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Timing of the last alfalfa cut

Written by the forage specialists at DuPont Pioneer

Tuesday, 27 August 2013

Deciding your fall alfalfa harvest schedule is like a juggling act – you need to think about your forage inventory and needs, potential yield, risk of winterkill and even harvest cost.

Robin Newell, DuPont Pioneer forage business manager, offers tips to help plan your final 2013 alfalfa harvest.

Last-cut timing
The tried-and-true practice for best winter survival is to wrap up the final harvest by early September.

“The thumb-rule is that alfalfa fields in the upper Midwest and Northeast should not be harvested between September 1 and October 15,” Newell shares.

This period allows build-up of carbohydrate reserves in the roots. This helps maintain the stand’s health and productivity into the following spring.

Alfalfa stands that are mowed during this critical period during the fall often lack vigorous regrowth next spring. The next year’s first-cut yields can be impacted adversely by mowing in this September to mid-October timeframe.

To mow or not to mow?
It’s best to avoid mowing during early fall, but what if your alfalfa is ready to cut in mid-September to late September? Consider your overall forage needs versus the risk of winter damage to the alfalfa stand.

If you really need the forage, consider waiting until after mid-October to harvest. Alfalfa quality does not decline as rapidly in the cooler weather typical of autumn.

Also, the amount of regrowth after mid-October is generally limited, so root reserves will not be significantly depleted following a late-October harvest.

Secondly, the amount of winter injury risk that can occur from harvesting during September or early October will depend on how much stress the alfalfa stand experienced during the year.

The number one stress factor that weighs into this decision is how many times you harvested the field this year. Fields cut three or four times prior to September 1 will be more susceptible to winter injury than fields cut twice. Also, fields that had uncontrolled potato leafhoppers during the summer will be at greater risk.

Third, it helps to maintain some alfalfa ‘straw’ for its snow-retention abilities. Snow is a great soil insulator. Soil temperatures at the four-inch depth stay in the low 20s with just a few inches of snow cover, despite air temperatures that get much colder.

Alfalfa crowns of winterhardy varieties can withstand soil temperatures of 17ºF, but lower soil temperatures will cause winter-damage. How confident are you of maintaining snow cover? Any lack of alfalfa straw to catch and hold snow increases the risk of winter-damage.

Waiting for Jack Frost
If you need to harvest the alfalfa one more time, consider waiting until after the first killing frost, when the temperature remains at 26ºF or less for at least six to eight hours. Waiting for this frost allows the plant to get as much energy into the roots as the growing conditions allow while still producing a crop for additional forage inventory.

Lifting the cutter bar 6 to 8 inches off the ground helps to leave enough stubble to trap some snow, providing insulation for the crop and increasing its chance for surviving the winter. But if the alfalfa stand will be retired this fall, you can take a fourth cutting prior to the killing frost.

“If you decide to take a last cutting after the frost, then make that last cutting as soon as practical after the frost to avoid leaf tissue loss, preserving most of the forage quality,” Newell reports.

“Leaves will begin to drop and stems will droop in a few days following the first freeze. The sooner you can harvest after the freeze, the better.”

Other strategies
As you reflect on your last alfalfa harvest of the season, here is a list of factors that can help minimize late-fall harvest problems and encourage healthy, productive stands for better winter survival:

• Don’t cut alfalfa during September through mid-October (four to six weeks before a killing frost)
• Harvest only well-established stands, not new seedings
• Maintain a high level of soil fertility with annual fertilization
• Apply a late-summer or fall application of potassium fertilizer
• Cut alfalfa at 6 to 8 inches high for snow retention and insulation against winter damage
• Avoid fall cutting fields that experienced stress from potato leafhoppers, drought or excessive soil moisture

While you weigh your options about your final alfalfa harvest, make sure to remember these few guidelines to help ensure winter survival of stands.

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