By Adam Varenhorst, Extension Field Crop Entomologist

There have been a lot of reports of alfalfa fields in South Dakota with a white or light-brown canopy (Figure 1). This discoloration is the result of extensive alfalfa weevil larvae feeding.

It is likely that the larvae will continue to be active for the next couple of weeks. Although cutting the alfalfa is a viable management strategy to reduce the alfalfa weevil feeding, it is important to also scout the alfalfa stubble after cutting.

In the past, we have observed significant stunting of alfalfa when the alfalfa weevil larvae feed on the remaining stubble. The alfalfa weevil larvae cause the majority of the defoliation and will feed on the terminal buds. This feeding can stunt the alfalfa’s growth.

A close inspection of an infested field will reveal plants with holes with a white edge (Figure 2). Large populations of alfalfa weevils can result in significant defoliation and reduced yields.

For more information on alfalfa weevils, scouting, and thresholds please visit our earlier article that covers all of these topics. If insecticide management is necessary for a field be sure to review the pre-harvest interval to determine when the alfalfa can be cut.