from MSU News Service

5/12/99 BOZEMAN -- Last fall's extended mild temperatures caused localized, heavy winter kill in alfalfa especially in Southwest Montana.

Dennis Cash, Montana State University agronomist, and Jack Riesselman, MSU plant pathologist, say the damaged plants show spongy, decayed root systems typical of winter injury. They advise that even where the crowns of some plants are only partially decayed and show some regrowth, the plants will produce only a partial crop and second crop regrowth will be marginal or non-existent.

John Maki, MSU Extension Agent in Beaverhead County, says the weather records for the Dillon area show why widespread injury occurred.

The first killing frost in that area usually occurs in the first week of September, but in 1998, there was no freeze at Dillon at all in September. That month had an average high temperature of 77.3 degrees Fahrenheit and a low of 45.6 degrees. The first killing frost finally occurred Oct. 5, but that was followed by a week of 70 degree weather which further delayed alfalfa dormancy. Through October and November, temperatures were mild and when there were a few cold periods, the alfalfa was insulated by snow cover. From Dec. 11 through 17 warm days and mild nights melted the insulating snow cover, so when temperatures did not rise above zero from Dec 18 through 23, serious injury to the less-than-hardened-off crop occurred.

Growers are now trying to figure out what they can do, and Cash and Riesselman make the following suggestions.

If winter kill was complete or nearly so, the best option is to rotate out of alfalfa. Complications exist if a winter dormant herbicide was applied for weed control earlier this spring. That includes products such as Sencor.

Labeled plant-back restrictions for barley and wheat following Sencor is eight months. For fall-applied Sencor, the crop may be interseeded with tolerant barley lines - see Sencor labels. This could provide forage for fall use. Most hay barley is not rated for Sencor sensitivity. However, that is of minimal concern since hay barley seed is very difficult to get now. Oats are more sensitive to Sencor than barley and should not be used in this situation.

For acres that have not been treated with persistent herbicides, producers have more options.

Interseeding with oats might be an option. Varieties that have performed well include Otana, Monida and Stampede with the later producing the greatest amount of forage.

Interseeding with alfalfa is risky due to a variety of factors including auto-toxicity. The level of auto-toxicity is greater in older stands (3+ years) than in younger stands. Rumors that less auto-toxicity exists when the same variety is planted back are untrue. While interseeding has been successful on rare occasions, it is generally a non-recommended practice. If you feel this is an option, we encourage you to treat the seed with metalaxyl to help reduce risk.

For Sencor treated, and for that matter non-treated acres, a good option would be interseeding with a forage pea. Peas are tolerant to Sencor and they do produce high quality forage for cattle. Peas seeded into alfalfa acres need to be treated with pea inoculum as the alfalfa strain will not go to pea. The forage pea Arvika or common Austrian winter pea could be utilized. Arvika stands upright and would be the variety of choice in fields that are almost entirely winter killed. In stands where 30 to 40 percent alfalfa remains, Austrians could be used as the remaining alfalfa will keep the crop upright. Seed should be placed 2 to 2.5 inches deep to help insure a good stand. Yields in the four ton range require more curing time than alfalfa prior to baling. When possible, green chopping is preferred.