Look For Alfalfa Weevils In Southern Indiana

Purdue University entomologists are encouraging hay growers in southern Indiana to be on the lookout for alfalfa weevils. When checking fields, examine alfalfa stems for evidence that alfalfa weevil larvae have been feeding on tips. The average size or length of weevil larvae should also be noted. Although large alfalfa weevil larvae are relatively easy to find, small larvae are difficult to see. Thus, very close examination of leaves may be required to detect pinhole feeding, small black fecal pellets and small off-white larvae.

Illinois Alfalfa Weevils May Be Munching

Alfalfa weevils may be feeding in southern Illinois in spite of wet, cool conditions that have prevailed through most of April, says Kevin Steffey, University of Illinois extension entomologist. Dennis Epplin, extension crop systems educator, has observed alfalfa weevil larval injury in one of his field trials at Ewing in Franklin County, so Steffey says it's likely that similar or worse injury could be noticeable throughout the southern quarter of the state. He tells hay growers to look for leaf-feeding injury first near the tops of plants. Small alfalfa weevil larvae often feed within the folded tip leaves, and pinholes are symptomatic of early season injury. As the larvae grow and consume more leaf tissue, more dramatic skeletonization of the leaves becomes apparent.

“With alfalfa hay currently worth more than it has been in the recent past, the rule-of-thumb economic threshold of three larvae per plant and 25-50% of tips being skeletonized likely will be questioned,” Steffey says. “A working group of field-crop extension entomologists will address this issue throughout 2008, but thus far we have no easy answers. So use your best judgment when making alfalfa weevil control decisions, and respect the potential for ecological backlash if lots of fields are sprayed when numbers of alfalfa weevils are relatively low.”

For more on insect thresholds, watch for the May issue of Hay & Forage Grower.