East Michigan vegetable update — July 26, 2017

Many more roadside markets have opened this week, as our main season crops are ripening and getting harvested in quantity.

Colorado potato beetle larvae eating smooth nightshade weeds in a cabbage field. A precarious truce. Photo by Ben Phillips, MSU Extension.
Colorado potato beetle larvae eating smooth nightshade weeds in a cabbage field. A precarious truce. Photo by Ben Phillips, MSU Extension.


We have warm and wet days ahead of us this week. Nights are predicted to get down to 60 degrees Fahrenheit and may reach dew points in many areas, which increases the amount of water that stays on leaves.

The following table includes growing degree-days (GDD) base 50 F since March 1, rainfall accumulations in inches since April 1, and soil temperature ranges (Fahrenheit over the last week) to date from Michigan State University Enviro-weather stations in the region.

GDD and rainfall accumulations as of July 26, 2017


GDD (+ added from July 5)

GDD 5-year average

Rainfall (+ added from July 5)

Rainfall 5-year average


1282 (+ 302)


11.79 (+ 1.83)



1294 (+ 291)


9.34 (+ 0.00)



1443 (+ 315)


14.78 (+ 2.77)



1351 (+ 299)


12.96 (+ 0.37)



1317 (+ 296)


18.04 (+ 7.72)



1318 (+ 293)


11.07 (+ 2.73)



1230 (+ 291)


20.03 (+ 0.46)



1326 (+ 298)


12.86 (+ 0.62)



1379 (+ 314)


12.31 (+ 3.66)



1213 (+ 292)


11.57 (+ 0.96)



Corn earworm catches remain low in sweet corn. At last checking, my Macomb County trap caught zero moths and the Tuscola County trap caught one moth over the last five days. We have been lucky so far and have not had any “airdrops” of moths from the southwest this year. In addition, field corn has begun silking.

At this point, sweet corn is like a small target among a sea of other egglaying sites. However, if you decide not to spray for earworm at this time, Michigan State University Extension advises looking out for western bean cutworm eggs. Normally, this pest would be controlled during earworm sprays. Their eggs can be found on the tops of corn leaves in small, tight clusters that turn purple over time. They are about the size of a dime.

Machine harvested pickles started two weeks ago. The last plantings are going in this week in areas that were flooded back in June. Growers affected by the rain were delayed by soil conditions for replanting and regularly scheduled plantings. Harvest is likely to go into mid-September for some contracts.

MSU Department of Plant, Soil and Microbial Sciences professor Mary Hausbeck’s downy mildew recommendations for 2017 suggests at least a three-product rotation of Gavel 75DF, Orondis Opti SC, Ranman 4SC, Zampro 4.4SC and Zing! SC. Each material needs to be tank-mixed with Bravo Weatherstik or Mancozeb.

Cantaloupes are being harvested, but watermelons are still sizing. See pickle section for fungicide recommendations for downy mildew. Growers should alternate those products with powdery mildew products like Quintec, Torino, Vivando or Rally.

Winter squash and pumpkins are setting lots of fruit right now. Powdery mildew can be found across the region now; prioritize a spray program soon if you have not already. Squash bug eggs are just starting to hatch this week.

Fresh market field tomato picks are continuing. The late blight reports from earlier this year have apparently been somewhat contained. It is still useful to have Bravo or Mancozeb applied as protectants against this disease when we have a string of dewy mornings and cloudy days.

Peppers are near harvest in many areas. The cold spring seemed to prevent much leaf mass and I predicted more sunscald on developing fruit. There has been some, but not as much as I expected. Bacterial leaf spot has appeared in some fields.  

Sweet onions are reaching the colossal size and are being dug and dried. Onion quality increases when the tops were deliberately bent over, or when they were pulled and laid on their side. They will continue to size up once they’ve been pulled.

I found what appeared to be a complex of downy mildew, purple blotch and stemphylium in our region. Stemphylium is known to show up on top of the dying tissue killed by downy and purple blotch. These diseases affect the leaves and not usually the bulbs. Control at this point is probably not required. However, seeded onions have a long way to go still, and these diseases are a serious yield-reducer that can open the door for bacterial pathogens to infect the bulb as well.

Cole crop plantings continue for fall harvest. Napa cabbage and other heading cole crops are being harvested weekly now. I had a nice discussion with some growers last night about the enormous size of Michigan cauliflower. They seem to agree that they get pressure from some of their buyers to make huge, county fair-winning cauliflower on every plant. This requires plant spacing between 20 and 30 inches in-row. As such, “self-blanching” types don’t actually self-blanch; more trips to the field are required to tie the leaves over heads, and large cauliflowers potentially mold in customer’s refrigerators if they can’t finish them.

Are customers more or less likely to buy another one after that happens? This is probably just a standard case for knowing your market. One thing the growers liked about tying was that the color-coded rubber bands make it easy for workers to know which plants to harvest on a given day. One trade-off to tighter, in-row spacing could be increased disease pressure.

Upcoming events

The Midwest Mechanical Weed Control Field Day is Sept. 26 at the MSU Horticulture Farm. For more information and registration, see “Midwest Mechanical Weed Control Field Day.”

Hotels are filling up for the Great Lakes Fruit and Vegetable EXPO, Dec. 5-7 in Grand Rapids, Michigan. The combination of grower-focused, research-backed presentations and an amazing exhibit hall make it a can’t-miss event.

Please contact me at phill406@msu.edu or 616-901-7513 to pick up any suspected disease samples from your farm, or send the diseased plant parts to MSU Diagnostic Services.

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