West central Michigan vegetable regional report – August 26, 2015

Cucurbit downy mildew will challenge late-season production of pickles and melons. Other late-season pests like powdery mildew and corn earworm have also ramped up in west Michigan.


Asparagus purple spot was visible on yellowing cladophylls on the base of asparagus fern this week. Note that warmer than normal temperatures are expected for the start of September; this could facilitate late development of this disease in fields where it has not been well controlled earlier in the year. Overall, growers report good fern health this growing season with few insect pests and some development of purple spot and rust.

Carrot foliar diseases including Alternaria leaf blight are present, as is typical for this time of year.

Cucurbit plantings in research plots showed new downy mildew lesions early this week given recent cool, rainy weather. Michigan State University Extension plant pathologist Mary Hausbeck expects a significant uptick in cucurbit downy mildew now, which will challenge late-season cucumber and cantaloupe plantings. Growers of these crops should consider a five-day spray program of cucurbit downy mildew products tank-mixed with a high, 3-pint rate of Bravo. See an example spray program for downy mildew.

Powdery mildew pressure has increased over the last week. Bacterial disease was identified as a cause of sunken, round fruit lesions in at least one west Michigan winter squash planting. Correct diagnosis is key as symptoms like this can have multiple causes. Note that with recent cool weather, growers may expect a three- to four-day pollination deficit due to low bee activity.

Onions have been challenged by Stemphyllium this year. Fungicides with this disease on the label include Quadris Top, Inspire Super and Fontelis. In general, the same products that can help with purple blotch can help with this disease, however Stemphylium is reportedly harder to control.

Tomato bacterial diseases, including bacterial spot and canker, have been present in west Michigan.

Sweet corn growers cooperating with MSU Extension noted very high trap catches of corn earworm over the last 1.5 weeks in west Michigan. Pheromone trap catches can help you determine appropriate spray intervals for controlling corn earworm in silking corn. If zero moths are being captured, sprays are not required or should only be applied on a weekly schedule for those with low tolerance for damage. For captures of one to 10 moths per night, a five- to seven-day spray program of pyrethroids is appropriate. For captures approaching 50-100 per night and above, a two- to three-day spray program will provide better protection.

Use tighter intervals as moth captures increase, temperatures increase or with heavy rains that lead to pesticide degradation. To use pheromone traps this way, it is critical to check them frequently, at least every other day this time of year. Note that resistance to pyrethroids is suspected in Indiana. If you suspect this is occurring on your farm, Radiant and Coragen can provide effective control.

Western bean cutworm moth captures declined again this week at two Oceana County traps, the main flight of this pest is past. I did capture a very low number of European corn borer moths each week for the past three weeks at an Oceana County trap set.

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