Southwest Michigan vegetable update – July 25, 2018
Thanks for the rain!
High temperatures ranged from 75 to 87 degrees Fahrenheit and lows from 54 to 67 F. There was 1.2 to 2.5 inches of much-needed rain across the area. It came slowly and with cool, cloudy conditions. It soaked in well and non-irrigated crops benefitted greatly. However, I am sure we will see an increase in disease incidence over the next week or so. The 50 F degree-day units are at 1,647 for 2018 compared to 1,621 for 2017 and 1,579 for the five-year average.
Bell pepper harvest has begun. Pay particular attention to aphid populations this time of year. It is easier to control small numbers than it is when they get out of hand. Under the right conditions, aphid populations increase quickly with females giving birth to 40 offspring a day and those offspring can start giving birth in seven days. The type of weather we will have over the next week will be ideal for aphids—warm but not hot and lower chances of rain. Aphids rarely outright kill a plant, but they are main vectors for virus diseases. The biggest problem comes from the honeydew they excrete while feeding. Honeydew makes plants and fruit sticky and provides food for sooty mold to grow.
Be alert for mite infestations in tomatoes and watermelon. Mites do best in hot, dry weather like we had over the previous three weeks. Rain over the weekend will provide a temporary setback, but a return to drier conditions will start them up again. Early infestations are often spotty in the field, so cover a wide area when you scout.
Cucurbit downy mildew is now present in the area, so it is time to use stronger control products. Morning dew conditions have also been good for powdery mildew to get started. Powdery mildew is of special concern to pumpkin growers; not only will it defoliate the plants exposing fruit to sunburn, but it can also get on the handles, giving a handle-less pumpkin at harvest time. Squash bugs are also in the near future. In large enough numbers, squash bugs will damage fruit and they vector diseases.
This is the time of year rust, aphids and earworms become a problem on sweet corn. Be careful spraying since bees forage heavily on corn pollen. Any cornfield in bloom needs spraying when bees are less active—at night if possible.
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