CUCUMBER (Cucumis sativus ‘Dasher II’)
Downy mildew; Pseudoperonospora cubensis
G. E. Vallad, B. Hughes, S. Kalb,
H. Adkison, and R. Willis
Department of Plant Pathology
University of Florida, GCREC
Wimauma, FL 33598
Evaluation of selected fungicides for management of downy mildew and target spot on cucumber, fall 2014.
On 24 Sept 2014, plots were established at the University of Florida’s Gulf Coast Research and Education Center in Balm, FL to assess the effect of
fungicides on the control of downy mildew on cucumber. Plots consisted of 10 ft-long bed sections within 300 ft-long, raised beds with 5 ft centerto-center bed spacing. Beds were covered with white virtually impermeable mulch and irrigated with a drip system. Seeds were sown at 12-in
spacing along beds skipping a 8-ft alley between plots. Treatments, including a non-treated control were arranged in a completely randomized block
design with each treatment repeated four times. Fungicide treatments were applied via foliar spray on 31 Oct, 7 Nov, 14 Nov, and 21 Nov
(corresponding with applications 1 to 4 below) with a CO2 back pack sprayer calibrated to deliver 60 gal/A at 40 psi. Plots were monitored regularly
for downy mildew, and rated on 6 Nov and 24 Nov after disease reached appreciable levels. Alternating applications of Quintec (6 fl oz/A) and
Procure 480SC (8 fl oz/A) were applied throughout the season to minimize the impact of powdery mildew. Conditions were favorable for rapid
disease development. During the trial period, 18 measurable rain events occurred for a total of 8.68 inches of rain, with average relative humidity
only dropping below 80% in 27 out of the 62 day trial period. Temperatures were seasonable, daily averages ranged from 79.9 to 47.5 °F, with only
14 days where daily temperatures averaged less than 65 °F. No phytotoxicity was associated with any of the treatments.
At the first rating, downy mildew severity ranged from 5.4 to 26.3%. Relative to the non-treated control, all treatments were effective at reducing
downy mildew on 6-Nov with the exception of Penncozeb (1-4), 2 lb; Presidio (1,3), 4 floz alt. Bravo (2,4), 2 pt; Zampro (1,3), 14 floz alt.
Bravo (2,4), 2 pt; RevusTop (1,3), 8 floz alt. Bravo (2,4), 2 pt; V-10365 (1-4), 6.5 floz; Ranman (1-4), 2.75 floz; Zampro (1-4), 14
floz; Presidio (1-4), 4 floz; and a program consisting of Presidio (1,3), 4 floz alt. Ranman (2), 2.75 floz alt. V-10208 (4), 8 floz and
Penncozeb (1-4), 2 lb. Treatments of Bravo (1-4), 2 p alt. Penncozeb (1-4), 2 lb; A20942D (1,3), 3.75 pt alt. Bravo (2,4), 2 pt; and V10365 (1-4), 13 floz exhibited the lowest levels of disease. By 24-Nov, disease severity ranged from 78.4 to 93.2%. Although
treatment differences were not statistically significant, the non-treated control exhibited the highest level of disease and A20942D
(1,3), 3.75 pt alt. Bravo (2,4), 2 pt the lowest level of disease.
Treatment (Apps.), rate/A
Disease Severity (%):y
6-Nov
z
24-Nov
Bravo (1-4), 2 pt
12.9 bcd
Penncozeb (1-4), 2 lb
Bravo (1-4), 2 pt;
Penncozeb (1-4), 2 lb
18.4 abc
89.6
7.6 de
83.8
Non-treated Control
Presidio (1,3), 4 floz;
Bravo (2,4), 2 pt
Zampro (1,3), 14 floz;
Activator 90 (1,3), 0.125 %(v/v);
Bravo (2,4), 2 pt
RevusTop (1,3), 8 floz;
Activator 90 (1,3), 0.125 %(v/v);
Bravo (2,4), 2 pt
A20942D (1,3), 3.75 pt;
Activator 90 (1,3), 0.125 %(v/v);
Bravo (2,4), 2 pt
V-10365 (1-4), 6.5 floz;
Silwet L77 (1-4), 0.125 %(v/v)
V-10365 (1-4), 9.75 floz;
Silwet L77 (1-4), 0.125 %(v/v)
V-10365 (1-4), 13 floz;
Silwet L77 (1-4), 0.125 %(v/v)
Ranman (1-4), 2.75 floz;
Silwet L77 (1-4), 0.125 %(v/v)
Zampro (1-4), 14 floz;
Silwet L77 (1-4), 0.125 %(v/v)
V-10208 (1-4), 8 floz;
Silwet L77 (1-4), 0.125 %(v/v)
Presidio (1-4), 4 floz;
Silwet L77 (1-4), 0.125 %(v/v)
Previcur Flex (1-4), 1.2 pts;
Silwet L77 (1-4), 0.125 %(v/v)
V-10365 (1-4), 9.75 floz;
V-10208 (1-4), 8 floz;
Silwet L77 (1-4), 0.125 %(v/v)
Ranman (1,3), 2.75 floz;
V-10208 (2,4), 8 floz;
Penncozeb (1-4), 2 lb
Ranman (1,3), 2.75 floz;
Zampro (2,4), 14 floz;
Penncozeb (1-4), 2 lb
Presidio (1,3), 4 floz;
Ranman (2), 2.75 floz;
V-10208 (4), 8 floz;
Penncozeb (1-4), 2 lb
26.3 a
93.2
18.4 abc
86.1
15.4 abc
87.2
15.4 abc
88.5
5.4 e
78.4
15.4 abc
92.8
10.8 cd
88.5
7.6 de
83.8
OxiPhos (1-4), 2.5 gal
P=
z
x
87.2
25.0 a
91.4
26.3 a
90.7
10.8 cd
88.5
22.1 ab
88.5
10.8 cd
84.8
10.8 cd
89.6
12.9 bcd
86.1
12.9 bcd
86.1
18.5 abc
91.0
26.2 a
91.8
< 0.0001
0.1765
Listed treatment rates are foliar-applied and on a per acre basis unless noted otherwise.
The severity of downy mildew was assessed as the percentage of canopy affected. The Horsfall-Barratt scale was used for all ratings, but values were converted to
mid-percentages prior to statistical analyses.
x
Values followed by the same letter are not statistically significant (P = 0.05) according to Fisher’s LSD test.
y