West central Michigan vegetable regional report – July 1, 2015

Weather continues to be favorable for earlier than normal disease development. Keep an eye out for symptoms and initiate controls promptly.

Crops

Asparagus growers reported that planting of new fields was largely finished early last week. Once cladophylls expand, it is time to put on a cover spray of fungicides and begin a regular program. Applications can be timed with the TomCast disease model using in-field weather sensors. This allows more efficient targeting of application to periods when disease risk is high, and is less likely to miss a key period than a calendar spray schedule.

Carrot fields were already showing symptoms and signs of early infection with Alternaria leaf blight in west Michigan. Given weather conditions, initiation of fungicide programs makes sense.

Cucurbit downy mildew has been confirmed from crop fields in southeast Michigan, Ontario and Ohio to date. Keep an eye out for this disease in melons and cantaloupe. Bacterial diseases have also been detected in pumpkins. Copper applications may help protect emerging foliage and slow spread of this disease, but must be made on a weekly schedule to have a chance of providing significant benefit. A one-time application or making applications on 10- to 14-day schedules will likely be ineffective. Copper materials at best can slow spread of bacterial blights, but cannot eradicate existing problems.

Onion thrips control programs are beginning. In general, cool, nighttime temperatures that slow crop growth do not favor rapid movement of systemic insecticides like Movento throughout the leaf tissue. This could lead to poorer than expected performance. Always apply Movento with a penetrating surfactant.

Potato and tomato growers should be aware that conditions have been very conducive for late blight this year. Michigan State University Extension advises growers to make destruction of volunteer potatoes a priority wherever this is practical. Late blight has been detected in Wisconsin as of last week. Keep abreast of its spread nationally at USAblight and keep updated on Michigan conditions at Michigan Late Blight Risk Monitoring.

Sweet corn growers report seeing European corn borer activity in sweet corn. Look for window pane feeding or shotholes in the whorl prior to tasseling, which could be caused by this pest. During the mid- to late whorl stage, check 20 plants at five locations. Insecticide applications could be worthwhile if at least 15 percent show damage and have larvae present. Tolerance of your buyers to damage will ultimately determine what threshold is feasible for your farm. Once tassels emerge, any larvae in the whorl move down the plant and bore into stalks or ears, after which they cannot be controlled with insecticides. This means tassel emergence is a good time for insecticide applications targeting this pest.

Now is a good time to put out traps for western bean cutworms. A universal moth trap (available at suppliers such as Great Lakes IPM) can be used in combination with a pheromone lure and pest kill strip to monitor emergence. Once moths are detected, include this pest on your list when scouting 20 plants at five locations for other pests.

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