West central Michigan vegetable regional report – July 2, 2014

Recent weather has created a challenge for growers, permitting disease while making access to fields for fungicide application challenging.

Asparagus

Wet and relatively warm weather over the past week could yet again promote development of asparagus rust and purple spot. Once cladophylls (the leaves of asparagus) have expanded, prompt application of fungicides will help prevent disease development. Fungicide sprays can be timed using the TomCast disease model, with data collected from weather sensors you can purchase and maintain yourself.

Carrots

Area scouts report at least one record of elevated aster leafhoppers in Oceana County carrots during the past week. Samples of leafhoppers from carrots have begun to show elevated infectivity, increasing the risk of aster yellows transmission.

Celery

Over the past two weeks, infectivity of aster leafhopper samples taken from carrots and celery has increased, elevating the risk of aster yellows.

Cucurbits

Michigan State University Extension downy mildew spore traps recorded one day of elevated spore captures in Bay County on June 18, but not in Saginaw or Monroe. Access spore counts www.veggies.msu.edu. New data for Saginaw and Monroe will be added soon. See “Downy mildew watch: Fungicides recommended for cucumber disease control” for more information on cucurbit downy mildew. Growers of susceptible crops may want to consider a preventive fungicide program this year given the weather.

Recent weather could also favor problems with Phytophthora capsici in area vine crop fields and other susceptible crops. Foliar fungicide applications can help protect the fruit. Applications of fungicides in the drip line are more effective at preventing crown and root rots than foliar applications. Read more information about Phytophthora capsici.

A recent pumpkin sample brought into our local office had squash vine borer eggs laid near the base of the plant. If you detect this pest, prompt application of an insecticide followed by a second application five days later will help kill larvae before they enter the vines.

Squash vine borer and squash bug
Eggs of (A) squash vine borer and (B) squash bug look similar. Squash vine borer eggs are reddish and disked-shaped and often lay on the stem. Once in the vine, larvae are difficult to control. Squash bug eggs are larger and lay in groups on the underside of leaves, often where two leaf veins intersect. Squash vine borer eggs were recently detected in Oceana County.

Onions

Wet weather has made getting into area fields to apply fungicides difficult, but also important. Learn more about effective fungicides from Mary Hausbeck’s 2013 Great Lakes Fruit and Vegetable Expo presentation.

Peppers

Recent warm, wet nights like we have recently had can promote bacterial leaf spot in peppers; however, it has been a while since a widespread outbreak of this disease has occurred. Symptoms include irregular brown lesions, sometimes with yellow borders, with severely affected leaves turning yellow and dropping. Importantly, these symptoms can be confused with symptoms arising from other causes. MSU Diagnostic Services can help you determine what is causing any observable lesions you might see. The best defense is use of tolerant varieties, there are varieties which combine tolerance to some races of bacterial leaf spot and Phytophthora capsici, another major disease.

Bacterial leaf spot
Bacterial leaf spot symptoms on peppers. Photo credit: Howard F. Schwartz, Colorado State University, Bugwood.org.

Potatoes and tomatoes

According to the Late Blight Risk Monitoring website, our cooler, drier weather means there will be a lower risk of late blight development through Sunday, July 6. However, continue to be on the lookout for symptoms given recent wet and warm weather.

Sweet corn

According to forecast models, the recent cold front and storms could have blown corn earworm adults into west and southwest Michigan Monday through Tuesday, June 30-July 1. Monitoring and protection for corn earworm are important between emergence of green silks and brown silks as silks are attractive to egglaying moths during this time period. Prior to mid-July, research suggests that any capture of corn earworm justifies treatment if sweet corn has green silk, while a threshold of 10 moths per night may be usable for corn silking after mid-July.

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