S71- 0 V POTATO INVESTIGATIONS LABORATORY
Mimeo Report POL 71-1 Revised December 1970
RESULTS OF 1969-70 TESTS FOR CHEMICAL CONTROL OF DOWNY MILDEW
IN CaBBAGE SEEDBEDS AT HASTINGS, FLORIDA
D. P. Weingartner, Asst. Plant Pathologist
Mimeo Repcrt POL 71-1 was revised since it stated Dithane M-45 was registered for
use on cabbage. Dithane M-45 is not registered for use on cabbage and cannot be
used on this crop. All copies of Mimeo Report POL 71-1 dated July 1970 should be
replaced with this report.
During the 1969-70 growing season fungicides were evaluated against downy mildew of
crucifers (caused by Peronospora parasitica) in cabbage seedbeds. Greenback cabbage
was planted on November 18, 169 and was grown following standard farming procedures
for the Hastings area. Beginning December 1, 1969, sprays were applied weekly to a
total of 3 applications in Test 1 and 5 applications in Test 2, respectively. All
fungicides were applied in 100 gallons of water per acre with a PTO driven sprayer.
Spray was delivered at 300 psi via 6 nozzles per r.w. Frequent rains (10 rainfalls
ttalling 8.33 inches) and cool temepratures provided ideal conditions for downy
mildew which was severe during the tests.
The copper compounds Kocide and Colloidox were severely phytotoxic to cabbage
seedlings. Excellent control of downy mildew was obtained with Manzate D (Table 1).
Commercial control of downy mildew was also obtained with P-lyram, Dithane M-45,
Dac.nil 2787, Thynon, Difolatan, and TC 904, however, n ne of these materials are
currently registered for use on cabbage. Slight flecking was observed on plants
treated with TC 904 which c,.ntains copper, Slight etiolation was observed on some
Difolatan treated plants in Test 2.
When compared to fungicide data collected at Hastings during other years, data from
these tests suggest that 3.0 lb. rates of Manzate D (as well ab several of the new
non-registered materials) provide downy mildew control comparable to that of chlora-
nil. Chloranil (Spergon) was for many years the standard fungicide used for con-
tr. lling downy mildew. However, availability of chloranil for grower use is un-
certain at the present time. Additional rates, however, must be tested in 1970
before the 3.0 lb. rate is recommended for grower use. Until additional data are
available, Manzate D and Dithane M-22 Special should be applied at 1.5 gallons per
acre in 100 gallons water. The c-pper containing Kocide and Colloidox should be
avoided since these chemicals injured cabbage seedlings under the conditions in
250 copies .F.A.S. Un~v. C' lcda
Table 1. Comparison of effectiveness of chemicals for control of downy mildew in cabbage seedbeds at
Hastings, Florida during the 1969-70 season.-1
Test 1 2/ Test 2 __
5/ % Seedlings No. Leaves % Seedlings No. Lesions
Treatment- Rate/100 Gal. Infected Infected Infected per Plant
Manzate D 80WP 3.0 Ib. 3.9 12.7 30.8 0.91
Manzate D 80WP + Benlate 50WP 3.0 lb+8.0 oz. 6.1 14.7 22.4 0.45
Dithane M-45 80WP 3.0 lb. 6.1 17.0 29.2 0.63
Polyram 80WP 3.0 lb. 6.0 22.7 55.9 1.48
Daconil 2787 75WP 3.0 lb. 9.1 31.2 78.7 3.45
Difolatan 4F 1.0 qt. 8.2 26.2 67.2 3.47
Thynon 75WP / 3.0 lb. 4.1 13.0 37.4 0.75
Tennessee TC 904 52E-/ 2.0 qt. 8.4 22.2 31.0 0.53
Kocide 101 56WP I/ 2.0 lb. -- 31.2 0.71
Colloid. (35% Copper oxychloride colloidal 1.0 qt. -- 19.0 0.30
Check 37.4 86.0 97.5 15-24
LSD .01 8.74 28.5 37.1 1.87
.05 6.25 21.0 27.5 1.57
1/ Average of 4 replications. Data collected from plants drawn from 6 feet of row in each plot.
2/ Final data taken 4 weeks after planting.
3/ Final data taken 8 weeks after planting.
4/ Severely phytotoxic.
5/ DuPont spreader sticker (6 oz./l00 gallon H20) added to all wettable powders except Kocide.
6/ Minor flecking.
POL 71-1 Page 2