Utah State University Extension
The alfalfa weevil is a major pest throughout Utah. It is a beetle with one generation per year. Eggs hatch in the spring, and the grub-like immature weevils (larvae) feed by chewing on the alfalfa foliage. In high numbers, alfalfa weevils can cause severe damage to Utah alfalfa. In any given year, however, the weevils are few enough in number in many fields to cause only minor damage. Monitor larval populations in early spring using sweep net or stem count methods. Insecticide resistance can be reduced by spraying only when needed, properly timing sprays, and rotating between modes of action.
Rim, Kaitlin; Clarine, Joseph; Price, Steven; and Ramirez, Ricardo, "Alfalfa Weevil in Utah" (2020). All Current Publications. Paper 843.