East Michigan vegetable update – May 27, 2020

A taste of summer this week and crop progress has been rapid.

Seedcorn maggot
Seedcorn maggot kills squash and bean seedlings by burrowing into the seed before emergence or into the stem after emergence. Photo by an anonymous Michigan grower.


We had a little taste of summer, but lower 60-70 degree Fahrenheit weather is in the forecast for the next week, and some rain by Friday, May 29. Warm overnight temperatures with high humidity are good conditions for diseases, so keep an eye on plants through this week, especially in high tunnels and hoop houses.

You can find more detailed weather information for your area by visiting the Michigan State University Enviroweather station closest to you:

Vegetable crop progress

I visited Imlay City, Michigan, last Friday, May 22, to check crop progress and have had updates sent to me by growers from other regions.

Asparagus pickings are in force. Asparagus beetles seem aggressive this year. Some slug damage has occurred on some fields as well.

Rhubarb are in force.

Carrots have at least one leaf and nurse crops were not killed in the fields I saw.

Seeded storage onions have at least two leaves and nurse crops have been killed.

Potatoes are emerged, but I do not see Colorado potato beetles yet.

Transplanted kale has three to four leaves. Cabbage white butterflies are out looking for crops to lay eggs on.

Tomatoes that were under plastic low tunnels and unheated high tunnels during the freezes experienced between 10% and 30% loss and were replaced with fresh transplants within the following week.

Lettuce has up to seven leaves.

Sweet corn has up to four leaves in places.

Green beans are emerged.

Strawberries are in full bloom. The first sets of flowers for some varieties had freeze-killed centers, but the new flowers are healthy.

Seed and root maggots in cole crops and onions are nearing their peak egglaying stages this week. Seed corn maggot has already been in its peak flight and egglaying since the beginning of May. For cole crops and onions, it could be a good time to target a spray on crops that are in the ground. A pyrethroid like zeta-cypermethrin (Mustang Maxx) works well. An organic option is spinosad (Entrust). Row covers work excellent for those with time, labor and small areas.

For seed corn maggot, soil temperatures play an important role in their development. Once soil temperatures at 4 inches reaches a maximum of 70 F for about four days in a row, the likelihood of maggot damage gets much lower. We are right on the cusp of that, with soil temperatures just maxing out at over 70 F at our coldest Enviroweather stations in the Thumb and Bay for the first time this season on May 26. Some stations on warmer sites have already had three consecutive days with soils at 4 inches over 70 F.

That said, we are heading into a cooler week, and peak flight is not quite over. Treatment may be necessary. Seeded crops are more likely to experience damage than transplants. Seed treatments such as Cruiser (thiamethoxam), diazinon, FarMore FI400 (thiamethoxam plus fungicides) and Poncho (permethrin) are somewhat common seed treatments.

For transplants, Capture LFR (bifenthrin), Platinum (thiamethoxam) and Sivanto (flupyradifurone) can be used in transplanter water, banded or in-furrow application with seeds or transplants, or as a chemigation through drip tape.

Admire (imidacloprid) and Verimark (chlorantraniliprole) can be used just like the products listed above but are also labeled for drenching transplant trays. Admire can be used within seven days of transplanting, and Verimark within 72 hours of transplanting.

Never use a transplant drench if you are direct-seeding treated seed. This double dose is not necessary and later hurts bees. Also, don’t use treated seed for transplants. The plants grow out of their insecticide before they get to the field, and any advantage of starting with a treated seed is lost.

Here is a table that summarizes the maggots of concern and the degree days that signify when they will be laying eggs in the areas around seedlings. I used Lapeer as an example. The onion maggot model is from NEWA, which calculates degree days differently.


Seed corn maggot emergence - base 39 F

Onion maggot emergence – base 40 F

Cabbage maggot emergence - base 43 F

Current degree days (Lapeer)




Overwintering flies start to emerge and lay eggs

201 (occurred April 10)

390 (occurred May 18)

298 (occurred 13 May)

Peak flight and egg laying of overwintering flies

342 (occurred on May 1)

735 (a spray could be targeted this week)

565 (a spray could be targeted this week)

Peak flight and egg laying of first generation flies




Peak flight and egg laying of second generation flies




Great Lakes Vegetable Producer’s Network

MSU Extension is participating in a live, weekly roundtable discussion during the growing season for commercial vegetable producers in the Great Lakes and Midwest region. Join us! We broadcast live via Zoom at 12:30 p.m. ET/11:30 a.m. CT every Wednesday from the first week of May to the first week of September. You must register to be a part of the live audience. If you have a pressing vegetable production issue that you would like discussed, simply email it, along with your phone number, to greatlakesvegwg@gmail.com. 

On-tap for next week, June 3: Hoop house nutrient management

Please contact me at phill406@msu.edu or 616-901-7513 with questions, concerns, or to schedule a farm visit. You can also send plant materials to MSU Plant & Pest Diagnostics.

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