As of May 1, alfalfa weevils have been insignificant pests this spring according to most extension field crop specialists. The one exception is that
Virgil Schmitt reported a large population in alfalfa on sandy ground in Clinton County. In this field, he noted that the population averaged at least two larvae per stem, and the field was sprayed by the farmer.
Was this population of two larvae per stem above the economic threshold? It depends. Factors to consider before spraying include the value of the forage ($/ton), cost of the insecticide, presence or absence of diseased larvae, and potential drought stress of the field (remember it was sandy ground and this is before the weekend rains). It is the answers to these questions that would help determine the necessity of spraying the field or not. If you are uncertain about whether a weevil population exceeds the economic threshold, then consult the table in the April 17, 2006, ICM Newsletter  for guidelines on treatment decisions. Even though they may be few and far between this spring, they can cause economic damage and field scouting is encouraged.
This article originally appeared on page 114 of the IC-496 (9) -- May 1, 2006 issue.