July 2005
Southern Cucs on the Skids
There have been several articles recently of how infectious downy mildew has become in southern cucumber production. A recent evaluation of fungicides for control of this disease was published in F&N Tests, and it provides some insight to how bad things have become. Cucumbers planted in NC in late August of 2004 were treated with fungicides (hollow cone nozzles applying 40 GPA @ 45 PSI) beginning at the two-leaf stage. Fourteen single or multiple fungicide combinations were applied every five days (shortened from the original design of seven days) due to intense fungal pressure. The plots were sprayed 11 times until frost killed the plants in early November. The yield of No. 1 cucumbers and culls per plot were tallied.
The non-treated plants produced no saleable or cull cucumbers. There was less than one saleable cucumber per plot for half of the treatments, some with very new chemistries (strobilurins, boscalid) as well as old proven chemistries (chlorothalonil, mefenoxam), which had performed well just the previous year. Treatment combinations that included cymoxanil/famoxadone (Tanos®), propamocarb (Previcur Flex®), cyazofamid (Ranman®), and zoxamide/mancozeb (Gavel®) performed well (between 7 and 19 saleable cucumbers per plot). This research illustrates the rapid pace of fungal disease evolution. The scary caveat to this story is that the research was done on a cultivar of cucumber (‘Jackson’) which is considered resistant to downy mildew. (F&N Tests, Vol. 60:V059).
