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 Title Page
 Station staff
 Potato diseases and insects
 Notes on potato seed troubles
 Insect enemies of the potato in...
 Index






Group Title: Bulletin / University of Florida. Agricultural Experiment Station ; no. 169
Title: Potato diseases and insects
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027127/00001
 Material Information
Title: Potato diseases and insects
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 101-163 : ill. ; 23 cm.
Language: English
Creator: Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1923
 Subjects
Subject: Potatoes -- Diseases and pests -- Florida   ( lcsh )
Potatoes -- Diseases and pests -- Control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references and index.
Statement of Responsibility: by G.F. Weber.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027127
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 by the source institution and holding location.
Resource Identifier: aleph - 000922818
oclc - 18171499
notis - AEN3327

Table of Contents
    Title Page
        Page 101
    Station staff
        Page 102
    Potato diseases and insects
        Page 103
        Late blight
            Page 103
            Page 104
            Page 105
            Page 106
            Page 107
            Page 108
            Page 109
            Page 110
            Page 111
            Page 112
        Bacterial wilt
            Page 113
            Page 114
        Blackleg
            Page 115
            Page 116
        Early blight
            Page 117
            Page 118
            Page 119
            Page 120
        Black scurf
            Page 121
            Page 122
        Southern wilt
            Page 123
            Page 124
        Mosaic
            Page 125
        Curly dwarf
            Page 126
        Leaf roll
            Page 127
        Fusarium wilt
            Page 128
            Page 129
        Common scab
            Page 130
        Silver scurf
            Page 131
        Spindle sprout
            Page 131
        Yellow dwarf
            Page 132
            Page 133
            Page 134
        Wart
            Page 135
        Powdery scab
            Page 136
            Page 137
    Notes on potato seed troubles
        Page 138
        General survey
            Page 138
            Page 139
            Page 140
        Certified seed increase the yield
            Page 141
            Page 142
            Page 143
        Potato seed disinfection
            Page 144
        Spraying
            Page 145
            Page 146
        Dusting
            Page 147
            Page 148
    Insect enemies of the potato in Florida
        Page 149
        Plant lice
            Page 149
            Page 150
        Leaf-hoppers
            Page 151
        Larget plant bugs
            Page 151
            Page 152
        Flea beetles
            Page 153
        Blister beetles
            Page 153
        Hornworms
            Page 154
        May beetles
            Page 154
        Colorado potato beetle
            Page 155
            Page 156
        Cutworms
            Page 157
            Page 158
        A general spray solution
            Page 159
        Root-knot
            Page 159
            Page 160
            Page 161
            Page 162
            Page 163
    Index
        Page 164
Full Text


December, 1923


UNIVERSITY OF FLORIDA

Agricultural Experiment Station




POTATO DISEASES AND INSECTS


By
G. F. WEBER


Fig. 1.-Seed potatoes bruised in transit


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


Bulletin 169







BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN,- Citra
W. L. WEAVER, Perry
J. C. COOPER, JR., Jacksonville
A. H. BLENDING, Leesburg
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
J. R. WATSON, A. M., Entomologist
R. W. RUPRECHT, Ph. D., Chemist
O. F. BURGER, D. Sc., Plant Pathologist
W. E. STOKES, M. S., Grass and Forage Crops Specialist
G. F. WEBER, Ph. D., Associate Plant Pathologist
A. S. RHOADS, Ph. D., Assistant Plant Pathologist
G. H. BLACKMON, Pecan Culturist
ED L. AYERS, B. S., Agriculturist
A. H. BEYER, M. S. Assistant Entomologist
C. E. BELL, B. S., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
RALPH STOUTAMIRE, B. S. A., Editor
HAROLD MOWRY, Assistant Horticulturist
ROBERT E. NOLEN, B. S. A., Lab. Asst. in Plant Pathology
RUBY NEWHALL, Secretary
IDA KEELING CRESAP, Librarian
MARY.E. Roux, Mailing Clerk
A. W. LELAND, Farm Foreman
K. H. GRAHAM, Auditor
RETTA MCQUARRIE, Assistant to Auditor
W. B. TISDALE, Ph. D., Associate Plant Pathologist, Tobacco Ex-
periment Station (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. G. KELLY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
J. H. JEFFERIES, Superintendent Citrus Experiment Station
(Lake Alfred)
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle
Glade)









POTATO DISEASES AND INSECTS
By G. F. WEBER1
Associate Plant Pathologist
The purpose of this bulletin is to place before the potato grow-
ers of Florida a brief report of the experimental work conducted
during the season of 1922-23, and to briefly describe and suggest
control methods for the most important diseases of the Irish
potato. A thoro survey of the Hastings area has been made,
and the diseases herein described, with the exception of wart and
powdery scab, have been found.

LATE BLIGHT

The disease known as late blight is caused by the fungus
Phytophthora infestans (Mont.) de By. From an economic
point of view it is the oldest and most serious potato disease in
Florida. It has been found in this state since 1903', when it
caused a reduction in yield of from 25 to 30 percent.












Fig. 2.-Half-grown potato plants killed by late blight
The disease appears early in the life of the plant. In fact,
plants have been found infected when only a few inches in
height. In northern states this disease appears late in the life
of the plant and is naturally called late blight. It was found in
fields that had been planted only six weeks. As the season pro-
gressed the weather became warmer and the disease was checked.
Thus, unless the disease is established and rapidly spreading be-
fore April 1 very little damage results.
'Mr. David G. A. Chellberg made all the photographs appearing in this
bulletin except where credit is given.
'Fla. Agri. Exp. Sta. Bul. 75: 181. 1904.









POTATO DISEASES AND INSECTS
By G. F. WEBER1
Associate Plant Pathologist
The purpose of this bulletin is to place before the potato grow-
ers of Florida a brief report of the experimental work conducted
during the season of 1922-23, and to briefly describe and suggest
control methods for the most important diseases of the Irish
potato. A thoro survey of the Hastings area has been made,
and the diseases herein described, with the exception of wart and
powdery scab, have been found.

LATE BLIGHT

The disease known as late blight is caused by the fungus
Phytophthora infestans (Mont.) de By. From an economic
point of view it is the oldest and most serious potato disease in
Florida. It has been found in this state since 1903', when it
caused a reduction in yield of from 25 to 30 percent.












Fig. 2.-Half-grown potato plants killed by late blight
The disease appears early in the life of the plant. In fact,
plants have been found infected when only a few inches in
height. In northern states this disease appears late in the life
of the plant and is naturally called late blight. It was found in
fields that had been planted only six weeks. As the season pro-
gressed the weather became warmer and the disease was checked.
Thus, unless the disease is established and rapidly spreading be-
fore April 1 very little damage results.
'Mr. David G. A. Chellberg made all the photographs appearing in this
bulletin except where credit is given.
'Fla. Agri. Exp. Sta. Bul. 75: 181. 1904.







Florida Agricultural Experiment Station


The fungus that causes this disease was undoubtedly intro-
duced into the state with shipments of northern-grown seed
(fig. 3). Last season it was very prevalent thruout the potato-
growing area of Florida.

















Fig. 3.-Late-blight infections on imported seed
DESCRIPTION OF LATE BLIGHT
The disease is first detected on the leaves, usually near the
edges, where large, more or less oval, water-soaked spots appear.
These spots rapidly enlarge, often involving the entire leaf. The
older parts of these spots turn brownish black, later drying and
wrinkling (fig. 4). When conditions are favorable one can see
readily a silvery White growth around the edges of the spots.
This is a mass of the fungus developing spores (fig. 5). The
spores become mature in a short time and are detached readily
and blown considerable distances by the wind to other fields,
where they attack other potato plants and develop the disease
(fig, 6).
Where the disease is severe the leaves are killed quickly and
the petioles and main stalks of the plants are attacked (fig. 7).
When the stems and petioles are first attacked water-soaked
streaks appear as the affected areas. These areas enlarge and
soon turn almost black. The leaves and tender parts of the
stems hang withered from the main stem which remains more or
less erect, even the killed and dried. Often tubers are attacked
by the fungus and severe rotting results. This trouble is of lit-






Bulletin 169, Potato Diseases and Insects


tie importance, however, since there are very few rains to carry
the spores to the tubers which are dug early and marketed im-
mediately.
CONTROL OF LATE BLIGHT
It is essential that tubers used for seed should be free from
the disease, since this is the chief means of spreading late blight
from one section of the country to another. When the plants are


Fig. 4.-Potato leaf showing late-blight infections on leaflets








Florida Agricultural Experiment Station


Fig. 5.-Late-blight fungus producing spores on the lower surface of a potato leaflet.
Enlarged 3 times






Bulletin 169, Potato Diseases and Insects


well out of the. ground they should be sprayed .with 5-5-50 bor-
deaux mixture or dusted with copper-lime dust of good quality.
The following experiments- for control- of -late -blight on -the
Irish potato plants were conducted last season.
DUSTING IRISH POTATOES WITH COPPER-LIME DUST
A series of dusting experiments, conducted in cooperation with
Wm. Scoville of Elkton in which copper-lime dust (6.8 percent
metallic copper) was used to control blight diseases, are of special
interest, since the fields dusted contained several different brands
of common seed. Two applications were made, in each of which
an average of about 20 pounds of dust to the acre was used. The
table below gives certain results of these experiments.
TABLE 1.--BRAND OF SEED POTATOES USED, YIELDS OF CHECK AND DUSTED
PLOTS IN BARRELS OF U. S. GRADE NO. 1 AND PERCENTAGE OF INCREASE
AND DECREASE IN YIELDS ON THE DUSTED PLOTS ON FARM OF
WM. SCOVILLE
Common Seed Yield in barrels to the acre, Percentage of
I U. S. Grade No. 1
Brand Check Dusted Increase Decrease
"A .......................... 33 35 6 ...................
"55" ......-................- I 33 40 18 I...................
"40" and "Page".... 1 20 33 40 ..................
"Bishop" -............. --42 38 I......-........---- 10
The poor stand in the dusted plot of the Bishop brand on dry
and poor sandy knolls probably accounts for the lower yield of
the dusted plot than of the check plot. In considering the yields
of the whole field the dusted plots averaged 45 barrels to the
acre, while the check plots averaged 40 barrels to the acre. Thus
the dusted plots yielded 11.2 percent more No. 1 potatoes than
did the check plots.
When the yields of 10,000 dusted and check 'plants are com-
pared the check plants yielded 47.7 barrels of U. S. Grade No. 1
potatoes against 58.3 barrels for the dusted. This is an 18-per-
cent increase in yield of the dusted over the check plants.
A 30-acre field of potatoes grown by Walter Proctor of Has-
tings was dusted, for the control of blight, with copper-lime dust
containing 6.8 percent metallic copper. Four applications were
made, using a total of 64 pounds of dust to the acre. Twenty
acres of the field were dusted in the daytime with more or less
wind blowing; one acre was left undusted as a check; and the
remaining nine acres were dusted with the same amount of dust
to the acre as the 20 acres, but the dust was applied in the night
when no wind was blowing,






108 Florida Agricultural Experiment Station












































Fig. 6.-Lower surface of a potato leaf showing late-blight infections:
The check plot produced 40 sacks of potatoes to the acre; The
plot dusted -in the daytime produced 53 sacks:.to the acre. The
plot dusted at night produced 70 sacks to the acre. Thus the







Bulletin 169, Potato Diseases and Insects


dusted plots yielded 35 percent better than the checks, the plots
dusted in the daytime yielding 25 percent better than the checks,
and the plots dusted at night yielding 43 percent better than the
checks. This plot also yielded 24 percent better than the plot
dusted in the daytime.
COMMERCIAL BORDEAUX PASTE VS. COPPER-LIME DUST
A spraying and dusting experiment was conducted by George
Atkinson at Federal Point. The plot, of a few acres, was planted
to both common and certified Maine seed. Half of the plants
grown from certified seed and half of the plants grown from
common seed were sprayed with liquid bordeaux made from bor-
deaux paste, to the strength of 4-4-50. The spray machine was
run both ways on each row with a tank pressure of 150 pounds
or more, the common type of nozzles being used. The sprayed
plots received the liquid applications on the same days as the
dust plot was dusted. The bordeaux paste cost 17 cents a pound
and 421/2 pounds were used to the acre, which resulted in a cost
of $7.22 an acre.
The bordeaux paste cost approximately twice as much as the
"dust to apply. The sprayed plots were the first to be attacked
by the blight.
The remaiining plants were dusted with copper-lime dust con-
taining 6 percent metallic copper. The plots that were dusted
received three applications, at intervals of from ten days to two
weeks. The fan of the dusting machine revolved approximately
from 2500 to 2800 times a minute. A total of 55 pounds of dust
was used to the acre at 121/2 cents a pound, resulting in a cost
of $6.87 an acre for the dust. The dusted plots were greener and
showed less blight during the last 60 days than the sprayed
plots. The yields of the dusted and sprayed plots of the common
seed, as well as the certified seed, were practically the same.
Since the yields were the same for the dusted and sprayed plots,
the most important factor was the cost of the spray material and
the cost of its application. The bordeaux paste cost 35 cents
more to the acre than the copper-lime dust, and the cost of ap-
plication for the former was twice as much as for the latter.
Consequently the dust was the more economical to use.
HOME-MADE BORDEAUX VS. COPPER-LIME DUST
A ten-acre field of potatoes grown by C. W. Smith of Hastings
was divided into two plots of five acres each. One five-acre plot
was dusted with copper-lime dust (6 percent metallic copper)







110 Florida Agricultural Experiment Station

and the other five-acre plot was sprayed with home-made bor-
deaux mixture (5-5-50 formula). Two applications.of the liquid
spray were applied ten days apart at a tank pressure of 175


Fig. 7.-Late-blight infections on petioles and main stem of potato plant


'jf^7~






Bulletin 169, Potato Diseases and Insects


pounds. Weather conditions were fair and windy and the plants
were dry. Two applications of dust were applied by a traction-
power duster on the same dates that the bordeaux was applied.
The weather was fair and windy but the plants were wet with
dew. A single row was left as a check, being neither sprayed nor
dusted.
TABLE 2.-HERE ARE SHOWN YIELDS OF DUSTED, SPRAYED AND CHECK
PLOTS OF IRISH POTATOES ON THE FARM OF C. W. SMITH
Treatment Yield to the acre Increase over checks
Dusted ...........................i 75.5 bbls. 15.5 bbls. 20.6%
Sprayed ............-.-.........- 75.0 bbls. 15.0 bbls. 20.0%
Check .... ...................... 60.0 bbls. -........................... ....... ... ...........
Table 2 shows a 20-percent better yield of sprayed and dusted
plots over the check plot, while the sprayed and dusted plots
produced approximately equal yields. Forty pounds of dust was
applied to the acre. At 121/ cents a pound the dust cost was
$5 an acre. The cost of application was calculated at 50 cents an
acre. The liquid bordeaux cost $1.60 for material and 80 cents
to apply for each acre. Therefore, in the two applications $3.10
was saved by using bordeaux.


Fig. 8.-Late blight followed by Fusarium infections on imported seed






Florida Agricultural Experiment Station


Half of another field was dusted five times while the remainder
was sprayed four times. Copper-lime dust and home-made bor-
deaux were used, respectively. In both cases the plants held up
well, dying with age. There was no difference in yield of the two
treated plots. A hundred and fifteen pounds of dust was used in
five applications at a cost of $14.38 an acre, to which was added
$1.25 for application. The cost of the material in the four appli-
cations of bordeaux mixture was $3.20 an acre to which was
added $2 for application. Thus, $10.43 was the amount saved to
the acre by applying home-made bordeaux mixture rather than
copper-lime dust.
Briefly summarized, the results obtained from the foregoing
experiments for the control of late blight are: Copper-lime dust
containing 6 percent of metallic copper, applied in six different
fields, resulted in increased yields averaging 25 percent over un-
dusted check plots. In only one instance was the yield less for
the dusted plot.
Dust also proved to be cheaper than bordeaux paste when the
control was approximately the same.
Home-made bordeaux mixture and copper-lime dust gave ap-
proximately the same control, but the latter cost over $10 an
acre more than the former.


Fig. 9.-Plant affected by bacterial wilt (lCft) compared with a healthy one





Bulletin 169, Potato Diseases and Insects


BACTERIAL WILT

This disease is caused by the bacterial organism known as
Bacterium solanacearum E. F. S. This organism also causes a
similar wilt of tomato, tobacco, eggplant, nasturtium, and many
other plants. It lives in the soil, and in dead vines in the field
and in potato tubers in storage from one season to another. The
disease is widespread in the state and causes considerable dam-
age every season. It is disseminated principally by the tubers
which are used for seed, and by rain, running water and certain
insects. Considerable reduction in the stand has been directly
attributed to the rotting of the seed pieces caused by this or-
ganism.
DESCRIPTION OF BACTERIAL WILT
Usually the first symptom of infection in a plant is a slight
wilting and drooping of the very young leaves at the ends of the
growing branches during the hottest period of the day. This
wilting disappears in the night and cannot be detected in the
morning, but the leaves wilt again during the day. The number of


Fig. 10.-Tubers showing discolored vascular ring, caused by bacterial wilt





114- Florida Agricultural Experiment Station

wilting leaves increases from day to day and soon the stems wilt
to such an extent that they do not recover thru the night (fig. 9).
From this time on the plant is quickly killed and the leaves
wither and drop, leaving
a naked stem which often
falls over.
A diseased plant shows
few outward symptoms
except the wilting until it
dies. A plant affected by
wilt will show darkened
areas in the stem when
cut in two. If a thin layer
of bark is cut off, black
streaks running length-
wise pof the stem will be
noticed. These streaks are
discolored water vessels
clogged with bacteria.
This clogging cuts off the
water supply; consequent-
ly the plant wilts. Healthy
plants are attacked and
killed during all stages of
growth.
Tubers on diseased
plants also become infect-
ed. When such a tuber is
cut open the presence of
the organism is indicated
by the brown color of the
vascular tissue located
about a fourth of an inch
beneath the skin (fig. 10).
In this way the organism
is carried in the seed.
Fig. 11.-The beginning of decay in the vascular Often the tubers begin to
ring, caused by bacterial wilt rot before they. are dug,
disintegrating in the soil and, thus, thoroly infecting it. Rains
and running water carry such infected soil to healthy plants.
Evidence of this was found commonly last season along the larger
irrigation ditches.






Bulletin 169, Potato Diseases and Insects


CONTROL OF BACTERIAL WILT
The first principle in the control of this disease is to plant
disease-free seed.
During the growing season the field should be carefully ob-
served for plants that show signs of wilting. They should be
removed from the fields and destroyed. This can be done con-
veniently during the cultivating season. The field should be gone
over before digging time and all diseased plants dug, removed
and destroyed. The tubers should not be sent to market with the
others because they rot quickly (fig. 11) in transit-a "leaky"
barrel is sold at a reduced price.
Plant clean seed and rogue (weed out) diseased plants.

BLACKLEG

Blackleg is caused by the bacterial organism Bacillus phytoph-
thorus Appel. The disease is scattered well over the entire potato


,~ &


Fig. 12.-Plants in field-one on left shows symptoms of blackleg, one on right is healthy






Florida Agricultural Experiment Station


area of the state. Last season several fields showed a 10-percent
loss, but as a whole the losses amounted to from 1 to 2 percent
only." The disease appears characteristically on the plants about
blossoming time, altho from 50 to 70 percent of the diseased
plants are killed before this time. No definite type of soil or
elevation showed the disease, but instead it was well scattered
thruout the fields.

DESCRIPTION OF BLACKLEG
On growing plants about blossoming time the first symptoms
of the disease are a slight yellowing of the foliage accompanied
by an inward rolling of the edges of the leaves. The petioles and
leaves tend to point
upward at an acute
angle, rather than re-
main horizontal (fig.
12). As the disease de-
velops the yellowing
becomes more marked
and such a plant can
be detected readily
twenty or thirty feet
away (fig. 13). When
such a plant is pulled
up the characteristic
black stem is exposed.
It is from this that the
common name black-
leg is derived (fig. 14).
This blackening of
the stem begins at the
seed piece and pro-
gresses up the stem
indefinitely, usually to
the surface of the soil,
the surface of the soil, Fig. 13.-Potato plant affected with blackleg (Courtesy
altho some plants have U. S. D. A.)
been found with the blackening within a few inches of the tops,
even on 16-inch vines. Large vines often fall over, due to this
weakening of the stem. On younger plants the disease works
rapidly and kills them completely before much yellowing of the
foliage is evident. These killed plants seldom tip over, but remain






Bulletin 169, Potato Diseases and Insects


erect, brown and dead. Tubers formed on diseased plants are
always infected and show a characteristic darkening of the under-
ground stem and vascular system. In advanced stages dark
blotches appear on the tubers
S..under the skin and a wet, soft
rot appears at the eyes. Infected
tubers rot rapidly in transit,
often resulting in a leaky barrel
on the market (fig. 15).
This disease can be distin-
guished readily from bacterial
wilt, previously discussed, by the
characteristic blackening of the
stem and the yellow color and
upright position of the leaves of
S'l diseased.plants. It is often quite
difficult to distinguish the disr
S.ease on the tubers.

CONTROL OF BLACKLEG
The most effective way to con-
trol this disease is by planting
Certified disease-free seed. In
this way the disease is not in-
produced into the field. If certi-
t fled seed are not available, pre-
l-'i cautionary measures should be
Fig. 14.-The blackened condition of the taken at cutting time so that the
rootstalk gave rise to the name "Black- bacteria are not spread from one
leg" (Courtesy U. S. D. A.)
tuber to another. All discolored
tubers should be discarded and all plants that show any symptoms
of the disease should be removed from the field and destroyed.

EARLY BLIGHT

Early blight is caused by the fungus Macrosporium solani E.
& M. This disease is found also on eggplant and tomato, being
caused by the same organism. In Florida the disease appears on
the leaves of the potato plant as soon as the weather begins to
warm up in the spring, usually in March. At this time the plants
are two months old or two-thirds grown; so, in periods favorable
for the development of the fungus, serious damage may be done.






Florida Agricultural Experiment Station


As early blight spreads and becomes serious, late blight begins
to disappear. In Florida late blight appears first, just the reverse












Fig. 15.-Different stages of the rot caused by blackleg
of the condition in northern states. The disease is common on
potatoes in all parts of the state and is generally of considerable
economic importance.

DESCRIPTION OF EARLY BLIGHT
This disease is first apparent by the presence of small, more
or less angular, chocolate-colored brown to black, sunken spots.
These rapidly enlarge under favorable conditions, remain the
same color, become more irregular in shape and develop a distinct
concentric zonation (fig. 17). Black ridges alternate with smooth
brown zones in such a way as to resemble a paper rifle target.
The black spots are often surrounded by yellow areas which


Fig. 16.-Potato plants in the field showing an attack of early blight





Bulletin 169, Potato Diseases and Insects 119
-i


V


Fi. 17.-Potato leaf showing characteristic markings or spots
Fig. 17.-Potato leaf showing characteristic markings or spots


caused by early


blight






Florida Agricultural Experiment Station


blend into the green. In severe cases the spots coalesce, killing
the whole leaf which quickly shrivels (fig. 16). The fungus forms
spores rapidly on the dark spots. They are loosened easily and
are spread great distances by the wind and rain. The mycelium
(threads of fungus growth) lives in the old dead leaves and stems
from one season to the next.
CONTROL OF EARLY BLIGHT
The field should be sprayed with 5-5-50 bordeaux mixture sev-
eral times. It would be very satisfactory to continue the late


Fig. 18.-Leaf showing scattered spots of early-blight infection






Bulletin 169, Potato Diseases and Insects


blight spraying for this purpose until nearly the last of the grow-
ing season. Sanitation should be practiced in the field. All dead
vines should be destroyed and during the early season weeds
along fences and roads should be kept cut.

BLACK SCURF
Black scurf is
very common in
Florida and is *
caused by the fun-
gus Corticium va-
gum B. & C. It is
found in practically
all potato fields as
well as upon practi-
cally all truck crops
and many other cul-
tivated plants in
Florida. The fungus
persists for indefi-
nite periods in the
soil, attacking al-
most all cultivated
plants when condi-
tions favor its
growth. It is wide-
spread in this state,
causing considera-
ble damage. It is
associated of t e n
with potatoes grow-
ing on low, poorly Fig. 19.-Potato stem blight due to black scurf (Courtesy
drained soil. U. S. D. A.)
DESCRIPTION OF BLACK SCURF
The fungus is detected easily'on the mature tubers in the form
of dark brown or black scurf-like spots on the skin of the po-
tato. These spots remind one very much of hard, dry soil (fig.
20). When rubbed with the finger they will not come off. If the
spot is punctured with a knife blade the flesh of the potato is
reached immediately, whereas the skin of the potato will be
found under specks of dried soil.







Florida Agricultural Experiment Station


When the infected seed is
planted, both the fungus and the
potato begin to grow. The young
sprouts often are infected before
they reach the surface of the
soil and in some instances are
killed, causing a considerable re-
duction in stand (fig. 19). Where
the infections are less severe the
thread-like strands of .the fun-
gus follow the stem above the
surface of the soil, covering it
with a white silky growth. Often
that part. of the plant above
ground produces aerial tubers
(fig. 21). These are small tuber-
like growths which develop in

- f-';: C.


.0

Fig. 21.-Little potato caused by black scurf (Cour-
tesy U. S. D. A.)


Fig. 20.-Black scurf on potato tuber (Cour-
tesy Nebr. Agri. .Exp. Sta.)
~1


the petiole axils on the
principal stems. Other
plants may become
more or less rosetted
and of a light greenish
color. The leaves and
petioles often tend to
point upward rather
than remain more or
less horizontal as is
natural of the potato.


CONTROL OF BLACK
SCURF

Plant only disease-
free seed. Treat the
seed with corrosive-
sublimate solution 'be-
fore planting according
to directions given in
the back of this bulle-
tin. Rotate crops.






Bulletin 169, Potato Diseases and Insects


SOUTHERN WILT


Southern wilt is a disease of
fungus Sclerotium rolfsii Sacc.
fields, appearing upon the plants


Irish potatoes caused by the
It is common in the potato
at all stages of their growth.


Fig. 22.-Potato plants attacked by southern wilt: left, badly wilted; right, showing
characteristic symptoms just before wilting
It flourishes especially during rainy seasons. It is not a disease
of potatoes alone, but has been found on dozens of other plants
such as tomatoes, peppers, peanuts, beans, etc. It is well dis-
tributed in Florida and occurs generally over the South.
DESCRIPTION OF SOUTHERN WILT
The early symptoms are very similar to some diseases previous-
ly described herein. The leaves first become light green, being
easily distinguished from the healthy darker green leaves (fig.
22). The blades and petioles tend to point upward and to cluster
together rather than to remain horizontal and spread. Closer
examination shows that the main stem is attacked by the fungus
sometimes an inch or two below, or occasionally slightly above,
the soil surface (fig. 23). This area is covered with a white silky
growth which clings close to the stem above the soil and grows
out into the soil lower down. Around the stem of the plant in the






Florida Agricultural Experiment Station


loose soil the fungus forms numerous small round or oval sclerotia
(seed or repro-
ductive bodies)
a little larger
than mustard
seed. These
i. bodies are al-
most white at
F first and as
they mature
the y become
light brown
and finally
dark bro w
and hard.. It is
by the presence
of these brown
sclerotia that
this disease
S- can be distin-
guished from
black scurf
when both dis-
eases are pres-
ent in the field
and the plants
/ are similarly
attacked at the
surface of the
soil.
The sclero-
tia might well
be compared to
the seed of
Fig. 23.-Stems of potato plant affected by southern wilt. Note f 1 o we r i n g
disintegration plants. The
fungus propagates itself and is disseminated by means of these
bodies. The sclerotia remain viable indefinitely in the soil until
favorable conditions present themselves, when they grow and
attack almost any kind of plant. This fungus also attacks the
tubers before they are dug, causing a soft watery rot which de-
velops rapidly and is exceedingly destructive.






Bulletin 169, Potato Diseases and Insects


CONTROL OF SOUTHERN WILT

No definite and effective control measures have been found for
this disease. Rotation is not desirable but may become necessary.
Rogueing, or removing diseased plants from the fields to prevent
the spread of the disease, should be practised strenuously. Fre-
quent cultivation will tend to check the disease.

MOSAIC

The cause of the disease known as mosaic is not definitely
known. It is common on potatoes in Florida and is also found on
numerous other plants, such as tomato, tobacco and poke weed.
It is evident on plants of all ages after they are a few inches high.
The disease does not kill the plants, but rather stunts them
and reduces their leaf surface so that the yield is lessened (fig.
24). The disease is state-wide and of common occurrence, how-


Fig. 24.-Potato mosaic; diseased and healthy plants


ever, the direct losses due to it are often exaggerated. The
Spaulding Rose No. 4 potato which is grown almost exclusively
around Hastings is more or less free from the disease, due prob-
ably to its resistance or immunity.
The disease is probably spread by sucking insects such as
aphis or plant lice, squash or stink bugs, and leaf-hoppers. It
is also carried by the tubers from season to season.






Florida Agricultural Experiment Station


DESCRIPTION OF MOSAIC
Mosaic on potatoes is characterized by a mottling of the leaf in
which yellowish or light green areas alternate with the green.
These, different shades occasionally blend into each other but
most often they are well defined. The mottling of the leaves is
the only well-defined symptom, altho diseased plants are often
stunted with crinkled leaves. The main stalks may be somewhat
enlarged and of a sturdy appearance (fig. 25).














Lw .


Fig. 25.-A mosaic-affected plant (right) compared with a healthy one (Spaulding Rose
variety)

CONTROL OF MOSAIC
Mosaic can be controlled by planting disease-free seed and by
controlling its insect enemies. Where the disease appears in the
field the plants should be removed and destroyed so that the
disease will not be spread to healthy plants.

CURLY DWARF

As with mosaic, the cause of curly dwarf is not known. It is
very common in Florida and it caused much more damage last
season than did mosaic.
The diseased plants are always stunted and the leaves are
undersized, being more truly oval in shape than healthy leaves.
The stems are usually small in diameter and the foliage is sparse
except at the top where it is more or less rosetted (fig. 26). The






Bulletin 169, Potato Diseases and Insects


Fig. 26.-Plaht affected by curly dwarf (right) compared With a healthy. one (Courtesy
U. S. D. A.)

veins in the leaves branching from the midribs are more promi-
nent in diseased than in healthy plants. The yield is very much
reduced by curly dwarf, since diseased plants produce practically
no marketable tubers.
Practically the only known method of eliminating this disease
is to plant disease-free seed.

LEAF ROLL

Leaf roll is another disease common on potatoes, the cause of
which is not known. It is very common and widespread in the
state. It has been found on several different varieties including
Spaulding Rose No. 4. The disease seldom causes the death of
the plant but it naturally lessens the yield. It is undoubtedly
spread by the distribution of infected seed.

DESCRIPTION OF LEAF ROLL
The disease is evident in the affected plants by the character-
istic rolling of the leaves in which the leaf edges tend to roll
upward and inward toward the midribs. There is some tendency
for the plants to be of a lighter green color than normally and
often the leaves and petioles point upward rather than remain
.horizontal as in healthy plants (fig. 27). These symptoms are






Florida Agricultural Experiment Station


very similar to those given for
blackleg, black scurf, and
southern blight, but in the
cases of these other diseases.
other characteristic symptoms
separate or distinguish them
from leaf roll

CONTROL OF LEAF ROLL
The only way to control this
disease is to plant vigorous,
disease-free seed.

FUSARIUM WILT

This wilt disease is caused
by the fungus Fusarium oxy-
sporum Schl. It has been
found generally distributed in Fig. 27.-Potato plant showing symptoms of
potato fields in the state. leaf roll (Courtesy Nebr. Agri. Exp. Sta.)
Usually it is not evident on the plants, 'until blossoming time
or soon afterward, when they are prematurely killed. The dis-
ease is often scattered in the fields rather than centralized in
certain areas.


Fig. 28.-Plant on left badly wilted by Fnsarium wilt; on right healthy






Bulletin 169, Potato Diseases and Insects


DESCRIPTION OF FUSARIUM WILT
Diseased plants show a premature yellowing of the basal leaves.
This yellowing gradually spreads to the leaves up the stem, being
accompanied by a wilt which at first occurs daily in the younger
leaves and which finally causes the whole plant to wither and die.
The leaves as they become yellow die and drop, leaving a more
or less bare, brown, rigid stem (fig. 28). In cases where the
disease is not so severe the plants are not killed but only show
the yellowing at the base and a slight wilting of the leaves at
the tips of the branches. If the stalk of the wilted plant is cut
aci ose near the lower end, the interior will be almost always of a
distinctive dark brown color. If the stem is split lengthwise,
discoloration extending considerable distances will be observed.
Tubers growing on diseased plants, when cut across, show a
browning of the vascular ring (fig. 29). The ring is about a
fourth of an inch below the skin, and the discoloration is usually
more pronounced at the stem end than at the blossom end. This
dark ring shows the presence of the fungus which causes the
disease and which is ready to infect the new plants grown from
this diseased tuber. This is the principal way in which the disease
is scattered over the country and carried over from one season
to another.

-..


"k. -- -'


Fig. 29.-Cut tubers showing discolored vascular ring caused by Fusarictm 'wilt organism
(Courtesy Nebr. Agri. Exp. Sta.)






Florida Agricultural Experiment Station


CONTROL OF FUSARIUM WILT
Here again the only recom-
mendation to be given that
Swill control the disease is the
planting of certified disease-
free seed. Rotation helps to
clean up infected soil. Seed
should be carefully sorted be-
fore and at cutting time, and
all tubers not perfectly white
and solid should be discarded
(fig. 30).

COMMON SCAB
This disease is caused by
Actinomyces scabies (Thax-
Fig. 30.-Decaying potato, caused by' Fusarium
wilt organism (Courtesy U, S. D. A.) ter) Giissorw. It does not occur
extensively in the potato areas of Florida. Last season the disease
was found to be very limited and the loss due to it was almost
negligible.
DESCRIPTION OF COMMON SCAB
The disease is confined entirely to the tubers. The spots on
them are at first small, shallow, and of a light brown color. Later
they become larger, darker colored and often penetrate the tuber
about a fourth of an inch deep
(fig. 31). When the spots are
numerous enough they coalesce,
causing the whole tuber to be-
come rough, scaly and pitted.
The ,yield is not materially re-
duced but the tubers, because of
these spots, do not sell well on
the market. The disease is intro-
duced with the seed and infects
the new tubers, especially when
the soil is more or less alkaline.
Because of the acid soil the dis-
ease is of minor importance in
Florida.






Bulletin 169, Potato Diseases and Insects


CONTROL' OF COMMON SCAB
If the soil is alkaline, select and plant only disease-free seed.
The'seed should be treated with a solution of corrosive sublimate
according to direction on page
145. Control methods are un-
necessary, if the soil is known
to be decidedly acid.

-SILVER SCURF

This disease is caused by
the fungus Spondylocladiumn
atrovirens Hartz. It has been
found rarely in Florida and
has not caused any serious
losses. The surface of the dis-
eased potatoes is covered 'with
more or less irregular brown-
ish spots or blotches which be-
come silvery in appearance,
especially when placed under
water (fig. 32). These spots,
which are only skin-deep,
open the way for considerable
evaporation thus resulting in
a shriveling of the tubers in
storage.
Do not plant tubers that
show indications of being af-
fected by this disease.

SPINDLE SPROUT

The cause of this disease is
not known. It is apparently a
disease transmitted to Flor-
ida especially among the poor-
er grades of seed. Tubers af-
fected with this disease can be
found often at seed-cutting
time. They show a large num-
Fig. 32.-Different stages of the development of bet of sprouts. They should
silver scurf (Courtesy U. S. D.' A.).






Bulletin 169, Potato Diseases and Insects


CONTROL' OF COMMON SCAB
If the soil is alkaline, select and plant only disease-free seed.
The'seed should be treated with a solution of corrosive sublimate
according to direction on page
145. Control methods are un-
necessary, if the soil is known
to be decidedly acid.

-SILVER SCURF

This disease is caused by
the fungus Spondylocladiumn
atrovirens Hartz. It has been
found rarely in Florida and
has not caused any serious
losses. The surface of the dis-
eased potatoes is covered 'with
more or less irregular brown-
ish spots or blotches which be-
come silvery in appearance,
especially when placed under
water (fig. 32). These spots,
which are only skin-deep,
open the way for considerable
evaporation thus resulting in
a shriveling of the tubers in
storage.
Do not plant tubers that
show indications of being af-
fected by this disease.

SPINDLE SPROUT

The cause of this disease is
not known. It is apparently a
disease transmitted to Flor-
ida especially among the poor-
er grades of seed. Tubers af-
fected with this disease can be
found often at seed-cutting
time. They show a large num-
Fig. 32.-Different stages of the development of bet of sprouts. They should
silver scurf (Courtesy U. S. D.' A.).






Florida Agricultural Experiment Station


not be planted because these sprouts remain weak and slender,
none of them producing marketable tubers (fig. 33). In the field
the diseased tubers produce a cluster of sprouts which grow
bushy and spindly.
Plant vigorous strains of certified seed, seed that were free
from this disease during the previous season.
















Fig. 33.-Sprouted tubers: left, healthy; right, affected by spindle sprout (Courtesy
U. S. D. A.

YELLOW DWARF

The cause of yellow dwarf is not known. It is a new disease
only recently reported from New York. It was found in a single
field near Elkton, but in this instance it was of no economic
consequence because of its scarcity. It is well to become acquaint-
ed with the symptoms since it has been found in the state and
there is a possibility of its proving disastrous in the future.

DESCRIPTION OF YELLOW DWARF

Plants showing characteristic symptoms of the disease are
somewhat yellowed, but the yellow is not so bright as the yel-
low of a plant affected with blackleg. Very often these yellowed
plants show a slight bluish. tinge when the sunlight strikes
them at a certain angle. The stems are usually thicker than the
stems of normal plants and the plant as a whole is typically
dwarfed. The terminal leaves are somewhat clustered or roset-
ted because of the short petioles. The tubers are severely mal-
formed, the most prominent characteristic being numerous deep






Bulletin 169, Potato Diseases and Insects


furrows which run lengthwise, being more prominent at the
blossom end of the tuber and disappearing toward the stem end
(fig. 34). Affected tubers are usually small, the largest grading
something like U. S. No. 2's.




























Fig. 34.-Characteristic yellow dwarf cracks (Courtesy Cornell Univ.)

According to Barrus and Chupp' the disease in New York
is characterized as follows: "The stalks of plants are shorter
than those of healthy plants but have about the same diameter
except toward the top where it is greater, giving such plants a
stockier appearance. The growing apex dies early and later
the axillary buds of the upper part are also killed. The stalk
becomes yellowish green in color thruout. A longitudinal section
of the entire length of a stalk reveals the presence in the upper
portion of rusty-colored specks in the pith and cortex at the
"Barrus, M. F., & Chupp, C. C. Yellow Dwarf of Potatoes. Phytopath.
12: 123-132. 1922.






Florida Agricultural Experiment Station


nodes. In some plants this speaking may be found in the tissues.
this discoloration of the cortex often becomes suffi-
ciently pronounced so that it can be observed from the outside
thru the epidermis. Orie could not, however, confuse yel-
low dwarf with other diseases after examining the tubers. *
The cracked condition is very characteristic of the disease. *
Another character of tubers affected with this disease that may
be depended on in diagnosis is the discoloration of the flesh.
This usually appears as rusty brown specks or areas surrounding
the pith area but discoloration does not appear as streaks. *
Not all tubers from affected plants show internal discoloration."
(See fig. 35.)
























Fig. 35.--Tubers showing internal spotting caused by yellow dwarf (Courtesy Cornell Univ.)

CONTROL OF YELLOW DWARF.
As very little is known of this disease, control methods cannot
be recommended. The county agent or a plant disease specialist
should be informed whenever growers suspect their plants of
being affected with yellow dwarf.






Bulletin 169, Potato Diseases and Insects


WART

This disease, caused by Synchytrium endobioticum (Schilb.)
Perc., has never been found in Florida. In fact, it has been found
only in limited districts in Pennsylvania, Maryland, and West
Virginia. These districts are strictly quarantined, but it is well
that Florida growers should have some idea of the disease be-
cause of its destructiveness and the possible danger of intro-
duction into the state. Growers should become familiar with the
symptoms of the disease and should send any suspicious speci-
mens to the Experiment Station immediately upon their discovery.

DESCRIPTION OF WART
The organism which causes wart lives in the soil and attacks
principally the tubers, altho infection may take place on any of
the younger tis-
sues of the roots,
stolons or stems
(fig. 36). Attacked
tubers show
brownish b 1 ac k,
spongy, rou g h,
warty outgrowths,
varying from small
growths to exceed-
ingly large knobs
which cover the
whole tuber, in
which case all re-
semblance of the
potato is lost.
These diseased
tubers when left in
I the soil disinte-
grate, leaving
spores which thor-
oly infect the soil
and which live sev-
eral years and are
-. able to reproduce
the disease when
Fin. 36.--Potato wart disease on plant and tubers (Courtesy potatoes are again
Penn. Agri. Exp. Sta.)






Florida Agricultural Experiment Station


Slanted in this soil. The disease
undoubtedly would prove very
Serious in the concentrated pota-
to-growing districts of Florida,
should it be introduced.

CONTROL OF WART

Plant only disease-free seed, so
as to prevent the introduction of
This dreaded disease. Examine
Fig. 37.-Cross section of a diseased tuber, the fields
showing relation of tuber and ware the fields at digging time and
growth (Courtesy Penn. Agri. Exp. Sta.) watch the grader for it.


POWDERY SCAB
Powdery scab is caused by a fungous organism known as
Spongospora subterranea (Wallr.) Johns. It has not been found
in Florida. It is present in different parts of the United States
and Canada. It has not proved as disastrous to potatoes as was
thought sometime ago. It is well to know the principal symptoms
so that seed affected with the disease can be avoided.


Fig. 38.-Powdery scab on potato (Courtesy U. S. D; A.)






Bulletin 169, Potato Diseases and Insects 137

DESCRIPTION OF POWDERY SCAB

Powdery scab is quite different from common scab, but one
must show the essential differences before the two may be dis-
tinguished easily. Spots caused by powdery scab on the tubers
when fully enlarged are seldom more than a fourth of an inch
in diameter, being much smaller than those caused by common
scab. The epidermis (thin outside skin) covering them ruptures,
exposing a dark brown powdery mass. The torn skin that pre-
viously covered the pustule surrounds it, adhering to the healthy
tissue (fig. 38). The powdery mass within these pustules con-
tains the spores which carry the organism from one season to
another and also disseminate it in the fields.
To control plant only certified seed.






Florida Agricultural Experiment Station


NOTES ON POTATO SEED TROUBLES
GENERAL SURVEY

A general inspection was made of the potato seed, obtained
from sources outside the state, during the latter part of Decem-
ber. The seed potatoes to be planted on 28 farms were examined
and, in every instance, irregular, sunken, dark-brown areas vary-
ing in size from minute spots to spots involving half of the area
of the tuber were found (fig. 39). This peculiar spotting was
found on all varieties of seed.


Fig. 39.-Potato affected by late-blight dry rot (Courtesy Cornell Univ.)

Cultural study showed that the spotting was caused by late
blight fungus, Phytophthora infestans (Mont.) de By. There
was a decided difference between certified and uncertified seed
as to the percentage of infected tubers and the amount of infec-
tion on individual tubers. Certified stock was always found to
be less spotted by the disease than common stock. Whether or
not this spotting of the tubers, which were used for seed, was
responsible in any way for the unusually destructive epidemic
of the late blight fungus later in the season is not known (fig. 3).


f" i j6~-~rC-r






Florida Agricultural Experiment Station


NOTES ON POTATO SEED TROUBLES
GENERAL SURVEY

A general inspection was made of the potato seed, obtained
from sources outside the state, during the latter part of Decem-
ber. The seed potatoes to be planted on 28 farms were examined
and, in every instance, irregular, sunken, dark-brown areas vary-
ing in size from minute spots to spots involving half of the area
of the tuber were found (fig. 39). This peculiar spotting was
found on all varieties of seed.


Fig. 39.-Potato affected by late-blight dry rot (Courtesy Cornell Univ.)

Cultural study showed that the spotting was caused by late
blight fungus, Phytophthora infestans (Mont.) de By. There
was a decided difference between certified and uncertified seed
as to the percentage of infected tubers and the amount of infec-
tion on individual tubers. Certified stock was always found to
be less spotted by the disease than common stock. Whether or
not this spotting of the tubers, which were used for seed, was
responsible in any way for the unusually destructive epidemic
of the late blight fungus later in the season is not known (fig. 3).


f" i j6~-~rC-r






Bulletin 169, Potato Diseases and Insects


Last year was the first'time that this condition of seed potatoes
was observed in this vicinity. The spotting was often so deep that
it was past the vascular layer and consequently disinfection of
the seed with corrosive sublimate was not considered advisable
(fig. 8).
Seed potatoes arrived at their Florida destination in such
bruised and cracked condition that in many instances 50 percent
of the tubers were totally unfit for seed. Most of the growers,
however, discarded only those parts of the tubers which showed
serious decay, doing this when the seed pieces were cut. The
cracked and bruised tubers undoubtedly became injured thru
rough handling while in transit. Practically all potatoes shipped
to Florida for seed are shipped in 150-pound burlap bags. Upon
arrival they are stored in the open usually. Bruised and cracked
tubers are subject to invasion by fungous parasites (fig. 1).
More than half of the seed that had to be discarded were thrown
out because of infections by the various Fusarium species.
Discarding decayed tubers or parts of tubers adjacent to the
potato field at the time the seed is cut is bad practice and should
be discontinued. The seed should be sorted, the good from the
bad, before cutting begins, in order to prevent the transference
of fungi from diseased to healthy tubers cut later. The decayed
tubers should be placed in containers and not left around the
edges of the potato field. They should be destroyed.
This large loss of seed to the growers can be avoided and some
immediate attention should be given to this problem. Seed should
be loaded for transportation at the place where it is grown and
unloaded where it is to be planted.
As a whole the condition of seed potatoes that are received in
the Hastings district was very unsatisfactory. It appeared that
a large percentage of the losses was due to rough handling.
During the third week of February the northern half of the
state was subjected to freezing temperatures on two nights. The
temperature at Gainesville, which is situated about sixty miles
west of Hastings, registered 25.5 degrees F. on one of those
nights. Observations were made in the potato fields following
these freezes. Previous to this time about 96 percent of the fields
showed the green plants in the different stages of development.
Many of the fields which were planted during December were
in blossom and the vines had almost hidden the ground. These
suffered very severely from the freeze. The vines were frozen
back 'until only a few inches of the ihain stalk remained.






Florida Agricultural Experiment Station


The largest percentage of the fields, however, were less severely
injured. The bulk of the growers planted during the first half
of January. The plants in these fields were several inches high
and were frozen to the ground. The fields in which the plants
were not out of the ground suffered no loss. Following the freeze
the plants appeared to be dormant as far as any growth above
ground was concerned for a period of ten days or two weeks.
Then new leaves and shoots developed and in a short while the
fields were green. The plants that were not out of the ground
on February 19 now forged ahead and became the largest and
most vigorous. They remained the best thruout the remainder
of the season. The plants that Were several inches high when
frozen revived quickly and, with certain exceptions, developed
healthy, vigorous tops.
A large number of the fields were visited and where the plants
failed to come back, the seed pieces were dug out. Two very dis-
tinct conditions were noted: First, the seed piece had for some
reason not sufficient vitality to send out another sprout, the eye
was too close to the cut edge or, in many instances, the seed
piece was the stem end of the original tuber. This condition pre-
vailed in almost all of the fields mentioned above in Which the
seed piece was hard and sound, apparently unaffected by any
disease.
Second, almost the same condition as given above was noted in
which the seed piece was unsound, or partly or wholly decayed.
A safe estimate would be that from 30 to 40 percent of the seed
pieces that failed to develop new sprouts were decayed. The per-
centage of seed pieces that failed to develop new sprouts ranged
from 5 to 50 percent, averaging about 15 percent. Counts were
made in 15 fields. It was noted that the stand in fields planted
with certified seed stock was reduced less by the freeze than in
other fields.
In fields where young tubers were set another condition arose.
The stems of some of the plants were frozen off to, or below, the
last node, leaving no place for the new bud to develop. In such
instances tubers from a quarter to half an inch in diameter de-
veloped sprouts from the blossom ends. These sprouts, except
in a very'few instances, never made U. S. Grade No. 3 potatoes.
Often the stem was frozen off just above the last node when,
consequently, the bud developed at that node. Usually when the
frozen stem was closer than half an inch from the bud, the bud






Bulletin 169, Potato Diseases and Insects


was finally killed by organisms which entered the old stem. This
condition became very conspicuous by April 1 (fig. 40). The
plants that were in blossom when frozen down revived with diffi-
culty, the stand was severely reduced and the surviving plants
developed slowly. Generally speaking the yield in these fields was
reduced from one-half to three-fourths.




























Fig. 40.-Potato plant showing result of freeze; secondary stalks developing

CERTIFIED SEED INCREASE THE YIELD
In the potato fields around Hastings only a small amount of the
seed planted were certified. Some of these fields planted with
certified seed were closely watched and in every case the yield
was decidedly greater than that from common stock (fig. 41).
A detailed study was made of a field belonging to Wm. Scoville
near Elkton, as it contained several kinds of seed, both certified







Florida Agricultural, Experiment Station


and uncertified. Counts were made in this 30-acre field of the
actual number of plants, the percentage of perfect stand obtained
and the number of diseased plants found in the field. The per-
centage of increase in yield was calculated for the acre and for
10.000 plants.

TABLE 3.-BRANDS OF SPAULDING ROSE NO. 4 POTATO SEED AND PER-
CENTAGE OF PERFECT STAND OBTAINED IN THE FIELD
ON FARM OF WM. SCOVILLE

Kind of Seed Percentage of Perfect Stand
New York Certified-...---.......----.................. .... 97.5
Minnesota Certified ........................................... 96.5
M aine Certified ............................. ...... ....... .... 93.0
"Bishop" Common .............................................. 95.0
"Humphrey" Common ........................................ 93.5
"40" Common ................................................... 93.0
"55" Com mon ..................................................... 93.0
"3" Com m on ........................................... ....... 93.0
"Page" Common ........................... ........ 92.0
"A" Com mon ................................................ .... 91.0

Actual counts in the field showed that there were 59 percent
more diseased plants in the field planted with common seed than
in those planted with certified seed.


Fig. 41.-The stand here is 97 percent perfect; planted with certified seed

The yields obtained from the certified fields and the common
fields were carefully recorded and the certified seed was found
to have produced an average of 54 barrels to the acre, andcommon
seed 44 barrels. This represents an increase in yield of 18 per-
cent, due to certified seed. .This increased yield netted $55. The
additional expense was $6.75. A profit, therefore, of $48.25 to
the acre was realized by planting certified seed.






Bulletin 169, Potato Diseases and Insects


This increase was due partly to the better stand obtained, but
even when the yield was computed for 10,000 plants it was
found that certified produced 11 percent better than the common
seed.
An accurate check was also made in a field owned by Geo.
Atkinson of Federal Point. These plots were small and were
carefully sprayed and dusted. The seed used were certified and
uncertified Maine stock. The common seed produced a yield of
55 barrels to the acre, while the certified seed produced 63 barrels
to the acre or an increase of 13 percent, At $5 a barrel the certi-
fied stock sold for $315 and the common for $275. The extra
cost for certified seed. was $6.75 to the acre. An acre profit of
$33.25 was realized where certified seed were used, rather than
common seed.

SEED FROM WYOMING
A barrel of certified Spaulding Rose No. 4 seed, grown under
irrigation, was secured from Torrington, Wyoming, to compare
with certified seed of that variety secured elsewhere. These seed
were uniform in size and shape, typical of the variety and free
from disease. They were cut and planted by Mr. Middleton at
Elkton in a field adjoining a planting of New York certified seed
of the same variety.
The growth during the season compared very favorably with
the New York certified seed. The vines were typical and their
color was good. There was slightly less disease present than in
the New York certified seed, there being less than 2 percent of
diseased plants. The yields from the two plantings were practi-
cally the same.
As a whole the Wyoming were as good as the New York seed.
They showed slightly less disease in the field. It is impossible
for the growers to use these seed, however, because their trans-
portation costs are three or four times greater than from New
York.
BLISS TRIUMPH SEED POTATOES FROM NEBRASKA
A barrel of selected Bliss Triumphs were secured from Neb-
raska to compare with Spaulding Rose No. 4's. These tubers were
cut and planted by Frank Johns of Hastings in a field adjoining a
planting of Spaulding Rose No. 4. During the growing season the
plants from the Bliss seed grew as well as the other variety. They
were slightly darker green in color, less branched and slightly






Florida Agricultural Experiment Station


more subject to attacks of late blight. As to other potato diseases,
there was slightly less blight among the Bliss Triumphs than
among the Spaulding Rose No. 4's. The former produced 54 bar-
rels to the acre, while the latter under the same conditions pro-
duced 50 barrels, or 7 percent less.

RUSSET RURAL SEED POTATOES FROM MICHIGAN
A barrel of selected Russet Rural seed potatoes were obtained
from the Michigan Potato Growers' Association to compare with
the Spaulding Rose No. 4 as to field conditions and yield. These
tubers were cut and planted by H. O. Hamm of Palatka, in the
center of a large field with plantings of Spaulding Rose No. 4
on each side.
The Rurals came up a little later than the Roses. They grew
very well and developed a less-branched, more erect top. There
was some late blight scattered over the whole field but the Rurals
showed less of it than the Rose.
The yield of the Rurals was better in both quantity and quality.
The tubers were practically all U. S. Grade No. 1 with less than
2 percent of U. S. Grade Nos. 2 and 3. The Rose developed some
larger tubers than the Rural but there .were also from 15 to 20
percent of U. S. Grade Nos. 2 and 3. Mr. Hamm says, "We think
enough of them to plant several acres another year so that we
can get a better test."

POTATO SEED DISINFECTION

A number of diseases, such as scab and black scurf,,are carried
on the surface of potatoes. The spores of almost all. potato
diseases might be carried on the surface of the tubers while yet
the tubers appeared free from all diseases. Consequently it is
urged that seed potatoes be treated with a disinfecting solution
before planting. This will not eliminate all diseases because
spores may be living in the soil and be spread during the growing
season.
Sort the potatoes carefully before treating, discarding bruised
and rotten tubers, and treat before cutting.

MERCURIC CHLORIDE TREATMENT
E perimental work elsewhere has shown that this disinfectant
is superior to, the formaldehyde treatment for black sctrf, which






Bulletin 169, Potato Diseases and Insects


is a very serious trouble in the state. The disinfecting solution is
prepared by mixing together:

Mercuric chloride (corrosive sublimate)...................... 4 ounces
W after ........................-......... .....................-.......-30 gallons
Soak the sound tubers in this solution from one and a half to
two hours and dry thoroly before planting. Do not use these pota-
toes for anything except to plant. They are deadly poisonous and
will kill poultry, livestock and human beings. Dissolve 4 ounces
of mercuric chloride crystals in 1 gallon of hot water, using a
stone crock or wooden bucket as the container; dilute this stock
solution until the whole is made up to 30 gallons. (The solution
will then be 1:1000 strength.) A barrel is a very satisfactory
container for the diluted solution.
This solution loses strength as it is used. To correct this add
1/2 ounce of mercuric chloride crystals to every 4 bushels of
potatoes treated for two hours. If treating for only one and a
half hours, add only 3/8 ounce of mercuric chloride crystals.
Keep the water in the barrel up to the original level. Do not use a
solution more than six or seven times for best results. Soaking
potatoes a few hours before treating will soften the fungi and
rinse off the dirt so that the disinfectant will be more effective.
Precautionary measures should be taken so as to reinfect thd
tubers after they are treated.

SPRAYING
BORDEAUX MIXTURE
This fungicide is used more than all other liquid solutions for
controlling leaf diseases of the potato, such as early and late
blight.
The success of spraying with bordeaux mixture depends largely
upon the method of making it.
For convenience stock solutions of bluestone and lime can be
made, each containing a pound of solid matter to each gallon of
water.
STOCK A, BLUESTONE: Dissolve at the rate of 1 pound of
bluestone to 1 gallon of water; put 50 pounds of bluestone into a
clean bag. and suspend it in the top of.a 50-gallon barrel of water.
It will dissolve over night. Never use a.metal container for this
purpose. Always stir the stock solution before taking any out.






Florida Agricultural Experiment Station


STOCK B, LIME: Unslacked lime should be used in making
bordeaux. Slake 50 pounds of lime and dissolve it in 50 gallons
of water. Be careful not to drown or burn the line while slaking.
Always stir the stock solution before taking any out. Do not stir
the stock solutions with the same stick.
These stock solutions will keep well for indefinite periods.
Some mark should be made on the inside of the containers at the
surface of the solutions so that water lost by evaporation can be
restored before the solutions are used. Keep the stock solutions
covered.
In making bordeaux mixture observe the following directions:
Dilute the required amount of bluestone solution to half of the
amount of spray to be made. Dilute the required amount of lime
in a separate container to half the amount of spray to be made.
Then, at the same time pour the contents of the two containers
into a third container, stirring the combined mixture as the two
are being poured together. It is essential that this mixture be
applied soon after it is made. It is worthless after 12 hours.

FOR DIFFERENT AMOUNTS OF 5-5-50 BORDEAUX MIXTURE
In making 50 gallons of the mixture, use 5 gallons of stock A,
diluted to 25 gallons, and 5 gallons of stock B, diluted to 25
gallons. Run both of these into the sprayer at the same time with
the agitator going.
To make 100 gallons of spray, use 10 gallons of stock A, diluted
to 50 gallons, and 10 gallons of stock B, diluted to 50 gallons. Mix
as above.
To make 200 gallons of spray, use 20 gallons of stock A, diluted
to 100 gallons, and 20 gallons of stock B, diluted to 100 gallons.
Mix as above.
To make 300 gallons of spray, use 30 gallons of stock A, diluted
to 150 gallons, and 30 gallons of stock B, diluted to 150 gallons.
Mix as above.
THE CENTRAL STATION
For convenience in filling the sprayer, one should have a plat-
form for the barrels high enough so that the diluted solutions can
be run from the barrels into the sprayer. This platform should be
large enough to hold the two barrels of stock solution and the
number of barrels needed for diluting. For the-200-gallon tank
the platform would have to hold six 50-gallon barrels.






Bulletin 169, Potato Diseases and Insects


If it is impractical to use the above method of mixing the bor-
deaux, the following method may be used: Pour the diluted lime
solution into the spray, tank, set the agitator going and add
slowly the diluted bluestone solution.
Spraying must be done thoroly to be a paying proposition. The
tank pressure should not be below .150 pounds. Three nozzles
should be used to each row, one on each side turned slightly up-
ward and one from the top turned down. The plants must be
covered completely so that the spores of the fungi will be killed
when they fall upon the plant. The spray should be applied often
enough to keep the growing plant well protected. This usually
calls for an application every ten days.

DUSTING

Dusting potatoes with copper-lime dust, altho yet in the ex-
perimental stage, has given much satisfaction, both as to con-
venience of application and results obtained in the control of
the blight diseases. The dust is made by commercial firms with
a guaranteed copper content. The dusting machine is similar to a
liquid spray machine, except that the dust is applied dry. The
most satisfactory power is obtained from a gasoline engine. The
revolution of the fan, which blows the dust onto the plants,
should never be less than 2500 revolutions a minute. Dusting in
the night is very effective, the plants being wet with dew at that
time. Quiet days with no wind are better than windy days. Al-
ways keep the dust dry and free from lumps.
The dust should be applied often enough to protect the.grow-
ing plants, usually every ten days or two weeks. The amount to
apply varies according to the size of the plants but should be
about 40 pounds to the acre for each application.

COPPER-LIME DUST VS. HOME-MADE BORDEAUX MIXTURE
The Vermont Agricultural Experiment Station has sprayed
potato plants with bordeaux mixture to control late blight over a
period of 20 years. During this time the average yield of the
plots was increased 105 bushels to the acre'. Several applications
of 5-5-50 bordeaux mixture applied correctly controls late blight
effectively. The actual cost of material in Florida for one acre
for one application is as follows:
'Lutman, B. F. Twenty Years Spraying for Potato Diseases, Potato
Diseases and the Weather. Vt. Agri. Exp. Sta. Bul. 159: 247. 1911.






Florida Agricultural Experiment Station


10 pounds bluestone @ $ .09...................... ... .... $ .90
10 pounds rock lime @ .01% ....... ....... ......... .15
100 gallons of water, no cost............................ .....
Total cost ....... .... ........ ..............................$1.05
Ten pounds of bluestone (copper sulphate) contains approximate-
ly two and a half pounds of metallic copper, which is the active
ingredient in controlling late blight.
In dusting and spraying potato plants to control late blight it is
essential that the same amount of metallic copper be applied to
the acre with the copper-lime dust as with the liquid bordeaux, if
comparable results are to be obtained. The commercial manu-
facturers guarantee the metallic copper content of their copper-
lime dust. The dust mostly used contains 6 percent of metallic
copper, which means 6 pounds of metallic copper to 100 pounds
of dust. With each application of 5-5-50 liquid bordeaux, 21/2
pounds of metallic copper is applied to the acre. Consequently,
it would be necessary to apply 42 pounds of copper-lime dust with
6 percent of metallic copper content at each application to have
the same amount of metallic copper applied to the acre.
There are a number of other factors to be considered before
the two fungicides can be closely compared; such as, time of ap-
plication, force with which the mixtures are applied, etc. Never-
theless, 'it is necessary first to apply equal amounts of metallic
copper, if comparisons are to be made.






Bulletin 169, Potato Diseases and Insects


INSECT ENEMIES OF THE POTATO
IN FLORIDA
(By J. R. Watson, Entomologist)
The Irish potato is not as seriously injured by insects in Florida
as in more northern states, since it is grown in the cooler months
of the year when most insects are inactive. The following are
some of the more important insect pests of potatoes, in this state,
together with their control measures.

PLANT LICE
Aphids suck the juices from the plant (fig. 43), stunting its
growth, causing the leaves to curl, turn yellow and finally die.
They multiply with great rapidity, often beginning when only a
week old and producing several young each day. During virtually
the entire year in Florida the individuals of most species bring
forth young parthenogenetically, that is, without the mating of
the sexes. Indeed, during summer the males are usually not
produced at all. The young are born alive and active, the eggs
hatching before they are laid. But with the coming of winter,
in more northern states, males and true females are produced
and eggs are laid which do not hatch until spring. Most indi-
viduals never acquire wings, but from time to time some do grow
wings, thus assisting in spreading the species from plant to
plant -(fig. 42).
Plant lice may be best controlled by the use of some form of
nicotine. Most growers prefer to put this material into the bor-
deaux when spraying for fungous diseases. If this is done, use
1 part of nicotine sulphate to 800 parts of the spray material.
However, should the grower wish to combat aphids alone when
there are no fungous diseases to fight, he can do so most quickly
by dusting with one of the
nicotine-sulphate-lime dusts
now on the market. These
dusts are best applied in the
/middle of the day when the
sun is hot. At this time the
action is more rapid. The
Sdust is much more quickly
Fig 42.-Aphis; a. winged female; b. wingless applied than is a liquid spray
female. Greatly enlarged (Courtesy U. S. D. A.)liquid






Bulletin 169, Potato Diseases and Insects


INSECT ENEMIES OF THE POTATO
IN FLORIDA
(By J. R. Watson, Entomologist)
The Irish potato is not as seriously injured by insects in Florida
as in more northern states, since it is grown in the cooler months
of the year when most insects are inactive. The following are
some of the more important insect pests of potatoes, in this state,
together with their control measures.

PLANT LICE
Aphids suck the juices from the plant (fig. 43), stunting its
growth, causing the leaves to curl, turn yellow and finally die.
They multiply with great rapidity, often beginning when only a
week old and producing several young each day. During virtually
the entire year in Florida the individuals of most species bring
forth young parthenogenetically, that is, without the mating of
the sexes. Indeed, during summer the males are usually not
produced at all. The young are born alive and active, the eggs
hatching before they are laid. But with the coming of winter,
in more northern states, males and true females are produced
and eggs are laid which do not hatch until spring. Most indi-
viduals never acquire wings, but from time to time some do grow
wings, thus assisting in spreading the species from plant to
plant -(fig. 42).
Plant lice may be best controlled by the use of some form of
nicotine. Most growers prefer to put this material into the bor-
deaux when spraying for fungous diseases. If this is done, use
1 part of nicotine sulphate to 800 parts of the spray material.
However, should the grower wish to combat aphids alone when
there are no fungous diseases to fight, he can do so most quickly
by dusting with one of the
nicotine-sulphate-lime dusts
now on the market. These
dusts are best applied in the
/middle of the day when the
sun is hot. At this time the
action is more rapid. The
Sdust is much more quickly
Fig 42.-Aphis; a. winged female; b. wingless applied than is a liquid spray
female. Greatly enlarged (Courtesy U. S. D. A.)liquid







150 Florida Agricultural Experiment Station


















































Fig. 43.--IIfestation of aphis (plant lice) on potato stem (Courtesy Maine Agri. Exp. Sta.)






Bulletin 169, Potato Diseases and Insects


LEAF-HOPPERS

Several species of jassids or leaf-hoppers (fig. 44), attack po-
tatoes, especially those planted in the fall. Like plant lice they
not only suck the sap out of the plant but have a distinct poisoning
effect on it. But it is as transmitters of fungous diseases that
they do most injury to the potato.


Fig. 44.-Bean leaf-hopper, an
insect injurious to the po-
tato: right, adult; left, wing
extended showing venation.
Much enlarged (Courtesy
U. S. D. A.)


These hoppers may be recognized as small
greenish insects which, when disturbed, hop
and fly some distance. They are consider-
ably larger and quicker of motion than the
aphids or plant lice. The leaves, if badly af-
fected, may become curled and twisted as a
result of these attacks, and they frequently
turn yellow or colorless about the edges, a
type of injury known as "hopperburn."
Jassids are best controlled by spraying
with nicotine sulphate added to the bor-
deaux spray, using 1 part of nicotine sulph-
ate to 800 parts of bordeaux.


LARGER PLANT BUGS

There are several species of large plant bugs which frequently
attack potatoes, particularly those planted near a hammock,
where the insects spend the winter and from which they emerge
in the spring and attack the crop.

"BIG-FOOTED PLANT BUG"

The largest of these is the "big-footed plant bug" (fig. 45.)
Like the other plant bugs these use for food the juices of succu-


J,




Fig. 45.-Big-footed ilant
bug. Natural size


lent, quickly growing plants of which the po-
tato is a favorite. It is not only very succu-
lent, but its large stems furnish sufficient
support for these heavy bugs. The insects
usually settle three or four inches below
the top, and the withdrawal of sap causes the
tip of the plant to wilt markedly. If the attack
is persistent, the top will die. It is probable
that the damage inflicted by this bug, as well
as the other plant bugs, is not due entirely






Bulletin 169, Potato Diseases and Insects


LEAF-HOPPERS

Several species of jassids or leaf-hoppers (fig. 44), attack po-
tatoes, especially those planted in the fall. Like plant lice they
not only suck the sap out of the plant but have a distinct poisoning
effect on it. But it is as transmitters of fungous diseases that
they do most injury to the potato.


Fig. 44.-Bean leaf-hopper, an
insect injurious to the po-
tato: right, adult; left, wing
extended showing venation.
Much enlarged (Courtesy
U. S. D. A.)


These hoppers may be recognized as small
greenish insects which, when disturbed, hop
and fly some distance. They are consider-
ably larger and quicker of motion than the
aphids or plant lice. The leaves, if badly af-
fected, may become curled and twisted as a
result of these attacks, and they frequently
turn yellow or colorless about the edges, a
type of injury known as "hopperburn."
Jassids are best controlled by spraying
with nicotine sulphate added to the bor-
deaux spray, using 1 part of nicotine sulph-
ate to 800 parts of bordeaux.


LARGER PLANT BUGS

There are several species of large plant bugs which frequently
attack potatoes, particularly those planted near a hammock,
where the insects spend the winter and from which they emerge
in the spring and attack the crop.

"BIG-FOOTED PLANT BUG"

The largest of these is the "big-footed plant bug" (fig. 45.)
Like the other plant bugs these use for food the juices of succu-


J,




Fig. 45.-Big-footed ilant
bug. Natural size


lent, quickly growing plants of which the po-
tato is a favorite. It is not only very succu-
lent, but its large stems furnish sufficient
support for these heavy bugs. The insects
usually settle three or four inches below
the top, and the withdrawal of sap causes the
tip of the plant to wilt markedly. If the attack
is persistent, the top will die. It is probable
that the damage inflicted by this bug, as well
as the other plant bugs, is not due entirely






Florida Agricultural Experiment Station


to the loss of sap-they may inject a poison into the punc-
ture.
These insects are so large and their effects on the plant so
conspicuous that collecting by hand is an easy matter. The wilted
tops show the location of the bugs (fig. 46). Two or three col-
lections during the season usually suffice. This bug is particularly
abundant in the early spring on thistles, which should be cut
down in the vicinity of the potato field.

PUMPKIN BUG

The second largest of these bugs is the pumpkin bug. The
adult is light green but the young are purple with yellow spots.
They inflict about the same type of injury as the big-footed plant
bug, and the method of control is practically the same.


Fig. 46.-Potato plant showing plant-bug injury. Note wilted leaves





Bulletin 169, Potato Diseases and Insects


LEAF-FOOTED PLANT BUG


menaeda or Jarssiu.
Fig. 47.-Leaf-footed plant bug.
Enlarged
FLEA BEETLES
These are small black or slate-colored beetles (fig. 48) that
get their name from their habit of quickly springing several
inches when disturbed. They eat the epidermis on one side of
the leaf and the soft interior cells, leaving the veins and other
hard parts intact.
Bordeaux mixture is usually effective in preventing the injury
of these insects. The mixture can be made more effective by
the addition of from 8 to 16 ounces of
powdered lead arsenate (or from 1 to 2
pounds of the paste) to 50 gallons of the
bordeaux.


K


A


:bib


Fig. 48.-Potato flea-beetle (left); eggplant flea-beetle (center), an insect enemy of the
potato; and tobacco flea-beetle (right), an insect enemy of the potato (Courtesy U. S. D. A.)
BLISTER BEETLES
These are long slender beetles which eat the potato leaves,
often completely stripping the vines. They move about in im-
mense swarms devouring all the potatoes in their path. There


( I


/ The third species is the leaf-footed
plant bug. It is a brownish insect with a
bright yellow line across the back (fig.
47). The shanks of the hind legs are ex-
panded into wide, leaf-like structures,
from which it gets its name. This insect
is more delicate than the big-footed and
pumpkin bugs, and can be killed by a
soap and tobacco spray, such as is recom-
i~ 1i 1 j" -'I





Bulletin 169, Potato Diseases and Insects


LEAF-FOOTED PLANT BUG


menaeda or Jarssiu.
Fig. 47.-Leaf-footed plant bug.
Enlarged
FLEA BEETLES
These are small black or slate-colored beetles (fig. 48) that
get their name from their habit of quickly springing several
inches when disturbed. They eat the epidermis on one side of
the leaf and the soft interior cells, leaving the veins and other
hard parts intact.
Bordeaux mixture is usually effective in preventing the injury
of these insects. The mixture can be made more effective by
the addition of from 8 to 16 ounces of
powdered lead arsenate (or from 1 to 2
pounds of the paste) to 50 gallons of the
bordeaux.


K


A


:bib


Fig. 48.-Potato flea-beetle (left); eggplant flea-beetle (center), an insect enemy of the
potato; and tobacco flea-beetle (right), an insect enemy of the potato (Courtesy U. S. D. A.)
BLISTER BEETLES
These are long slender beetles which eat the potato leaves,
often completely stripping the vines. They move about in im-
mense swarms devouring all the potatoes in their path. There


( I


/ The third species is the leaf-footed
plant bug. It is a brownish insect with a
bright yellow line across the back (fig.
47). The shanks of the hind legs are ex-
panded into wide, leaf-like structures,
from which it gets its name. This insect
is more delicate than the big-footed and
pumpkin bugs, and can be killed by a
soap and tobacco spray, such as is recom-
i~ 1i 1 j" -'I






Florida Agricultural Experiment Station


are several species of them. Some are striped lengthwise with
black and white (fig. 49), others are plain slate colored, and some
almost brown or black. Blister beetles are often called "old
fashioned potato beetles" to distinguish them from the more re-
cent arrival, the Colorado potato beetle.












Fig. 49.-Black blister beetle (left), margined blister beetle and striped blister beetle.
Enlarged (Courtesy U. S. D. A.)

Blister beetles can be controlled by mixing 1 pound of lead
arsenate to each 50 gallons of the bordeaux spray. If they occur
near the edge of the potato field, they can be driven out by a
bundle of twigs used as a whip: This is better than killing them
with lead arsenate, as the young of these beetles feed on the
eggs of grasshoppers and are, therefore, highly beneficial.

HORNWORMS
There are several species of hornworms that feed upon pota-
toes. They are large greenish caterpillars with a strong curved
horn on the posterior part of the body. They are the young of the
hawk moths or hummingbird moths, as they are often called.
They are large-bodied moths that fly at twilight or on very
cloudy days.
These insects are so large and conspicuous they can be picked
off the vines easily and fed to chickens that, incidentally, appre-
ciate them very much. If they become too abundant, they can be
controlled with lead arsenate mixed with the bordeaux spray, as
recommended for blister beetles.

MAY BEETLES
These large fleshy-white grubs (fig.. 50), so injurious to grass
lands, do some damage.,to potatoes by eating them when planted






Florida Agricultural Experiment Station


are several species of them. Some are striped lengthwise with
black and white (fig. 49), others are plain slate colored, and some
almost brown or black. Blister beetles are often called "old
fashioned potato beetles" to distinguish them from the more re-
cent arrival, the Colorado potato beetle.












Fig. 49.-Black blister beetle (left), margined blister beetle and striped blister beetle.
Enlarged (Courtesy U. S. D. A.)

Blister beetles can be controlled by mixing 1 pound of lead
arsenate to each 50 gallons of the bordeaux spray. If they occur
near the edge of the potato field, they can be driven out by a
bundle of twigs used as a whip: This is better than killing them
with lead arsenate, as the young of these beetles feed on the
eggs of grasshoppers and are, therefore, highly beneficial.

HORNWORMS
There are several species of hornworms that feed upon pota-
toes. They are large greenish caterpillars with a strong curved
horn on the posterior part of the body. They are the young of the
hawk moths or hummingbird moths, as they are often called.
They are large-bodied moths that fly at twilight or on very
cloudy days.
These insects are so large and conspicuous they can be picked
off the vines easily and fed to chickens that, incidentally, appre-
ciate them very much. If they become too abundant, they can be
controlled with lead arsenate mixed with the bordeaux spray, as
recommended for blister beetles.

MAY BEETLES
These large fleshy-white grubs (fig.. 50), so injurious to grass
lands, do some damage.,to potatoes by eating them when planted






Bulletin 169, Potato Diseases and Insects


on land. that was previously in grass. Usually they do not eat
more than half of the potato, hollowing it out on one side. The
main stem of the plant is seldom eaten. These grubs are a favo-
rite food of moles which, in tunneling the ground for the grubs,
do more damage to the potatoes than do the grubs. By ridding
his fields of white grubs, the farmer will greatly lessen the num-
ber of moles. Moles do not, as is commonly supposed, feed largely
on vegetable matter but break off the roots and subterranean
stems of plants in their search for insects.
White grubs are
slow-growing and
very long-lived. All
spend many
months in the lar-
val stage, some as
much as three
years. When full- a
gron the grubs Fig. 50.-May-beetle or June bug: a. adult; b. pupa; c. egg;
grown the gr d. young grub; e. full-grown grub. Natural size (Courtesy
form pupae in U.S.D.A.)
earthen cells in the ground. The adults are the well-known "June-
bugs" or "May-beetles" which are so abundant about street and
other lights at night. The white grubs are active thruout the
year in Florida.
The only practical control for this pest is to rid the ground of
the grubs as thoroly as possible before the crop is planted. It is
best to do this when the ground is plowed. Encourage chickens
and turkeys and such wild birds as crows and blackbirds to follow
the plow. Hogs in the field also destroy many of the grubs. It
is particularly important to take these precautions, if there has
been much grass on the land. Skunks are persistent enemies of
white grubs as well as of other insects and should be protected
by farmers.

COLORADO POTATO BEETLE

This notorious pest (figs. 51 and 52) of the northern potato
grower fortunately has not made its appearance in the main po-
tato-growing areas of Florida; it is present only in the northern
tier of counties. The infested area is spreading slowly but the
beetle probably never will be as severe in the central part of the
state as it is in the northern counties, because it is in hibernation
or winter quarters during most of the period when potatoes are






Florida Agricultural Experiment Station


r


Fig. 51.-Section of potato plant showing the Colorado potato beetle at work: a. beetle;
b and b. egg masses; c and c. half-grown larvae; d and d. mature larvae (Courtesy
U. S. D. A.)
growing. In the northern and western counties of the state, dur-
ing the summer when there are no potatoes, this beetle feeds on
tomatoes, horse nettles and other wild species of Solanum. These
weeds should be de-
stroyed if found near
potatq fields in those
counties.
SI The insect can be
controlled by lead ar-
S b e senate. When pota-
Fig. 52.--Colorado potato beetle: a. beetle; b. larvae or toes are regularly
"slug;" c. pupa. Enlarged (Courtesy U. S. D. A.)





Bulletin 169, Potato Diseases and Insects


sprayed with bordeaux, as they should be as a precaution against
blight, the lead arsenate can be added to that solution.

CUTWORMS

Cutworms are very fond of any succulent plant, and are trouble-
some to most truck and garden crops. They gnaw off the young
plants just above the ground, which means their destruction.
Cutworms (fig. 53) are the almost hairless larvae of any of sev-
eral species of moths of the Noctuid family. The moths are
night-fliers and are commonly seen about lights. They are gray-
ish or brownish in color and most of them have on their fore
wings small silvery markings, dots or dashes.


e K
aAl


Fig. 53.-Cutworm: a and b. larva
d. moth; e. wing of moth
Natural size (Courtesy U. S.


In Florida they do not hiber-
nate but are active and breed
thruout the year, altho neither
the moths nor the caterpillars
are active during the coldest
nights of the winter. The cater-
pillars remain active at a lower
temperature than the moths, but
the latter are to be seen about
lights during warm nights even
in midwinter. The worms sus-
pend operations during the cold-
est nights only, when the tem-
perature drops below 45 de-
grees F.
There' are no definite broods;
caterpillars of all sizes, and eggs
e ; c. Pue and moths, are to be found at the
D. A.) same time.


The moths by preference lay their eggs on grasses in heavy
sod land. The larvae feed on the grasses (fig. 54). Consequently,
on land that has had considerable grass, the cutworms are most
troublesome. As long as the grass is available there is so much
food in proportion to the number of worms that their feeding is
scarcely noticeable. But when such land is plowed, the normal
food supply of the caterpillars is cut off and they concentrate
upon the relatively small amount of vegetation supplied by the
farmers' crops.


ja






Florida Agricultural Experiment Station


When grass.:land is plowed, measures should
be taken to kill the cutworms present before a
crop is :planted. To do. this, prepare the land
ten days or -two, weeks before the potatoes are
to be planted. During that time many of the
cutworms,will, leave or die of starvation and
the remainder will develop a good appetite. A
day or two before the, crppis to.be planted, cut
Some green and succulent plants,; such as, col-
lards; rape, cowpeas, etc.; and dip into. a strong
b. solution of paris green,, about an ounce to a
F gallon of, water. Scatter this, about the field
Fi. m4.- s o cu- after sunset for the hungry cutworms to:feed
worm-inoth: a. single ms to f
egg really enlrgd; upon during the night. Instead of the green ma-
b. egg mass :on' tigh t .Ie
natural size (courtesy trial the following poisoned bait may be used:
U. S. D. A.)

Bran ....................---------------.................. 20 pounds
Cottonseed meal .......:................-...... .................. 5 pounds
Paris green ................... .... ....-........--.... ,.... ... 1"' pound
W after .......-.....:... .......... ... ..... ............................ 2 gallons

Mix the bran, cottonseed meal and paris green thoroly while
still dry; then wet until it is decidedly damp, not sloppy, and of
such consistency that it will fall in fine flakes when sown broad-
cast over the land. This should be put out after sunset so that
it will be fresh and attractive when the worms come out at night
to feed. If the following day is cloudy, the bait will remain at-
tractive for the second night; otherwise it will need to be re-
newed, if the cutworms have not been brought under control. If
properly sown, it will fall in such small flakes that fowls or other
birds will not pick it up. Instead of both cottonseed meal and
bran, either may be used alone, in which case use 25 pounds. The
moist mixture must be made up-fresh each day from sweet fresh
material, but the dry mixture will keep indefinitely.
In a small garden or in a field where there are but few cut-
worms, the.easiest, quickest and cheapest method of dealing with
them is to walk thru the patch in the early morning and:look for
plants which were cut the night ,before. By scratching the earth
away from the Ubase of the plants .the worms usually. may. be
found at a depth, of not more than an inch. They may be .col-
lected and fed to chickens.: .. .






Bulletin 169, Potato Diseases and Insects


A GENERAL SPRAY SOLUTION

The grower will notice from the above that either lead arsenate
or nicotine sulphate in bordeaux mixture will control any of the
common potato insects. The grower can put both nicotine sulphate
and lead arsenate in the bordeaux solution and thus have a specific
remedy for all the common potato insects as well as the fungous
diseases.

ROOT-KNOT

Root-knot derives its name from the large irregular, swollen,
knots on the tubers of plants affected by the nematode.
Severely affected plants soon turn yellow, cease growing and
die prematurely. Those less severely affected may remain alive
for some time, appearing sickly and stunted and producing only
small potatoes covered with wart-like swellings (fig. 55).
The minute worm or nematode, Heterodera radicicola (Atkin-
son), which causes this peculiar root disease, bores into the tubers
of the potato to feed upon the sap. As it feeds it gives off a
poison which stimulates the plant to form the gall or knot. The
worm is a member of a large group which includes the hookworm,
"vinegar eel" and many intestinal worms. All are known as
"round worms" or "eel worms," and technically as nematodes.
They are very small, even the adults being barely visible to the
naked eye. Most of them are found in the top foot or two of soil.
However, they may occur in small numbers considerably deeper,
particularly in loose soils. Only in small numbers are they ever
found in the surface of dry soils.
The adult male and the young nematodes are long and slender
and can make their way thru the soil from plant to plant; but the
adult female is pear-shaped and capable of little or no motion.
Even the young can make their way but slowly thru the soil, only
ten or fifteen feet a year. It has been determined that soil dry
enough to blow about contains few or no living nematodes. Wind
is, therefore, not much of a factor in the spread of the disease.
They are carried with refuse containing infested plant parts and
by surface water running from a contaminated soil. The root-
knot organism is distributed from one locality to another chiefly
with diseased plants, bulbs, nursery stock and tubers.
It is important to keep the soil free from the nematode. A
new field is free or nearly free. Any uninfested field can be


159






Bulletin 169, Potato Diseases and Insects


A GENERAL SPRAY SOLUTION

The grower will notice from the above that either lead arsenate
or nicotine sulphate in bordeaux mixture will control any of the
common potato insects. The grower can put both nicotine sulphate
and lead arsenate in the bordeaux solution and thus have a specific
remedy for all the common potato insects as well as the fungous
diseases.

ROOT-KNOT

Root-knot derives its name from the large irregular, swollen,
knots on the tubers of plants affected by the nematode.
Severely affected plants soon turn yellow, cease growing and
die prematurely. Those less severely affected may remain alive
for some time, appearing sickly and stunted and producing only
small potatoes covered with wart-like swellings (fig. 55).
The minute worm or nematode, Heterodera radicicola (Atkin-
son), which causes this peculiar root disease, bores into the tubers
of the potato to feed upon the sap. As it feeds it gives off a
poison which stimulates the plant to form the gall or knot. The
worm is a member of a large group which includes the hookworm,
"vinegar eel" and many intestinal worms. All are known as
"round worms" or "eel worms," and technically as nematodes.
They are very small, even the adults being barely visible to the
naked eye. Most of them are found in the top foot or two of soil.
However, they may occur in small numbers considerably deeper,
particularly in loose soils. Only in small numbers are they ever
found in the surface of dry soils.
The adult male and the young nematodes are long and slender
and can make their way thru the soil from plant to plant; but the
adult female is pear-shaped and capable of little or no motion.
Even the young can make their way but slowly thru the soil, only
ten or fifteen feet a year. It has been determined that soil dry
enough to blow about contains few or no living nematodes. Wind
is, therefore, not much of a factor in the spread of the disease.
They are carried with refuse containing infested plant parts and
by surface water running from a contaminated soil. The root-
knot organism is distributed from one locality to another chiefly
with diseased plants, bulbs, nursery stock and tubers.
It is important to keep the soil free from the nematode. A
new field is free or nearly free. Any uninfested field can be


159






Florida Agricultural Experiment Station


kept in this condition for-a long time, if precautions are ob-
served to prevent its intro-
duction.

HOST PLANTS

Root-knot affects a great
number of cultivated and
wild plants. All truck crops
are subject to it but there i
are several field crops, such
as corn and velvet beans,
that are free from attack.
Plants on heavy clay soils
suffer little from the dis-
ease. Lands that are regu-
larly under water each year .
for several months are free .
of the pest. Light sandy
soils are especially suited to
its development.

LIFE HISTORY
From hatching time to
hatching time, or the life
cycle, requires about four
weeks. In Florida, and oth-
er regions with a similar
climate, probably f r o m
eight to ten generations are
produced each year, and
each female may lay more
than 500 eggs. It is evident
that the nematodes will in-
crease rapidly in number, if
conditions are favorable.
The presence of live roots
of plants on Which the nem-
atodes can live, a proper
combination of air and
moisture and a sufficiently Fig. 5.-Potatoeo showing wart-like protuber-
anes ,caused. by .the root-knot nematode







Bulletin 169, Potato Diseases and Insects


high temperature, are the chief requirements for the nematodes'
rapid multiplication and growth.
Nematodes are least active during the cooler and drier weather
of winter. In the latitude of Gainesville they generally do com-
paratively little damage between November 1 and April 1. Further
south they are more destructive in winter. They are more de-
structive in all sections during summer.

CONTROL
Sometimes the number of nematodes in the soil decrease
markedly without any active.measures being taken against them.
Like all other animals, the root-knot nematode has its enemies.
The principal ones in this case are other nematodes, species which
prey upon the one herein discussed. Doubtless the presence in
the soil of these and other enemies often reduces the trouble. It
is never safe, however, to depend on this natural control. Gen-
erally, if the grower wishes to reduce the infestation, he must
take active measures to combat the worms.
Greenhouses, seedbeds and other especially valuable tracts of
trucking lands may be freed of nematodes by treating with steam,
hot water or chemicals. These methods are too costly for potato
growers.
The cheapest and most practical method of controlling nema-
todes in potato fields is to grow velvet beans on the land during
summer. Corn can be planted with the velvet beans without
greatly interfering, altho it is sometimes attacked by nematodes.
The velvet beans should be kept under constant cultivation. A
crust should never be allowed to form on the surface for this in-
terferes with the free passage of air into the soil, and in the ab-
sence of air nematodes are apt to encyst; i. e., form a hard thick
shell about themselves and lie dormant in the soil until condi-
tions are again favorable for growth.
For use in nematode or root-knot control the bunch velvet bean
has an advantage over the ordinary running beans, in that it
allows constant cultivation. Running beans make cultivation im-
possible during the latter part of the season at least. Velvet
beans are practically immune to root-knot. This is not true of
any variety of cowpeas, altho the Iron, Brabham and Victory are
highly resistant.
It is felt that this is the most economical method of ridding
potato land of nematodes. The experience of the last two years







Florida Agricultural Experiment Station


at the Experiment Station indicates that one summer is sufficient
to reduce the number of nematodes to the point where a crop of
potatoes can be grown successfully on the land. But in order to
reduce them to this point, cultivation must be frequent, at least
once a week and certainly after every rain which packs the soil.
All weeds must be kept out of the velvet beans by occasional hoe-
ings; otherwise some of the weeds would act as host plants for
the nematodes, and thus carry them over and defeat the purpose
of the summer treatment.
In order to shade the land satisfactorily, bush velvet beans
should be planted much thicker than running varieties, in fact,
almost as thick as cowpeas. The rows should be not over three
and a half (31/2) feet apart and the beans not over 12 inches
apart in the rows. To insure a good stand plant considerably
thicker than here advised. If plowed under in the fall, the beans
will add a large amount of humus to the soil and leave it much
richer in plant food. These are additional benefits to be derived
from the growing of bunch velvet beans (a legume) which should
not be overlooked.
Altho the labor of cultivating and hoeing the beans thruout
summer is no small item, it is an expense well worth making, if
the truck land is seriously infested with nematodes. Further-
more, by practicing this method one avoids the expense of clear-
ing the land in the fall, a necessary operation when the land is
allowed to lie out all summer and to grow a heavy crop of weeds
and grass. The labor of clearing such land frequently will be as
great as the expense of cultivating the crop of velvet beans.
This method of treating land has given as satisfactory results
as the old method of growing resistant plants on the land for
two or three years, and has the great advantage of the grower's
being able to use his land every year, not losing one or two sea-
sons.
Like all velvet beans the bunch variety is likely to be attacked
in August and September by the velvet bean caterpillar. Indeed,
experience during the last two years indicates.that to this moth
the bunch variety is one of the most attractive varieties of the
velvet bean. This insect works up each year from the south, ar-
riving earlier and being most destructive in the most southern
counties.
Growers using the velvet-bean method to control root-knot,
must be prepared to combat this caterpillar. This is done best by
dusting the plants with a mixture of equal parts of lead-arsenate






Bulletin 169, Potato Diseases and Insects 163

powder and air-slaked lime. Velvet beans are burned easily by
arsenicals; therefore, only the best grade of lead arsenate should
be used, and the lime must be air-slaked perfectly. Do not use
paris green or calcium arsenate on velvet beans. To get an even
distribution of the powder, a dusting machine is essential. A
hand duster that will do the work can be purchased for about $15.
Tests conducted at the Experiment Station during the last two
years indicate that sulphur applied to the soil at the rate of from
250 to 500 pounds to the acre is very helpful in keeping down
nematodes, althq it does not do so as thoroly as the velvet-bean
method. Applied to the soil before the crop was planted, sulphur,
up to 500 pounds to the acre, proved very beneficial to the crop,
but large amounts, 1000 pounds or more to the acre, was very
injurious.









INDEX


Aphids, 149
Atkinson, Geo., cooperation of, 109

Bacterial wilt, 113
control of, 115
description of, 113
Beetle, blister, 153
Colorado potato, 155
flea, 153
May, 154
Big-footed plant bug, 151
Blackleg, 115
control of, 117
description of, 116
Black scurf, 121
control of, 122
description of, 121
Blight, early, 117
Blister beetle, 153
Bordeaux mixture, for blight con-
trol, 109
to make, 145
vs. copper-lime dust, 109, 147

Certified seed, 141
Chellberg, David G. A., assistance
of, 103
Colorado potato beetle, 155
Common scab, 130
control of, 131
description of, 130
Copper-lime dust for potatoes, 107
vs. bordeaux mixture, 147
vs. bordeaux paste, 109
Curly dwarf, 126
Cutworm controlled by poisoned bran
bait, 158
Disinfection of potato seed, 144
Dusting for disease control, 147
with copper-lime dust, 107

Early blight, 117
control of, 120
description of, 118

Flea beetle, 153
Fusarium wilt, 128
control of, 130
description of, 129

Hamm, H. 0., cooperation of, 144
Hornworms, 154

Insect enemies of potato, 149
control of, 159

Johns, Frank, cooperation of, 143

Late blight, 103
control of, 105
description of, 104


Leaf-footed plant bug, 153
Leaf-hopper, 151
Leaf roll, 127

May beetle, 154
Mercuric chloride as seed disinfect-
ant, 144
Michigan, seed from, 144
Mosaic, 125
control of, 126
description of, 126

Nebraska, seed from, 143
Nematode, root-knot, 159

Plant bug, big-footed, 151
leaf-footed, 153
Plant lice, 149
Poisoned bran bait for cutworms, 158
Potato seed, imported, 104
troubles, 138
Powdery scab, 136
control of, 137
description of, 137
Proctor, Walter, cooperation of, 107
Pumpkin bug, 152

Root-knot, 159
control of, 161

Scab. common, 130
powdery. 136
Scoville, Wm., cooperation of, 107,
141
Seed potato troubles, 138
Silver scurf, 131
Smith, C. W., cooperation of, 109
Southern wilt, 123
control of, 125
description of, 123
Spindle sprout, 131
Spraying potatoes for insect control,
159
Spray preparation, 145

Velvet beans, bunch, to control root-
knot, 162

Wart, 135
control of, 135
description of, 135
Watson, J. R., contribution by, 149
Weber. G. H.. author. 101, 103
Wilt, bacterial, 113
fusarium, 128
southern, 123
Wyoming, seed from, 143
Yellow dwarf. 132
control of, 134
description of, 132




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