Irish potato disease investigations, 1924-25

Material Information

Irish potato disease investigations, 1924-25 a preliminary report
Series Title:
Bulletin University of Florida. Agricultural Experiment Station
Gratz, L. O ( Levi Otto ), b. 1894
Place of Publication:
Gainesville Fla
University of Florida Agricultural Experiment Station
Publication Date:
Physical Description:
23 p. : ill. ; 23 cm.


Subjects / Keywords:
Potatoes -- Diseases and pests -- Florida ( lcsh )
Potatoes -- Diseases and pests -- Control -- Florida ( lcsh )
bibliography ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references.
General Note:
Cover title.
This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Florida Sea Grant technical series, the Florida Geological Survey series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
Statement of Responsibility:
by L. O. Gratz.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
027161457 ( ALEPH )
18171645 ( OCLC )
AEN3339 ( NOTIS )

Full Text

November, 1925

Agricultural Experiment Station


(A Preliminary Report)



FIG. 1.-Black scurf on potato tubers.

Bulletins will be

sent free upon application to the Experiment Station,

Bulletin 176


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


WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT. B. S., Vice Director and Animal Industrialist
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entonmologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUFRECHT, Ph.1D., Chemist
R. M. BARNETTE, Ph. D., Assistant Chemist.
C. E. BELL, M. S. Assistant Chemist
E. W. COWAN, A. M., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
O. F. BURGER, D. Sc., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKS, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Grass and Forage Crops Specialist
W. A. LEUKEL, Ph. D., Assistant Grass and Forage Crops Specialist
A. F. CAMP, Ph. D., Plant Physiologist, Cotton Investigations
W. A. CARVER, Ph. D., Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
OUIDA DAVIS ABBOTT. Ph. D.. Head. Home Economics Research
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S. A., Pecan Culturist
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
J. G. KELLY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. 0. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
W. A. KUNTZ, A. M., Assistant Plant Pathologist
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)

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

(A Preliminary Report)

The Irish potato crop in Florida totalled over 5,000 cars-in
1925. This crop, grown for the early market, is one of-the
more valuable crops of the state.
It is impossible to estimate accurately the losses caused by
the various diseases which affect the potato. However, it' is
obvious that with the various blights, wilts, degeneration dis-
eases, etc, the losses amount to thousands of dollars anmnally,
It is because of these troubles of the potato industry that
Hastings Laboratory, a branch of the Florida Experiment
Station, was started in Hastings, the largest potato growing
section of the state, in August, 1923. The laboratory was made
possible thru the direct appeal of the growers which resulted
in the passing of a special appropriation by the State Legis-
The purpose of this bulletin is to show in brief some of the
existing problems and to give results of preliminary experi-
ments conducted during the past two years.
The diseases prevalent on Florida potatoes are identical with
those found in Northern sections where the seed potatoes are
grown. The symptoms of the various diseases which are ex-
hibited here and in the North have been observed to be similar.
This indicates that similar control methods should be effective.
Many of the potato diseases are tuber-borne. Scab and rhizoc-
tonia are carried on the tuber and can be controlled by proper
methods of seed treatment as far as infection from that'source
is concerned. Blackleg, and the degeneration diseases such as
mosaic, spindle tuber, leaf roll, and others, are carried in the
tubers and cannot be controlled, with present knowledge of
these .diseases, anywhere except in the field which is to pro-
duce the seed stock. This field in the first place should be
planted with as nearly disease-free seed potatoes as possible.
It should not be very near another field with a high percentage
of disease because of insects which carry the disease from field
to field. Further, the field should be gone over several times
thruout the growing season and all unhealthy plants with their
tubers removed from the field. To produce maximum yields
we cannot rely on seed treatment and dusting, alone, but must

Florida Agricultural Experiment Station

he much concerned in the section and growers in that section
which constantly produce the highest quality seed stock.

All seed potato producing states are attempting to deliver
high-yielding, disease-free seed stock. Such stock is sold under
a special tag issued at shipping time by proper inspection offi-
cials of the state. This certifies that the product in that par-
ticular container was carefully inspected at intervals from
the beginning of the season until shipping time and that it was
found to be reasonably free from disease. This tag further
signifies that the grower has attempted to produce good stock
by some of the best known cultural methods. Such a tag,
however, cannot guarantee a perfect condition. It is the only
guarantee which the buyer has at the present time that he is
paying for high quality seed potatoes, unless he goes into these
fields himself to observe the growing, digging, and shipping of
his particular stock, or relies absolutely on his grower.
If it were possible for him to inspect the fields himself it
would necessitate a knowledge of the symptoms and effect of
the various diseases at least as good as that of the state inspec-
tors who are trained for their work. If this system of certifi-
cation is not followed each grower is dependent, for the quality
delivered him, on his buyer and on the integrity of the grower
from whom he purchases. It is well for the grower to beware
of bogus individual certification tags as these frequently are
but selling schemes for inferior stock.
In Maine, where most of the seed potatoes used in Florida
have been grown the past few years, certified seed potatoes in
1925 must conform to the following regulations:

Prerequisites to Entering Potatoes for Certification
1. It is recommended that potatoes entered for certification be grown
upon land that was not in potatoes the previous season and that fields so
entered be isolated, as far as possible, from other potato fields planted
with other strains of seed.
2. It is recommended that the seed be from certified stock after hav-
ing secured field records of the same from the inspection service to deter-
mine relative value for seed. It is also recommended that the seed be as
free as possible from common scab and rhizoctonia and be disinfected
with corrosive sublimate.
3. It is required that the crop be well cared for and be kept reason-
ably free from weeds and from insect injuries. It is also required that
Bordeaux mixture spray be used to control late blight.
4. All applications for inspection must be mailed to the State De-
partment of Agriculture not later than June 15th.

Bulletin 176, Irish Potato Disease Investigations

Number of Inspections
There shall be at least three regular inspections during the season.
The first shall be of the plant during the time of bloom; the second of
the plant as late as possible while the vines are still green; the third
shall be an inspection of the crop at shipping time. At the option of the
chief inspector, additional examinations may be made of individual fields
and stocks of tubers.

First Inspection-Field
1. More than 1.5 percent varietal mixtures will disqualify.
2. More than 3 percent mosaic will disqualify; more than 2 percent
leaf-roll will disqualify; more than 2 percent blackleg will disqualify;
more than 2 percent wilt will disqualify; more than 3 percent other weak
hills will disqualify. A combination of diseased and weak hills equaling
8 percent will disqualfy.
3. All weak and diseased hills, of the types mentioned, must be re-
moved at once under the inspector's direction and supervision.
4. The inspector will disqualify if fields entered for inspection are
nearer than 250 feet to other potatoes carrying more than a passing
allowance for mosaic and leaf-roll.

Second Inspection-Field
1. More than 0.5 percent varietal mixtures will disqualify.
2. More than 2 percent mosaic will disqualify; more than 1 percent
leaf-roll will disqualify; more than 1 percent blackleg will disqualify;
more than 1 percent wilt will disqualify; more than 5 percent spindle
tuber will disqualify; more than 1 percent other weak hills will disqualify.
A combination of diseased and weak hills equaling 7 percent will dis-
3. All weak and badly diseased hills are to be removed during inspec-
4. At this inspection a sufficient number of hills per acre shall be
dug in such a manner as to secure a representative sample. Five per-
cent producing conspicuously less than average yield or off types such as
spindle tuber or giant hill will disqualify.
Third Inspection-Shipping Time
1. Maine certified seed potatoes shall equal or exceed U. S. Grade
No. 1.
2. The inspector present at this time will be instructed to put up such
seed stock as he would like to receive if he were the buyer.
3. Special care must be taken to remove all tubers of a long spindling
These regulations, obviously, in a large measure are aimed
at those diseases which cannot be controlled by any known
method of vine treatment, and are therefore of direct impor-
tance to us.

The immediate problems in which we are interested at pres-
ent are alternaria spots on seed potatoes, seed-piece decay soon
after planting, seed treatment, blight control, and the yielding
qualities of different strains and varieties.

Florida Agricultural Experiment Station

Alternaria Spots
These lesions caused by Alternaria solani E. & M. (the same
fungus which causes early blight) are dark, sunken areas of
various shapes, surrounded by raised irregular borders. (Fig-
ure 3.) They are usually shallow, but as time goes on the de-
pression may take on deep crater-like characteristics (Figure
3, B), or may remain shallow and spread over an area over half
an inch in diameter (Figure 3, C). After the potato has been
kept in Southern storage for several weeks a small spot on the
exterior of the tuber is no more a criterion as to the amount of
decay within the tuber (Figure 3, D).

FIG. 2.-Early blight on a potato leaf.

Temperature and moisture conditions are factors which are
closely related to the development of this disease. In Novem-
ber, 1923, the first shipment of potatoes from Maine into the
Hastings section was severely affected with fusarium dry rot
which had started from spots such as just described. Later
shipments were not affected with dry rot but were affected with
this trouble which we know now to be caused by this "early
blight" fungus. Early in September, 1924, the writer dug sev-
eral lots of potatoes in Aroostook County, Maine, for experi-
mental purposes of another sort. These were dug when the
vines were green, and no early blight was observed in any of
the fields. No spots were observed on any of the tubers. The
samples were placed in bags and stored in a cool cellar for
several weeks and then in their containers were placed in bar-
rels and shipped by express to Boston and boat to Florida.

Bulletin 176, Irish Potato Disease Investigations

FIG. 3.-A, Lesions on tuber shipped to Florida in October. B. Le-
sions on end of a tuber kept in laboratory for a month after
arrival in Florida. C, Lesions on tuber from a lot shipped by
local freight from Maine to Florida in October. D, Tuber split
lengthwise showing small shallow spots on the surface, and the
large decayed portion within the tuber underneath these spots.
Note eye destroyed by decay.

Florida Agricultural Experiment Station

When they arrived almost all of the tubers were badly affected
with this disease (Figure 3, A). Fusarium rot followed rapid-
ly, but not in all cases. About this time a small local shipment
was sent by boat to a Florida grower. These potatoes were
in a worse shape even than those samples shipped in to the
laboratory (Figure 3, C). It was very easy to isolate the
causal organism, from any of the lesions.
In November, 1924, several weeks after this badly diseased
shipment had arrived, a carlot of Maine potatoes was inspected
on the docks in Jacksonville. Several lesions were observed on
all tubers, but these were not over 1/8 inch or so in diameter.
A number of warehouses were visited in Aroostook County
by a laboratory assistant in December, 1924, about the time the
bulk of the seed potatoes for Florida were being loaded for
shipment. Fifty percent or more of the, tubers were affected.
Few spots only were found per tuber, and these were but 1/16
or 1/8 inch in diameter and oftentimes easily overlooked unless
the dirt was brushed off. One carlot was followed thru to
Florida. On arrival the spots had increased to two or three
times their size at time of shipment but were still small as
compared with the October shipment. The Fahrenheit tem-
peratures of these tubers in transit were 35 degrees in the
warehouse, 40 degrees when the, car (refrigerator) was sealed,
41 degrees on arrival in Boston, 43 degrees on ship the first
day, 46 degrees the second day, 52 degrees the third day and
on arrival in Savannah. The potatoes were cold when they
Arrived at Hastings four days later, the temperature at this
time was from 50 degrees to 58 'degrees. This temperature
r-nge was apparently too low for the development of the fun-
gus, as according to Rands' the cardinal temperatures for the
development of Alternaria solani E. & M. are 34 to 38 degrees
minimum, 99 to 113 degrees maximum and 79 to 83 degrees
optimum. No temperature records are available for the Octo-
ber shipment. The comparisons of average air temperatures
along the route of travel indicate those of October the more
favorable. (Table 1.)
Good growth of this fungus on artificial media in a few pre-
liminary trials at temperatures from 68 degrees to 85 degrees
was obtained, with slightly less rapid growth at the lower tem-

1Rands, R. D. Early blight of potato and related plants. TLniv. Wis-
consin, Agr. Exp. Sta. Research Bul. 42: 1-48, 1917.

Bulletin 176, Irish Potato Disease Investigations


October 15 to 30, 1925 I | |

Maximum ....................... 53.5. 61.2 63.063.5167.1 67.0 65.9 70.4 69.470.2 71.2
Minimum .......................... 38.2 44.747.748.0 45.5 52.1 56.4 51.856.754.860.2
December 10 to 25, 1925 1 I I I
Maximum .............................. 21.5 32.136.740.6 42.6 50.0 60.0 64.0
Minimum .......................... 11.2 23.4 29.2 31.3130.4 39.2 45.0142.6146.1146.4 50.4
*Obtained by averaging the daily temperatures at those points given.

Judging by the foregoing facts we must conclude that the
early fall temperatures are approaching the optimum for the
development of the fungus causing alternaria lesions and there-
fore the very early shipment of Northern potatoes into Florida
cannot be recommended. It is also believed that immaturity
and bruising are important contributing factors to this trouble.
The fungus causing this disease has hitherto been reported
as not injurious to the tubers, but as causing the blighting of
vines only. These lesions have been observed on seed potatoes
arriving in Florida for several years, and were frequently con-
fused with late blight lesions, or cankers caused by Corticium va-
gum B. & C. (rhizoctonia). Soon after the writer first observed
this trouble in 1923 and consistently isolated the fungus, he drew
the attention of the Maine pathologists to the condition of the
.seed potatoes when they arrived at their destination. Their
later investigation2 demonstrated that this trouble was obvious
in Maine, but that the spots were small. They further demon-
strated that this fungus was the same one which caused the
foliage disease, early blight. This tuber spotting has been ob-
.served and the fungus isolated from potatoes shipped to Florida
from Maine, New Jersey, New York, Wisconsin, and in a few
instances from home-grown potatoes which were kept for sev-
eral weeks after digging. No lesions have been observed at
digging time. The fungus was isolated from Early Rose, Spaul-
ding Rose No. 4, Irish Cobblers, Green Mountains, and Smooth
Rurals. It appears that the Spaulding is the most susceptible
*of these varieties.

'Folsom, Donald, and Bonde, Reiner. Alternaria solani as a cause of
-tuber rot in potatoes. Phytopathology 15: 282-286. 1925.

Florida Agricultural Experiment Station

The actual loss due to this disease is brought about in two
ways. First, by producing lesions which either start in an
eye, or later cover an eye (Figure 3, D), and destroy the germi-
nating power of that seed piece; second, by providing infection
courts for the dry rot organisms. Usually these latter do not
gain entrance into the tuber unless the skin is broken. How-
ever, when they are permitted to enter they develop very rapid-
ly under our climatic conditions.
Slight differences in the size and number of these lesions
have been observed from time to time in the different lots of
Spauldings which have been shipped in. It is thought these
differences are due to climatic factors rather than to degrees
of resistance of the various strains.
It has not been demonstrated conclusively that these lesions
are responsible for epidemics of early blight, but it is reason-
able to believe that this is possible. Two field observations
were made which indicate this to be the case. In 1924 one field
which was planted with seed potatoes containing numerous
lesions suffered an epidemic of alternaria blight which killed the
vines three or four weeks before maturity. This field showed
no such epidemic the following year. In 1925 it was noticed
that the earliest planted field in the potato section, planted
from the badly affected October shipment, likewise was affected
severely with early blight. Similarly, the experimental plots,
planted with the badly spotted samples dug by the writer in
Maine, were affected with early blight long before the remain-
der of the field which was planted about the same time but
with seed potatoes not as badly spotted at planting time.

Early in 1924 the growers were occasioned considerable worry
by many of the seed pieces rotting in the field within 10 or 20
days after planting. An examination of many fields revealed
that approximately 40 percent of all the seed pieces were af-
fected by a semi-soft, watery, brownish rot, giving off a rather
pungent odor. This was not the white, soft rot due to excessive
water, nor was it due to fertilizer injury (Figure 4). A con-
siderable number of skips resulted but the damage was not as
great as was first expected, as many of the plants could estab-
lish a good root system before the complete decay of the seed
piece. Very rarely was it observed that the interiors of the
young stems were discolored, or that a wilt was produced. No

Bulletin 176, Irish Potato Disease Investigations

evidence was found which would indicate that the disease origi-
nated from the seed potatoes, but everything pointed to the
fact that it had its origin from the soil.

FIG. 4.-Seed pieces taken from the
soil, showing brownish rot start-
ing from the cut surface.
In 1925 this condition was again observed, being less severe
than the year before, and worse in the early planted fields in
the Federal Point section than elsewhere. The symptoms were
similar to those of the year previous. It was determined by
actual count that there was more decay of the seed pieces on the
"high white spots" than in the level portions of the field
(Table 2).

Decaying Seed Pieces Causing
Missing Weak Total Weak
Hills Hills I and Missing
Sandy high spot ...........-------... 8 30 38
Level ground adjoining above......| 3 10 13
This year, as in 1924, a species of fusarium was again isolated
consistently. The disease was produced without difficulty by
artificially inoculating sterilized soil and clean seed pieces with
the fungus originally isolated. Reisolation yielded the same
fungus. Control pots were kept consisting of both sterilized
and unsterilized soil. In the case of the former the seed pieces
when not inoculated remained sound, while in the latter in a
few preliminary tests they became diseased. The conclusion

Florida Agricultural Experiment Station

is that the causal factor is a soil organism common to our soils.
and is not introduced with the seed piece.
Field observations and preliminary trials under controlled
conditions indicate here again that moisture and temperature
are factors, among others which are intimately related with
the development of the fungus.
It is frequently claimed that treating the seed pieces with
sulphur or other drying agents would prevent their decay.
Butler3 gives data where such treatment is of no advantage.
Information has been obtained the past two years which tends
to agree with the work of Butler. A large number of seed
pieces were treated with various materials and the seed pieces
examined at digging time.
1924.-Average percentages of two trials of 50 hills each of treated seed
pieces 120 days after planting.

o U), C: 1:

Planted after having been
freshly cut ............- ...-- ...-- 12 8 37 43
cut 24 hours ...........--.- 14 3 5 78
dusted with lime .............. 28 5 12 55
dusted with plaster Paris.. 43 5 11 41
dusted with cement ............ 29 7 9 55
dusted with sulphur .......... 1 0 1 15 84
1925.-Percentage of decay out of a total of 75 treated seed pieces 103
days after planting.


dusted with lime .... 85 4 11 0
dusted with cement ......-- 89 3 8 0
cut and dusted with sulphur 53 9 36 2
5 days before planting
dusted with sulphur .......... 46 12 40 2
'Butler, 0. Is it necessary to treat the potato seed-piece with a drier
after cutting? New Hampshire Agr. Col. Press Bul.: 130. 1922.

Bulletin 176, Irish Potato Disease Investigations

. p


FIG. 5.-Potatoes affected with rhizoctonia disease.



----- : 1


Florida Agricultural Experiment Station

Two years' trials possibly do not warrant absolute conclu-
sions but, similar to Butler's data, the seed pieces treated with
sulphur yielded the lowest percentage of sound seed pieces
(Table 3). According to our data no treatment can be guaran-
teed to control decay of seed pieces.

The Rhizoctonia disease of potatoes caused by Corticium
vagum B. & C. is found probably in all countries where pota-
toes are grown. The potato is only one host among about 75
attacked by this fungus. The reports of losses vary from 5
to 50 percent or even higher. According to Chupp4, the bene-
ficial results gained from treating the seed potatoes in .New
York is about five or six barrels per acre. Since the causal or-
ganism is common to all soils it is not reasonable to expect that
the term certified seed should insure absolute freedom from the
disease. Neither is this a disease to be controlled absolutely by
severe inspection regulations and hard roguing in the field
where the seed potatoes are grown. Treating the seed potatoes
is a more thoro guarantee of a rhizoctonia-free field as far as
the seed stock is concerned.
Experiments along this line have been conducted the past
two seasons with promising results. The method followed was
to treat the seed potatoes several weeks before planting for 11/
hours in a cold 1:1,000 solution of corrosive sublimate, drying
the tubers rapidly after treating them, but not in direct sun-
light. The results are given in Table 4.

Treated Untreated

Yield in Bbls. Yield in Bbls. V
Year Plot U.S. Grade 9 U. S. Grade

I | No. 1. No. 2 I No. 1 I No. 2 |
1924 ...... 1 37.8 11.1 48.9 28.6 8.7 37.3 11.6
2 15.1 15.1 30.2 19.0 14.3 33.3 -3.1
1925 ...... 1 62.5 10.4 72.9 59.0 12.1 71.1 1.8
2 ..... 58.1* ...... ..... 54.5* 3.6*
3 ..... 60.6* ...... 53.0*I 7.6*
*Not graded, but field barrels only.
'Chupp, Charles. Manual of vegetable garden diseases. p. 1-647.
(Reference on p. 367-379.) 1925.

Bulletin 176, Irish Potato Disease Investigations

In another instance in 1925 where a number of bags of pota-
toes had been treated as described above the stand for some
reason was slightly poorer and comparative yields were not ob-
tained. Here, however, large differences in the percentages of
stem lesions were noticed when the plants were but two or
three inches above the ground (Table 5).
Total Number of I
Hills Examined I Stems Affected with Lesions
I Actual I Percentage
Treated ............................ 700 2 I 0.285
Untreated ....................... 400 I 58 I 14.500

This same section of the field was later.examined. Only a
comparative few of the many stems affected soon after plant-
ing had actually produced rhizoctonia hills, but at digging
time the results of treating were very obvious. No hills were
found affected with rhizoctonia out of 400 plants examined
where the seed potatoes had been treated, and 5.8 percent of
the hills where the seed potatoes had not been treated were
rhizoctonia hills.
The chief reason for experimental work in spraying and dust-
ing is now not so much to discover whether or not it is a pay-
ing proposition, or to convince the grower that these measures
are necessary, but to perfect the, methods of application and
to adapt them to the particular locality where they are to be used.
Most growers in the state are convinced that blight can be
controlled. A few are not, but are learning by bitter experi-
ence that it is possible. Frequent failures to control the disease
have been observed but in these cases the first application of
the fungicide was not made until the disease was seen on the
leaves. It must be remembered that spraying or dusting cannot
be a cure, but must be a preventive. In this state very few
growers are known who apply home-made Bordeaux mixture.
The others are using the commercial copper-lime dusts.
In 1924 two plots of approximately 15 acres each, on the
farm of G. W. Proctor & Son, were devoted to comparative
tests of three strengths of commercial copper-lime dust. No
copper injury was observed in any of these plots in these ex-
periments. Late blight was not in evidence. Early blight
(Alternaria solani) was severe and was not controlled by any

Florida Agricultural Experiment Station

FIG. 6.-Late blight of potatoes, showing the withered stem.
of the dusts, it being as severe in the dusted as in the undusted
rows. The yields are given in Table 6.
No difference in appearance of the vines was observed thru-
out the season except that the check rows died about 10 days
before the dusted rows. A rather consistent increase will be
observed in dusted rows over check rows, even in view of the
fact that no late blight was to be found in the field.


Bulletin 176, Irish Potato Disease Investigations

20-80, 25-75. AND 30-70 PERCENT COPPER-LIME DUST.

33.8 15 30-70 17 1 55.2*
35.3 18 25-75 15 61.8*
35.8 4 check 4 48.1 East plot dusted 4 times,
38.6 12 20-80 12 53.1 and the west plot 3 times.
31.3 16 30-70 17 47.4 17/2 rows constitute an
40.8 16 25-75 13 43.7 acre.
35.0 17 20-80 13 44.4
42.0 7 check 7 47.2
33.4 9 30-70 9 47.2 All dusting was done at
38.8 16 25-75 16 42.6 night at approximately 10-
45.3 17 20-80 18 41.4 day intervals.
45.9 16 30-70 17 41.4
37.9 4 check 6 32.1 Machine used-T reaction
40.1 12 25-75 12 46.7 power duster.
39.5 17 20-80 16 41.4
46.7 16 30-70 17 30.9 Dust used -Commercial
43.3 17 25-75 16 42.6 dust.
38.5 5 check 6 35.4
42.5 12 20-80 12 39.8
*Dug one week later than remainder of field.

In addition to the above, five alternating beds were dusted
at night, and the remaining five the following morning. Usu-
ally, however, there was plenty of moisture on the leaves when
dusted in the morning, making it possible for the dust to ad-
here. No difference in yields or appearance in leaves was ob-
In 1925 experiments were conducted on the same farm as be-
fore on two five-acre plots to determine the relative efficiency
of copper-lime dust and liquid Bordeaux mixture. The aim
from the outset was to apply the same amount of metallic cop-
per per application and thruout the season in the spray as in
the dust. The dust was applied early in the morning when
there was no wind and plenty of moisture on the foliage, and
the spray later in the day when the foliage was dry. Approxi-
mately 70 gallons of a 4-4-50 Bordeaux mixture per acre per
application was applied at 200 pounds pressure and about 21
pounds of copper-lime dust with a guaranteed analysis of 6.8
percent metallic copper content was applied at each application.
In this way about 1.4 pounds of metallic copper was applied in

Florida Agricultural Experiment Station

each fungicide. Contrary to last year, late blight but no early
blight was present. Commercial control of the former was ob-
tained in all cases. Spots of the disease were seen in both
dusted and sprayed rows. The general appearance at one time
was that of a field which was just becoming badly infected with
the disease.




70.0 F 4 1
79.8 F 8 F
76.2 4
60.3 4 | 2
76.5 8
73.3 4
68.4 4 3
70.0 9
66.8 4
58.6 4 4
76.9 8
57.0 !4
66.0 4 5
79.0 8
77.4 4
Machines used:


F 20-80 dust
F 20-80 dust
S20-80 dust
[ check
I Bordeaux
I Bordeaux
1 20-80 dust
1 20-80 dust
S20-80 dust
I Bordeaux
20-80 dust
S20-80 dust
Traction power

Calculated Yield in Barrels

o C

3 48.5- 17.4 65.9
9 41.4 19.1 60.5
4 37.0 [ 16.0 53.0
4 41.8 16.0 57.8
8 49.6 17.3 66.9
4 45.4 17.3 1 62.7
4 53.4 I 18.4 71.8
10 1 48.8 t 22.2 71.0
4 49.5 17.3 66.8
4 44.5 16.0 1 60.5
8 47.5 16.6 64.1
4 47.5 16.0 63.5
4 43.8 18.4 62.2
8 52.9 12.6 -65.5
4 44.7 16.0 60.7
duster and traction power sprayer.

The important difference between this and some other com-
mercial fields was that several thoro applications of the fungi-
cide had been made before any of the fungus spores were pres-
ent, with the result that the disease could not become estab-
lished. In the other fields referred to the fungicide was ap-
plied after the fungus had become established, resulting in a
rapid destruction of the vines with the consequent low yields.
All check rows were killed by the disease about 15 to 20 days
before the maturing of the treated vines. The results are given
in Table 7.
Approximately the same yields were obtained where the vines
were dusted as where they were sprayed. A consistent decrease
in yield is observed in the check rows thruout the experiments.
Several comparisons were made on single rows 206 feet long
on the farm of C. W. Brown, between small, medium, and large

Bulletin 176, Irish Potato Disease Investigations


n Calculated
P, yield in bbls. Percentage
z.3 per acre
**aI .X ---- ---
| Total Mar- No. 1 Mar- Culls
S& c3 ketable ketable
1 I Bordeaux 69.9 64.8 74.2 92.7 1 7.3
2 1 20-80 dust 19 66.4 60.6 70.4 91.2 8.8
3 1 check 46.6 39.1 54.2 83.9 16.1
4 1 Bordeaux 62.9 55.5 68.3 88.2 11.8
5 | 20-80 dust 35 59.0 51.1 64.9 86.6 13.4
6 1 check I 51.2 41.6 50.7 81.2 18.8
7 Bordeaux 48.0 41.9 60.6 87.3 12.7
8 20-80 dust 47 50.9 44.0 58.5 86.4 13.6
9 I check I 45.6 37.7 50.8 82.6 17.4
10 Bordeaux 73.1 67.6 70.2 92.4 7.6
11 1 20-80 dust 19 53.8 46.4 58.0 86.2 13.8
12 I check I 65.8 57.2 60.6 I 86.9 13.1
13 | Bordeaux 72.5 68.0 75.1 93.7 6.3
14 20-80 dust 35 69.9 62.7 67.9 89.7 10.3
15 1 check 70.2 63.4 67.6 90.3 9.7
16 Bordeaux I 67.3 61.3 69.5 91.0 9.0
17 20-80 dust 47 70.0 63.1 65.8 90.1 9.9
18 check 1 58.3 51.3 59.5 88.0 12.0

amounts of dust, no treatment, and Bordeaux mixture. Four
applications were made at 10-day intervals with a hand duster,
and a knapsack sprayer. The actual amount of dust applied is
indicated in Table 8. About 75 gallons of Bordeaux
mixture (5-5-50) per acre per application was applied at a pres-
sure as constant as the particular type sprayer would permit.
The check rows died at least 15 days, and the vines in the dusted
rows, a week before those in the sprayed rows. The increase
in yield in the treated vines over the untreated is consistent.
The sprayed rows in every case produced the highest percent-
age of marketable and prime potatoes, and usually the largest
total and largest marketable yield. The progressive increase
of culls from sprayed to dusted rows and then to check rows is
also worthy of note. No conclusions can be drawn as to the
proper amount of dust required for maximum control.'
Preliminary experiments on single rows 206 feet long were
conducted with the hand duster to obtain information as to the
proper interval between succeeding applications of dust. It was
impossible to adjust the machine so that exactly the same
amount of dust could be applied at each application. Three
rows were dusted every five days, receiving in all seven applica-

Florida Agricultural Experiment Station

tions of an average of 31 pounds of copper-lime dust per appli-
cation; three rows were dusted every 10 days, receiving thru
the season four applications of an average of 28 pounds of dust;
and three rows were dusted every 15 days, receiving a total of
three applications averaging 33 pounds per application.
No conclusions as to the frequency of applications can be
drawn from the data obtained. The following observations are
noteworthy: In all but two cases there is an increase of total
yield of the dusted rows over the undusted. An increase of
total marketable potatoes is found in every case except one,
and an increase in percentage marketable is found in every
case. The increase of primes is from 3 to 11 percent in every
instance, and a large decrease in culls is observed in every
dusted row.

Interval Calculated Yields in Percentage
Days Barrels Per Acre
STotal Marketable No. 1 1 Marketable I Culls
5 .....I 75.5 70.7 74.4 93.6 6.4
Check .... 63.0 57.5 66.0 91.2 8.8
10 ...... 57.5 53.2 66.6 92.5 7.5
Check .... 59.1 I 52.4 58.0 88.6 1 11.4
15 ...... 54.0 49.2 65.5 91.1 8.9
Check .... 51.9 44.7 54.7 86.1 1 13.9
5 ...--.... 47.2 41.5 58.6 87.9 12,1
Check .... 53.5 46.5 55.1 86.9 I 13.1
10 ........ 53.4 48.3 63.4 90.4 9.6
Check .... 46.2 40.4 53.6 87.4 12.6
15 ........ 49.3 44.3 63.2 89.8 [ 10.2
Check .... 50.1 43.6 53.8 87.0 I 13.0
It is at once obvious that the actual benefit of dusting or
spraying is not ascertained by merely comparing the yield in
the field, but must be observed from the differences in the
amount of marketable potatoes produced.
Strain, source, and variety tests were conducted both years.
Because of the complications brought about by the regularly
recurring water furrows in'practically all fields in this section,
it is often impossible to compare several varieties or strains
directly, but. each must be compared with a common strain.
This method was followed exclusively in 1924. This particular
check strain (marked R in Table 10) yielded poorly but
consistently in all of the tests. Because of its poor showing

Yield I (Maine Spauldings)
__ _Yield
Variety and Source I -- Check ld
1 No. 1 No. 2 Total Strain No. 1 No. 2 Total
1 Spauldings, Maine, uncert. 31.2 15.8 47.0 A* Uncert. 24.1 11.6 35.7
2 Spauldings, Maine, uncert. 30.1 12.6 42.7 E cert. 36.8 12.7 49.5
3 Spauldings, Maine, uncert. 30.1 12.6 42.7 F 42.6 12.7 55.3
4 Spauldings, Maine, uncert. 30.7 10.0 40.7 R 29.4 9.7 39.1
5 Spauldings, Maine, uncert. 43.1 14.5 57.6 R 17.5 13.7 31.2
A* Spauldings, Maine, uncert. i 33.9 12.5 46.3 R 30.5 7.2 37.7 3.
B Spauldings, Maine, cert. 36.5 7.4 43.9 R 24.9 7.8 32.7 -
C Spauldings, Maine, cert. 45.5 11.6 57.1 R 27.3 9.8 37.1
D Spauldings, Maine, cert. 44.0 11.4 55.4 R 30.7 11.6 42.3
E Spauldings, Maine, cert. 33.6 10.0 43.6 R 21.9 11.1 33.0
F Spauldings, Maine, cert. 34.4 10.3 44.7 R 21.7 10.1 31.8
NYH Spauldings, New York, cert. 36.7 11.6 48.3 P 20.9 12.9 33.8 0
NYA Spauldings, New York, cert. 22.8 12.9 35.7 k 25.9 10.3 36.2
W Spauldings, Wisconsin, uncert. 24.4 13.4 37.8 R 22.5 10.8 33.3 g-
M Spaudings, Minnesota, uncert. 10.7 10.3 21.0 R 19.9 9.9 29.8
1 A** Spauldings, Maine, cert. i 27.0 16.7 43.7 R 30.9 14.3 45.2
1 B** Spauldings, Maine, cert. 29.4 16.7 46.1 R 23.1 4.9 28.0
1 C** Spauldings, Maine, cert. I 27.0 14.3 41.3 R 28.6 12.7 i 41.3
B7 Bliss, New York, uncert. 17.7 9.5 27.2 R 18.8 7.7 26.5
B10 Bliss, Minnesota, uncert. 14.2 12.7 26.9 R 23.5 17.2 40.7
B14 Bliss, Wisconsin, cert. 24.8 9.2 : 34.0 R 16.6 14.8 31.4
B17 Bliss, Wisconsin, uncert. 15.5 12.3 27.8 R 29.3 13.1 42.4
C 8 Cobblers, New York, cert. 27.5 11.1 38.6 R 19.4 11.2 30.6
C12 Cobblers, Michigan, cert. 27.8 6.8 34.6 R 21.4 14.5 35.9
M 9 Gr. Mts., New York, cert. 38.9 13.5 52.4 R 20.6 15.3 35.9
M11 Gr. Mts., Michigan, cert. 37.3 11.6 48.9 R 19.6 13.6 3 33.2
R13 Rural Russets, Michigan, cert. 29.0 5.5 34.5 R 20.2 16.6 36.6

*With individual or bogus certification tag.
**Single trials only.



TABLE 10.-YIELDS (in barrels) OBTAINED

Florida Agricultural Experiment Station

here it was at once discarded by its growers in Maine for fur-
ther seed purposes. Different strains as represented in Table
10 can be compared by keeping the check strain as a guide.
Each figure in this table represents not the result of a single
trial but the average of three trials.
An inspection of Table 10 will reveal the. following
facts: The uncertified strain outyielded the check strain (R)
wherever compared, but ,underyielded two other certified
strains (E, F). Five certified strains outyielded the check
strain in all cases. Individually certified strain A outyielded
the pbor yielding check strain R but underyielded the uncerti-
fied strain with which it was compared in three different trials,
This strain when studied with reference to the other certified
strains and their checks .does not compare very favorably with
them in that it produced a smaller number of primes .and a
larger percentage of number 2 potatoes.
The 'Ne -York Spauldings yielded about the same as the check
strain, or a little higher in one instance while the Wisconsin
strain' yielded more and the Minnesota strain was consistently
very low. The Bliss Triumphs gave small and the Russets aver-
age yields, the' Cobblers outyielded their checks, and the Green
Mountains were consistent high yielders. In another trial on
different farms the Spauldings were outyielded by both Irish
Cobblers and-,Green Mountains.
Sinrilar tests were conducted in 1925. These samples were
not, checked against a common strain but were planted and rep-
licated in such a way as to equalize the influence of the water
furroys. The data are given in Table 11.
The comparative test of the' Maine strains (1-18) was con-
ducted in cooperation with the State Deplartment of Agricul-
ture 6f Maine.: Most of these strains, as noted below, yielded
about alike. Strains c, 2, 5, and 13 seemed,to be the exceptions,
and gave rather outstanding yields. Strain c was treated with
corrosive sublimate but this does not account for the large dif-
frencie in yield between this strain and the table stock (x).
Following are the disease readings for these two strains:
:: I__ c x
Mosaic .... ........... 3.0 percent j 12.0 percent
Blac f e ..................................... 0.0 3.0
L(-t'-r. I ..l.. ................................ 0.0 1.0 "
Rhizoctunia ............................. 0.0 2.0 "
"Weak hills ....... .... .... 0.0 100.0 "
Stand :........i........................0.0 I 88.0
*Spindle Tuber and dwarfed plants not included in above classification.

Bulletin 176, Irish Potato Disease Investigations 23

Variety and Source Yield
No. 1 No. 2 | Total
*x Spauldings, Maine, table stock 33.1 14.2 47.3
*c Spauldings, Maine, certified 74.8 17.1 91.9
1 63.6 12.1 75.7
2 72.0 10.8 82.8
3 61.3 12.5 73.8
4 59.6 11.2 70.8
5 81.1 11.5 92.6
6 62.0 12.1 74.1
7 62.9 12.1 75.0
8 59.1 10.4 69.5
9 61.7 12.5 74.2
10 62.7 12.9 75.6
11 52.1 13.8 65.9
12 62.9 9.9 72.8
13 72.0 12.5 84.5
14 62.5 12.1 74.6
15 uncertified 67.8 9.8 77.6
16 certified 64.6 10.4 75.0
17 61.2 10.8 72.0
18 1 62.5 10.0 72.5
A 1 31.2 18.7 49.9
B New York 17.1 14.0 31.1
C Cobblers, Maine, 45.0 14.0 59.0
D Gr. Mts. 35.0 15.6 50.6
E Bliss, Nebraska, 71.8 20.5 92.3
*Single trial.
1-18-Averages of 4 replications.
A-D-Averages of 10 replications.

Strain 15, uncertified, yielded as well, or better than the cer-
tified strains. Last year there was a surplus of good quality
seed potatoes, and it was understood late in the season that
this lot came from the same bin as the certified stock which
was sold by this same grower at the beginning of the season.
This (x & 15) simply illustrates the point that when buying un-
certified seed potatoes it is impossible to judge the quality, and
the shipment may consist of a poor quality of table stock, or
of a high grade of seed stock.
The variety test (A-D) was conducted on a field which received
no treatment for blight control. Late blight was very severe
several weeks before the maturity of the plants. All varieties
but the Bliss were killed prematurely, while this strain, being
earlier, was practically ready for digging. This accounts in
part for the large difference in yield. Here, as last year, the
Cobblers and Green Mountains equaled or outyielded the