Minnesota Crop News > 2001-2008 Archives
May 29, 2008
Managing Hail Damaged Alfalfa
Dan Undersander and Krishona Martinson, University of Wisconsin and University of Minnesota
Recent localized hail damaged numerous alfalfa fields and has raised questions regarding harvest management of hail damaged alfalfa, especially considering the time of year and proximity to harvest. Hail damaged fields vary in degree of severity, ranging from some terminal bud and leaf damage to completely defoliated plants (Figures 1 and 2). Stands may also be lodged by accompanying wind and rain.
Figure 1. Alfalfa damaged by hail.
Figure 2. Alfalfa terminal bud damage from hail.
Alfalfa grows from the terminal (highest) portions of the plant. If these are damaged, growth is stopped on that stem. Thus, hail damage causes loss from physical removal of forage and from terminated growth, requiring the plant to begin new shoots for growth.
Yield losses will be in relation to the percentage defoliation. Data collected at University of Wisconsin Marshfield Research Agricultural Station suggest that alfalfa yield losses from hail damage on first cutting will be approximately 35 pounds of dry matter per acre for each percent defoliation occurring with two weeks of harvest (Figure 3). This occurred on stands where the undamaged yield was 2.25 tons dry matter per acre. Hail damage losses for later cuttings are usually less. Forage quality losses from hail also occur, since the highest quality portions of the plants are removed. However, these losses are small relative the yield loss.
Figure 3. Effect of Hail Defoliation on Alfalfa Yield.
Hail damage occurring earlier than two weeks before harvest generally occurs to plants short enough and with potential crown exposure to light. These plants will put out new shoots and produce a hay crop, although somewhat delayed. If defoliation from hail was greater than 50% within two weeks of harvest, and intention is to make haylage, flail chop remaining forage back onto ground immediately, as harvesting residue with the next cutting may adversely affect fermentation of next cutting.
When harvesting lodged alfalfa research has indicated that disc mowers, especially those with angled knives, will pick up more forage than sickle bar mowers. Harvesting against the direction the forage is leaning allows more downed forage to be harvested. With both mower types, tilt the cutter bar or discs forward to increase forage picked up. When using a sicklebar mower, move the reel forward and down, and increase reel speed to help pick up downed forage.
Additional recommendations include:
- If alfalfa is within two weeks of harvest and lodged, wait 3 to 4 days to allow stand to recover and then harvest.
- If alfalfa is within two weeks of harvest and less than 50% of terminal buds are damaged, allow the stand to mature to normal harvest schedule and then harvest. Yield will be reduced, but undamaged buds will continue to grow and produce additional yield.
- If alfalfa is within two weeks of harvest and greater than 50% of terminal buds are damaged, then harvest immediately (if justified by yield). Little additional growth will occur (to the extent that terminal buds have been destroyed) except growth coming from new stems. However, this growth will most likely be more beneficial and contribute more to yield in the next cutting. If yield does not justify harvest, wait if intending to harvest hay. Flail chop residue back onto ground (to remove from next cutting) if intention is haylage.
- If alfalfa is not within two weeks of harvest (stands generally 12 inches or less in height), wait for stand to regrow from new shoots, and harvest when forage is at normal harvest height and quality. Do nothing if intending to harvest hay. Flail chop residue back onto ground (to remove from next cutting) if intention is haylage.