West central Michigan vegetable regional report – May 25, 2016

Warm, dry weather has favored field work in the last week. Pest activity could pick up in coming weeks.

An onion plant with its flag leaf, one extended true leaf and a second true leaf emerging. This is the stage at which Goaltender can be applied based on the label. Photo: Ben Werling, MSU Extension.

An onion plant with its flag leaf, one extended true leaf and a second true leaf emerging. This is the stage at which Goaltender can be applied based on the label. Photo: Ben Werling, MSU Extension.

Asparagus harvest ramped up this week with warmer days and nights in west central Michigan. Common asparagus beetle activity has been ongoing, but egglaying has been spotty.

Bean planting is starting or expected to start this week on small and large farms in west Michigan.

Carrot and celery scouts should start to sweep for aster leafhoppers. To date, consultants report no captures in west Michigan carrots. However, leafhoppers were detected in Allegan County celery this week and yesterday, May 24, I did find leafhoppers at very low numbers in one Oceana County carrot field. Infectivity was 5.9 percent for the Allegan County sample, leading to a threshold of nine leafhoppers per 100 sweeps for carrots and six leafhoppers per 100 sweeps for celery.

Cole crop growers should be aware that degree-day models predicting peak egglaying by cabbage maggot may have recently reached peak levels, based on weather data from the Standale/Walker, Sparta and Hudsonville Enviro-weather stations. To the north, it is expected to start over the next week in Hart and Fremont. Flea beetles continue to be an early spring challenge for small-scale, diversified farms. According to the Cornell Organic Production and IPM Guide, Pyganic was most consistently effective in university trials at providing some level of chemical control. Row covers are an effective non-chemical control for protecting young plants.

Cucurbit planting including winter squash was expected to start at some Oceana County locations in the next week. Organic growers have asked me about causes of stand loss in cucurbits. One potential cause can be seedcorn maggot, which conventional growers typically use seed treatments to protect against. Currently, degree-day models predict we are between peaks of seedcorn maggot egglaying in Hart, Hudsonville, Fremont and Standale/Walker, Michigan. Peak egglaying by flies emerging from overwintered pupae likely occurred at the end of April. Past research estimated that eggs laid by these spring flies should pass through the damaging larval stage to the non-damaging pupal stage after an additional 376 degree-days base 39 degrees Fahrenheit, which has or will happen soon at most of these stations.

According to Enviro-weather’s seedcorn maggot model, egglaying by the next generation of flies (the offspring of the spring ones) is starting or should start soon, but is not expected to reach peak intensity in the next six days. Once soil temperatures are consistently reaching 70 F over multiple days at 4 inches, risk of this pest should be reduced. Waiting two and a half to three weeks after incorporating live cover crops will also reduce risk, as females prefer laying eggs into freshly decomposing vegetation and manure.

Predicted dates of peak egglaying by seedcorn maggot, degree-days (DD) since the predicted peak, DD until the next expected peak and forecast accumulation based on Enviro-weather data from select stations and a DD model for this pest.

Weather station

Predicted date of peak egglaying by overwintered flies

DD base 39 F since predicted peak egglaying

DD base 39 F to next peak

DD base 39 F forecast for 5/25-5/30

Hart

4/27

342

551

174

Hudsonville

4/20

508

398

199

Fremont

4/25

388

509

190

Standale/Walker

4/20

322

417

206

Onions were in the one to two leaf stage in Ottawa County this week. Goaltender can be applied at the one true leaf stage to provide post-emergence control of select weeds with four or less leaves and pre-emergence activity. Onions are to have one true leaf plus a second emerging. Most barley covers were dead or dying.

For potatoes and tomatoes, growers reported volunteer potatoes were emerging in Ottawa and Kent counties this week. Potatoes developing from infected tubers are the single most important source of new inoculum that contributes to epidemics when weather is right. Killing overwintered and volunteer potatoes will reduce risk you have an early outbreak that destroys your crop before harvest. Volunteer potatoes can be killed with roundup or tillage.

Sweet corn growers may want to be on the lookout for black cutworm damage in the coming weeks. According to Insect Forecast, weather conditions will produce a moderate risk of a flight for southwest Michigan today, May 25. Young sweet corn planted into weedy fields will be at most risk. Given winter annual weed survival was high in some areas this spring, conditions could be good for moths to lay eggs. Hatching caterpillars can then move to vegetables once weeds die. Target fields you know had high spring weed pressure for scouting. To date, traps in Montcalm County have not captured high numbers, but a flight was detected to the south in Lansing, Michigan.

True armyworms have also been captured this spring to our south. Michigan State University Extension advises growers to watch fields that follow a heavy rye cover with sweet corn, as females can lay eggs on the rye. Hatching caterpillars can then move to your sweet corn once the rye is worked in and sweet corn emerges. Both of these pests can be very spotty, but very damaging in the few fields where they do occur. They are easy to control with, for example, permethrin if detected before significant damage is done. If you are interested in using pheromone traps to monitor for these pests, contact me at .(JavaScript must be enabled to view this email address) or 231-873-2129.

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