The first pest problem affecting alfalfa every year is usually the alfalfa weevil. This year is no exception (Figure 1). All larvae sampled throughout north central Kansas., have been in the 1st instar (up until April 3), which means they will probably be feeding for another 2-3 weeks at temperatures between 50-90 °F. Feeding by the tiny 1st instar larvae starts on the terminals/leaves, resulting in small pin-prick holes in growing foliage (Figure 2). If left unchecked, alfalfa weevils can defoliate plants prior to the 1st cutting. A common treatment threshold is 30-50% infestation level. For more information relative to alfalfa weevil management, please refer to the KSRE Alfalfa Insect Pest Management Guide, recently updated for 2023 - https://bookstore.ksre.ksu.edu/pubs/MF809.pdf.
Figure 1. 1st instar alfalfa weevil larva. Photo by Cody Wyckoff, K-State Research and Extension.
Figure 2: Alfalfa foliage showing damage by weevil larva. Photo by Cody Wyckoff, K-State Research and Extension.
Jeff Whitworth, Extension Entomology Specialist
jwhitwor@ksu.edu
Tags: insects alfalfa alfalfa weevils