Warm temperatures, after a long cool season, have brought out a swarm of insect pests of concern to Missouri farmers, says a University of Missouri entomologist.

Alfalfa weevils are getting the attention of hay producers, while black cutworms are of concern to corn farmers. Both are likely to require control measures this spring, said Wayne Bailey, MU Extension entomologist.

“With 80-degree temperatures, the bugs are going crazy,” Bailey said. “And they are looking for food.”

Farmers in Howell County, Mo., near the Arkansas border, are already spraying alfalfa fields to control the weevil, which can severely damage the first cutting of hay.

Warm weather has also given alfalfa a growth spurt, which may help its defense against the pest, Bailey said. “In the past, when we had warm, wet, early springs, we've had a buildup of a fungus that kills the weevil,” Bailey said. “This year, however, the cold weather has delayed the fungus control.” The weevils are growing ahead of their natural predators now.

If the alfalfa continues to grow rapidly, it may be ready to harvest early, eliminating the need to spray, Bailey said. Alfalfa is normally cut when 10 percent of the plants are in bloom. However, to reduce weevil damage, the crop can be cut a week early.

Bailey said warm nights have revealed “heavy flights” of black cutworm moths, a corn pest. The larvae of the moths cut off seedling corn plants.

Before the corn plants emerge to provide cutworm food, the black cutworm larvae are surviving on henbit and other broadleaf winter annuals. “It's been a good year for henbit,” Bailey said. That is the mass of purl flowers showing in farm fields now.

As farmers plant, particularly no-till into crop fields, the henbit will be sprayed. The cutworm larvae will move from henbit roots to corn roots.

An insecticide for cutworm control can be applied at planting time. However, MU pest management specialists recommend waiting until damage is seen in the field.


Duane Dailey is a news coordinator for MU Extension and ag information.