Crossing your fingers for minimal alfalfa winterkill right now? Alfalfa weevil larvae are another hayfield destructor to keep top of mind. Alfalfa weevil larvae are an early-season problem. Larvae emerge between February and April, depending on the geography. They feed on young alfalfa plants and can cause damage to first cutting and to the crown buds of second cutting regrowth.
Ahead of this year’s season, learn more about this damaging insect and how to avoid serious damage.
1) Leaf damage removes valuable nutrition.
Lime green larvae consume leaves, and that is no coincidence. Valuable nutrition is stored in leaves. According to Hay & Forage Grower, leaves contain two to four times more crude protein than stems.
2) Scouting is essential.
In upper Midwest states, May through June is the right time to begin watching for alfalfa weevil larvae. Scouting is critical, so work with your crop adviser to determine an appropriate method for monitoring your fields, likely multiple times. Early signs of larval feeding appear as tiny pinholes in leaves. Larvae can grow and feed quickly. It can take just three days from when you notice tiny pinholes in leaves to the skeletonization of a plant.
This video from the University of Wisconsin Extension provides some great guidance and strategies for scouting. They recommend considering a control measure when 40% of stems have some sort of defoliation (not to be confused with 40% defoliation).
3) Early cutting can limit destruction but will not eliminate it.
Many experts recommend early cutting of alfalfa as a control method for alfalfa weevil destruction. However, your crop adviser could suggest an economic threshold has been reached, and an insecticide application is warranted.
4) Look for an insecticide with lasting residual control.
Insecticide choices for alfalfa weevil larvae are increasingly limited. If you are looking for a fast-acting insecticide with a short preharvest interval, Steward® EC insecticide from FMC is one of the options available to alfalfa growers. Steward EC insecticide acts fast against alfalfa weevil larvae and provides 14 days of residual control with a short seven-day preharvest interval.
Read a more in-depth discussion about applying Steward EC insecticide in this agronomic update from FMC. Or hear from FMC Technical Service Manager Bruce Steward in this Tech Talk video.