Earworm populations are heavy in corn. What does this mean for cotton, soy? – AgFax

Feeding a cornfield. Photo: Justin Ballou, South Carolina

Populations of the corn ear (aka the heartworm, legume, tomato fruit worm) are much higher in corn than usual. Maize is a breeding ground for this pest, and a high corn population usually means a high population later in the season for crops such as cotton, sorghum, soybeans.

However, many other things can affect the survival of corn callus, as they must complete development on corn, pupate in the soil, appear, mate, and survive and thrive on these crops during July and August. So while high pressure in corn is no guarantee that the pressure will be strong in other crops, we just need to remember 2016.

The large population and high survival of Bt maize during 2016 turned into serious problems in cotton production. 2022 is the same. Read on to find out why and what to do.

Why do we see this?

With all the work done on the corn borer, we still don’t understand enough of their biology to answer that question. The corn galosh population is generally higher after cold winters and dry springs and summers.

Although the winter was cold, we certainly had dry weather in some areas of the state. I have also noticed that populations of corn cob worms tend to be heavier in corn that suffers from drought.

One (of many) reasons why we are seeing population growth is increased resistance to Bt. The corn borer is resistant to Bt toxins produced by all maize hybrids except the hybrids Agrisure Viptera, Leptera and Trecepta (if you find earworms in hybrids with these trade names, contact your local Extension representative).

Bt maize has a depressant effect on the population, actually reducing injuries in areas where more maize has been sown. However, resistance to Bt increases over time and we can expect that corn damage and population will also increase.

What do I do in corn?

Nothing. Galosh corn does not cause crop loss when planted in a timely manner (demonstrated in Alabama, North Carolina and South Carolina, as well as in the south).

One reason is that the ears of corn can compensate for the nutrition of the corn husk (usually limited to the tip – see photo at the top of the article) by filling up the heavier kernels at the bottom of the cob. This is one of the reasons why non-Bt-hybrid-shelters with good genetics yield so well when planted in a timely manner.

However, there is a limit to compensation. The plant can no longer compensate for about 50 damaged nuclei. We see situations where several larvae are in the ear or when the fall of an army worm is also present. It is more common in later planted corn.

Even in these situations, foliar insecticides will not affect the population and should not be used to control corn cob in field corn (many sweet corn growers spray every day for several weeks to try to eliminate corn corn).

What should I do to prepare cotton, sorghum and soy?

Pay close attention to the NCCE light trap network. It is run by county agents and manufacturers to help us know when to scout, and usually goes online every year in July. When the trap is picked up, it’s time to explore other crops in which the corn borer lays eggs. Later planted crops will be at greater risk. Earworm populations are heavy in corn. What does this mean for cotton, soy? – AgFax

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