Southeast Michigan vegetable update – June 3, 2020

A week of warm weather helps plants grow but may cause unseasonably early disease development.

Striped cucumber beetles feeding on a squash seedling
Striped cucumber beetles feeding on a squash seedling. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org.

Weather

A warm week pushed crops (and weeds) forward. A new weather front will move through our region Thursday, June 4, through Friday night, bringing with it scattered showers. The next weather system will bring cooler but still seasonable temperatures and dry conditions over the weekend into Monday.

The hot and humid nights over the last week may mean we see plant diseases set in earlier this year than is typical. If you see suspected plant disease when walking fields, look into it and don’t assume it is too early for these issues. Feel free to contact me, and note that Michigan State University Plant & Pest Diagnostics is accepting samples under modified procedures.

This weather has also been conducive for aphids and thrips.

The table below shows rainfall totals for the Michigan State University 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 five years, while Deerfield is over four years. Soil temperature range in Fahrenheit at 2-inch soil depth over the last week, and rainfall is in inches. Frozen precipitation is not included. For a refresher on degree-days and how to get this information in your area, see “Accessing growing degree days with Enviro-weather” from MSU Extension.

Rainfall and degree day totals as of June 3

Station

Degree days (base 42)

Degree days (base 50)

5-year degree day average (base 50)

Soil temperature range

Rainfall since April 1

Commerce

714

368

444.2

58.9-69.4

7.08 (+0.19)

Deerfield

821

436

532.4

57-86.8

6.28 (+0.27)

Hudson

722

371

482.4

55.1-61.7

7.16 (+0.48)

Crop updates

Two caterpillars comparison
Both of these caterpillars are a similar size, just one is reaching the end of its time feeding (lower, diamondback moth) and the other is just getting started (imported cabbage worm, top). Photos by Marissa Schuh, MSU Extension.

Cole crop planting has wrapped on some farms. Flea beetles and diamondback moth are still active, and imported cabbageworm larvae are also starting to be detected. Brassicas have a couple kinds caterpillars that love to eat them, but these larvae vary in how much damage they are capable of. By being able to tell the three caterpillars commonly found on cole crops apart, you can make better management decisions. This can be hard because size isn’t the only consideration when making an identification.

The two caterpillars currently being found are imported cabbage worm and diamondback moth. Imported cabbageworm is green, velvety and develops a yellow stripe down it’s body as it grows. Diamondback moth caterpillars are always under a half-inch long with a green body that tapers and a V on their rear. They wiggle violently and produce silk strands when disturbed. For thresholds, see “Cole crops insect management” from MSU Extension. For control options, see the “Midwest Vegetable Guide.”

I also saw winged aphids on some cabbage plants. The weather we’ve had has been conducive for aphids, so another bug to keep your eye out for when you walk fields. Also, look out for the many natural enemies that eat aphids, including lady beetles, minute pirate bugs and lacewing larvae. These insects will be killed by any broad-spectrum insecticides used to control aphids and the above caterpillars.

Direct seeded cucumbers have germinated and have one to two true leaves.

Striped cucumber beetles are active and feeding, the threshold in cucumbers is one beetle per plant because their ability to transmit bacterial wilt. For direct-seed cucumbers, seeds treated with thiamethoxam should be providing adequate control. If trying to manage this insect organically, trap crops are a good tool. If wanting to use an organic control product, there are a couple with labels. Growers have reported getting good control using Pyganic 5.0 with an acid buffer. The pyganic has to contact beetles in order to be effective because it can degrade quickly, so the spray needs to be timed when beetles are active. All parts of this equation were important for good control.

For beets and spinach, spinach leaf miner larvae have caused extensive leaf damage on some farms.

Purdue University has released information from a small scale trial on organic controls for aphids in their trial in hoop house strawberries. Their small-scale trial, which started when aphid populations were already high, found that Azera and Pyganic were effective.

Pepper planting is finishing up.

For potato growers, Colorado potato beetles are out and laying eggs.

Pumpkins and winter squash are almost done being planted. Note that cucumbers beetles are out.

I got a report this week of cutworm damage in processing tomato. The most commonly encountered cutworm in our area is black cutworm. These caterpillars are dark and hide during the day, either in the soil if it’s dry or under plants and debris if the soil is wet. They are active at night. Fields most at risk of cutting will be those where winter annual weeds were disked up shortly before planting.

Don’t spray just because of this report—scout first! Scout either at dawn or in the evening when caterpillars are active. Pigweed can be a helpful indicator of cutworm presence, as cutworms like to feed on them and the undersides of leaves are red, making it highly visible if the plant has been cut. According to “Vegetable insect management” by R. Foster and B. Flood, 2005, a suggested treatment threshold for tomatoes is one cutworm larvae per 100 plants. For a list of treatment options, see the “Midwest Vegetable Production Guide.”

Sweet corn planting is ongoing. The first flight of European corn borer is emerging according to the Deerfield Enviroweather Model. Note that cutworms are active in our area, though sweet corn taller than 6 inches typically isn’t fed cut by this pest. Armyworm is also present; you’re most likely to find these guys in the whorl.

Reach out

Please contact me at schuhmar@msu.edu or 517-264-5309 with questions, concerns or to schedule a field visit. I have the ability to do field visits on a limited basis.

Great Lakes Vegetable Producer’s Network

The Great Lakes Vegetable Producer's Network is a live weekly roundtable discussion during the growing-season for commercial vegetable producers in the Great Lakes and Midwest region. It is broadcast live via Zoom at 12:30 ET/11:30 CT every Wednesday from the first week of May to the first week of September. Listen live or later. 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 10: Do’s and Don’ts for Sending Samples and Reading Results

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