Southeast Michigan vegetable update – Aug. 7, 2018

Hooray, more rain! High humidity, coupled with morning fog and heavy dew, mean environmental conditions are ripe for disease development.

The leaf in the background has white areas around the veins cause by its genetics. The leaf in the foreground has discrete areas where powdery mildew has become established on the leaf.
The leaf in the background has white areas around the veins cause by its genetics. The leaf in the foreground has discrete areas where powdery mildew has become established on the leaf. Photo: Marissa Schuh, MSU Extension


Most of our region has received a fair amount of rain in the last week, which was much needed.

The more humid nights and morning fog we have, the better the weather is for disease transmission and development. Michigan State University Extension advises staying on top of fungicide applications. Just because things look good now, does not mean it will stay that way.

The table below presents rainfall (in inches) for the MSU Enviroweather stations in southeast Michigan, as well as degree days calculated using the Baskerville-Emin Method. Degree day average for Commerce and Hudson is over 5 years, while Deerfield is over 2 years. Rainfall is in inches, with parenthesis indicating precipitation accumulations since last week’s report.

Rainfall and Degree Day Totals as of August 1, 2018


Degree Days (Base 42)

Degree Days (Base 50)

5-Year Degree Day Average (Base 50)

Rainfall since April 1st





14.23 (+0.33)





12.68 (+1.21)





14.74 (+0.57)


Cabbage harvest is ongoing. Note that there are cabbage maggots flying right now; the flies you deal with next spring are being laid as eggs now. Prompt destruction of harvested crop residue reduces the egg laying spots for both cabbage maggot and swede midge. Another consideration for next year is what cover crops you establish now. I’ve seen brassica diseases like black rot in radish cover crops, so I would advise going with a different cover crop if cole crops are in a field’s rotation.

In cucumbers and melons, downy mildew reports continue to roll in from other parts of Michigan and neighboring states. Both watermelon and cantaloupe harvest will pick up in the next week.

Tablestock and specialty potato harvest is ongoing. I’ve gotten reports of white grub feeding on both conventional and organic farms. No late blight has been reported in Michigan.

Winter squash and pumpkins continue to add size and mature. Bacterial leaf spot and powdery mildew are appearing. There are many products available to help control powdery mildew. Pumpkins especially benefit from a good program, as the season is long and powdery mildew can infect the handle and cause it to fall off.

There can sometimes be confusion over identification of powdery mildew vs varietal appearances. Some varieties of winter squash and pumpkins (as well as summer squash and zucchini) have white areas around the veins. This is not a disease, it is just something in the genetics of the variety. Powdery mildew will have more concentrated, pronounced areas on the leaf. You will also see discrete white areas on the bottoms of the leaves.

Squash bug nymphs have emerged. Treatment now is much more effective than treatment when the insects reach adulthood. To avoid leaf and fruit damage, consider a treatment if you are finding nymphs in your field. There are many conventional options available, including pyrethroids and Sevin XLR Plus. For organic producers Azera may be something permitted by your organic certifier. Spraying later in the day will help protect pollinators.

Sweet corn harvest is ongoing. Corn earworm catches continue to be low, western bean cutworm catches are going down as well.

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

General notes and meetings

  • Growers growing vegetables in greenhouses should consider attending the Biological Control in Protected Agriculture Short Course August 21 in Kalamazoo. The expert speaker and hands-on elements make it a useful course for those wanting to up the biological control game.
  • Curious about uses of drones in agriculture? Attend the Tri-State UAV Field Day Aug. 27 in Ohio. Contact Ricardo Costa (, 573-639-8971) for more information and registration.
  • Organic growers are invited to attend the Organic Management Field Day September 19 at Kellogg Biological Station.
  • 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, December 4-6, 2018, in Grand Rapids. 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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