Corn Earworm in Soybeans

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Corn Earworm

The insect goes by many common names such as corn earworm, soybean pod worm, cotton ball worm, due to many of the different crops that infest. This caterpillar’s life stage of the Corn earworm is the most serious impact pest on North Carolina soybeans. Soybean field infestation normally occurs in later July and into August following several build-up generations in other crops. Corn earworm overwinters as pupae in the soil in this pupae changes to a moth in April to May period, and from a fly to World stage corn or wild host and lays eggs for the first generation. 

Following several weeks of development first-generation moths emerge around the time when corn pollinates and is strongly attracted to fresh corn silks for laying the second generation of eggs. Corn ears provide protection and a good food source and a large increase in population is realized during the second generation. But after developing in the ears larvae eat through the husk and drop to the ground and pupate in the soil. Moths of the second generation emerge from cornfields from mid-July and into early to mid-August and seek soybean, cotton, peanut, sorghum, another crop and wild plant host. This is often concurrent with the time period when soybeans are attracted to corn earworm which is immediately prior to flowering until early pod set. 

There’s also a September moth flight in very late-planted soybeans that are sometimes suitable past the blooming early pod in stage for egg-laying and small caterpillar survival. Yearly fluctuations in the population may be great with how populations alter often occurring in seasons of early warm and dry weather. In some years a 4th generation may actually emerge. The July August moth flight is monitored throughout North Carolina each year and presented in Extension reports as corn earworm or bollworm moth trap catches. This information can be very helpful for determining when to scout soybeans.

So for some, the adult corn earworm is a robust light brownish tan, rust tan, or olive tan, to Olive fast-flying moth, with a 1/2 to 1 1/2 inch wingspan. This moth has greenish eyes when living, and a prominent dark spot on each forewing. The moths are active during the evening and dark hours but can be commonly seen in fields during the day. Eggs lay individually on soybean terminals, flowers, and leaves and eggs may be easily seen with a round white to the yellowish egg of about the size of a period. Caterpillars have a 5 pair of fleshy pro-legs and range in size from 1/16 of an inch which is newly hatched to 1 and 3/4 inch with late-stage. When these larvae fall from the soybean plant they usually curl into a tight circle. Color varies considerably but larvae are usually brown with a dark head and larger leaves made range from green yellowish to black with distinct cream-colored heads and bands running the length of the body. The head color on large larvae is usually orange.