Armyworm active in high-risk corn fields
click image to zoomHigh risk field, corn emerging in burned down cereal rye.
A random inspection of a two-leaf cornfield, no-tilled into a burned down grassy cover crop in west central Indiana revealed some armyworm leaf feeding (see accompanying pictures). While carefully looking under crop/cover debris, armyworm larvae about a ½ inch long were found. Because armyworm primarily feed at night, careful searching in the vicinity of damaged plants in necessary to find these small larvae. Initially the damage appears negligible to the plant, but as the armyworm increase in size, so does their appetite. These small larvae are easy to treat/kill with insecticides, the larger ones are not as easily controlled!
High-risk crops are those where dense grassy vegetation (e.g., wheat, grass hay, grass cover crops) still exist have generally been burned-down for planting. Corn that has been no-tilled into a grass cover crop (ESPECIALLY ANNUAL RYE) should be inspected immediately for armyworm feeding. Hatched larvae will move from the dying grasses to emerging/emerged corn. There is nothing that resembles armyworm feeding at this time of year - armyworm feeding gives corn a ragged appearance, with feeding extending from the leaf margin toward the midrib. Depending on the armyworm population, most of the plant can be consumed. Severe damage is often compared to pencils sticking out of the ground.
click image to zoomSmall armyworm on damaged leaf. Don’t be complacent with Bt corn hybrids, as high armyworm infestations will still cause significant damage before the insecticidal proteins in Bt corn reduce their feeding. Seed-applied insecticides, even highrates, will NOT control armyworm. In short, there is no inplant or on-seed solution that will allow you to avoid scouting on this one. Remember, once armyworm larvae reach an inch or more in length, they eat a tremendous amount of foliage in a short period of time and become harder to kill. Large areas of seedling corn can be wiped out overnight under heavy infestations.
Sweet dreams and happy scouting!
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