Title: Evaluation of fungicides for control of downy mildew of cabbage at Hastings, Florida during the 1966-67 season
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 Material Information
Title: Evaluation of fungicides for control of downy mildew of cabbage at Hastings, Florida during the 1966-67 season
Physical Description: Book
Creator: Hosford, Robert M.
Publisher: Potato Investigations Laboratory,
Copyright Date: 1967
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Bibliographic ID: UF00076284
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 133520641 - OCLC

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POTATO INVESTIGATIONS LABORATORY
Hastings, Florida


Mimeo Report POL 67-5


OCT 27 1337


SJune 1967 .


EVALUATION OF FUNGICIDES FOR CONTROL OF DOWNY MILDEW OF
CABBAGE AT HASTINGS, FLORIDA DURING THE 1966-67 SEASON
R. M. Hosford, Jr., Asst. Plant Pathologist

Seed bed--In the cabbage seed bed, downy mildew (Peronospora parasitica) severely
stunted or killed high percentages of unprotected seedlings in the Hastings area
during the 1966-67 cabbage season. Nine foliage spray treatments were compared
for effectiveness in controlling the disease. Each treatment was applied a total
of ten times at 2 to 3 day intervals. King Cole variety was planted on October
14, 1966. Spraying commenced on emergence at a rate of 100 gallons/acre and was
increased to 150 gallons/acre as the seedlings grew. The sprayer had 6 nozzles
per row and was operated at 300 psi. Disease control was estimated by (1) count-
ing the number of plants affected and (2) weighing the seedlings at transplanting.


Table 1.
mildew in
Treatment


Comparis
the cabbie


Spergon (48W) +
Dithane M22 (80W)
(Maneb)
Spergon (48W)
Dithane M22 (80W)
Dithane M45 (80W)
Manzate D (80W)
Polyram (80W)
Daconil 2787 (75W)
Dithane Z78 (75W)
Triton B 1956
Check


on of chemicals for their
age seed bed at Hastings,
Concentration
(in 100 gallons)
3 lbs.
1.5 lbs.


4
2
2
2
2
1.5
2
10


Ibs.
lbs. @
lbs. @
lbs. @
lbs.
lbs.
lbs.
ounces


effectiveness in controlling downy
Florida during the 1966-67 season.
Mildew Average weight of
Rating* plants/plot (grams)
1.13 a 328.3


1.27
1.70
2.28
2.48
3.55
4.08
4.20
5.00
5.00


514.3
319.0
415.0
337.0
299.7
286.0
287.7
154.3
151.0


* Rating system: 0 = 0% of seedlings infected, 1 = 20% infected, 2 = 40%, 3 =
60%, 4 = 80%, 5 = 1004 and no control. Treatments having same letter are not
significantly different.
@ Plus 6 ounces of Triton B 1956.
@@ Plus 6 ounces of Dupont Spray Sticker.

Discussion: Spergon (chloranil) or maneb type formulations gave a better control
of downy mildew than the other treatments, and gave enough protection to enable
the seedlings to grow beyond the young extremely susceptible stage. While this
protection is adequate, it is not complete and must be applied 2 to 3 times a week.
The manufacturer of Spergon (U. S. Rubber Co.) has given notice that the production
of Spergon is being discontinued (personal communication).


I


/63(5v










Field Trials--As cabbage heads neared maturity during the 1966-67 season, lesions
or black spots caused by downy mildew appeared upon them. Seven spray treatments
were compared for effectiveness in controlling the spotting. The cabbage
variety tested was King Cole. Each treatment was applied a total of four times
at weekly intervals. The sprayer had 6 nozzles/row, and it was set at 300 psi
to deliver 100 gallons per/acre. Spraying was concluded on March 9, 1967 and
disease control was estimated when the cabbage were ready for harvest on March
13, 1967. Mildew ratings were made by observation. Results are presented in
Table 2.

Table 2. Comparison of chemicals for their effectiveness in controlling downy
mildew on cabbage approaching maturity at Hastings, Florida during the 1966-67
season.
Treatment Concentration Mildew
(in 100 gallons) Rating*
Fermate
(Ferbam 7616 active) 4.0 lbs. 3.30
Polyram 1.5 lbs. 2.78
Dithane M22 80W 1.5 lbs. @ 2.72
(Maneb)
Manzate D 80W 1.5 lbs. @ 2.64
Dithane M45 80W 1.5 lbs. @ 2.64
Fermate (76% Ferbam) 2.0 lbs.
+ Terraclor 75W 2.0 Ibs. 2.63
Unsprayed check 2.18
LSD .05 .35
LSD .01 .48

* Rating system: 1 = 30 or more lesions per head, 2 = 15 to 30 lesion, 3 =
6 15 lesions, 4 = 1 5 lesions, 5 = no lesions.
@ Plus 6 ounces of Triton B 1956.
@@ Plus 6 ounces of Dupont Sprary Stickers.

Discussion: Ferbam at 4.0 pounds per acre produced a significantly better con-
trol of downy mildew than Maneb. The other treatments were not significantly
different from Maneb. All treatments produced a significant reduction in lesions
compared to the unsprayed check at the 5% significance level. Since Ferbam
leaves a black deposit on the cabbage head, it would be undersirable as a spray
for maturing cabbage heads. However, it may be very desirable as a spray for
cabbage seedlings in the seed bed, where a better control is needed and a black
deposit would not be objectionable.


200 copies




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