Fall frost and alfalfa: Risk management in play for growers

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The lingering impact of this year’s drought has some producers debating whether to cut their alfalfa before a killing frost to ensure their livestock have sufficient stored forage or to not cut it to ensure the plants have less risk of winter injury, an Ohio State University Extension educator said.

The drought has impacted producers throughout the 2012 growing season in Ohio hard this year, causing some to risk a fall cutting for livestock feed to survive the winter and spring period because earlier harvests yields left their hay and silage supplies low, said Rory Lewandowski, an agricultural and natural resources educator for OSU Extension.

During the fall, winter-hardy alfalfa plants go through a hardening process, which involves reduced herbage production and increased carbohydrate storage in the plants’ roots. Growers are typically recommended not to cut alfalfa between about mid-September until after a killing frost to protect root reserves, he said

Killing frost for alfalfa is 24 to 25 degrees for more than 4 hours, Lewandowski said.

“Some producers are saying they can’t worry about the long-term impact but have to consider their circumstances now,” he said. “Because of the drought, livestock producers need all the forage they can get so many livestock owners are cutting hay fields regardless of the calendar or weather forecast.

“Due to this year's drought, most livestock owners need to use whatever forage is available, and I expect to see fields harvested or grazed following a killing freeze.”

The normal process is that alfalfa regrows by mobilizing and using carbohydrate root reserves to produce new leaf growth after a cutting, said Lewandowski.

“At some point, there is enough new leaf area that sugars manufactured by photosynthesis meet the plants’ growth needs and have surplus to put back into root reserves,” he said. “If management during the growing season has left low levels of root reserves and the plant is cut in the late fall, that burns more reserves to start growth.

“Then if the growing season ends before the plant can grow enough leaves to restore those root reserves, there is risk of the plant dying over the winter.”

Whether or not alfalfa cut before a killing frost dies over the winter depends on the cutting date in the fall, the age of the stand, whether the stand is planted on a well-drained site and the soil’s fertility, Lewandowski said.

“Stands that have maintained good soil fertility, especially soil potassium levels and that have kept soil pH close to that 6.8 level will have a reduced risk of winter kill,” he said. “And growers who use improved genetic varieties with good disease resistance and overwintering levels can also reduce their risk.

“It’s really about risk management.”



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