Alfalfa Plant Bugs Showing Up in Abundance

Greenish brown bugs on a white sweep net cloth.
Figure 1. Alfalfa plant bug adults and nymphs captured with a sweep net. Courtesy: Adam Varenhorst

Written collaboratively by Patrick Wagner, Adam Varenhorst, Philip Rozeboom, and Bradley McManus.

Originally Submitted: June 12, 2023

There have been several insect pests showing up early in alfalfa this season, including the alfalfa plant bug. Although they typically don’t surpass the economic threshold, alfalfa plant bugs have appeared in very large numbers this past week while scouting alfalfa near Aurora and South Shore. Both adults and nymphs were present in the infested field (Figure 1).

Identification

Alfalfa plant bug nymphs are small, bright green in color, and do not have fully developed wings. Alfalfa plant bug adults are approximately three-eighths of an inch long and pale green to brown in color (Figure 2). They are nearly twice the size of Lygus bugs (Figure 3), although the two can sometimes be confused.

Alfalfa Plant Bug

Greenish brown bug on a white background.
Figure 2. Alfalfa plant bug adult (Adelphocoris lineolatus). Courtesy: Patrick Wagner

Lygus Bug

Brown bug on green leaf with green background.
Figure 3. Lygus bug adult (Lygus sp.). Courtesy: Adam Varenhorst

Alfalfa plant bugs feed on the leaves, buds, and flowers of alfalfa plants using piercing-sucking mouthparts. This feeding injury can lead to crumpled leaves, flowers aborting, stunting and reduced forage quality of the affected crop. Heavy infestations may cause the plants to show signs similar to drought stress.

Scouting and Management

To scout for alfalfa plant bugs, use a 15-inch diameter sweep net and conduct a series of pendulum sweeps throughout the field. Insecticide treatment may be warranted if populations reach approximately 20 to 30 bugs per 10 pendulum sweeps (this includes nymphs and adults). The fields sampled so far in eastern South Dakota have far exceeded this threshold.

For a list of insecticides currently labeled for plant bugs, refer to the latest South Dakota Pest Management Guides for Alfalfa and Oilseeds. Check under the products approved for use on lygus bugs.

Related Topics

Forage

Related Content

Multiple grasshoppers feeding on a corn ear.

Grasshopper Populations Continue to Cause Issues in South Dakota

Recent reports of crop loss along field edges indicate that grasshopper populations in some areas of South Dakota are well above threshold. Unfortunately, crops are often the target of these moving populations.

Green Canada thistle with whitened leaves at the top. Various green plants throughout.

White Thistle Disease: Biological management at work

White thistle disease can be seen among many Canada thistle plants throughout South Dakota this growing season. Plants infected with the disease exhibit significant reductions in both growth and seed head compared with non-infected plants.

True armyworm caterpillar on a corn leaf.

Reports of Pyrethroid Failures for True Armyworm Caterpillar Management

True armyworm caterpillars reached thresholds in oats and wheat in many areas of South Dakota recently. Management efforts to reduce populations had varying levels of success, with SDSU Extension receiving numerous reports of pyrethroid insecticide failures.