Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Downy mildew on cucumber was confirmed on the Eastern Shore of Maryland on July 7, 2009. The processing cucumber scout that found the original infection reports that symptoms, but not sporulation, were present since June 30. The original field had been sprayed, which may have suppressed initial sporulation. There are many cucumber fields affected, which comprise approximately 300 acres. Therefore, all commercial cucumber growers should apply targeted fungicides for control of downy mildew.
The following are the most effective materials (always tank-mix these products with a protectant such as chlorothalonil at 1.5-3 pt 6F/A or OLF, or mancozeb at 3.0 lb 75DF/A):
● Ranman at 2.1-2.75 fl oz 400SC/A plus an adjuvant
● Presidio at 3.0-4.0 fl oz 4SC/A
● Previcur Flex at 1.2 pt 6F/A
● Tanos at 8.0 oz 50WDG/A
● Curzate at 3.2 oz 60DF/A
The NCSU forecasting website ranks these fungicides as follows:
Ranking of Efficacy for Fungicides to Control Downy Mildew
| Fungicide |
Activity Rating1 |
| Presidio2 |
4.5 |
| Ranman |
4.5 |
| Previcur Flex |
3.5 |
| Curzate |
3 |
| Gavel & mancozeb |
2.5 |
| Bravo |
2 |
15 = excellent, 1 = low activity
2Presidio has plant back restrictions, so read the label carefully before selecting that product.
Growers of other cucurbit crops (pumpkin, muskmelon, squash, and watermelon) should aggressively scout their fields. In addition, they should be on a good standard maintenance program that includes chlorothalonil or mancozeb.
Fortunately the weather in the last several days has not been that favorable for long distance spread and survival of the spores. The forecast site states that the risk of downy is low through Thursday, July 9. Check the website often for the latest forecast at http://cdm.ipmpipe.org.