By Scout Nelson
Farmers in South Dakota are advised to keep a close watch on alfalfa fields this season as alfalfa weevil larvae become active. Recent weather changes slightly slowed their activity, but it is expected to increase with warmer temperatures.
Degree day calculations help track weevil activity, but they do not always match what is seen in the field. That is why regular scouting is still the best way to detect weevils early and take action if needed.
Both adult weevils and larvae can damage alfalfa by feeding on the leaves and terminal buds. Larger infestations can lead to serious defoliation and even stunted plant growth. Routine scouting helps prevent such losses.
The easiest way to scout for weevils is by using a sweep net and a five-gallon bucket. First, sweep the plants to check if larvae are present. If found, farmers should measure their population size.
This is done by walking in a “Z” pattern through the field and sampling 30 plants. Gently pull each plant and hit it inside the bucket to collect any larvae. Count the larvae and measure plant height to determine if treatment is needed.
Management decisions should be based on thresholds that match the average number of larvae and plant height. Tables from local extension offices can help determine when to take action.
Farmers should refer to the latest pest guide for proper products and application rates. Some failures have been reported with pyrethroid insecticides, so unusual results should be shared with local experts for further testing.
Photo Credit: south-dakota-state-university
Categories: South Dakota, Crops, Education, Sustainable Agriculture