If you grow alfalfa, it’s time to begin scouting your fields for alfalfa weevils.
Ron Hammond, an
“Alfalfa weevil feeding is tied to temperatures. The need for scouting is especially true in southern counties where heat unit accumulation has reached the 300 heat units needed for egg hatch and beginning feeding,” said
To effectively scout alfalfa fields, entomologists recommend that growers collect a series of three 10-stem randomly selected samples from various locations in a field. Place the stems in a bucket and vigorously shake them, counting the number of alfalfa larvae that fall into the bucket. In addition, the height of the alfalfa should be recorded.
“Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa,” said
The adult alfalfa weevil is a small, brown, snout-nosed beetle with a dark stripe down its back. The alfalfa weevil larva is green with a black head and a white stripe down its back. The larvae develop through four stages, or instars. Larvae that are in their 3rd or 4th instar cause the most foliar injury. First cuttings of alfalfa are at the highest risk for defoliation damage.
“Fields that are severely defoliated are left with a brown or bronze appearance,” said
The alfalfa weevil is controlled naturally by parasitoids, beneficial species that prey on the weevil and help keep its populations in check. In cases of high populations, the alfalfa weevil can be controlled with insecticides.
For more information on the alfalfa weevil, how to scout for it and how to control it, consult