Shake-Bucket Scouting of Alfalfa Weevil

"SHAKE-BUCKET" SCOUTING OF ALFALFA WEEVIL
Peak egg numbers for alfalfa weevil typically occur in January and February. Hatching of eggs and onset of larval feeding usually occurs in February and March. The recommended time to begin checking fields for larval infestations is after accumulation of 150 degree days (DD) for alfalfa weevil development from January 1 (usually about March 1). The "shake-bucket" method described in OSU Current Report #7177 is designed to use the following three types of information for the most accurate means available to make decisions regarding the need for spraying to control weevil larvae. The total DD accumulated from January 1 provides a measure of weather conditions for development of the alfalfa weevil, and can be obtained from the Oklahoma Mesonet System or can be calculated by use of temperature data available from local weather forecasts and instructions in CR #7177. The plant height of alfalfa is measured at the time of sampling to provide an estimate of the ability of the crop to withstand feeding damage. These two items are used along with the number of weevil larvae shaken from each 30-stem sample of alfalfa to make decisions regarding the need for spraying as directed on the recommendation table found in CR#7177. When spraying is recommended based on results of scouting, information on insecticides registered for control of alfalfa weevil can be found in OSU Extension Facts #7150. Because of the probability of a hard freeze occurring during March, use of a short-residual insecticide such as methyl parathion that can be applied at relatively low cost should be considered when populations of weevil larvae reach the economic threshold in late February and early March. If alfalfa is damaged by freezing at some point after the application, less investment will have been lost. A more expensive, long-residual insecticide application is much more likely to be profitable after mid-March.
Richard Berberet, Alfalfa Entomologist Department of Entomology and Plant Pathology Oklahoma State University

	Oklahoma State University Stillwater, OK
Oklahoma Alfalfa Oklahoma Cooperative Extension Service Oklahoma Agricultural Experiment Station