Pest season is kicking into high gear in alfalfa fields throughout the U.S. and Canada. Many states are on alert for alfalfa weevil infestations and experts advise regular scouting.

In parts of South Dakota, weevils are showing up in record numbers. “It appears that the weevil activity has lagged approximately three weeks behind,” says Anitha Chirumamilla, South Dakota State University Extension entomology field specialist.

In two western counties, Fall River and Butte, almost every alfalfa field holds weevil numbers beyond economic thresholds and the damage appears significant, she reports.

Chirumamilla recommends two weevil management strategies – early harvest or chemcial control. Weevil larvae in fields appear to number more than 75 larvae on 30 stems at 16”, which justifies the use of insecticides, she says.

The larvae of alfalfa butterflies are also infesting South Dakota fields and can feed on entire alfalfa leaves.

Now that alfalfa first cutting is underway, farmers should scout for potato leafhoppers, which can stunt the plants and significantly reduce yield if infesting at heavy populations.

In Pennsylvania, potato leafhopper infestations are “ramping up,” says John Tooker, Extension entomologist at Penn State University. He recommends that growers monitor pest numbers to determine if treatment is needed.

In Nebraska, alfalfa weevil populations appear to be high, according to Jeff Bradshaw, University of Nebraska Extension entomologist.

“I have had quite a few growers contact me regarding treatment thresholds and questions about insecticide efficacy,” he says. “I believe that the cool start to the season has extended the activity of alfalfa weevils further through the season. There is some concern about populations persisting beyond cutting.”

Growers should check with their chemical suppliers to find the best product for controlling alfalfa weevil, Bradshaw suggests.

Minnesota alfalfa growers should continue to check for alfalfa weevil larvae through second-crop harvest, says Dan Martens, University of Minnesota Extension educator.

In Utah, this year’s weevil troubles have been limited to alfalfa fields water-stressed due to a lower water table and a lack of irrigation, according to Ricardo Ramirez, Utah State University Extension entomologist.

Because treatment strategies have not been effective, some experts believe they’re dealing with a different strain of weevil, Ramirez says.

Clover root curculio, an insect that is increasing in number and causing increased damage in Idaho, seems to be moving south, Ramirez says.

“Unfortunately, we have had less success (than Idaho growers) finding the damaging larval stages that feed on the roots, even in growers’ fields” suspected of being infested with clover root curculio. “More investigation is needed here and few management options for soil dwelling pests exist,” he says.

Oklahoma and Missouri are two of several states where grasshoppers are a growing concern. Grasshoppers can consume 25-50% of their body weight in alfalfa each day, so infestations can significantly impact yield, warns Tom Royer, Oklahoma State University Extension entomologist.

Alfalfa growers should take action by July 1 if they want to limit the potential damage from feeding grasshoppers, he says. Some farmers report up to 50 grasshoppers per square foot in their alfalfa fields; that’s when it’s probably time to spray, adds Wayne Bailey, Univeristy of Missouri Extension entomologist. “Grasshoppers are easier to kill when they are small.”

Contact Anitha Chirumamilla at 605-394-1722 or anitha.chirumamilla@sdstate.edu; Dan Martens at dan.martens@co.benton.mn.us or 320-968-5077; Tom Royer at tom.royer@okstate.edu or 405-744-5527; John Tooker at 814-865-7082 or tooker@psu.edu; Jeff Bradshaw at jbradshaw2@unl.edu or 308-632-1369; Wayne Bailey at BaileyW@missouri.edu or 573-882-2838; and Ricardo Ramirez at 435-797-8088 or ricardo.ramirez@usu.edu.