Southwest Michigan vegetable update – Aug. 15, 2018

Time to increase protection against corn earworm/tomato fruitworm.

Corn earworm larva
Corn earworm larva. Photo by Ron Goldy, MSU Extension.


High temperatures ranged from 77 to 86 degrees Fahrenheit and lows from 61 to 64 F. There was only about 0.10 of an inch of rain across the area. We are getting quite dry, so rain would be welcomed for non-irrigated crops. The 50 F degree-day units are at 2,101 for 2018 compared to 2,018 for 2017 and 1,999 for the five-year average. We are not too far off from a normal year temperature-wise.

Crop reports

This is the time of year sweet corn and tomato growers need to increase protection against corn earworm/tomato fruitworm (they are the same insect). Field corn silks are drying down, which greatly reduces egglaying sites. Females will then seek fresh silks and other plants, with late sweet corn and tomato fruit being particularly attractive. Those I am finding this morning, Aug. 15, in my sweet corn are about 0.25 to 0.5 inch long (see photo).

Moth catches have increased across the whole state, meaning all sweet corn and tomato producers need to be aware. The females lay eggs at night, usually only a few per ear or fruit. Generally, there will only be one larva per ear or fruit since the one that hatches first eats the others. Larvae vary in color from green to brown, and when full-grown approach 2 inches long.

Corn earworm does not overwinter in our area and moves north as the season progresses. This yearly migration can change which products will control them—what worked last year may not work this year. Successful control often depends on what products previous generations were exposed to as they migrated north, and how well southern growers rotated control products. One of your best sources of information is to contact your seed supplier to see what they have heard. They sell over a wide area and will often keep in contact with their southern customers, so they often know what products have or have not been working.

For control on corn, apply control products every three days while the silks are fresh. The reason for the tightened interval during this time is because silks elongate over several days, and the control product will only be on that portion exposed during application. New silk area will emerge that was not exposed, providing safe sites for the female to lay eggs. Products need to be on the silk so when eggs hatch, larvae encounter the product before entering the ear tip. Once in the ear tip, they are safe from just about anything. This tightened interval is not as important for tomato fruit since fruit do not expand that quickly.

For products that will potentially control this insect, refer to the “Midwest Vegetable Production Guide for Commercial Growers 2018.”

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