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April 10, 2007

Mild winter could mean more damage by alfalfa weevil

WEST LAFAYETTE, Ind. - The past several years of mild winters have led to increased populations of many insect species, including the alfalfa weevil, and growers can expect the weevil to be a nuisance again this year, said a Purdue University expert.

"Now is the time for growers to get out and scout their fields for the alfalfa weevil in the larval stage," said Christian Krupke, a field crops pest management specialist. "With early feedings, the tips of the alfalfa leaves will have a repeating pattern on them from being chewed on before the shoot opened up."

When taking samples from a field, it is best to walk in an M-shaped pattern and gather five stems from each touchpoint, totaling 25 stems. Each stem should be examined for evidence of feeding by the alfalfa weevil, maturity of the stem and stem length.

Most damage from the alfalfa weevil is done during the larval stage. A heavy infestation of larvae can consume enough foliage that an entire field may take on a grayish appearance.

Damage from the alfalfa weevil is most evident around the Ohio River, primarily because that is where most of Indiana's alfalfa is grown, Krupke said. Even with infestation, growers should be prudent and always scout before applying chemicals because buyers want a high-quality, chemical-free forage to feed their horses, he said.

The alfalfa weevil larva is a small, light green worm with a black head and three light stripes on its body.

Additional information on insect control in alfalfa is available online at http://www.entm.purdue.edu/fieldcropsipm/insects/alfalfaweevil.cfm.

Writer: Julie Douglas, (765) 496-1050, douglajk@purdue.edu

Source: Christian Krupke, (765) 494-4912, ckrupke@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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