In addition to checking alfalfa stands for winter injury, it is time to start thinking about scouting for alfalfa weevil. With warm temperatures this year, alfalfa weevil development is well ahead of schedule compared to recent years, and adults have emerged from their overwintering sites to lay eggs in alfalfa stems in southern Iowa.
Alfalfa growth is off to the races in many parts of Iowa, and we have heard reports from around the state that insects are very active in alfalfa as well. Field agronomists, especially in southern Iowa, have reported that hay is being cut early due to alfalfa weevil pressure, and they are seeing quite a few aphids as well. If you have not yet done so, consider scouting alfalfa for these pests to ensure that a timely management decision can be made.
In addition to checking alfalfa stands for winter injury, it is time to start thinking about scouting for alfalfa weevil. Despite recent warm temperatures, alfalfa weevil development is slightly behind last year. However, it is likely adults have emerged from their overwintering sites to lay eggs in alfalfa stems in southern Iowa.
The cooler temperatures this spring have slowed down alfalfa growth, but alfalfa weevil could already be active based on growing degree day (GDD) accumulation since January 1. We recommend beginning to scout for alfalfa weevils once 200 GDD have accumulated (base 48°F) south of I-80 or 250 GDD have accumulated north of I-80.
In addition to checking alfalfa stands for winter injury, it is time to start thinking about scouting for alfalfa weevil. Even with recent cool temperatures, overwintering alfalfa weevil adults have become active, made their way to alfalfa fields, and have likely begun laying eggs in stems. Alfalfa weevil is a cool-season pest and is able to survive less than ideal temperatures by moving under residue or near the crown.
The larvae and adults of alfalfa weevil (Hypera postica) are the primary defoliators in alfalfa. Heavy infestations can reduce tonnage and forage quality. Use this article to learn how to identify alfalfa weevil and properly scout for and manage this pest.
Adult: Adult alfalfa weevils are approximately ¼ inch long beetles with a blunt “snout,” thick golden hairs covering the body, and a distinct dark, narrow stripe down the back (Photo 1).
Most people are already finished with their first cutting of alfalfa throughout Iowa, but each of our 10 field agronomists reports that alfalfa weevil activity continues and has been much worse than they’ve seen in over a decade. Lance Scott in southwest Iowa took this short video to show significant injury. Alfalfa weevil only has one generation per year.
This past week brought a range of field activities from replanting and POST herbicide applications to putting up hay and sidedressing nitrogen. Herbicide injury and carryover, dry conditions, yellow corn, and alfalfa weevils have been some of the more common issues ISU Extension field agronomists have observed in fields this week. Read on for more specifics for what’s happening in different regions across the state.
Northwest Iowa
While the rain may have limited fieldwork across the state this past week, it was much welcomed in many areas that have been on the drier side. Most of the corn and soybeans that have been planted are now emerged. Two of the more common issues seen in fields this past week included alfalfa weevils in alfalfa fields and weeds getting a nice start in some crop fields. Read on to learn more about what ISU Extension and Outreach field agronomists are hearing and seeing across the state.
Northwest Iowa
Adult alfalfa weevils become active and start laying eggs as soon as temperatures exceed 48°F. Like other insects, the development of alfalfa weevil depends on temperature, and we can use accumulation of growing degree days (GDD) to predict activity. Alfalfa weevil egg hatching begins when 200-300 GDD (base 48°F) have accumulated since January 1.
