the pecan; Illinois on the Mockernut (Carya alba);
Kansas on Carya olivaeformis; Florida on the Water hickory
(Hicoria aquatica); and Wisconsin on the Pignut (Carya cordi-
formis).
The disease is well established on the susceptible varieties in
Florida.
ECONOMIC IMPORTANCE
Pecan scab is the most serious disease of the pecan and has
been considered as such by growers and pathologists for years.
The loss caused by this disease varies from nothing on the more
resistant varieties to 100 percent on the more susceptible ones
in wet years. On varieties such as Delmas, Van Deman and
Schley from 75 to 100 percent of the crop is often a total loss in
unsprayed orchards. Considering the fact that the pecan crop
of the United States was valued at $7,791,197 in 1919 and the
Florida crop at $340,000 in 1923, the economic importance of
such a disease can readily be seen.
The amount of damage varies according to the season and
variety. In normal years, that is years of normal rainfall-
about 55 inches in western Florida-the following amount of
loss due to scab may be expected in unsprayed orchards. Geor-
gia Giant and Delmas, 75-100 percent; Van Deman and Schley,
50-100 percent; Alley, 50-100 percent; Pabst, 75-100 percent





Florida Agricultural Experiment Station


tion of Tubeuf's "Diseases of Plants," reports Fusicladium effu-
sum Wint. as having been found on the Hornbeam (Carpinus
Americana), while Ellis and Everhart reported finding Fusicla-
dium effusum Wint. var. carpinieum on the Hornbeam (Carpinus
Americana).
The disease caused by Fusicladium effusum Wint. is of little
economic importance on any of the species mentioned above ex-
cept on the pecan, where it causes the disease known as pecan
scab, which is responsible for losses of thousands of dollars
annually.
GEOGRAPHICAL DISTRIBUTION
Pecan scab was first described by Winter in 1885 from a
specimen on the Mockernut (Carya alba) received from Illinois
in 1882. At the present time it is distributed over the larger
part of the pecan belt of the Southeast and has been found in the
following states: Alabama, Arkansas, Florida, Georgia, Louis-
iana, Mississippi, North Carolina, Oklahoma, South Carolina and
Texas on the pecan; Illinois on the Mockernut (Carya alba);
Kansas on Carya olivaeformis; Florida on the Water hickory
(Hicoria aquatica); and Wisconsin on the Pignut (Carya cordi-
formis).
The disease is well established on the susceptible varieties in
Florida.
ECONOMIC IMPORTANCE
Pecan scab is the most serious disease of the pecan and has
been considered as such by growers and pathologists for years.
The loss caused by this disease varies from nothing on the more
resistant varieties to 100 percent on the more susceptible ones
in wet years. On varieties such as Delmas, Van Deman and
Schley from 75 to 100 percent of the crop is often a total loss in
unsprayed orchards. Considering the fact that the pecan crop
of the United States was valued at $7,791,197 in 1919 and the
Florida crop at $340,000 in 1923, the economic importance of
such a disease can readily be seen.
The amount of damage varies according to the season and
variety. In normal years, that is years of normal rainfall-
about 55 inches in western Florida-the following amount of
loss due to scab may be expected in unsprayed orchards. Geor-
gia Giant and Delmas, 75-100 percent; Van Deman and Schley,
50-100 percent; Alley, 50-100 percent; Pabst, 75-100 percent






Bulletin 181, Pecan Scab


west of the Apalachicola River, 0-10 percent east of it; Curtis,
0-50 percent infection but very little loss; Moore, a varying
amount of scab but not much loss. These and other estimates
are found in Table I.

TABLE I.-PERCENTAGE OF PECAN CROP LOST BY SCAB IN UNSPRAYED
FLORIDA ORCHARDS (Estimated).


Variety INormal Wet
Alley v......... .... 75-1001 100
Bradley .................---...
Curtis ....-..........-.. 0-10 0-25
Delmas ................. --. 75-100 100
Frotscher .....................0 Tr
Georgia ......--......... 75-100 100
Moneymaker ................. Tr
Moore ........... ....... ...... 0-25 10-30
President .... ... ....... Tr
Schley ........................... 50-100 100
Stuart ............. .......... 0 Tr
Success ........................ 0-15 15-50
Van Deman ................. 50-100 100
Pabst .... ........................... 0-100 0-100

I I


Remarks

-.- ......... .. .... .. -.. ----- --
.................... ........ ..................







East of River
Junction 0-10%.
West of River
Junction 75-100%.___


SYMPTOMS
The disease affects the leaves, young twigs and nuts of the
pecan. The damage to the leaves is slight, altho partial defolia-
tion may occur. Young twigs are often killed back on the more
susceptible varieties, but the most serious damage is done to the
nuts. Considerable damage is done in the nursery thru the
shrivelling of the leaves, the killing back of the young shoots and
the hardening of the bark, resulting in difficulty in budding
operations.
The earlier stages are similar on all parts of the host affected,
altho the appearance may differ somewhat according to weather
conditions and the growth condition of the host. In warm
damp weather the disease makes its appearance by small raised,
round, velvety, green fungous spots on the surface with appar-
ently no immediate injuries to the underlying tissues. In drier
weather the fungous growth is not so conspicuous, altho the
injuries caused by the disease may be seen.

ON THE LEAVES
Shortly after the buds have opened in the spring a small spot
of scab may be noticed on either side of the leaves and on both the
primary and secondary leaf stem or petioles. The mid-ribs and






Florida Agricultural Experiment Station


veins show more spots than any other part of the leaf and both
here and on the leaf stems they may be slightly elongated. The
spots vary in size from a small speck to a quarter of an inch iq
diameter and on the leaf stem they may coalesce (run together)
until the spot may become an inch or more in length. Figure 1181
is a photograph of pecan scab on the under side of a young leaf.
As the infection grows older it often extends thru to the other
side of the leaf where it is noticed as a hard, black or brown spot.
As the leaves become older the spots enlarge, losing the velvet-
like fungous growth, leaving a dark, hard spot with gray edges.
(Figure 119.) With the growth of the leaf tissues these spots
often crack and later drop out. Where numerous spots are found
on the petioles the falling of leaflets or even of entire leaves oc-
curs, but the chief importance of leaf infection lies in the fact
that it is an ever-present source of infection for the nuts.


Fig 119.-Old scab infections on pecan leaf and petiole.






Bulletin 181, Pecan Scab


ON THE TWIGS
The disease as it occurs on the twigs differs but little from that
on the leaves and nuts. As on the mid-ribs and petioles, the
growth of the tissue generally gives the spot an elongated ap-
pearance while a swelling of the tissue immediately surround-





















Fig. 120.-Scab on pecan twigs, present season's growth.
ing the spot makes it appear to be sunken. Thus the diseased
area appears as a flat, round center of fungous growth in a dark,
concave depression in the bark. (Figures 120 and 121.) The lat-
ter may last for several seasons, altho no injury has been noticed
after the first year. Under certain conditions the injury, prior
to the development of the velvet-like fungous mass, may appear
as a darkening of the bark.
ON THE NUTS
The most serious infections are found on the nuts. If badly
infected when young they will drop long before maturing, while
infected ones remaining on the tree until harvest are apt to be
misshapen and not well filled.
Early in the spring the young nuts may be peppered with the
small, round, characteristic, olive-green fungous spots. Owing
to the fleshy nature of the green hulls the infected areas are at





Florida Agricultural Experiment Station


first more or less sunken in the green soft tissue. Under favor-
able weather conditions these spots increase in size with the
growth of the hull until several may coalesce, causing large dark
diseased areas. (See figure
122.) If this condition oc-
curs early in the season the
diseased areas may entirely
cover the nut, arresting the
development and often caus-
ing the nut to drop.
In cases where the infec-,
tion occurs later in the sea-
son these larger infected
areas become brown or black
and more or less furrowed
and cracked, thus forming
an entrance for other fungi.
Frequently pink mold&
(Cephalothecium sp.) enters
at this time, causing a de-
cay. In cases of severe in-
fection the deeper tissues
may become involved and
the hull clings tightly to the
shell so that it is sometimes
impossible to separate the
two. Under conditions of
light infection such as are
found in well sprayed or-
chards, the spots on the ma-
ture nuts may be round,
raised, black and hard. At
other times the spots lose
their velvet-like gro wth
leaving only a smooth, black
spot which may again be-
Fig. 121.-Scab on pecan twigs more come velvety and produce
than a year old. spores in the spring.
Figure 125 shows the comparison in size and maturity of bad-
ly infected and disease-free nuts of the Schley variety at harvest
time.






Bulletin 181, Pecan Scab


Altho the leaves are generally more infected than the nuts on
some varieties, such as the Delmas and Van Deman, the oppo-
site is true with others.


Fig. 122.-Scab on pecans, showing large diseased areas.


CAUSAL ORGANISM


The more or less egg-shaped, hyaline or dark olive-gray spores
(seed-like bodies) are borne on the end of the short upright coni-
diophores. The spores are generally dark colored, altho about 10
percent are hyaline (transparent, glass-like). About 1 percent
are one septate, (having one dividing wall), the rest being con-
tinuous. Altho they are not usually found in chains, they are
occasionally borne as such.
Owing to the difference in the susceptibility of the several
varieties it was thought that there might be more than one
strain of the fungus and an attempt to discover this fact was
made by measuring the spores. The microscope was calibrated
so that each space on the micrometer was equal to 1.3 microns.






Florida Agricultural Experiment Station


Measurements of spores were made from materials secured froni
various localities thruout the state. (Fig. 123.) At the present




8-d .Im ....
35 V ,'.\
















fungus collected from seven varieties of Pecans as designated in the legend.


time not enough variation has been found to suggest the pres-
ence of more than one strain except in the case of Delmas, where
considerable variation was noticed between the spores secured
from the Campville district and those from other parts of the
state. The measurements of the spores have been arranged
according to variety in Table II.
Resting spores (chlamydospores) are common in culture and
are occasionally found in the field. They are generally round
and thick-walled and vary in color, the majority being dark
colored.

The mycelium is olive-black to burnt umber in color and forms
a layer on the surface from which the short, erect conidiophores
are raised. They are of the same color as the mycelium and
range from 30 to 60 microns in length.
S*
4.


























are occasionally found in the field. They are generally round
and thick-walled and vary in color, the majority being dark



a layer on the surface from which the short, erect conidiophores
are raised. They are of the same color as the mycelium and
range from 30 to 60 microns in length.






Bulletin 181, Pecan Scab


TABLE II.-VARIATION IN SPORE LENGTH IN THE DIFFERENT STRAINS OF
THE SCAB FUNGUS FOUND ON VARIOUS VARIETIES OF PECANS.
Specin Number of Spores Measuring (In Microns)
Specimen 10.4 13.0 15.6 18.220.8 23.4 26.0j 28.61 31.2 33.8

Variety o o

Alley 756 8 20 28_ 30l l 4 _
107 | i36 38 20 6 i
107-2 11 36 40 11 2
109 3 7 28 40 17 3 2
Delmas 119 7 24 34 18 8 6 2 1
120 1 9 27 26 17 11 5 2 2
121 4 20 48 19 8
122 2 10 16 37 22 10 3 ____
Pabst 119 136 31 11 3 I
San Saba 1401 5 20 32 31 11 1I I
354 13 37 34 16
360 1 16 30 38 14 2
367 I 19 31 133 14 2 1
375 5 21 40 25 9
376 18 32 34 11 5
Schley 379 j 1 7 28 45 16 3
381 10 28 40 17 4 1
397 9 19 37 23 10 2
398 1 1 15 33 25 16 5 3 0 1
399 4 12 26 30 17 7 2 0 1
400 | 4 9 26 27 21 10 3
622 3 11 27 38 14 4 2 1
623 5 12 28 31 11 11 2
624 1 10 23 40 24 2
Seedling 629 3 14 24 29 23 5 1
630 1 3 19 36 23 9 6 3
631 | 2 14 21 31 19 7 4 2
Success 857 4 13 27 131 18 3 11 3
1054 15 53 24 7 1
Unknown 1056 10 20 34 33 3
1063 1 7 29 40 13 6 4
503 1 12 35 31 15 4 2
511 8 25 33 25 9
533 2 9 24 31 26 8
536 2 12 27 35 22 2
Van Deman 537 1 13 31 34 19 2
538 2 12 22 35 17 9 3
554 3 17 39 23 14 4
560 6 17 39 27 9 2
561 3 26 38 23 8 1





Florida Agricultural Experiment Station


PHYSIOLOGY

CULTURAL STUDIES
The cultural characteristics and the reactions of the organ1
ism to the various media and the various temperatures were|
studied in the following experiments. Transfers were made]
from a pure culture of Fusicladium effusum Wint. to slants of
each of the following media; cornmeal agar, nutrient cornmeal
agar, prune agar, rice tubes, cornmeal tubes, potato agar with
no dextrose and potato agar with 2 and 4 percent dextrose re-
spectively. These were placed in incubators regulated at 59, 68,
77 and 86 degrees Fahrenheit.
The fungus grew best at 68 and 77 degrees Fahrenheit on
cornmeal agar, nutrient cornmeal agar and potato agar contain-
ing 2 percent dextrose. Visible growth appeared in from four to
nine days and sporulation occurred from nine to 20 days. The
organism sporulated freely on cornmeal and nutrient cornmeal
agar and sporulated sparingly on the potato dextrose agars. No
sporulation occurred on the cornmeal tubes.

SPORE GERMINATION
Spore germination tests were made at various times thruout
the year. A small amount of sterile distilled water was poured
into a small porcelain dish, and with a sterile scalpel spores
were removed from scab lesions and placed in water. After a
large number of spores had been transferred in this manner, a
drop of the water containing spores was placed on a ringed
slide. The slide was placed under the microscope and examined
to observe whether any spores were present. They were then
left at room temperature and watched for growth at two-hour
intervals.
All germination tests conducted in the fall of 1923 failed to
show any germinating spores. Besides being conducted as the
above tests were, a 1 percent solution of cane sugar was used
and the spores were also kept at the following temperatures:
59, 68, 77 and 86 degrees Fahrenheit.
All tests conducted during the growing season were success-
ful, approximately 100 percent of the spores germinating.


260






Bulletin 181, Pecan Scab


FACTORS INFLUENCING INFECTION
TEMPERATURE RELATIONS
The amount of infection on all varieties is influenced by sev-
eral factors, chief among which are: temperature, humidity and
the age of the tissue attacked.
In a study of the cultural characteristics the fungus was trans-
ferred to slants of various media and placed in constant tem-
perature incubators at 59, 68, 77 and 86 degrees Fahrenheit. In
each case the shortest period of incubation and the greatest
amount of growth were obtained at 77 degrees Fahrenheit, while
the longest period of incubation and the smallest amount of
growth were found at 59 and 86 degrees Fahrenheit. The re-
sults of these studies may be seen in Tables VI and VII.
Germination tests using hanging drops as explained in the
previous section were conducted at room temperature, 50, 59 and
68 degrees Fahrenheit. Over 90 percent of the spores germi-
nated at all temperatures. The poorest growth at the end of the
first day was at 50 degrees Fahrenheit, where an average length
of 43 microns was obtained, while the best growth was at room
temperature, where the average length at the end of the first
day was 78 microns.
The following table (III) gives the length of the germ tubes
of the germinating spores at 10 degrees Centigrade and at room
temperature at the end of 6 hours.

TABLE III.-LENGTH OF GERM TUBES OF THE SPORES AT THE END OF SIX
HOURS.
Temperature Length of Tube in Microns
10C 5 120 1 26 49 50
Room Temp. 47 67 67 52 32
122 66 50 39 13
143 73 104 31 104
69 169 106 133 78
93 65 17 91

During the season of 1924 the periods of greatest infection
were found in April and July. The mean temperature for April
was 80 degrees Fahrenheit and for July, 89.6 degrees Fahren-
heit. The heavy rainfall which occurred during July probably
accounts for the heavy infection during that month.
In the laboratory it has been found that the optimum tempera-
ture for the development of this fungus is 25 degrees Centi-
grade or 77 degrees Fahrenheit. This is upheld by observations






262 Florida Agricultural Experiment Station

in the field when a sufficient amount of rain has fallen to insure
germination of the spores and later infection of the host.
HUMIDITY
Humidity is as necessary for growth of scab as temperature
The most susceptible varieties, such as San Saba, Halbert, Geor-
gia Giant, Delmas, etc., are resistant to scab in western Texas,
where, altho the temperature is high enough for heavy infec-
tions, the rainfall is extremely light. Scab is a greater problem
in Florida and other pecan producing areas along the gulf, where
the rainfall during the summer months is heavy, than in locali-
ties farther inland where the rainfall is less.
A study of the scab situation for 1924 shows that the rainfall
for April, when the scab infection was medium, was 5.80 inches,
for May when the infection was at a standstill was 0.19 inches
and for July when the peak of the infection was reached the
rainfall was 14.45 inches.
A study of the literature on the subject revealed the fact that
the worst infections occurred during the years of the heaviest
rainfall, while light infections always occurred in years of light
rainfall.










i
.._ ... 1 .














-_ L~ -. .. --. .-.... .
V --i _.. __ .




Fig. 124.-Chart showing the correlation between amount of rainfall
and percentage of new scab infection on Van Deman by weeks during the
season of 1923. The shaded portion shows the amount of rainfall and the
line above indicates the amount of scab infection. Note that the amount
of infection rises after a period of prolonged rainfall.






Bulletin 181, Pecan Scab


Figure 124 consists of a graph showing the amount of rain--
fall by weeks and the approximate amount of scab infection as
noticed on a Van Deman tree on the College of Agriculture farm
during the season of 1924.

AGE OF TISSUE

Young tissue seems to be more susceptible than old tissue.
This is especially true in the case of twigs and leaves. In the
inoculation experiments later described no infections were se-
cured on leaves more than two weeks old.
Apparently twigs under a year old are susceptible to scab but
older ones are not. It has been noticed that nursery stock of
certain varieties is known to be resistant, when bearing trees of
the same varieties are extremely susceptible. This is especially
true of Curtis, Kennedy and President in nurseries visited.
The nuts are susceptible from about three weeks after the time
of fertilization of the flower until the formation of the milk
stage. Nuts badly infected early in the season generally fall to
the ground before half grown and those remaining on the tree
until fall are generally infected after they are half grown. The
majority of the crop on the Van Deman, mentioned above, showed
no infection July 10, 1924. Many of these nuts dropped before
maturity because of scab and every one remaining on the tree
until harvest was badly diseased. These undoubtedly became in-
fected after July 10, at which time they were approximately
half grown.
STUDIES AND RESULTS

The study of scab was started the middle of November and
by that time the spores had lost their vitality because germina-
tion tests gave negative results. Early in the spring, however,
the fungus was isolated by the dilution method on cornmeal
agar.
During the fall of 1923 unsuccessful attempts at isolation of
the fungus were made on potato dextrose agar (2 percent dex-
trose), pecan twig agar, pecan leaf agar and pecan twig plugs.
Shortly before the scab appeared in the spring an unpublished
manuscript by F. V. Rand (8) was sent to the writer, by Mr.
Rand in which it was stated that the organism rarely sporulated
on potato agar but that it produced spores more freely on corn-





Florida Agricultural Experiment Station


meal agar. Therefore when scab appeared, both potato dextrose
and cornmeal agars were used in the isolation work.
On May 10, a non-sporulating fungus, isolated from Schley on
May 1, was found to resemble Fusicladium effusum Wint. and
was transferred to cornmeal agar slants. On July 14 an iso-
lation from Van Deman was found to be scab and was trans-
ferred to cornmeal agar slants. These cultures were given num-
ber and used in the inoculation experiments later described.
The fungus is easily isolated during the summer months.

INOCULATION EXPERIMENTS
Inoculation experiments were started in April and were con-
tinued until the end of August. The earlier experiments were
conducted in the greenhouse while during the summer they were
conducted in the field, principally in the variety orchard on the
Experiment Station farm. Before any experiments were con-
ducted in this orchard each tree was carefully examined for
scab. No scab was found.
The following is a typical inoculation experiment as conducted.
Twenty seedlings in the horticultural grounds were used in this
experiment. On July 14 every other seedling in the experiment
was sprayed with sterile distilled water, bagged, tied and la-
belled. These were the checks. The remaining seedlings were
then sprayed with a suspension of spores from strain 2X in ster-
ile distilled water, bagged, tied and labelled. The results are
shown in Table IV. None of the check trees ever developed scab
while seven of the inoculated trees developed scab in from nine
to 17 days.
SPORE PRODUCTION
The young spots found on the leaves in the spring produce
abundant spores, the entire velvet-like surface being a mass of
spores. This condition is found thruout the growing season on
the younger spots. As the leaves grow older the fungus appar-
ently stops sporulating (producing spores) and the spots become
hard and black.
The infections on the nuts and twigs produce spores from the
time of the first appearance of the spores until late fall. Spores
have been easily secured from infected twigs and nuts at all
times during the growing season, but not during the winter. All
attempts to germinate the few spores secured during the winter
have failed.


264





Florida Agricultural Experiment Station


meal agar. Therefore when scab appeared, both potato dextrose
and cornmeal agars were used in the isolation work.
On May 10, a non-sporulating fungus, isolated from Schley on
May 1, was found to resemble Fusicladium effusum Wint. and
was transferred to cornmeal agar slants. On July 14 an iso-
lation from Van Deman was found to be scab and was trans-
ferred to cornmeal agar slants. These cultures were given num-
ber and used in the inoculation experiments later described.
The fungus is easily isolated during the summer months.

INOCULATION EXPERIMENTS
Inoculation experiments were started in April and were con-
tinued until the end of August. The earlier experiments were
conducted in the greenhouse while during the summer they were
conducted in the field, principally in the variety orchard on the
Experiment Station farm. Before any experiments were con-
ducted in this orchard each tree was carefully examined for
scab. No scab was found.
The following is a typical inoculation experiment as conducted.
Twenty seedlings in the horticultural grounds were used in this
experiment. On July 14 every other seedling in the experiment
was sprayed with sterile distilled water, bagged, tied and la-
belled. These were the checks. The remaining seedlings were
then sprayed with a suspension of spores from strain 2X in ster-
ile distilled water, bagged, tied and labelled. The results are
shown in Table IV. None of the check trees ever developed scab
while seven of the inoculated trees developed scab in from nine
to 17 days.
SPORE PRODUCTION
The young spots found on the leaves in the spring produce
abundant spores, the entire velvet-like surface being a mass of
spores. This condition is found thruout the growing season on
the younger spots. As the leaves grow older the fungus appar-
ently stops sporulating (producing spores) and the spots become
hard and black.
The infections on the nuts and twigs produce spores from the
time of the first appearance of the spores until late fall. Spores
have been easily secured from infected twigs and nuts at all
times during the growing season, but not during the winter. All
attempts to germinate the few spores secured during the winter
have failed.


264






Bulletin 181, Pecan Scab


TABLE IV.-RESULTS OF INOCULATION EXPERIMENT 5, BEGUN JULY 24,
1924.
Trees No.
Date ...............-------- 1 2 3 4 5 6 7 8 9 9 [ 10
7/14 .......- .....In.oe.Ch'k Inoc. Ch'k Inoc. ]Ch'k Inoc. I Ch'k Inoc.] Ch'k
7/19 -............. -- --- .. ... ---------- ..- ...--- --.. ..-- -- I ...--.
7/21 .... -. --- I--- -- -- -------- .- -I -- --- --
7/23 ......................... Scab ...... .. ............ .........-.-- Scab
7/25 ....... .... ... Scab ...... |Scab ....... Scab ........ Scab ....... ..... ......
7/27 .................... Scab ........ Scab ........ Scab I....... Scab .... ..... -.... ....
7/29 ................. .. Scab ........ Scab ....... Scab ........ Sc b .......-- ..--- ..-
8/1 .......................... Scab ........ |Scab ........ Scab ........ Scab ...... ..... .. ....
8/3 ...................... Scab ........ JScab I...... Scab ........ Scab ...... ......
Trees No.
Date .....-.-..............- 11 12 13 14 15 16 17 18 919 20
7/14 ....................... cInoc. Ch'k Inoc. Ch'k Inoe. Ch'k Inoc. Ch'k Inoc.l Ch'k
7/19 .-....-...--.......-. .- ----- ....... ------- ------ -------- --------
7/21 .....---.... .....-..- .- -------- ------- -------- ----- --- --------- -- --- --------
7/23 -...........---- ..........- -.-.....- .--. -- ---- .----.--
7/25 ... ........... .........-.. ---- ..- -------- --- -- -------- ------- -------- IScab --...
S I I cut]
7/27 ........... -.......... Scab --... i..-- .-- o----- off .....- Scab ......
7/29 .... .... ....... Scab ... .. ........ ---- ------ -------- Scab ........
8/1 ..... ......... Scab i-... .. -------- ;- --- Scab -.....--. -....-- ..- IS ab -...
8/3 ........... ...........-.....Scab --------. ..*..... ........ iScab I--........- .... I ... j Scab ...

Spores are produced by the old infections in the spring. In-
fected hulls and twigs showing no spores when collected in the
fall, were kept in the laboratory during the winter and when ex-
amined in the spring the old lesions on the material were pro-
ducing an abundance of spores.
Resting spores (chlamydospores) are also produced by the
fungus thruout the growing season. No ascigerous or other per-
fect stage has been found.

SOURCE OF INFECTION

The primary source of infections in the early spring are the
old diseased twigs and husks remaining on the tree and diseased
husks on the ground. Examination of infected trees in the
spring will show severely diseased areas surrounding old in-
fected husks and twigs. The leaves on the lowest branches of
the trees become more generally infected than those on other
parts of the tree.
During the growing season the diseased leaves furnish a
source of secondary infection on the nuts and twigs.





Florida Agricultural Experiment Station


In general it may be said that infected twigs, husks and leavelj
furnish a source of the spring infection and that leaf infections
furnish the spores that infect the twigs and nuts.

MODES OF OVER-WINTERING
Former investigators, in studying the methods by which the!
fungus is carried over from one season to another, have come
to the conclusion that the fungus exists thru the winter on twigs,
leaves and nut hulls.
Hume, 1910, (5) stated that altho it has not been definitely
determined how the fungus is carried over from one season to
another it is believed to exist thru the winter on the twigs, or on
old hulls, either on the tree or on the ground or both, and on
dead leaves.
Lloyd and Ridgway, 1910, (6) stated that this fungus lived in
part on living portions of the plant and in part on the dead
leaves, especially passing the winter in this manner, and that,
during the winter, spores developed which ripened in the spring
and upon being transferred to young leaves produced scab.
Observations made revealed the fact that scab lesions on in-
fected twigs and hulls which are producing numerous spores in
the fall, apparently cease producing spores during the winter
and begin in the spring. Material which failed to show any
spores when collected during the late fall and winter was kept
in the laboratory and examined in the spring. When the exami-
nation was made during March many spores were secured with-
out any trouble from this material.
Early observations in orchards of susceptible varieties in-
variably disclosed many scab-infected leaves surrounding old
infected husks which had remained on the tree thruout the win-
ter, while the infection on the rest of the tree was much lighter.
Up to the present time no perfect stage of the fungus has been
found and it is likely that the new infections in the spring are
started by spores from old scab spots which have been carried
over the winter on old twigs, husks and leaves.

MODES OF DISSEMINATION
Pecan scab may be spread thru the dissemination of its spores
by means of various agencies, chief among which are wind, rain,
insects and man.





Florida Agricultural Experiment Station


In general it may be said that infected twigs, husks and leavelj
furnish a source of the spring infection and that leaf infections
furnish the spores that infect the twigs and nuts.

MODES OF OVER-WINTERING
Former investigators, in studying the methods by which the!
fungus is carried over from one season to another, have come
to the conclusion that the fungus exists thru the winter on twigs,
leaves and nut hulls.
Hume, 1910, (5) stated that altho it has not been definitely
determined how the fungus is carried over from one season to
another it is believed to exist thru the winter on the twigs, or on
old hulls, either on the tree or on the ground or both, and on
dead leaves.
Lloyd and Ridgway, 1910, (6) stated that this fungus lived in
part on living portions of the plant and in part on the dead
leaves, especially passing the winter in this manner, and that,
during the winter, spores developed which ripened in the spring
and upon being transferred to young leaves produced scab.
Observations made revealed the fact that scab lesions on in-
fected twigs and hulls which are producing numerous spores in
the fall, apparently cease producing spores during the winter
and begin in the spring. Material which failed to show any
spores when collected during the late fall and winter was kept
in the laboratory and examined in the spring. When the exami-
nation was made during March many spores were secured with-
out any trouble from this material.
Early observations in orchards of susceptible varieties in-
variably disclosed many scab-infected leaves surrounding old
infected husks which had remained on the tree thruout the win-
ter, while the infection on the rest of the tree was much lighter.
Up to the present time no perfect stage of the fungus has been
found and it is likely that the new infections in the spring are
started by spores from old scab spots which have been carried
over the winter on old twigs, husks and leaves.

MODES OF DISSEMINATION
Pecan scab may be spread thru the dissemination of its spores
by means of various agencies, chief among which are wind, rain,
insects and man.






Bulletin 181, Pecan Scab


Wind and rain form the main methods of distribution. The
spores may be carried a great distance by the wind and then
light on a pecan tree. This, in all probability, accounts for the
presence of scab on isolated trees. Scab is distributed over the
tree by means of rains and heavy dews, since spores from small
spots in the upper part of the tree may be washed down thru
the tree and come to rest on leaves thruout the tree, thus spread-
ing the disease to uninfected parts.
At times insects aid in the dissemination of pecan scab, and
in 1911, Waite, (9) published the following:
"An interesting feature in relation to the life history of the
disease was found, namely that a plant louse, which becomes
common on the pecan in May, punctures the epidermis in a
regular way along the veins and leaflets. The punctures of the
plant louse are used as points of entrance by the Fusicladium.
The fungus is also assisted in its germination and growth by
the honeydew which is copiously secreted by this aphis. The fun-
gus can also enter by the direct way by piercing the epidermis,
and such disease spots are regularly located over the leaves,
fruit and twigs. Spots due to the aphids are arranged in regu-
lar lines along the veinlets and often far exceed in number all
other spots on the leaves."
This condition was observed by the writer during the latter
part of May in an orchard near Benson Springs. This orchard
was badly infected with aphids and the leaves were covered
with scab which acted as a sooty mold growing on the honeydew
secreted by the aphids. In this case the scab was a superficial
growth on the honeydew and none was noticed to have entered
the leaf.
Scab has been found in punctures made by the pumpkin bug
but it is impossible, at the present time, to state whether these
infections occurred before, or after the injury.
Man undoubtedly plays a large part in the distribution of scab
to disease-free territories by shipping into and planting diseased
trees in such communities.

TIME OF NATURAL INFECTION
The time of natural infection depends upon several factors,
such as stage of growth, humidity and temperature.
Infection cannot take place in the spring until the new foliage
appears, and so the earliest infections can generally be found on






Florida Agricultural Experiment Station


nursery stock which forces out growth earlier than the bearing
trees. Thus the date of first infection in the spring varies ac-
cording to the locality and the season. Table V gives the dates
of first appearance of scab for several states for the years 1922,I
1924-25.

TABLE V.-DATES OF THE FIRST REPORT OF PECAN SCAB, 1922, 1924-25.
State Place Year Date
Mississippi Ocean Springs 1922 May 10 Data for 1922
from Plant Dis-
South Carolina Orangeburg 1922 June 25 ease Bulletin, Vol.
I VI, No. 10.
Florida I 1922 April 2
Florida IGainesville 1924 April 6
Florida Gainesville 1925 March 15 On Nursery
t Stock.
Florida Monticello 1925 May On Bearing
Trees.
The scab appeared about two weeks after the buds opened,
often before the leaf was more than one-third grown. In the
inoculation experiments no infections were secured on leaves
more than two weeks old when inoculated.
Scab has been observed on young nuts three weeks after the
pistillate flowers had dried, altho infection may occur on them
at any time thruout the growing season. On a Van Deman tree
kept under close observation thruout the year, 90 percent of the
nuts became infected after they were half grown.

PERIOD OF INCUBATION

A longer time is required for the incubation of the organism
in the field than in the laboratory. The organism has required
from four to 11 days from isolation to its first appearance, ac-
cording to the media used. Generally, in isolation, the first
signs of growth appear after four days. When the dilution
method is used a longer time is required. Table VI shows the
length of time required for incubation on the various media used
in the study of culture characteristics at different temperatures.
The time required for the disease to show up on the tree in the
field inoculation experiments varied from five to 21 days, the
shortest time being on young leaf growth on Van Deman. A
young leaf may become infected 21 days before infection be-
comes visible.






Bulletin 181, Pecan Scab


Table VII shows the length of time required for incubation
in the inoculation experiments, the experiments being referred
to by number as used in the discussion on the subject.

TABLE VI.-INCUBATION PERIOD OR LENGTH OF TIME REQUIRED BY PECAN
SCAB FUNGUS TO BEGIN GROWTH ON VARIOUS MEDIA AT DIFFERENT
TEMPERATURES.
Media 150C ( 20*C 25CC 30C
Cornmeal agar ................... 4 days 4 days i 4 days 4 days
Cornmeal tubes ..................... 4 days 4 days 4 days 6 days
Nutrient cornmeal agar ..........--. 5 days 4 days 4 days 4 days
Prune agar ....................... 7 days 8 days 7 days 7 days
Rice tubes .... ............ ....... 5 days 5 days 4 days 6 days
Potato agar-no dextrose ...........-- 5 days 6 days 4 days 5 days
Potato agar-2% dextrose................. 8 days 4 days 4 days 5 days
Potato agar-4% dextrose ............ 5 days 4 days 4 days 4 days
TABLE VII.-LENGTH OF TIME REQUIRED FOR PECAN SCAB FUNGUS TO
CAUSE DISEASE ON INOCULATED PECAN TREES.
Days Exp. 1 Exp. 2 Exp.3 Exp.4 Exp.5 Exp.6
5.... I -- 4 twigs ... -
7 .-. .-- 1 tree -
9 ...... 2 trees ....
11 ... .. 3 trees .
13 ---.- -. -- --- 1 tree .
14 .1 tree 3 twigs i
18 ...- -- --. -- 1 tree .
21 ..... 1 tree .... ---___
A comparison of these tables reveals the fact that a longer
time is required for the incubation of the organism in the field
than in the laboratory.

EFFECTS ON THE PHYSIOLOGY OF THE HOST

Beyond the spotting of the leaves and, in cases of severe in-
fection, the dropping of the leaflets or even entire leaves, the
injurious effect of leaf infections on the tree as a whole is
negligible.
Severe infections on young twigs cause a drying up of the
twig and a hardening of the bark, which may ultimately kill the
twig for a distance of several inches. Even where the injury is
not so severe as to cause death, the infected areas become hard
and brittle, making budding operations difficult.
In cases of severe infection the young nuts generally fall long
before maturity. Infected nuts remaining on the tree fail to
mature and are often undersized and misshapen. When severe-
ly infected the surface of the husk is covered with many cracks
due to the organism and at times deeper infections cause the





Florida Agricultural Experiment Station


Fig. 125.-Scab infection caused the nuts in the top row to be dwarfed.
Bottom row, normal nuts.
husk to adhere to the shell so that it is impossible to separate the
two.
Young trees may be infected with scab without any lasting
effects when the twig infection is light. In cases of severe twig
infection considerable injury is produced and in the case of
seedlings or small buds, a permanent stunting of growth may
be caused by the killing back of the younger twigs. Leaf infec-
tion except in the case of seedlings, and unusually severe attacks,
produces no permanent injurious effects on the tree as a whole.
The infection on the nuts prevents maturity and thus, in the
case of extremely susceptible varieties, reduces the chances of
reproduction.
SUSCEPTIBILITY AND RESISTANCE IN VARIETIES OF
THE HOST
When pecan scab first appeared to be of economic importance
it was noticed that certain varieties and certain seedlings were
badly infected while others were free from disease. By 1910 the
situation in Florida became so acute that the growing of Geor-
gia Giant, Halbert, San Saba and other varieties was abandoned
because of their susceptibility to scab. These were top-worked
to Delmas, Van Deman and Schley, which were considered to
be resistant, altho scab had been reported on Delmas previous to
that time. By 1915 Delmas had become so susceptible as to be






Bulletin 181, Pecan Scab


considered a total loss and was being top-worked to Schley. At
the present time, under the conditions found in the commercial
pecan belt of Florida, Van Deman and Schley are nearly as sus-
ceptible as Delmas.
The problem of varietal susceptibility has puzzled pathologists
for years. Not only do apparently resistant varieties become at
first slightly susceptible and gradually increase in susceptibility,
but a variety may be susceptible in one locality and resistant 100
miles away, as stated below. A variety can apparently be ex-
tremely susceptible in the nursery and at the same time be re-
sistant when a bearing tree. In several nurseries visited the
blocks of Curtis and President were badly infected while bear-
ing trees of these varieties in orchards adjoining the nursery
were only slightly infected. On the other hand the opposite was
true of Schley.
In general, the statement that the farther from the coast an
orchard is located, the more resistant it is likely to be, was held
for a number of years, and as late as 1916 Schley was resistant
in the Albany district, altho it had been severely infected dur-
ing the seasons of 1911 and 1912 according to Demaree (2). In
1917 and 1918 it again became susceptible and at the present
time constant spraying is necessary in that district to insure
a crop.
As late as 1920 Moore was considered resistant in Florida, buL
during the past three seasons it has been moderately attacked.
The same variety may be susceptible in one locality and re-
sistant in another. Van Deman, which is extremely susceptible
in Florida, is reported as being resistant in Alabama and Miss-
issippi, altho Miles (7) reports having found Van Deman scab-
bing severely in Alabama during the past season. Neal' stated
in February, 1925 that Van Deman is still considered as resis-
tant in Mississippi.
At the present time the most susceptible varieties in Florida,
with the exception of Georgia Giant and the Western varieties
which are not grown to any extent, are: Delmas, Van Deman,
Schley, Alley, Pabst, Moore, Kennedy and Curtis. Other varie-
ties as, Success, Rising, Randall, Moneymaker, Stuart, James,
President and Simmons are slightly susceptible since they have
been found to be infected at various times. The more resistant
varieties are: Teche, Frotscher, Stuart and Moneymaker.

Personal correspondence.






272 Florida Agricultural Experiment Station

Table VIII is a list of the several varieties giving the date oF
the first report of scab on each variety in each state.

TABLE VIII.-DATES WHEN PECAN SCAB WAS FIRST REPORTED IN TH
VARIOUS STATES.
Is ~ ~ tS t,+


Variety a a





Pecan ................ 19061192311906119031
Alley ................. 19121912
Atlanta ........ ..... 1911
Beverage .......... 1924
Bradley .........-. 1911
Capitol ... .... 1918
Columbia ......... 1924
Curtis .............. 1923
Delmas .......... 11922 1911 1911j
Dewey ............... 19241911
Farley ............... 1924
Frotscher .......... 1912 1912
Georgia Giant.. .1923 1924 1918
Halbert ........ ...191011912
James ........ .... I 19241
Kennedy .......-.. 1923
Lone Star........... 1923
Mantura ............ 1912
Mobile ....---......- 1923 1912
Moneymaker ...( 1911 1911
Moore ........-...- .. 1923 1922
Nelson ....... 1923 1912
Pabst ............... 1923 19231912
President 1...... 1923 1911
Randall ......... 1923
Rising ........ 1924
Rome ...... ..... 1911
Russell -.......... 1925
San Saba ....... 1910 1918
Schley .............. 1923 1912 1912
Scott ............ 1923
Seedling .......... 192311918
Simmons ........... 1924
Sovereign .........
Stuart ..............- 1912
Success .... ........ 1923 1912
Van Deman ..... 1923 1911 1911
Zink ...........- .. 1923
C. alba ........- 1
C. amara ........
C. cordiformis. ..
C. oliveformis .. 1923
H. aquatica .......1923


a a a I





1 19061191211907 190319071
|1924




1911
I 11922
i'"l


1918
1912




|


1911


1922





Bulletin 181, Pecan Scab


CLIMATIC RELATIONS
As is the case with many fungous diseases, scab thrives in
cool or warm, damp weather, rather than in hot, dry weather.
It has been impossible to compile sufficient data on this sub-
ject in such a short time but a thoro study of the literature on
the subject, and a start towards a complete compilation of the
necessary data has been made.
Demaree (2) and others state that in the past scab has been
more prevalent near the coast than farther inland. They state
that previous to 1918 scab was unknown in the Albany district
on varieties other than Georgia Giant and the Western varieties,
altho at the same time Delmas, Van Deman and Schley were
susceptible at Monticello and Thomasville. This condition has
probably been due to climatic factors.
The spring of 1924, in the Gainesville district, presented a case
of excellent weather for the propagation of scab. The young
growth appeared from the middle of March until the middle of
April, depending upon the variety. At this time the mean tem-
perature was 69.35 degrees Fahrenheit. The first scab was no-
ticed on April 6, and from then until the middle of May, the
amount of scab on susceptible varieties increased until from 25
to 50 percent of the new growth on the trees was infected. The
rainfall for April was 5.80 inches, and the mean temperature
69.4 degrees Fahrenheit with a mean maximum of 80.4 degrees
Fahrenheit and a mean minimum of 58.3 degrees Fahrenheit.
During May the amount of new growth was much less than in
the previous month, and it stopped entirely after the first week.
The scab grew less until the 15th, after which no new scab was
noticed until after June 10. The rainfall for May was 0.19
inches. The mean temperature, 74.3 degrees Fahrenheit, the
mean maximum 87 degrees Fahrenheit, and the mean minimum
61.6 degrees Fahrenheit. During June both the new growth
and the subsequent scab infection were resumed until July, when
the greatest amount of infection for the whole season was found.
This infection was continued until the middle of August when
the weather became warmer and the rainfall less. The new
growth was becoming scarce at this time and by the last of
August little new scab was found.





Florida Agricultural Experiment Station


Figure 124 shows the amount of rainfall by inches and the
approximate amount of the scab on the Van Deman tree on the)
College farm.
San Saba, Halbert and Burkett do well in the western part
of Texas where the weather is hot and the rainfall small, but
these varieties are found to be susceptible to scab even in the
eastern part of Texas, and when they are brought to Florida
they scab so badly as to make it nearly an impossibility to grow
them.
The fungus causing pecan scab thrives wherever the rainfall
is plentiful and the temperature medium. It may be possible
that rainfall in number of days' rather than in number of inches
is the most important factor.

SUMMARY
Pecan scab is caused by the fungus Fusicladium effusum
Wint., first described by Winter in 1885, found on the Mocker-
nut (Carya alba) at Cobden, Illinois.
Most varieties of the pecan and several wild species of hick-
ory (Hicoria spp.) are susceptible to the disease.
It affects the leaves, nuts and twigs, the most serious injury
being to the nuts.
The fungus may be recognized by the slightly raised olive-
black, velvety spots on either side of the leaf, altho more often
occurring along the midrib or veins. On the young nuts the
spots appear as being sunken in the green tissue, while on more
mature nuts the surface of the husk is cracked and rough. The
infected twigs may be killed. The fungus appears as black,
raised, round spots in a concave depression on the twigs.
The young leaves are readily attacked by the fungus for two
weeks after unfolding.
The twigs may be attacked during the first year's growth;
older twigs are resistant to the disease.
The nuts may be attacked by the disease from three weeks
after setting until the milk stage. Nuts badly infected when
young drop before they are half grown.
Nursery stock of resistant varieties such as Curtis, President
and Kennedy may be extremely susceptible to scab.
The infection is more severe during moist or rainy weather.





Bulletin 181, Pecan Scab 275

San Saba, Halbert and Delmas, which are extremely suscep-
tible in Florida, are practically immune to scab in western
Texas.
The pecan scab fungus was isolated and grown in pure cul-
ture in the laboratory.
Inoculation experiments on trees in the field and greenhouse
were successful.
The growth of the fungus is poor at 59 and 86 degrees Fahren-
heit on different media in the laboratory. The best tempera-
ture for growth on media in the laboratory is 77 degrees
Fahrenheit.
The period of incubation requires from five to 21 days in the
field and from four to nine days in the laboratory.
The disease is carried thru the winter by continued life in the
fungus which apparently renews spore production in the spring.






276 Florida Agricultural Experiment Station


LITERATURE CITED
(1) DAVIS, J. J.
1924. NOTES ON PARASITIC FUNGI IN WISCONSIN, IX, X, XI, JULY
1924. p. 261.
(2) DEMAREE, J. B.
1921. SPRAYING PECAN TREES. Ga. Fla. Pecan Growers Assoc.
Proc. 1921, p. 11-16.
(3) ELLIS, J. B. AND LANGLOIS, B. M.
1888. FUSICLADIUM CARYIGENUM ELLIS AND LANGLOIS ON CARYA
OLIVAEFORMIS. Jour. Mycol. IV. p. 124.
(4) FAIRCHILD, D. G.
1889. KELLERMAN AND SINGLES KANSAS FUNGI. Jour. Mycol.,
Vol. 5. p. 161.
(5) HUME, H. H.
1910. THE PECAN AND ITS CULTURE. p. 103.
(6) LLOYD, F. C. AND RIDGWAY, C. S.
1910. Bul. 32, Ala. Dept. Agri. Mar. 1910. p. 5-9.
(7) MILES, L. E.
1925. Paper read before the Alabama Nurserymen at Birming-
ham, Jan. 26-7, 1925.
(8) RAND, F. V.
1913. Unpublished manuscript.
(9) WAITE, M. B.
1911. PECAN SCAB. Sci. N. S. 33, No. 837, p. 77-78.
(10) WINTER
1885. Jour. Mycol. Vol. I, p. 101.




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