Stink bugs in corn
The V4 to V5 stage in corn is when stink bug damage is apparent.
Stink bugs feed by injecting salivary enzymes into plants and sucking up plant juices. In young corn, this creates a characteristic pattern of circular holes with yellow margins that are very apparent as the whorl unrolls. In severe cases, plants may be twisted and deformed or the growing point may even die. The pictures below are of suspected brown stink bug damaged plants in an MSU weed control study. Only plots that were weedy then sprayed had injury; stink bugs likely moved off the dying weeds onto the corn.
Stink bugs in corn are difficult to manage by scouting and using a threshold since the damage appears several weeks after feeding. However, early planting and good weed control prior to planting are two ways to reduce stink bug injury.
Note: The damage in the MSU study was not caused by brown marmorated stink bug. We have plenty of other stink bug species in Michigan. It will likely be two to three years before significant numbers of the marmorated species appear in field crops in the state.
Probable stink bug damage
Dr. DiFonzo's work is funded in part by MSU's AgBioResearch.