Southwest Michigan vegetable update – June 20, 2018

This is not the year to stretch spray intervals.


High temperatures ranged from 75 to 92 degrees Fahrenheit and lows from 52 to 72 F. There was 0.75 to 1.25 inches of rain across the area. The 50 F degree-day units are at 870 for 2018 compared to 968 for 2017 and 851 for the five-year average.

Crop reports

Harvest has begun from direct-seeded zucchini and yellow squash. Harvest has also begun for low tunnel-grown cucumbers.

Low tunnels do not have the desired effect this year. Their biggest advantage is during sunny, cool weather, and we have experienced a lot of cloudy, cool weather. The hot temperatures over Memorial Day weekend also proved to be a problem in tunneled plantings by aborting flowers in some fields, even though the tunnel was open.

No significant insect or diseases have been reported. However, weather conditions have been ideal for disease spread and development, which could easily show up later in the season. We have had several mornings and days of high humidity and periods of significant leaf wetness. We have also experienced several hard, driving rains, which move diseases from soil to plant and then within the plant—even in a raised bed, plastic mulch system.

We have also experienced cloudy, windy, cool conditions, which are ideal for spread of cucurbit downy mildew and other wind-borne diseases. Be sure your plantings are adequately protected and do not try to get extra days out of your spray program. Stretching spray intervals is not wise under these conditions—it only works with dry, sunny weather.

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