West central Michigan vegetable regional report - July 17, 2013

Cucurbit downy mildew is present in West Michigan, as well as other insects and diseases.

Asparagus. Cladophylls have emerged in many Oceana County asparagus fields, and fungicide sprays have begun on both young and full-season fields. Many growers use the TomCast disease model to time sprays for purple spot disease of asparagus. Asparagus rust uredospore lesions were also present in three Oceana County fields I visited this week. An alternation of Bravo (a.i. chlorothalonil) and Folicur (a.i. tebuconazole) is the mainstay of asparagus disease management. Chlorothalonil provides protection against purple spot and rust, while tebuconazole provides both protective and some curative activity for rust (but not purple spot). Common asparagus beetle and Japanese beetle continue to be active in asparagus.

Uredial lesions on asparagus
Uredial lesions of asparagus rust disease on asparagus fern.

Carrots. Carrot fungicide sprays have been made to control foliar diseases in Oceana County. Fungicide applications can be timed using the TomCast disease model in combination with in-field weather sensors, similar to asparagus.

Celery. Scouts report that aster leafhopper numbers have continued to be relatively low as of July 16, while aphids continue to be present in some locations. Growers who started celery under frost covers have been harvesting for the last few weeks in Ottawa County, and harvest of celery grown outside of frost covers either started this week or will begin next week. Late plantings of celery will likely be finished within the next week. With recent hot, dry weather, be on the lookout for increases in two-spotted spider mite populations. Spider mites can be controlled using Oberon (a.i. spiromesifen). View the special local needs label for use on celery.

Cucurbits. Cucurbit downy mildew was detected in three Michigan counties, including Allegan County. Growers of cucumbers and melons, and also squash and pumpkins, should begin downy mildew spray programs now if they have not already. To learn more about downy mildew management, visit veggies.msu.edu. Reporting the presence of this disease to Michigan State University Extension educators is important; as it can help neighboring growers in your area prevent problems with this disease.

Powdery mildew has been detected in southwest and southeast Michigan. Symptoms of Phytophthora capsici have also been detected in southwest Michigan, but Phytophthora has not yet been confirmed as the causal agent. Aphid populations have been relatively high this year, much higher than is typical this early in the season, so aphid-vectored viruses could be more prevalent. For example, Watermelon mosaic virus has been detected in two locations in Michigan to date. However, there are multiple viruses that infect cucurbits. MSU Diagnostic Services can run molecular tests to detect which are present if you suspect they are in a cucurbit planting. Accurate diagnosis is key, as some viruses have severe effects on marketable yield, while others can be tolerated in some cucurbits.

Squash bug adults and eggs have been detected in the state and in West Michigan, and squash vine borer eggs have been detected in a homeowner planting in Muskegon County. See the Michigan State University Extension article “Monitor for insect pests in your cucurbit crops” from 2012 to learn more about these pests.

Onions. Onion thrips numbers have been relatively low so far in onions, but will begin to increase with recent hot, drier weather. Movento (a.i. spirotetramat) has been recommended for thrips control early in the season in applications made in two consecutive weeks. This product can be very effective early in the season when thrips numbers are low; it can help keep these early populations lower for longer, reducing the number of sprays made to onions. However, it is less effective once thrips populations become high and build. With recent hot weather, thrips populations could build. If they become much larger than 1 thrips/leaf (threshold for control), consider switching to a mid-season product such as Agri-Mek (a.i. abamectin; make in back-to- back weekly applications if thrips exceed threshold). If they are above but still near the 1 thrips/leaf threshold, a second application of Movento could still be effective. Conserve Radiant (a.i. spinetoram) for periods when thrips numbers become especially high, which typically occurs toward the end of the season.

Potatoes and tomatoes. Late blight has been detected in Allegan County as of last week. Dr. Hausbeck mentioned that fungicide programs based on a rotation of chlorothalonil and strobilurins (e.g., for control of early blight in tomato) can help prevent late blight. However, if it is confirmed as present in your county, a material specific to oomycetes (Phytophthora infestans, which causes late blight, is an oomycete) should be used. View for more information on late blight control in potatoes, and for tomatoes.

Sweet corn. I have continued to capture corn earworm moths in an Oceana County location through this Monday, July 15. Silking sweet corn should be protected against this pest. Western bean cutworm activity has also begun. I captured an adult this week in Oceana County, but have yet to find any egg masses in sweet corn.

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