Southwest Michigan vegetable update – July 24, 2019

Hot weather brings unwanted consequences.

Zucchini fruit with spray burn
Zucchini fruit with spray burn due to application under high temperature and humidity. Note the copper residue in the burned areas. Photo courtesy of Beth Hubbard.


The 50-degree Fahrenheit degree-day units are at 1,400 for 2019 compared to 1,633 for 2018 and 1,574 for the five-year average. We had around an inch of rain across the area for the week. Temperatures ranged from 71 to 93 F for highs and 53 to 77 F for lows.

High temperatures, especially at night, from last week could result in flower drop on peppers and tomatoes. Some growers also experienced spray burn on some crops due to the high temperature and humidity, especially if copper was included (see photo). Copper products should be applied under quickly drying conditions no matter the temperature since they can damage plant tissue if they dry slowly.

Pollination problems may also show up. Under high temperatures, flowers open and close quickly and bees often stay in the hive to help keep it cool. Therefore, cucurbit flowers may not have been visited as many times as needed for good fruit set. Expect higher numbers of poorly shaped fruit (crooked, fat at one end and skinny at the other, etc.) for a couple harvests.

Crop reports

Sweet corn is being harvested. Some growers have noted early plantings have some mature ears while other plants in the same planting have ears that are seven to 10 days away. This is indicative of delayed plant emergence and growth. Growers can also expect harvest timing of the first two or three plantings to be off, either with gaps or gluts.

I have not heard any reports or seen any cucurbit downy mildew in the area. A return to cooler temperatures will increase spore movement, especially if the weather also turns cloudy and wet. This is the time of season for squash vine borer and early activity of squash bug. Growers of squash and pumpkins should be applying protective products for squash vine borer at this time and scouting fields for squash bug activity. To protect pollinators, do your best to apply your products when the flowers are not open. On most days, cucurbit flowers open early morning and are closed by noon. Time sprays for outside this window.

Tomato harvest has begun. Producers have noted that fresh market tomato plants set to the field in mid- to late May have a bottom set of fruit and are missing the second set, but have a third and fourth set. This will cause a lot of weight to be in the upper half of staked tomato plants. This could make them prone to falling over later in the season, especially if high winds are experienced.

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