Why’s My Alfalfa Field Turning White?

Aflafla field with light colored alfalfa mixed in with green alfalfa.
Figure 1. Alfalfa weevil damage to alfalfa field. Courtesy: Frank Peairs, Colorado State University, Bugwood.org.
Alfalfa plant that has numerous holes in the leaves.
Figure 2. Alfalfa that has been heavily defoliated by alfalfa weevil larvae. Courtesy: Whitney Cranshaw, Colorado State University, Bugwood.org.

Originally Submitted: June 3, 2021

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 threholds 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.

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.