This is the right time of year to see adult alfalfa snout beetle (ASB) emerging and leaving the alfalfa/hay fields that they overwintered in and spent the last two years in. They can also be found feeding on clovers, dandelions, dogwood, wild carrot and strawberries.
Alfalfa snout beetle adults can’t fly. So they are easy to spot as leave their original field and march along field edges’ and across roads to find new host fields to infest (Figure 1). They are bigger than alfalfa weevil adults but are similar in shape, both being snout beetles (like mini versions of Mr. Snuffleupagus, without the fur). These adults can feed on the foliage of hosts but that injury is minor. The real concern are the eggs that they lay in the soil which will become larvae (grubs) in later June. These larvae feed on the lateral and tap roots of the plants from June to November (Figure 2). Roots dug up in the fall or next year will have corkscrew tunneling along the tap root or the plants can be girdled causing dieback. Above ground symptoms of yellowing and poor overwintering are often misdiagnosed and often this injury isn’t noticed until after winter in the second year. These larvae stay in the soil for a second year as non-feed grubs till they pupate in the fall to become adults and emerge in the spring of year 3.
Now is the best time to look for and report any new sightings of ASB adults to Tracey Baute (firstname.lastname@example.org). Based on surveys done by Gilles Quesnel, we know infestations exist or existed on Wolfe Island, and in fields in the Prescott/Brockville area, Kemptville and Ottawa at the Central Experimental Farm (Figure 3). New reports of adults near fields in Finch and Merrickville–Wolford also came in this week (green dots).
Chemical options have not been successful against this pest. The most effective strategy based on decades of research from Cornell in New York is to apply biocontrol nematodes on fields with larvae present. So watching where these adults are going now will help flag fields that should be scouted with a shovel this fall to dig up roots and see if the larvae are present. New seedings and 1st year production fields are best to target biocontrol nematode applications next spring to get the best results, though they can be applied to more mature stands too. It usually takes two years for the nematodes to reach a level that they can effectively suppress ASB but the nematodes persist in the soil for many years. So they only need to be applied once. Anyone interested in considering biocontrol nematode applications can contact Tracey directly.