West central Michigan vegetable regional report – August 12, 2015

Warm weather has helped speed crop progress.

Japanese beetle damage. All photos by Ben Werling, MSU Extension

Japanese beetle damage. All photos by Ben Werling, MSU Extension

Crops

Asparagus disease management is the current focus in the growing region. Fern was being defoliated by Japanese beetle again this week at an Oceana County location. Some growers report seeing minor rust in locations that have had this disease in the past.

Carrot growers continue applying irrigation water this week in west Michigan. Aster yellows symptoms were present in fields I visited, but some growers report it is not widespread.

Cucurbit downy mildew was detected on butternut squash last week in west Michigan. This is unusual, as the mating type we typically have in Michigan mostly affects melons and cucumbers, but not squash and pumpkins. Growers report that powdery mildew has been present earlier and has been harder to control this year at some Ottawa County locations. Quintec and Torino are two good powdery mildew products. Both have fairly long residual activity and can be applied roughly every two weeks. Note that there is no material that has significant “back action” that will take care of existing powdery mildew colonies.

cucurbit downy mildew on leaf 
A butternut leaf from a west Michigan field diagnosed with cucurbit downy mildew.

Squash bug eggs and nymphs were present in one Ottawa County winter squash field I visited this week. Eggs of this pest are found on the underside of leaves, bronze colored and lie at the “V” formed by the junction of two veins. They take roughly seven to 10 days to hatch. Hatching nymphs are the easiest to control at this stage, and take four to six weeks to reach adulthood. If you find an average of one or more egg masses per plant before or after flowering, treatment could be beneficial. Damaged leaves can turn brown and die.

squash bug nymphs 
Squash bug nymphs hatching from an egg mass. This pest is easiest to control when nymphs are young.

Potato and tomato growers can apply chlorothalonil-based products on a weekly schedule before late blight is detected. The late blight forecaster suggests weather could create a high risk of spread for three to four out of the next five days at west central and southwest Michigan through Aug. 16.

The insect forecaster for sweet corn predicts a very low chance of a corn earworm flight through next weekend. So far growers I spoke to noted minimal damage due to caterpillar pests of sweet corn.

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