West central Michigan vegetable update – July 18, 2018

Irrigation has remained a major focus, with some insects and diseases to report.

For asparagus, if you have asparagus beetle larvae and adults, a mix of carbaryl and permethrin has been a standard fern spray. If all stages are present, eggs may hatch after insecticides are applied and residual activity has worn off, so additional applications may be needed. Both products also have activity against Japanese beetle.s 

Celery scouts reported aphid colonization on scattered plants in recent days. Movento (active ingredient spirotetramat, three-day pre-harvest interval) applied with a penetrating surfactant is effective for aphid control. Scouts have also reported spotted mites. The miticide Oberon (seven-day pre-harvest interval) is available through a Special Local Needs label.

For cole crops, cabbage looper larvae have been noted by Michigan State University scouting interns in some parts of the state. If you are an organic grower, consider using spinosad if cabbage looper is the dominant caterpillar. Cabbage looper larvae are distinct in their movement, they form a loop as they move like inchworms across the plant. Otherwise, B.t. can provide effective control of diamondback moth and imported cabbage worm.

For cucurbits, virus symptoms have started to show up in southwest Michigan. Powdery mildew was present on one organic farm I visited Monday, July 16, and growers have been applying powdery mildew fungicides in Oceana and Ottawa counties. The Midwest Vegetable Production guide has a helpful table of fungicides (pg. 125) that shows efficacy for this and other diseases.

For peppers, tomatoes and potatoes, tomato spotted wilt virus has been detected at additional sites, including in west central Michigan. Infected pepper plants are mottled, distorted and stunted, and will not produce marketable fruit. Infection happens when transplants are grown in greenhouses with flowers where cuttings used to start flowers provide the initial source of virus. Western flower thrips then move virus from the flowers to the vegetable transplants within the greenhouse. Secondary spread within the field is thought to be minimal, so the key to managing this disease is in the greenhouse.

Degree-day models suggest the second generation of European corn borer should be flying. Pepper growers with fruit over 0.5 of an inch in size should consider using effective caterpillar materials. Coragen (active ingredient chlorantraniliprole, one-day pre-harvest interval) and Harvanta (active ingredient cyclaniliprole, one-day pe-harvest interval) are highly effective products that can help conserve beneficials. Avaunt (active ingredient indoxacarb, three-day pre-harvest interval) and Radiant (active ingredient spinetoram, one-day pre-harvest interval) are other selective materials with activity against European corn borer. Orthene and the pyrethroids remain important parts of grower spray programs.

Sweet corn scouts have reported some early caterpillar infestations. Some of these issues are thought to be from first generation European corn borer. Applying a pyrethroid just as tassels emerge can help control caterpillars of this pest, as they move out of the whorl onto the plant at this time before boring into plants and ears.

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