West central Michigan vegetable regional report – June 15, 2016

Insect activity is picking up in West central Michigan.

For asparagus, some growers may continue harvest through next week in Oceana County, while other fields may shut down this week. Some growers report spear diameter has been decreasing. Processors were still seeking asparagus early this week.

For carrots, sweeps for leafhoppers can capture a number of insects in addition to aster leafhoppers. Aster leafhoppers are torpedo shaped, olive green on top and dark underneath. The most similar lookalike is potato leafhopper which, unlike aster leafhopper, is neon green.

For celery, scouts report finding winged aphids, but no colonies to date. Keep an eye out for aphids. Movento (a.i. spirotetramat) applied with a penetrating surfactant is an effective treatment.

For cole crops, note that Swede midge has not yet been detected in West Michigan. Detections to date have been from the eastern part of the lower peninsula. Learn more about this pest here.

For cucurbits, I have seen two examples of foliar diseases already developing in transplanted squash. Consider submitting a sample to the MSU diagnostic lab to determine its cause. There are multiple foliar diseases that produce similar symptoms, but require very different management approaches. In 2015, some winter squash growers struggled with angular leaf spot, which showed both foliar and fruit symptoms. This is a seedborne bacterial disease that infects cotyledons when they emerge from the seed. Rainsplash and overhead irrigation can then move the pathogen from leaves onto fruit. If you have confirmed this as a consistent problem on your farm, copper is your main preventive option, but it is most effective when applications begin when plants have their first true leaves. Weekly applications are necessary, as application at 14 day intervals will likely provide little benefit. Because it is seedborne, whether or not a problem develops will be a matter of chance. If you do start a copper intensive program, you can scout your plants later this month, and if no symptoms have developed, consider discontinuing the weekly, intensive copper program.

Brown spots and holes on a cucumber plant. Brown dots on spaghetti squash.

Left: A cucumber plant showing foliar symptoms of angular leaf spot. Photo: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org. Right: Spaghetti squash from 2015 showing fruit symptoms of infection with angular leaf spot. Photo: Ben Werling, MSU Extension.

Striped cucumber beetle activity is continuing. Note that plants become much more tolerant of feeding and bacterial wilt as they get older. This means plant protection (as provided by a seed treatment, at-plant drench or row covers) is most important early on. Later, plants can tolerate a fair number of beetles without economic loss. This means you can save time, money and conserve pollinators by applying broad-spectrum sprays based on thresholds. You can count beetles on multiple plants at five locations per field to get an idea of pressure and compare counts to the below thresholds, provided by Dr. Celeste Welty of Ohio State University Extension at the 2015 Great Lakes Fruit & Vegetable Expo.

Plant stages and corresponding spray thresholds

Plant stage


Cotyledon and 1 leaf

0.5 beetles/plant

2-4 true leaves

1 beetle/plant

>4 true leaves

3 beetles/plant

For onions, thrips numbers are higher than typically is normal this time of year. Now is a good time to apply Movento and an appropriate surfactant based on scouting data, especially given the forecast for warm upcoming weather.

For potatoes, Colorado potato beetle activity is continuing, with adults, eggs and small larvae active to our east in Montcalm County potatoes.

For sweet corn, it’s time to stock up on pheromone for the July-August time period. Two pests it is helpful to monitor for include corn earworm (Helicoverpa zea) and western bean cutworm (Striacosta albicosta). Pheromone is available from Great Lakes IPM. Traps for corn earworm can be placed out when your first planting silks. Traps for western bean cutworm can be placed out when tassels begin to form. For corn earworm, you can use either a Heliothis trap, available form Great Lakes IPM, or a wire Hartstack trap, available form Bob Poppe’s Service (Lexington, IL 61753, (309) 275-5477). Hartstack traps are more durable but more expensive. For Western bean cutworm, you can purchase a universal bucket trap from Great Lakes IPM in addition to insecticidal strips. You only need two lures per trap for Western bean cutworm (replace once in August after traps have been out for July), but will need to change corn earworm lures every two weeks.

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