No. 13/June 18, 1998
Have Stink Bugs Been in Your Corn?
Although this article is undoubtedly after the fact, I'm putting this information in the Bulletin for your reference and for anyone who might be scratching his or her head over a mysterious and as yet nondiagnosed problem. Entomologists in Kentucky have reported that stink bugs have caused some problems in some no-till corn fields in their state. Although I have not been able to verify that stink bugs were responsible for any of our problems in corn this spring, some of the reports I received sounded suspiciously like stink bug injury. Consequently, I'll offer some information about this infrequently occurring pest so that you can have it available as you visit fields in which the "problem" has not been identified. Although I am not suggesting that stink bugs are responsible for all of these unsolved mysteries, you should consider stink bugs as you engage your diagnostic skills.
Stink bug at the base of a corn plant.
Stink bug feeding on corn is sporadic. Potential for injury usually increases when winter weather is mild (how about that), wheat or rye is planted as a winter cover crop, and corn is planted without tillage. Stink bug nymphs and adults insert their piercing-sucking mouthparts into the stem and inject digestive enzymes and other compounds that can be phytotoxic or cause growth abnormalities. Symptoms include lines of tiny holes surrounded by yellow to necrotic tissue, twisted leaves or stalks; tillering, stunting, and wilting; and plant death. Yields of injured plants may be reduced by 50 percent or more. Injury usually is most severe on small plants. Injury is worst when planters are not adjusted properly and partially open seed slots allow the stink bugs access to the underground stem and growing point of small seedlings.
Corn seedling injured by stink bug.
Two species of stink bugs may injure corn seedlings. Onespotted and brown stink bugs are similar in appearance. As adults, both are shield shaped, brown, and measure 2/5- to 3/5-inch long and about 1/3-inch wide. Male onespotted stink bugs have a prominent dark spot near the tip of the underside of the abdomen. Both species overwinter as adults in vegetation in or near cultivated fields. The most favorable overwintering habitats are alfalfa, wheat, or rye cover crops, or fall-seeded small grains. Adults emerge in the spring and feed for 2 to 4 weeks before females begin laying eggs. After the early stages of corn growth, injury to corn usually is insignificant.
Section of corn stem showing necrotic tissue caused by stink bug injury.
If you find characteristic rows of holes (necrotic areas surrounded by yellow tissue), excessive tillering, and/or necrosis inside the stalk, stink bugs might have been responsible. However, you may not find the stink bugs now. Even if you did, economic thresholds have not been established. So put this information on your "diagnosis" shelf for future reference.
Kevin Steffey (firstname.lastname@example.org), Extension Entomology, (217)333-6652