Southeast Michigan vegetable update – Aug. 15, 2018

Late blight has been reported in Monroe County. Corn earworm populations are high.

Western bean cutworm
The main pest in this ear is a western bean cutworm larva, recognized by the dark area with thin white stripes behind the head capsule. The other larvae is a sap beetle larvae, which typically only show up in ears that have been damaged by weather or other pests. Photo by Marissa Schuh, MSU Extension.


The table below presents rainfall (in inches) for the Michigan State University Enviroweather stations in southeast Michigan, as well as growing degree-days (GDD) calculated using the Baskerville-Emin Method. Degree-day average for Commerce and Hudson is over five years, while Deerfield is over two years.

Rainfall is in inches, with parenthesis indicating precipitation accumulations since last week’s report.

Rainfall and GDD totals as of Aug. 15




5-year GDD50

Rainfall since April 1





14.24 (+0.01)





12.86 (+0.18)





15.4 (+0.66)


In cole crops, diamondback moth and imported cabbageworm are the main pests being encountered. Thrips are present at low levels in some fields.

Late blight has been found in potatoes in Monroe County. Potato and tomato growers should protect their crops and keep an eye out for late blight symptoms. Chlorothalonil is a useful tool, but there are many products available for potatoes and tomatoes.

In sweet corn, we are starting to catch higher numbers of corn earworm in traps. This, when coupled with the drying of field corn silks, means corn earworm pressure is the highest it has been this year. Current trap catches in Monroe County suggest sprays should be conducted every two to four days (the hotter it is, the shorter the interval).

Research at Ohio State University suggests pyrethroids are most effective when pressure is low, but under high pressure alternative chemistries improve control. If using pyrethroids, use the highest labelled rate during times of high corn earworm pressure. OSU trials suggest Hero is the most effective pyrethroid for corn earworm control. If you are looking at an alternative product, Radiant, Coragen and Besiege (a tank-mix of Coragen and Warrior) provide good control. Treatment can cease when 90 percent of the field’s silks are brown.

For more information, including considerations when thinking about spraying Bt corn, see OSU Extension’s article “Corn earworm alert!!!” (Just note, we are getting lower trap counts in Michigan.)

If you are currently harvesting corn and finding worms, it is likely western bean cutworm (see photo). In an untreated sweet corn variety trial, I am finding high numbers of western bean cutworm. Most of this corn was tasseling a few weeks ago, during peak western bean cutworm flight. These caterpillars can bore through the husk or enter through silks, and there can be multiple caterpillars in one ear.

Contact me at any time with pest ID requests and questions, either at 517-264-5309 or at I tweet about what I’m seeing @SoutheastMIVeg.

General notes and meeting announcements

Growing vegetables in greenhouses? Consider attending the Biological Control in Protected Agriculture Short Course Aug. 21 in Kalamazoo, Michigan. The expert speaker and hands-on elements make it a useful course for those wanting to up the biological control game.

Curious about using drones in agriculture? Attend the Tri-State UAV Field Day Aug. 27 in Ohio. Contact Ricardo Costa at or 573-639-8971 for more information and registration.

Organic growers are invited to attend the Organic Management Field Day Sept. 19 at the Kellogg Biological Station in Hickory Corners, Michigan.

The Midwest Mechanical Weed Control Field Day is Sept. 26 at the PrairiErth Farm (2073 2000 Ave, Atlanta, IL 61723). See in-row cultivation tools demonstrated on vegetable crops, a trade show and grower experiences with mechanical cultivation. The field day begins at 9:30 a.m. and wraps up around 4 p.m. The event registration is $20, lunch included. Check out the Mechanical Vegetable Cultivation Facebook page for more information.

It is never too early to make accommodations to attend Great Lakes Fruit and Vegetable EXPO, Dec. 4-6 in Grand Rapids, Michigan. Hotel blocks are open and tend to go fast. The combination of grower-focused, research-backed presentations and an exhibit hall featuring a diverse set of vendors make it a can’t-miss event.

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