West central Michigan vegetable regional report – July 9, 2014

Continue to keep on top of disease control programs in this very wet year.

Asparagus

Asparagus purple spot disease development increases when fern is wet and temperatures are warm during this wet period. The TomCast disease model can help you target fungicide sprays for this disease to coincide with periods when the duration of warm, wet periods has passed a threshold beyond which disease development is likely. Asparagus purple spot can defoliate fields once lesions spread to the cladophylls, causing them to die and fall off the plant. These cladophylls are the photosynthetic powerhouse of asparagus, so protecting them is important. The fungicide Bravo (a.i. chlorothalonil) is the foundation of purple spot control programs.

Carrots

Twenty-two percent of aster leafhoppers from an Oceana County carrot field were infected with aster yellows from a sample taken July 2, 2014. At this infectivity, the threshold is 2 leafhoppers per 100 sweeps for both carrots and celery.

Celery

Early blight was confirmed as present in a Southwest Michigan location. This disease can be both soil and seed borne, and can be spread by water splash, field workers and farm machinery. Not all plantings may have the same severity of this disease, so consider working in severely affected fields at the end of the day after you have worked in other locations; this is a good general disease control strategy. At the end of the day, power-washing equipment can help remove disease-carrying plant debris or soil.

Local scouts report that aphid colonies were detected in west Michigan celery this week, which is much earlier than the normal first detection date of late July/early August.

Cole crops

Farmers started planting direct-seeded broccoli in Oceana County over the past week. Cabbage harvest continued to progress at one Ottawa County location this week.

Cucurbits

Michigan State University traps captured cucurbit downy mildew spores in Monroe, Saginaw and Bay counties. Access spore counts at veggies.msu.edu. The furthest north this disease has been confirmed to date is Maryland, with a confirmation from cucumber on July 3. This continues to be a year when a preventive cucurbit downy mildew program could be beneficial for susceptible crops such as pickles and cucumbers. Products for use in such a program can be found in “Spray Recommendations for Downy Mildew”, by Mary Hausbeck.

Onions

Symptoms associated with bacterial leaf blight were observable at a Southwest Michigan location yesterday. For thrips control, remember that if you sprayed Movento (a.i. spirotetramat) in a given week (call this “Week 1” of the thrips season), either spray it again the following week on Week 2 or skip an application of this product if thrips are below threshold. If thrips are below threshold, allowing you to skip a second application of Movento in Week 2 of your thrips control season, move to another chemistry if an application becomes necessary in Week 3. Agri-Mek (a.i. abamectin) is one option for use in Weeks 3-4 of the typical 8 weeks thrips are active. Remember to always use a penetrating surfactant with products such as Movento and Agri-Mek. Also remember that tank-mixing Movento with chlorothalonil reduces its efficacy; other fungicides should be fine.

Potatoes and tomatoes

Late blight was detected recently in Howe, Indiana, and the strain was analyzed and found to be Ridomil-sensitive. According to www.lateblight.org, risk of late blight spread will be high for 2 out of the next 5 days through July 13. If you detect late blight in potatoes, please contact Michigan State University Extension, as prompt sampling will help determine what fungicides might best control the strain. Research has shown that two applications of Ridomil (a.i. mefenoxam) can help protect potato tubers against some tuber diseases, which could be especially important given the extremely saturated soils growers face; this could help protect against disease-related storage problems later. Michigan State University’s Willie Kirk suggested that given the extremely wet year, a third application of Ridomil might be warranted given these benefits. Early blight and bacterial disease have been detected in tomatoes in different parts of the state.

Sweet corn

According to forecast models, there is a low risk of continued corn earworm migration this week. Two corn earworm moths were captured over the past 7 days in an Ottawa County location. 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. No western bean cutworms were captured over the past week to our west in Montcalm County.

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