Southwest Michigan vegetable update – July 29, 2020
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Weather
Temperatures for the week at the Southwest Michigan Research and Extension Center ranged from 80 to 94 degrees Fahrenheit for highs and 61 to 69 F for lows. The 50 F degree-day units are at 1,736 for 2020 compared to 1,529 for 2019 and 1,690 for the five-year average. There was only a trace of rainfall across the area for the week and non-irrigated fields are beginning to show drought stress.
Crop reports
Harvest is now taking place on all vegetable crop species.
Harvest is finished on most early cucumber, yellow squash and zucchini plantings. As soon as harvest is finished on these crops, plants need to be removed or killed. This can be done either by chopping or through a contact herbicide. Quick removal helps reduce disease pressure this year for other fields in the case of a wind borne disease like downy mildew, and long-term pressure for that field in the case of soil borne diseases that overwinter in our climate such as Phytophthora. A contact herbicide is preferred for cucumbers since the leaves will quickly dry down and minimize downy mildew spread. Good coverage is important for maximum leaf contact and plant death.
The hot, dry weather has allowed for buildup of certain insects, namely mites on tomatoes and watermelon, and aphids on peppers. Early control is important for both insects since under the right conditions populations can rapidly increase. Fields infested with mites often have visible hot spots where a pregnant female was blown by the wind and deposited to that spot and began to lay her eggs. These areas are often observable by standing on the high spot of the field or through drone observation.
Aphids in high enough numbers can economically damage crops through their feeding and subsequent development of sooty mold. However, they are also responsible for transmission of many virus diseases, and reducing total aphid numbers may help in reducing virus spread.
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