Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Downy mildew was confirmed June 2 in Maryland (Caroline County). In addition, I have unconfirmed, but credible, reports from Wicomico County. I believe that the strain that is present will only cause disease on cucumbers. Therefore only cucumbers should receive fungicides targeted for downy mildew. (All cucurbits should continue to receive protective fungicides). The conventional fungicides that have performed best in University trials in the past year are Ranman, Zampro, and Previcur Flex. Zampro is a newly registered product, which looked very good in my trial. Additional materials, which are targeted for downy mildew and can be used as tank mix or alternation partners include Tanos, Forum, Curzate, and Presidio.
In the summer of 2013, I performed a trial on fungicides that are commonly used in organic production (have an OMRI label). Downy mildew was heavy in this trial, and my results indicated that the available products performed very differently. I applied Champ alone on a weekly schedule, or every other week in alternation with Actinovate, Oxidate, Regalia or Serenade. Champ alone performed well in reducing disease, however phytotoxicity occurred. All of the alternation treatments reduced downy mildew compared to no treatment. When Champ was alternated with another fungicide, downy mildew in August was reduced by 65% (Oxidate), 76% (Actinovate), 77% (Regalia) and 85% (Serenade) compared to non-treated plots. Champ alternated with Serenade performed best over the season on downy mildew. (Note that where powdery mildew was severe, Regalia also performed well).