COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
STATE OF FLORIDA
COLLEGE OF AGRICULTURE, AGRICULTURAL EXTENSION SERVICE
UNIVERSITY OF FLORIDA, AND COUNTY AGENT AND
UNITED STATES DEPARTMENT Vegetable Crop Special HOME DEMONSTRATION WORK
OF AGRICULTURE, COOPERATING VW G E1TA1G II GAINESVILLE, FLORIDA
No. 20 May 30, 1953
ER. COTJItY AGENT:
For you boys looking for that slack season in Florida vegetable production. let
me know when you find it. You might have wound-up some phases, but in my book, it's
a three-ring circus!
We've heard some fine Research reports to the industry lately...here are some
of them, credited to individuals, dealing mostly with insect and disease control.
Mr. Norman Hayslip, Entomologist
Indian River Field Laboratory, Ft. Pierce
WIREWORMS--aldrin and heptachlor superior.
W. H. Thames, Jr., Entomologist at Belle Glade, has continued his work with
wireworms on the pa.t and muck soils. He has found aldrin and heptachlor superior
Wireworm damage can be reduced but cannot be eliminated when there are heav
infestations. Control is satisfactory when the population of wireworms is light
Present work with corn consists of studies of banded versus broadcast treat-
ments, and the proper time interval between applying the treatment and planting the
INSECTICIDE COMBINATIONS--combat insect resistance,
W. G. Genung, Entomologist at Belle Glade, has found the imported cabbageworm
to be resistant to DDT. He obtained good control using a mixture of 1/2 pound 15
percent wettable parathion plus 1-1/4 pounds of 40 percent wettable toxaphene per
100 gallons of spray.
Mr. Genung is finding insecticide mixtures such as this one very effective in
controlling most of the insects attacking cabbage. Mixtures of parathion and DDT
have also proved effective. (DDT plus parathion is proving to be a very useful mix-
ture for the control of tomato insects.)
Refinements in the use of DDT for the control of corn earworms are being worked
out by Entomologists J. W. Wilson, Sanford (spraying methods), W. H. Thames, Jr.,
Belle Glade (time and number of applications), and Norman C. Hayslip at Ft. Pierce
To date, the bas_ spray combination for severe infestations is 4 quarts of 25
percent DDT emulsion mixed with 2.5 gallons of white mineral oil. This mixture is
added to water to make 50 gallons of spray, and applied to one acre.
Four flat fan nozzles per row which deliver a coarse spray at about an 80-degree
angle have given good results. The nozzles should be directed into the silking zone
from slightly above. The first application should be made one day after the first
silks appear, with 4 additional treatments every 48 hours.
For light to moderate corn earworm infestation (usually in the fall, winter and
early spring) 3 to 4 quarts of 25 percent DDT emulsion will give a high percentage
of worm-free ears without the addition of mineral oil. The use of mineral oil should
be restricted to late spring plantings when the earworm infestations have been most
Dr. Robert A. Conover, Plant Pathologist
Sub-Tropical Experiment Station, Homestead
NEW FUNGICIDE--experimental LO 738
In fungicide experiments on tomatoes LO 738 gave control of late blight and
yield of fruit eaual to that obtained with nabam-zinc, or zineb sprays. The same
was true in Dr. Ruehle's potato experiment--equal control and yield. On sweet corn,
with northern leaf blight present (R. turcicum), disease control was again equal as
was the yield. In none of these experiments was any indication of plant injury ob-
ANTIBIOTICS--streptomycin and bacterial spot.
Three sprays of streptomycin sulfate, applied to tomato and pepper seedlings
at 5 day intervals, gave excellent control of bacterial spot until the plants reach-
ed transplanting size. Obviously, these experiments are strictly preliminary; much
further work must be done before this control method can be used effectively and
economically. Other preparations of streptomycin and judicious use of the treat-
ment may reduce its present high cost so that it can be used in plant beds.
It is felt that, as far as the Lower East Coast is concerned, the control of
this disease in tomato and pepper plantbeds would sharply reduce the incidence of
the disease in the field. In this area, plants are usually infected when set in
the field thus setting the stage for a flare-up should hard rains occur. Elimi-
nation of this source of the disease should go far toward reducing losses in the
field, except perhaps during prolonged rainy periods.
SMET CORN FUNGICIDES--a case of injury.
Some results of fungicide experiments on sweet corn probably should be circu-
lated. Sprays containing manzate, or nabam and manganese, applied on a 5-day
schedule, caused rather severe injury every time they were applied before tasseling.
The injury occurred in the whorl and near leaf bases--in areas where the spray con-
tacted meristematic tissue.
The manganese-containing dithiocarbamates should be used with great caution
particularly on young corn, and their use in certain situations may cause severe
injury. There is some evidence that certain varieties are more susceptible than
Dr. A. H. Eddins, Plant Pathologist in Charge
Potato Investigations Laboratory, Hastings
POTATO LATE BLIGHT--fungicides and varieties.
Different fungicides have been tested for the control of late blight of pota-
toes at the Laboratory for several years. Several materials have given good con-
trol of the disease including nabam, mandate and a new chemical known as LO-738.
A number of promising new late blight-resistant potato varieties and seedling
selections developed by the U.S.D.A. and cooperating states are grown each year at
the Laboratory. The object of this work is to find a blight-resistant variety
that is superior in yield and market qualities to the blight-susceptible variety,
Sebago, which is now grown on 95 percent of the Hastings acreage. Progress is be-
ing made as several new blight-resistant selections have proved equal or superior
to Sebago and some of these may be increased for commercial production.
COCRY RINGSPOT OF POTATOES--a real puzzler.
Corky ringspot of potatoes which appeared in three fields at Hastings in 1946
has spread and is of major importance on farms in several localities in the area.
This sgil-borne disease disfigures the surface and discolors the flesh of tubers.
It may ruin the salability of a substantial portion of an affected crop. It has
been present in European countries for 30 years but its cause is unknown. Tests
made at Hastings and in European countries show that it is not carried in the tu-
No means of controlling the trouble are known and fields in which it has
caused severe losses at Hastings have been abandoned for potato culture. Soil
treatments with uramon, cyanamid, lime and sulfur have given no control.
Observations indicated that the physical condition of the soil may affect
development of the trouble. This is being investigated. However, this year break-
ing the plowsole by chiseling the land gave negative results.
Different potato varieties and seedling selections have been grown in infested
soil to determine their reaction to the disease. Results obtained thus far indi-
cate that some selections are more resistant than others.
Dr. Eddins feels corky ringspot is the most puzzling potato disease he has
encountered. It may be due to a fungus, bacterium or virus or it may prove to be
due to a nutritional deficiency or to some unknown soil condition. Much work re-
mains to be done to determine the cause of the trouble and to develop means of con-
Dr. J. M. Walter, Plant Pathologist
Gulf Coast Experiment Station, Bradenton
MAITALUCIE--panacea...no. Step in right direction.
In March the Gulf Coast Experiment Station released under the name MANALUCIE
a new high-quality, large-fruited tomato with resistance to husarium wilt and to
the following foliage diseases: gray leaf spot, leaf mold, early blight, and black
Despite its hereditary resistances to this number of foliage diseases, this
new variety, if found otherwise satisfactory by the growers, is not expected to
allow them tocomit any considerable number of applications of fungicides. It is
definitely susceptible to late blight and bacterial spot. What we do expect is
that the variety may greatly simplify the complex problem of the grower in decid-
ing what fungicide to apply and when.
For example, it is very common for a tomato crop to be attacked by both gray
leaf spot and bacterial spot during the month of September. Manalucie's resistance
to gray leaf spot will allow the grower to concentrate on control of bacterial spot
at such times. Cop-er fungicides, which are not effective against gray leaf spot,
are the best mean of defense we have now against bacterial snot.
PYTHIUM--possibilities cucumber growers might consider.
This disease, which affects oly the portion of the fruit surface that makes
contact with the soil, caused severe losses to the cucumber growers in all produc-
ing sections of the southern two-thirds of the State.
The disease has not been thoroughly studied, but, since some growers are los-
ing from 65 to 75 percent of their fruits, it seemed high time to undertake a study
of control of this soil fungus with the materials which are now on the market and
certain new chemicals that have shown effectiveness against similar soil-fungus
A trial on this question, now in progress, shows that on plots receiving no
treatment whatever, the Pythium disease is making culls of approximately 1 percent
of the fruits. In comparison with this, the nabam-zinc sulfate schedule recommend-
ed for control of downy mildew shows 25 percent of the fruits affected by Pythium.
This fungicide schedule, which must be followed by the cucumber-grower in the West
Coast area if he is to save his crop from fast-working downy mildew, is considered
the standard of comparison in the current experiment.
The best soil treatments involving fungicides now available to the grower have
reduced the percentage of infected fruits to approximately 15 percent. This saving
of 40 percent of the fruits, that would otherwise be lost to Pythium, may be a
possibility warranting consideration by the grower, but we are not ijn position yet
to make a recommendation to growers.
The least expensive of the fungicides that gave this result is Copper A in a
very heavy dose applied to the soil surface before the vines start running. An
application amounting to 1250 gallons per acre of Copper A spray (Copper A at 5
pounds per 100 gallons) would cost the grower between $18 and $20 per acre. Fur-
ther study of the problem will be required. Certain new chemicals under observa-
tion at present offer good promise for the future, but it will be some time before
the necessary information can be obtained and these chemicals can become available
to the growers.
GHOST SPOT AID BOTRYTIS (gray mold)--more details.
Gray mold, caused by Botrytis cinerea, was very severe on the large acreages
of sand land tomatoes grown by the Ft. Pierce style of culture during the past win-
ter. Following this, ghost spot broke-out in mid-February, becoming very abundant
in the Immokalee-Devil's Garden area by mid-February and making its appearance by
the middle of April in nearly all other sections.
The growers of the Immokalee-Devil's Garden and Fort Pierce sections became
greatly alarmed by the abundance of ghost spot, and since the 18th of March, Dr.
J. F. Darby, Pathologist at the Indian River Field Laboratory and Dr. Walter have
spent considerable time trying to determine whether ghost spot is caused by Botrytis
cinerea. British plant pathologists reported 15 years ago that this is the case,
but their work has not been accepted in the United States except possibly by Dr.
Darty. Both Drs. Darby and Walter made as many inoculations of young tomato fruits
as they possibly could, following the technique described by the British workers.
Results are unsatisfactory and inconclusive, The inoculations with Botrytis
cinerea spores have resulted with fair regularity in the small necrotic specks typi-
cal of the centers of ghost spots as found on tomatoes in the field. Inoculated
fruits have not proceeded to produce the silvery halos to a degree to match those
on fruits as found in the field.
Other points of interest in connection with this problem are as follows:
(1) Ghost spot appeared in considerable amounts on the tomatoes of the
Homestead area by April 1. Drs. Conover and Walter made a careful search but could
not find gray mold on the leaves, stems, and fruits of the tomato plants in that
(2) Dr. Darby's results during the past two winters show clearly that
phygon XL is effective against gray mold. However, this fungicide does not result
in significantly less ghost spot than do other fungicides used in the same trials,
the latter fungicides, of course, not being effective against gray mold.
Dr. John F. Darby, Plant Pathologist
Indian River Field Laboratory, Ft. Pierce
BOTRYTIS (gray mold) CONTROL RESULTS--phygon timing seems critical.
The most effective control of gray mold obtained during 2 years of study has
been with the use of 3/4 pound of phygon XL per 100 gallons water.
The timing of the applications appears to be of critical importance. Consider-
ation of all the experimental data and field observations suggest that the first
application should be made before the plants fall over and while the lower and in-
ner leaves can be completely covered with the spray.
Although a study of the size of the nozzle orifice has been somewhat limited,
evidence indicates that this should be as large as possible so that the spray drop-
lets will be large enough to push aside the outer leaves and wet the inner more
The number of applications of phygon XL necessary to control botrytis has not
been determined; however, from field observations it would appear that at least 6
applications are necessary for control.
It also appears that phygon XL will not control gray mold after it has covered
the lower, more inaccessible leaves. Data collected indicates that phygon XL is
not sufficiently effective against gray leaf spot.
(CCoRCTED copies of "The Effect of Fungicides on Yield and Disease Control of Gro-
then's Globe Tomatoes", distributed at the Indian River Field Laboratory's 1952
annual field day, will be supplied on request.)
Forrest E. Myers
FEM/blp Assistant Vegetable
250 copies Crop Specialist