Southeast Michigan vegetable update – July 25, 2018

Things to have on your radar this week: aphids, squash bug, powdery mildew, western bean cutworm and the season’s first report of downy mildew in Michigan.

Bacterial wilt
Photo 1. The strings of liquid between the sections of this vine indicated the cucumber plant has bacterial wilt. Photo by Charles Averre, North Carolina State University,


More northern parts of the region received some rain, though rain has been patchy south of Detroit, Michigan. The front moving in Thursday afternoon, July 26, may bring sporadic, minimal rain, as well as temperatures that are cooler than normal for this time of year. This weather system is likely to stay in our area until early August.

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 July 25


GDD (Base 42)

GDD (base 50)

5-year GDD average (base 50)

Rainfall since April 1





12.91 (+2.26)





10.28 (+0.35)





13.01 (+0.58)

*Two-year GDD average.


In cucumbers and melons, downy mildew has been confirmed in Berrien County cucumbers. The dry conditions in our area will hamper downy mildew development, so general protectants like Mancozeb or Bravo should be adequate. Keep an eye out for downy symptoms, especially if you are in an area that has gotten some rain and we start to get more morning dew. If downy is reported closer to our region, I will make an effort to alert growers. For more information on the report and on this year’s recommended products, see MSU Extension plant pathologist Mary Hausbeck’s article, “Downy mildew found in Michigan cucumbers in 2018.”

The dryness has caused some cucurbit plantings to look a little fried, though in some fields there is more going on. If you have plants wilting in the field, pull up the plant and make sure the roots are healthy. If those look healthy, get a knife and cut down from the crown. You may find a squash vine borer larva feeding. In instances I’ve seen this year, looking for an entrance hole and frass wasn’t enough, it was only after cutting into the root were we able to find the larvae feeding.

If there’s no larvae and the plants with damage seem to be scattered throughout the field, it may be bacterial wilt. This disease is vectored by cucumber beetles, and cucumbers are very susceptible to it. You can do a quick and dirty check for this disease by cutting vertically through a wilted vine. Bring the ends together then pull them apart slowly. If the disease is present, you will see a stream connecting the two vines as they’re pulled apart—it reminds me of strings of melted cheese, others describe it as syrupy (Photo 1). Remove plants that display the wilting and this symptom to get rid of a bacterial source.

While many fungal diseases are being kept in check by the lack of moisture, cucurbit powdery mildew doesn’t need much moisture to develop. Some pumpkin plantings have been held back by the rain, but any planting where things are beyond the bush stage should receive preventative fungicide treatments. Page 125 of the Midwest Vegetable Production Guide has a useful table that runs down different fungicides and gives a rating for how effective they are against assorted cucurbit diseases; it is a useful tool when deciding what products you’re interested in.

Regarding insects in cucurbits, we are having good weather for aphids, who like it cool and dry. Squash bugs are also laying eggs. This is a pest that is most easily controlled as nymphs, so as these eggs hatch, consider control measures. There are many conventional products available (see the Midwest Vegetable Production Guide for a full list), just make sure you are getting them on when nymphs are out. For organic production, Azera may be a product you can use, depending on your certifier.

In the pepper world, bell peppers are being harvested. Banana peppers are sizing alright, all things considered. Blossom end rot is easily found in some plantings. Degree-day models suggest the second generation of European corn borer is flying. Consider a chemistry that is more selective and leaves natural enemies in place when targeting this pest; this will help prevent aphid and thrips populations from getting out of control.

Coragen and Harvanta have short pre-harvest intervals, are effective at controlling caterpillar pests and are selective enough to preserve beneficial insect populations. Harvanta is also labelled for thrips, radiant is highly effective against thrips and can keep European corn borer at bay if the pressure is modest. There are a variety of other less selective chemistries that will take care of European corn borer, see the Midwest Vegetable Production Guide for the full listing.

In potatoes, vine kill has begun and some light harvesting is taking place. No late blight has been reported in our region.

Sweet corn harvest continues. Corn earworm catches continue to be minimal and field corn is silking in some areas, so pressure is low. The weather front that is moving in over the next few days is coming in from Canada, so corn earworm pressure should continue to be low until the next weather system rolls in.

Western bean cutworm peak flight is upon us, meaning scouting fields for eggs and even larvae is advisable (Photo 2). For the full overview, see “Scout sweet corn for western bean cutworms” from MSU Extension.

Finally, rust is present in some fields.

WBC feeding in tassel

Photo 2. After hatching, western bean cutworm larvae move into the whorl and tassel, feeding on the tender new tissue. If looking at tassels, you will likely notice frass before you notice caterpillars. Photo by Marissa Schuh, MSU Extension.

Large-scale staked tomato harvest will begin in the next week. Note the weather conditions are right for aphid populations to increase.

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

General notes and meetings announcement

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 on Sept. 19 at the 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, 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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