Ontario reports downy mildew on cucumber and cantaloupe

Michigan cucurbit growers should protect their crops from downy mildew.

Downy mildew symptoms on cucumber. Photo by Mary Hausbeck, MSU.
Downy mildew symptoms on cucumber. Photo by Mary Hausbeck, MSU.

Downy mildew has been reported in Essex County in Ontario, Canada, putting the pathogen within easy striking distance of Michigan’s cucurbit crops. This pattern of downy mildew being detected in our immediate region around the time of July 4, 2017, has become well-established.

If fungicide sprays have not been applied to the most susceptible crops including cucumbers, cantaloupe and watermelon, this is an appropriate time to begin a fungicide program (see table below). For downy mildew symptoms on other cucurbit crops, see our tip sheet, “Monitoring and Managing Cucurbit Downy Mildew.”

Spore trapping for the pathogen has been ongoing in Michigan and downy mildew spores have not been found in significant numbers. This information is posted and updated each day and can be viewed at MSU’s Downy Mildew News.

Reports of downy mildew have increased across many counties in the southeastern U.S. in the last 10 days. States with the disease include Georgia, North Carolina, Alabama, Florida, South Carolina and Texas. In the northeastern U.S., downy mildew has been reported in Maryland. You can view confirmed outbreaks across the U.S. at the Cucurbit Downy Mildew Forecasting website.

Preferred downy mildew fungicides


Active ingredient


Comments (maximum applications per season)

Orondis Opti*

oxathiapiprolin/ chlorothalonil

45/ M05

Make no more than two sequential applications before rotating to a fungicide with a different mode of action (FRAC). Use either soil applications of Orondis or foliar applications of Orondis Opti A, but not both for disease control. Do not use for more than one-third of the total foliar fungicide applications. (6)

Ranman 4SC*



Mix with chlorothalonil or mancozeb. (6)

Gavel 75DF

mancozeb/ zoxamide

M03/ 22

Mix with chlorothalonil or other downy mildew fungicide. (8)

Zampro 4.4SC

ametoctradin/ dimethomorph


Mix with chlorothalonil or mancozeb. Labeled for application via drip as a foliar spray. (4)

Zing! SC

zoxamide/ chlorothalonil

22/ M05

Mix with mancozeb or other downy mildew fungicide. (8)

*Orondis Opti and Ranman have performed exceptionally well in Michigan trials.

Dr. Hausbeck’s work is funded in part by MSU’s AgBioResearch.

This material is based upon work that is supported by the National Institute of Food and AgricultureU.S. Department of Agriculture, under award number 2016-68004-24931.

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