Alfalfa Weevil

Crop Impact of Alfalfa Weevil

The feeding behavior of alfalfa weevils can result in defoliation, where they consume the leaf tissue, leaving behind a characteristic "skeletonizing" effect. This can weaken the plants and reduce their ability to photosynthesize, ultimately affecting their overall health and productivity.

Severe infestations of alfalfa weevils can result in stunted growth, reduced biomass production, and even plant death in extreme cases. Additionally, the feeding damage can make the plants more susceptible to other pests and diseases, further compromising their health.

(Image Credit: Chris O'Hare, FBN)

How to Identify Alfalfa Weevils

Identifying alfalfa weevils at different stages of their lifecycle is crucial for effective management and control. Here's how farmers can identify alfalfa weevils from eggs to adult:

1. Eggs

Appearance: Alfalfa weevil eggs are very small, oval, and slightly yellowish. They are typically laid in clusters and are inserted into the plant tissue, making them difficult to see without magnification.
Location: Eggs are usually laid in the stems and crowns of alfalfa plants.
Timing: Egg laying begins in early spring as temperatures start to rise.

2. Larvae

Appearance: Newly hatched larvae are small, about 1/16 inch long, and light green with a white stripe down the back. As they grow, they can reach up to 3/8 inch in length. The head is dark brown to black.
Behavior: Larvae feed on alfalfa leaves, starting from the tips and moving downward, creating a distinctive "skeletonizing" effect on the leaves.
Timing: Larvae are most commonly observed from late winter through early summer, depending on the climate.

3. Pupae

Appearance: The pupal stage is a transitional phase where the larva transforms into an adult. Pupae are found in cocoon-like structures in the soil or leaf litter near the base of the plant.
Timing: Pupation occurs after the larvae have completed their feeding, typically in late spring to early summer.

4. Adults

Appearance: Adult alfalfa weevils are about 1/4 inch long, brownish-gray with a darker stripe down the middle of the back, and have a distinctive snout. Their body is covered with fine hairs.
Behavior: Adults can cause damage by feeding on alfalfa leaves, but they are more likely to feed on the flowers and pods. After feeding and mating, females lay eggs for the next generation.
Timing: Adults are most active in late spring and early summer. After the summer heat, they often seek shelter and become less active, re-emerging in the fall to feed before overwintering.

(Image Credit: Chris O'Hare, FBN)

Timing of Alfalfa Weevil Impact

Alfalfa weevils typically impact crops during the spring and early summer months. The severity of the impact can vary depending on the region and local climate conditions.

Geographic Impact of Alfalfa Weevils

In general, regions with milder winters and earlier spring warming tend to experience earlier and more significant alfalfa weevil infestations. These regions include:

Southern United States: States such as Texas, Oklahoma, New Mexico, and Arizona often experience early infestations due to their warmer climates.
Southwestern United States: States like California, Nevada, and Utah can also be affected by alfalfa weevils, particularly in the southern and central parts of these states.
Midwestern United States: States in the Midwest, including Kansas, Nebraska, and Missouri, can experience alfalfa weevil infestations, although the severity may vary depending on the specific location.
Eastern United States: States in the eastern part of the country, such as Kentucky, Tennessee, and Virginia, can also be impacted by alfalfa weevils, especially in areas with suitable climate conditions.

(Image Credit: Frank Peairs, Colorado State University, Bugwood.org)

How to Manage Alfalfa Weevils

Farmers should regularly scout their fields, especially from late winter through early summer, to detect and manage alfalfa weevil populations effectively. Look for signs of feeding damage and the presence of larvae on the leaves. Insecticide applications may be necessary when infestations are heavy and economic thresholds are reached. It's important to follow integrated pest management (IPM) practices, including the use of economic thresholds, to decide when control measures are warranted.

It's essential to monitor local weather conditions and adjust your scouting and management practices accordingly, as the timing of alfalfa weevil life stages can vary with local climate conditions.

To manage alfalfa weevils, farmers can consider using insecticides. Two relevant products include Willowood Lambda-Cy 1EC, which contains Lambda-Cyhalothrin, and GCS Bifenthrin LFC, which contains Bifenthrin. Both of these products, based on similarity with labeled products, may be labeled for use on alfalfa weevil.

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