Problems with alfalfa weevils, coupled with the earlier dry conditions, have been really severe this year. Alfalfa weevils are a severe pest before the first cutting every year. However, their feeding damage, coupled with the dry conditions, has really impacted the alfalfa this year. Fortunately, most of the weevil population is pupating and/or has reached the adult stage (Figure 1).
Figure 1. Alfalfa weevil life cycle. Photos by Jeff Whitworth, K-State Research and Extension.
There is some concern about the number of adults remaining in the fields, but adults do not feed as voraciously as larvae and they will be exiting alfalfa fields at the 1st cutting. They cause some concern as they feed a little on stems, called “barking”, and a little windowpaning /pinholing in leaves (Figure 2), which causes very little yield loss. Also, Figure 3 shows the kind of damage alfalfa weevils can do if not treated. Figure 4 shows the difference between using 8 gallons of carrier (water)/acre vs. 15 gallons/acre. However, either scenario is better than using nothing at all.
Figure 2. Alfalfa weevil windowpaning/pinholing. Photo by Jeff Whitworth, K-State Research and Extension.
Figure 3. Treated vs. untreated research plots. Photo by Jeff Whitworth, K-State Research and Extension.
Figure 4. The same plot as shown in Figure 3 but the left side had 8 gal/acre carrier applied and the right side had 15 gal/acre carrier applied. Photo by Jeff Whitworth, K-State Research and Extension.
There are also some pea aphids in most alfalfa fields but also a relatively healthy population of lady beetles and other beneficials which should control the aphids.
More information on alfalfa insect management is available in this publication: https://bookstore.ksre.ksu.edu/pubs/MF809.pdf
Jeff Whitworth, Extension Entomology
Tags: alfalfa insects alfalfa weevils