Southeast Michigan vegetable update – Aug. 2, 2017

Cooler weather fronts moving in by week’s end will promote development of diseases like downy mildew and late blight. Sweet corn pest pressure remains low.


Last week’s predicted rain failed to materialize, leading to dry conditions in un-irrigated fields. Once again, as we move towards the weekend there is a chance of rain. A new front moving in from Canada will bring in cooler weather, making things feel more like early fall than early August. This will likely persist for a week or two, with more typical summer temperatures moving in by mid-month. This cooler weather, when combined with dense leaf canopies, means there will be an increased risk of disease.

The table below presents rainfall in inches for the Michigan State University Enviroweather stations in southeast Michigan with the amount of change from last week reported. Growing degree-days (GDD) starting March 1 were calculated using the Baskerville-Emin Method.

Rainfall and GDD totals as of Aug. 2, 2017

Enviroweather station

GDD base 50

5-year GDD average base 50

Rainfall since April 1 (inches)


1596 (+148)


9.52 (+0)


1852 (+144)


11.71 (+0)


1662 (130)


12.71 (+0)


Cabbage harvest and planting is ongoing. Other cole crops are being harvested.

Cucumber harvest on smaller farms continues. Downy mildew has claimed many of the early plantings.

Muskmelon is being harvested on some operations. I’ve seen some fusarium wilt, which can cause plants to die as the roots become brown and rotted. If this is a consistent problem on your operation, consider experimenting with a resistant variety in the future.

I’ve also seen fields with high aphid pressure. Aphids can vector viruses and the honeydew they produce can cause mold issues. Look for leaves that are curling or glistening (even at the heat of the day), and investigating the underside will likely reveal small, green insect colonies. There aren’t firm thresholds, but if you’re concerned about moldy leaves and fruit, many treatments are available for aphids (Brigade, Warrior, etc.)

Pepper harvest is ongoing. This week, I caught no European corn borers in Washtenaw and Monroe counties, and I caught one in Lenawee County. Coragen and Orthene provide good control of this pest in trials, though Coragen’s one-day pre-harvest interval (versus Orthene’s seven-day pre-harvest interval) make it a better choice in fields that are slated to be harvested.  The Deerfield Enviroweather station is predicting the flight of this pest will wrap up at the end of the week. Some bacterial diseases are also present.

Potatoes are showing disease symptoms. Late blight has popped up in a couple of states and in Ontario in the last week, but none has been reported in Michigan recently. I have seen botrytis, early blight and alternaria in local fields. As potato canopies become dense, MSU Extension advises keeping an eye out for the disease, especially in areas where spray coverage may be poor (i.e., next to power lines or other objects in the field).

Processing tomato harvest will begin soon. I’ve seen some fields with high incidence of foliar diseases and, with increased incidence of late blight in Ontario, it is critical to keep up with routine fungicide application to protect from late blight and more common foliar diseases.

Staked tomatoes are being harvested on smaller farms, and larger scale harvest will begin soon. Be aware there has been an uptick in late blight in Ontario, so keep an eye out for this disease in areas where the leaf canopy is dense and spray coverage may be limited. I continue to see incidence of various bacterial diseases; Kocide 3000 and other copper products will help keep these diseases in check.

Harvest continues in sweet corn, with good quality reported. Corn earworm population remains low; I captured 16 moths in a six-day interval in Lenawee and Monroe counties this week. Western bean cutworm is also still flying across the region according to my trap catches. European corn borer’s second generation will likely conclude their flight by week’s end, according to the Deerfield Enviroweather station.

Squash bug nymphs are out and vine crop growers should check their field for nymphs and treat accordingly. This is a pest I see a lot of damage from later in August, when squash bugs are adults and hard to treat, so scouting and treatment now can prevent them from becoming a headache later.

Contact me any time at 517-264-5309 or for pest and disease sampling. I make updates regularly on Twitter at @SoutheastMIVeg.


Small operation farmers are welcome to attend the Small Farm Pest Management: Informed Decisions and Sustainable Approaches Aug. 13 in Ann Arbor, Michigan. This program will cover IPM approaches to managing a variety of insects in vegetable systems.

Growers with greenhouse and floriculture aspects to their farms may be interested in attending the 2017 Greenhouse Production, Plant Health and Marketing Conference Sept. 13 in Lansing, Michigan. A wide range of topics will be covered, with a focus on increasing plant quality, safety and sales. For more information, see “Register now for 2017 Greenhouse Production, Plant Health and Marketing Conference.”

The Midwest Mechanical Weed Control Field Day is Sept. 26 at the MSU Horticulture Farm. This meeting will feature mechanical weeders from the U.S. and Europe, as well as the experiences of farmers who use these tools. 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. 

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