UNL has been tracking an unusual insect pest the past couple of years in northeast Nebraska that may be a potential concern to farmers growing corn after rye or other grass cover crops. A number of producers and crop scouts have reported stunted corn plants at V1 to V2 with brown flagging in their fields due to the wheat stem maggot (WSM), a species of Chloropid fly. These are small flies that are typically about 1/8 inch long with black and yellow markings. The wheat stem maggot overwinters in the stem of its host plants as a larva and emerges in May to begin feeding.
Common stalk borer eggs have hatched throughout Nebraska and scouting should begin when 1300-1400 degree days have accumulated (Figure 1). This is when larvae start moving into corn and other crops. Stalk borer growth is based on accumulated degree days since January 1, using a base of 41°F.
Potato leafhoppers have been reported in alfalfa in southeastern and northeastern Nebraska. This is somewhat earlier than usual and growers should be alert to potential damage and protecting their alfalfa where numbers indicate treatment thresholds would be met.
Examination of an alfalfa field in northeast Nebraska this week revealed some alfalfa weevil larvae (under threshold at just over one larvae/sweep) and a surprisingly high population of pea aphids. This was somewhat unexpected due to the recent winds and rain which often dislodge aphids from plant stems, resulting in reduced pea aphid numbers. See story for biocontrol information and aphid scouting and treatment recommendations.
Guide to identifying and managing alfalfa and clover leaf weevils in alfalfa. While research in northeast Nebraska has shown that clover leaf weevil larva feeding does not cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting. This is why it's important to correctly identify the type of weevil feeding causing damage.
As corn begins to emerge, be alert to the potential for damage from early season insects such as cutworms, wireworms, or white grubs. High risk factors and identification and treatment guides for these major early season insects are included.