By Sebe Brown
Extension Entomologist, LSU AgCenter
I have had some reports of armyworms and leaffooted bugs in commercial wheat fields. True armyworms are primarily an early season (spring) pest with a strong preference for grass crops. Usually greenish in color with orange strips running down the lateral edges of the body, true armyworms typically feed at night and during overcast days. During the day, true armyworms can be found under debris and thatch on the soil surface. In Louisiana infestations normally occur in April, but with the unseasonably warm weather, early infestations from a multitude of pests can be expected. Scout for this pest during the early morning, late evening or look for larvae on or under the soil surface. Larvae feed on the foliage of wheat plants from the base and gradually work their way up towards the flag leaf. Once the wheat has reached milk stage, the plant can tolerate greater levels of defoliation and see little to no yield loss. However, if armyworms begin to feed on or clip the wheat heads substantial yield losses can occur. Thresholds for Louisiana are 5 or more larvae per square foot with foliage loss occurring. True armyworms can be controlled with pyrethroids. If an application for armyworms is justified, use enough carrier to adequately penetrate the wheat canopy. Applications made during the late morning or afternoon may miss some armyworms in thatch or near the soil surface when direct sunlight and warm temperatures are abundant.
Leaffooted bugs are similar to stink bugs with regards to their piercing sucking mouth parts and foul odor excreted when they are disturbed. These insects are characterized by flattened leaf like expansions arising from the hind legs and a white strip running across the central part of the back. Leaffooted bugs are very flighty and can easily migrate in and out of wheat fields from adjacent weed hosts such as thistle. Flights of this pest can come from adjacent fields where burndown applications have been recently applied removing their primary host. Louisiana currently does not have a threshold for these pests and control can be quite difficult with pyrethroids. This insect is a minor pest of wheat. However, if your wheat is lodged with them and they have not migrated out of your field within a few days or been blown out by the torrential down pours this spring, a pyrethroid application can be made. If an application is deemed necessary, a high label rate of a strong pyrethroid should be used.
Aphids seem to be less of a problem this season than in previous years. The threshold for green bugs in wheat is 300-800 aphids per linear foot in wheat 6-16 inches in height. Pyrethroid applications made for other pests such as true armyworms can effectively suppress populations of green bugs. Many of the fields I have scouted have high numbers of natural enemies. These beneficial insects provide a free service in reducing aphid populations; however, aphids have the ability to outnumber their natural enemies in a short time frame.
With fungicide applications going out, tank mixing a pyrethroid in while covering ground is an option if insect pests have begun to be a problem. However, a jar test to assess fungicide/insecticide compatibility may be necessary prior to application.
For more information concerning insect pest management, contact your local LSU AgCenter parish agent, LSU AgCenter specialist, or your agricultural consultant.