Southeast Michigan vegetable update — July 19, 2017

High dew points and warm, overnight temperatures encourage foliar disease development. Check pre-tassel corn for western bean cutworm, and powdery mildew and downy mildew are appearing in vine crops.

Squash bug eggs are copper-colored and laid in easily noticed masses. Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo,
Squash bug eggs are copper-colored and laid in easily noticed masses. Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo,


Weather is warm and will likely continue to be so. There is a chance of rain as we move towards the weekend, but models suggest the end of the month and the beginning of August will be drier than normal.

High dew points and warm, overnight temperatures are helping warm-season crops grow, but these conditions are ideal for foliar disease. Keep an eye out regardless of what is being grown.

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, are calculated using the Baskerville-Emin Method.

Rainfall and GDD totals as of July 19, 2017

Enviroweather station

GDD base 50

5-year GDD average base 50

Rainfall since April 1 (inches)


1,300 (+144)


9.47 (+0.46)


1,541 (+162)

Not available

11.32 (+0.21)


1,378 (+148)


12.41 (+0.2)


Carrots in other parts of the state are developing foliar diseases earlier than normal. Catching these diseases early is key, so scout fields looking for spots and blighted areas on foliage, especially new leaves. For a listing of available products, see the “Midwest Vegetable Production Guide.”

Cole crop harvest continues and planting for fall harvests has begun. In some parts of the state, thrips are becoming a problem in cabbage. In plants with waxy leaves, using some kind of surfactant such as a non-ionic surfactant will help the product stick to the plant’s hydrophobic leaves.

As fields are harvested, remember that residue destruction can aid in controlling diseases such as black rot and reduce future populations of pests like cabbage maggot. Planting cover crops can improve a variety of soil characteristics and keep soil in place over the winter, especially in winters like we had last year, with minimal snow cover and high winds. The Midwest Cover Crops Council decision tool can be useful in figuring out viable options for your farm.

Cucumber harvest is ongoing. Downy mildew has been confirmed in Lenawee and Monroe counties, as well as in counties in the Bay, which suggests that pathogen is well-established in the region and protective fungicides should be applied. MSU Extension plant pathologist Mary Hausbeck’s recommended downy mildew fungicides for 2017 are Orondis Opti, Ranman 4SC, Gavel 75DF, Zampro 4.4SC and Zing! SC. Orondis and Ranman have performed well in Michigan trials.

The Orondis label states that no more than one-third of sprays in total spray programs can be Orondis. Michigan has a 24c special needs label that states if you apply two or fewer total sprays, one or both can be Orondis. This change is useful for cucumbers nearing harvest.

Recent fungicide trials in Michigan and elsewhere have found that Presidio, Previcur Flex and Tanos have reduced effectiveness in controlling downy mildew. For suggested tank-mixes and more information on downy mildew, see “Downy mildew confirmed on cucumber in Michigan and Ohio” from MSU Extension.

If you suspect downy mildew is in your fields, please contact me at 517-264-5309 to arrange for sample pickup; even if the disease has already been confirmed in your county, the Hausbeck lab is studying the population of downy mildew in Michigan and sample submission can aid in better understanding the disease.

Some pepper plantings are nearing harvest. The second generation of European Corn Borer have begun emerging, traps in Lenawee, Monroe, and Washtenaw counties each caught 1 moth each in the last week.

Sweet corn harvest has begun. Corn earworm traps in Lenawee and Monroe counties are consistently capturing low numbers of moths, with the Lenawee Country trap capturing 1.2 moths per night and the Monroe County trap capturing an average of two moths per night. As more field corn begins silking, moths will also move into field corn.

With this low level of captures, treating every four to five days should provide sufficient earworm control. The resistance of some corn earworm populations to pyrethroids can increase the cost of treatment. Research in Ohio has suggested that when corn earworm populations are low (such as now), products like Warrior applied at the highest rate can control corn earworm. When trapping shows populations rising, switching to products like Coragen and Radiant will be needed for control.

While there are premixes of Coragen and pyrethroids available, only a small portion of the product is actually Coragen, so you may be better off buying Coragen separately and creating your own tank-mixes. Another consideration is confirming your sprayer is providing adequate coverage to silks before jumping to the conclusion that the corn earworm population in your area is resistant to pyrethroids.

Western bean cutworm populations are starting to peak, and peak flight is likely to occur over the next week. In the last week, 64 moths were caught in Lenawee County and 107 were caught in Monroe County. All corn (field, sweet, Bt) should be scouted for the eggs of this pest in the next week or two. Focus efforts on pre-tassel corn, which is preferred for egglaying.

Western bean cutworm eggs are laid in masses the size of a dime on the upper side of the leaf and are concentrated in the top third of the plant, which in my experience makes eggs easy to see when walking through fields. The larvae are typically controlled by a corn earworm spray program, but last year I heard many reports of damage that sounded like this pest (moldy ears with a hole bored through the husk, ears with multiple caterpillars), so scouting now is warranted.

Trapping in peppers suggest that European corn borer is out in low numbers.

Finally, as early sweet corn fields are harvested, consider planting a cover crop to improve soil characteristics and hold the soil over the winter. The Midwest Cover Crops Council decision tool takes into account your soil type as well as your goals for improving soil in suggesting cover crops.

I’m seeing an increase in various bacterial diseases in tomatoes.

Muskmelon and watermelon growers should refer to the above section for downy mildew recommendations. Recent fungicide trials in Michigan and elsewhere have found that Presidio, Previcur Flex and Tanos have reduced effectiveness in controlling downy mildew. For pictures of symptoms, see the Hausbeck lab’s “Downy Mildew Symptoms.”

Powdery mildew is starting to pop up in winter squash and pumpkins. As time goes on, the chance of downy mildew appearing in these crops increases. Squash bug eggs and nymphs are present in fields. This is a pest that is best dealt with in the nymph stage, so if you are finding egg masses in your field, consider treatment.

There are many products available for conventional growers, including Admire PRO, Mustang MAXX, Sevin XLR PLUS and Warrior II. For organic growers, Azera may be allowed depending on your organic certifier. For a full listing, see the “Midwest Vegetable Production Guide.”

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


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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