West central Michigan vegetable regional report - August 20, 2014

Keeping on top of disease problems remains a significant challenge for Michigan vegetable growers.

Asparagus fern with purple spot lesions evident as brown spots. Lesions can girdle the stems and leaves, defoliating a field and reducing yield the following year.

Asparagus fern with purple spot lesions evident as brown spots. Lesions can girdle the stems and leaves, defoliating a field and reducing yield the following year.


With recent wet weather, continue to keep an eye on disease weather models and apply controls for asparagus purple spot. Yesterday, the damage this disease can create was evident in an experimental plot where products were not applied. Lesions were present all over the plant and the soil between rows was covered with a carpet of dropped leaves. Though this year has been dry, we have still had early morning dews and, with recent warmer temperatures and more rain predicted, it could progress further.

Cole crops

Diamondback moth larvae and aphids were present in a commercial broccoli planting in West Michigan this past week. Michigan State University Extension reminds growers that control of diamondback moth, and other caterpillars, becomes especially crucial just prior and during broccoli head formation. Larvae serve as contaminants as they can enter and even pupate in the head. Pyrethroids can provide control of caterpillars in cole crops, while the product Coragen is also an excellent option which has longer residual activity.


Cucurbit downy mildew was detected in nine counties in Michigan as of last week and weather early this week is very conducive to spread. Growers of cantaloupe and cucumbers should apply effective downy mildew products on a five day schedule. Rotation between different fungicides will be important to avoid selection for resistance. A good program could include either Previcur Flex (a.i. Propamocarb hydrochloride, 2 day PHI, FRAC 28) or Presidio (a.i. fluopicolide, 2 day PHI, FRAC 43) alternated with the fungicide Ranman (a.i. cyazofamid, 0 day PHI, FRAC 21). Each of these can be tank mixed with either mancozeb or chlorothalonil products. Recent preliminary data and observations suggest resistance management will be important for this pathogen. To stay abreast of cucurbit downy mildew and learn how to identify and control it, access Mary Hausbeck’s website at veggies.msu.edu.

Powdery mildew continues to progress in the state. Effective products include Quintec (a.i. quinoxyfen, 3 day PHI, FRAC13) and Torino (a.i. cyfluenamid, 0 day PHI, FRAC U6). Later-season control of powdery mildew will be of especial concern to growers needing to maintain higher sugar content in their cucurbits and growers of jack-o-lantern pumpkins, since powdery mildew can compromise handles.


Growers should continue to use products that prevent problems with onion downy mildew. This disease has devastated onions in at least one location to date and could continue to be a problem for the remainder of the growing season. Products to consider using include Forum (a.i. dimethomorph), Zampro (a.i. ametoctradin/dimethomorph), and Gavel (a.i. mancozeb/zoxamide). A new supplemental label for Gavel use in onions is now available.

Potatoes and tomatoes

Late blight has been confirmed from 50 potato fields in Montcalm County to our east, also in Allegan, Kent and Gratiot counties. Forecast risk is high for development on all of the next five days at most West Michigan locations through Sunday; see www.lateblight.org. Protectants applied for other diseases will help keep a problem from developing, but inclusion of late-blight specific products under high risk conditions is important. These include products such as Presidio, Revus Top, and Ranman among others, which target the group of pathogens that the late blight organism belongs to.

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