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19
May
2014
Earworms and Stinkbugs in Young Corn
Author: Glenn Studebaker, Extension Entomologist

We are seeing a few corn earworms showing up in whorl stage non-Bt corn. Right now all we are seeing is a few scattered plants showing feeding damage. Upon inspection of the plant, a single corn earworm can be found down in the whorl. Corn can withstand and recover from this type of feeding with no yield loss unless there is a significant amount of defoliation. Treatment level is 3-6 caterpillars per plant, which rarely occurs with corn earworm because they are cannibalistic. Generally, if that many caterpillars are found in a whorl it is the fall armyworm. At this time we are not picking up any falls in corn. There is another caterpillar that can also be found in whorl stage corn at this time of year, the southwestern corn borer. This pest can be much more damaging than corn earworm, therefore the treatment threshold is much lower. It is pretty easy to tell the difference between the two by observing the feeding damage. Earworms will leave uneven, ragged defoliation patterns on the leaves (see first image below). Earworm DamageCorn borers, because they bore into the plant, will leave a line of small circular-shaped holes across the leaves that are apparent as the leaves unfold. Feeding by small larvae will often be in the form of window-paning on the leaves (see second image below). Southwestern Corn Borer Damage Treatment level for southwestern corn borer in whorl stage corn should be initiated when 25% of the plants are infested. Sprays should be applied with a higher volume of water directed into the whorls.
We are also getting some reports of stink bug damage in seedling corn. This damage is mostly near field borders. Damage appears as stunted plants often with smooth-edged irregular shaped holes with a yellow/white halo around the edge. Usually by the time we see the damage, the stink bugs have already moved on. Later, some of these plants may produce excessive tillars if the growing point was affected by feeding. Young corn should be checked for stink bugs at this time. The predominant species we usually see is the brown stink bug. Treatment level on seedling corn is when stink bugs are seen on 10% of the plants. Look for stink bugs near the base of the plant near the soil line. See MP144 Insecticide Recommendations for Arkansas for a list of recommended insecticides.


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