West central Michigan vegetable regional report – July 13, 2016

Cucurbit downy mildew is in east Michigan, and more insects have been on the move.

Powdery mildew colonies on transplanted squash earlier this week. Look on leaves deep in the canopy for early infections. Photo: Ben Werling, MSU Extension.

Powdery mildew colonies on transplanted squash earlier this week. Look on leaves deep in the canopy for early infections. Photo: Ben Werling, MSU Extension.

Asparagus growers should be mindful that high dew points and overnight temperatures will be conducive to asparagus purple spot development. Japanese beetle activity was continuing last week in asparagus research plots and seemed to have increased. Carbaryl and permethrin are effective controls.

Cucurbit growers should be aware that downy mildew was detected in cucumbers in Bay and Saint Clair counties. Learn how to look for this pathogen in “Downy Mildew Symptoms on Cucumber.” Note, this pathogen is different from powdery mildew, and is most damaging to cucumbers and melons.

For powdery mildew, growers can check leaves inside the canopy for early detection. Powdery mildew fungicide programs can be made based on scouting and thresholds with careful scouting: Begin applications once one leaf in 45 has colonies. Remember the pathogen can colonize both sides of leaves. Powdery mildew was visible in one Ottawa County field of transplanted squash yesterday, July 12, has been reported from commercial yellow squash to our east, and we have received homeowner reports as well.

Quintec and Torino are effective products for powdery mildew prevention. Four applications of Quintec are allowed per year, only two may be made in a row before switching to a different mode of action. Two applications of Torino may be applied in a year. Remember, the powdery mildew pathogen has a history of resistance development, so rotating modes of action is important for this pathogen.

Squash vine borer was causing patchy damage in a commercial squash planting this year. Typically, this pest is only a minor nuisance to larger growers. Moths of this pests are showy and can be seen flying during the day above plants. Eggs are red, disc-shaped and laid singly on stems. For control, pesticides need to be on the plant before eggs hatch – once larvae enter plants, they are protected. There is one generation of this pest per year, but the flight is fairly long. Currently, Michigan State University Enviro-weather predicts this pest is flying and laying eggs. Symptoms include wilted runners. If you see these, look for an entrance hole with frass and a caterpillar inside.

Some growers have also been making frequent copper applications to cucurbits, and given the hot weather, it is important to be mindful of conditions creating phytotoxicity. These include acidic spray tank pH, applications during hot weather and accumulation of copper caused by low rainfall, followed by a high rain event that leads to a release of copper ions. Learn more at “How Copper Sprays Work and Avoiding Phytotoxicity” by Cornell University Cooperative Extension.

For sweet corn, growers report observing caterpillars either earlier in the tassel or on harvested ears in some west Michigan locations this week, with boring into ears observed at one location. It is time to be checking corn earworm traps and keeping an eye out for other caterpillar pests. Note, corn earworm does not bore into ears. However, European corn borer overwinters here and lays eggs in whorl stage corn. Caterpillars feed in the whorl and then move out of it at tassel emergence.

Unlike corn earworm, European corn borer caterpillars can bore into the sides and shanks of ears. Whorl stage corn can be scouted by looking for characteristic shot-hole damage in emerging leaves: examine 20 plants at five locations and treat if more than 15 show evidence of damage and larvae are still present. Later, pheromone traps can be used, however in recent years this pest has not been abundant due to the advent of Bt field corn. Local populations could still build in areas without high amounts of Bt corn. You can use Heliothis traps with the “Iowa” strain pheromone lure to monitor for this pest. Again, it has typically not been a problem in recent years, but it pays to be on the lookout, as it seems to be a buggier than normal year.

Western bean cutworm may be another pest to watch out for this year. MSU Extension advises that traps should be out now for this pest. Western bean cutworm can also bore into ears and, unlike the cannibalistic corn earworm, multiple caterpillars can coexist happily in ears.

Risk of late blight development for tomatoes and potatoes is high for three out of the five days, today through Sunday, based on the weather forecast at the Holland, Grand Rapids, Kalamazoo and Muskegon Enviro-weather stations. Weekly applications of chlorothalonil or mancozeb can help prevent problems with this disease and early blight.

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