Southwest Michigan vegetable update – Aug. 7, 2019

Now is not the time to relax your disease and insect control.

Tomato plants showing bacterial spot
Tomato plants showing bacterial spot. Photo by Ron Goldy, MSU Extension.


The 50-degree Fahrenheit degree-day units are at 1,695 for 2019 compared to 1,925 for 2018 and 1,871 for the five-year average. We had variable rainfall across the area ranging from 0.25 to 1 inch. Temperatures ranged from 73 F – 88 F for highs and 56 F – 63 F for lows. Good weather has allowed harvest activities to continue with little problems. The rain on Tuesday, Aug. 6, stopped harvest for part of the day.

Crop reports

Eggplant harvest has begun.

Sweet corn producers have reported early plantings having variable maturity. Plants in the same planting vary from a harvestable ear to just silking. This was due to cold weather at planting time causing variable emergence and plant growth. Later plantings should have more uniform maturity.

Disease report

Vine crop producers need to be diligent in their downy and powdery mildew control. Downy mildew was first observed July 28 and we have had good weather for spread, especially on Aug. 6 (cool and wet). Current control recommendations, observance maps and spore counts can be found at MSU Downy Mildew News. Vine crop fields should also be removed soon after last harvest so they cannot serve as an inoculum source for remaining plantings. This is when powdery mildew also begins to show up. It is favored by heavy dews that often occur at this time of year. Control is important especially on fall squash and pumpkins since it can cause early defoliation leading to sunburn. It can also attack pumpkin handles, causing them to dry up and fall off leading to a handle-less fruit.

Bacterial diseases of pepper and especially tomato are becoming a problem (see photo). There is little that can be done once the disease is expressed in the field. Copper products no longer have an effect since the disease is resistant to them. The best control for tomatoes is with Agromycin in the greenhouse prior to the plants being removed, but it cannot be used in the field. Control for peppers starts with using tolerant varieties. However, no single variety is tolerant to all known races. Dry weather will help as will waiting to harvest when plants are dry.

Insect report

Insects present in the field are squash bugs, cucumber beetles, corn earworms/tomato fruit worms, European corn borers, mites and aphids. All are problems in themselves but many can also transmit virus and other diseases. Insects are best controlled when they are small and before they reach large numbers. Mites and aphids are often found in “hot spots,” so look for areas that have off-colored plants or are showing curling leaves.

The irregular maturity of sweet corn has caused some growers to wonder about corn earworm control. As long as you you will be harvesting from the field, you need to continue to protect the fresh silk. Do not give up just because a few plants are starting to show mature ears.

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