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Alfalfa Snout Beetle

Description
The alfalfa snout beetle, which has been damaging alfalfa since the early 1930s, has now spread to additional counties. The pest occurs nowhere else in the northwestern hemisphere except Oswego, Jefferson, Cayuga, Wayne, Lewis, St. Lawrence, Clinton, Essex, and Franklin Counties of New York and in Ontario, Canada, bordering the St. Lawrence River. Further spread is considered to be a serious threat to alfalfa growers because the alfalfa snout beetle makes growing alfalfa very difficult and expensive. The larvae feed on the alfalfa roots and kill the plant by severing the plant root system. Major plant injury and resultant death occurs during late August through November, usually after the final harvest of the season. With the major plant damage and plant death occurring so late in the season, many producers fail to notice the loss of alfalfa stand until spring and often blame “winter kill” for the loss of stand rather than insect damage. Some growers have been forced to grow only grass hay because of the destructive damage by this insect to alfalfa and clover.

The adults are mottled gray and humpbacked, do not fly, are about 1/2 inch long, and are all females. Beetles are transported in gravel, hay, farm equipment, and water and disperse by walking. Circumstantial evidence also indicates the adults are transported with the movement of beehives. Suspected new infestations should be brought to the attention of the local Cornell Cooperative Extension educator and alfalfa fields with uncharacteristic amounts of winter kill should be investigated for the presence of this insect.

Severe feeding damage
Undamaged root

Management
The use of an insecticide for the control of this insect has not been shown to be effective and is not recommended. Populations can be reduced and maintained with the stringent use of a three-year alfalfa rotation (seeding year + two production years). The use of biological control nematodes in an ongoing Extension area-wide program is currently quite successful with producers learning to rear and apply their own biocontrol nematodes. Alfalfa snout beetle resistant alfalfa is also being developed and holds great promise but research strongly suggests that the insect population needs to be reduced with biocontrol nematodes before resistant alfalfa is introduced into the system. Otherwise the insect may be too numerous and overrun the resistance in the alfalfa.

In trials conducted by Julie Hansen, Don Viands, Jaime Crawford, Elson Shields, and Tony Testa, some varieties have shown increased resistance to the alfalfa snout beetle.

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