Corn Earworm Risk

Corn earworm (Figure 1) can be a serious pest of a number of crops, including sweet corn, tomatoes (a.k.a. tomato fruitworm), field corn, and soybeans (a.k.a. soybean podworm). In years following a mild winter, we can have high levels of corn earworm that are able to survive in our soils as immatures. The result can be high populations early in the year.  However, this past winter we did not have a mild winter due to the Polar Vortex. So, overwintering survival of corn earworm was very low, and early season risk should be very low.  Populations will rebound this summer when corn earworm moths migrate from Gulf States carried on weather systems coming up from the South.

Figure 1. Corn earworms are variable in color in the field. (Photo: Ric Bessin, UK)

Figure 1. Corn earworms are variable in color in the field. (Photo: Ric Bessin, UK)

Generally, when producers plant sweet corn early, they have a much lower risk of corn earworm attack, particularly when following a cold winter.  However, June-planted sweet corn is at a much higher risk of corn earworm attack.  The key period of attack is during silking and the silks are fresh. The fresh silks produce volatile chemicals that attract the female moths.  After the silks dry, plants are not as attractive for egg laying.

Determining Corn Earworm Risk

So how do we determine the risk of corn earworm egg laying and the need to insecticide sprays?  It is through pheromone trapping. We use pheromome traps (Figure 2) to capture corn earworm male moths, which give us an idea of population levels in the area. During silking, if we capture up to 10 moths per week, we would spray every 5 days until the silks dry. If we capture up to 350 moths per week we treat every 4 days, and over 350 moths we treat every 3 days.

Figure 2. A cone trap used to monitor corn earworm. (Photo: Ric Bessin, UK)

Figure 2. A cone trap used to monitor corn earworm. (Photo: Ric Bessin, UK)

Reducing Corn Earworm Risk

Producers also have several types of Bt sweet corn to help lower the risk of damage due to corn earworm. They are sold as Attribute sweet corn, Performance sweet corn, or Attribute II sweet corn.  Each of these has different types of Bt genes, providing varying levels of control of corn earworm and other pests.  Bt sweet corn does not eliminate the need for insecticide sprays always, but does reduce the risk.

Additional Information

For more information, consult the publication Corn Earworm Management In Sweet Corn (ENT-318) available online at http://www2.ca.uky.edu/entomology/entfacts/entfactpdf/ef318.pdf

 

By Ric Bessin, Extension Entomologist

 

Posted in Vegetables
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