Pretty but Menacing: Little Yellow Butterflies in Alfalfa Fields

Alfalfa fields may appear more yellow and white than green in some areas with outbreaks of alfalfa caterpillar butterflies. Although these butterflies are pretty, in this case looks are deceiving. With high numbers of butterflies, it serves as a warning sign as they can be serious pests of alfalfa. The larvae consume entire leaves and can strip a plant. This causes significant reductions in yield and quality.

Recommendations for control:

• Start sweeping for alfalfa caterpillars during early summer and continue through early fall
• Take weekly sweep net samples to determine counts of these pests along with their parasitoid wasp natural enemies.
• In alfalfa, the caterpillars are often controlled adequately through timely cutting, naturally occurring diseases, and several parasitic wasps; thresholds for treatment are relatively high at 10 larvae per sweep.