Sampling an alfalfa field to determine the extent of alfalfa weevil damage and average stage of weevil development is best accomplished by walking through the field in an “M-shaped pattern.” Ten alfalfa stems should be examined in each of 5 representative areas of the field for a total of 50 stems from the entire field. Consider that south-facing slopes and/or sandy soils warm sooner and should be prioritized for sampling. Each stem should be examined for: (1) evidence of feeding (pin-hole and skeletonized) by alfalfa weevil larvae; (2) maturity of the stem, i.e. pre-bud, bud and/or flowers; and (3) stem length. The average size (length) of weevil larvae should also be noted. Although large alfalfa weevil larvae are relatively easy to find, small larvae are difficult to see; so very close examination of leaves may be required to detect “pin-hole” feeding, small black fecal pellets and small off-white larvae. This video will further explain the proper sampling technique, and show alfalfa weevil feeding damage.
