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Scout your alfalfa stands now for signs of injury

By Janet Kubat Willette

Date Modified: 04/25/2012 9:36 PM

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ROCHESTER, MINN. — Now is the time to be scouting alfalfa to determine if the stand is good enough to keep.

Alfalfa is running about a month ahead of normal, said Lisa Behnken, a regional University of Minnesota Extension educator based in Rochester. If warmer temperatures continue, farmers could be harvesting their first crop of hay about the time they're usually planting soybeans.

The early spring means farmers have more options than normal if alfalfa stands were damaged by drought stress or winter injury.

A good way to determine stand yield potential is to measure several square foot areas across the field. Most men's shoes are about a foot, so frame the alfalfa in a L-shape created by your shoes or build a square foot measuring device to take with you to the field.

Stands with more than 55 stems per square foot have excellent yield potential. Some yield reduction is to be expected in fields with 40 to 55 stems per square foot and farmers should consider taking action on stands with fewer than 39 stems per square foot.

When scouting fields, it's also a good idea to evaluate roots. Plants will put on six to 10 inches of growth even if they are injured, Behnken said. Healthy roots are firm and white in color. Roots with winter injury are gray and mushy. If 50 percent or more of the root appears injured, the plant will most likely die.

Alfalfa stands may not be stressed so much by winter injury as by the drought that began the second half of last summer and continued through fall and winter, Behnken said.

Older stands may have been weakened before winter by drought stress and stands seeded in August may have had a tough time getting established due to lack of moisture, Behnken said.

On March 28, she walked through an alfalfa plot across from University Center Rochester. The plot was seeded last August. About half the plot is thickening with 30 to 35 stems per square foot. The other half has 10 or fewer stems per square foot.

The difference in the two halves is that one had greater weed pressure and more oat stubble than the other. Also, volunteer oats stole moisture from the newly seeded alfalfa.

On March 18, U of M integrated pest management specialist Fritz Breitenbach interseeded across the plot at 14 pounds of seed. Seedlings are already poking through the soil.

Conditions were great at the time, Behnken said.

The soil is mellow so there's no need for farmers to till in order to replant. A no-till drill works as does a planter with good downward pressure.

Another reason to not till the soil is to conserve moisture. Each time the soil is worked, moisture is lost.

Select a good yielding, disease resistant alfalfa variety for replanting, Behnken said. Plant a good, strong variety that will perform three or four years. Farmers have a great window of time now to seed alfalfa before getting busy with row crops.

There is no need to plant a cover crop with the alfalfa sown this spring because last fall's alfalfa will provide cover and if not tilled, there is little erosion.

Replanting is an option for fields seeded last fall, but not for older stands because of autotoxicity. Autotoxicity is a process where established plants produce a chemical that reduces the growth of new plants.

Extension educator Randy Pepin runs through a laundry list of considerations in his weekly column, including: "Will oatlage provide the quality forage I desire? Can I plant more acres with corn silage varieties and increase corn silage in my ration this year? What other alternative crops are available and what are the yield and forage quality trade-offs?"

Behnken said farmers may want to graze their alfalfa and then rip it up and plant something else there or they could rip up the stand now and plant another forage crop.

The calendar is on farmers' side, she said.