High number of downy mildew sporangia detected in Monroe County

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Spore trapping in Michigan began last week and a high number of downy mildew sporangia have been picked up in Monroe County (http://plantpathology.msu.edu/labs/hausbeck/Research/2009DMSporetraptotals.pdf). What is especially concerning about these spore counts is that two days’ counts exceeded 400 sporangia. A sporangial concentration of 400 is an amount that we would expect to see when there is an infected cucurbit crop within the vicinity.

It is very possible that there is a downy mildew-infected cucurbit crop in or near Monroe County. Growers, scouts, and extension personnel should be especially vigilant in scouting cucurbit plantings. In the past, cucumbers and melons have been more susceptible to downy mildew than the other cucurbits such as pumpkins and squash. Scouting efforts should be focused on cucumbers and melons when looking for downy mildew. Early-planted cucurbit crops growing in tunnels should be examined carefully for any indication of downy mildew. The tunnel acts as a humid mini-greenhouse that favors downy mildew infection and development. Remember, even cotyledon leaves of young pickle plantings are susceptible and have become infected with the disease in previous years.

Growers of cucumbers and melons in Southeast Michigan should begin applying downy mildew fungicides immediately. Fungicides that are recommended to protect against downy mildew are listed below.

Spore trap tapes from other Michigan counties being monitored are being processed. Thus far, there are low concentrations of sporangia in the eastern side of the state where much of the pickle acreage is located. These low counts indicate that there is a low influx of sporangia making their way into these growing areas and infection in the near future is likely. Information regarding the west side of the state is not yet available, but those updates should be available within a couple of days. Just as soon as results are available, the numbers will be posted on the website and updated throughout the growing season.

Cucumber
Cucumber Table

Vine crops, such as zucchini, squash, pumpkin, melon and gourds
Vine crop table

[Please note: Gavel 75WG and Dithane are not registered on some vine crops.]

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