Managing Hail Damage in Alfalfa

July 2, 2024 12:25 PM
Blog Post

Many areas in Iowa were impacted by hail this past week. Hailstorms are an unpredictable and formidable adversary for producers, capable of inflicting significant damage on crops, forage, and livestock. The impact of hail can be extensive, from shredded leaves to battered stems and bruised animals. However, there are strategies and solutions that can help assess and mitigate the damage and pave the way for recovery. This article will delve into options for managing hail damage in alfalfa stands.

Figure 1: Hail in Southern Iowa. Photo Credit: Patrick Wall.

Hail can cause leaf loss and damage to stems, buds, and the terminal bud. Depending on the stand maturity, loss of the top few inches can lead to significant yield losses, particularly in less mature alfalfa. High leaf loss will decrease forage quality, as leaves are higher in quality than stems.

Assessment of an alfalfa stand begins with evaluating the terminal bud on the stems. The terminal bud (apical meristem) is the growing point of the stem located at the top. This growing point is responsible for the growth of the stem, leaves, and flowers. If the terminal bud is removed or severely damaged, new growth will not occur from the top of the stem. Instead, new growth will occur from the crown or axillary buds, which will be much slower.

Damage to a new stand can be fatal, depending on the extent of damage and whether the plant has an established crown. There should be a ridge where the above-ground growth and the root growth meet. Crown development typically occurs when the plants are about 3-4 inches tall. Plants with damaged terminal buds but without a crown will die. Interseeding damaged new stands (< 1 year old) can help thicken without the concern of autotoxicity. If there are more than 25 plants per square foot, the stand should be okay to leave. Alfalfa taller than 6 inches should have developed crowns and will most likely regrow from the crown.

The balance between damage and proximity to harvest is crucial in production years. If you are within two weeks of harvest and more than half of the terminal buds and/or stems are damaged, it is suggested to harvest after 3-4 days to allow any lodged stems to recover. If lodging was minimal, harvest right away. The stems would have little growth as most of the main growing points were damaged.

If lodging is severe, there are a few strategies to help harvest. Disc mowers with angled knives are better at picking up the forage than sickle bar mowers. Harvesting against the downed forage and titling the cutting bar/discs forward will help pick up the forage.

If you are within two weeks of harvest and less than half of the terminal buds are damaged, allow the plants to grow until the cutting period and then harvest. There will be reduced yield from the damaged stems, but the undamaged stems will continue to grow. Additionally, if branches and leaves remain, regrowth can occur from axillary buds near the base of the stem, although this is slower regrowth than from the crown.

If the alfalfa is less than 12 inches tall, wait for the stand to regrow from new shoots. Harvest should occur at the normal height and quality requirements. However, if this cutting is going to be ensiled, it is recommended to cut the stand to 4-6 inches to allow for even growth and remove the old material to avoid mold growth that could cause problems in ensiling.

When cutting damage stands early, extending the harvest interval for the regrowth can be very beneficial in replenishing root carbohydrate reserves for future persistence.

Hail can lead to DM losses, decline in forage quality, and reduced growth. Hail is hard to predict and avoid, but we can make the best out of a bad situation based on the harvest schedule and how much damage was done to the field.

Adapted by Shelby Gruss, Iowa State University, from “Managing Hail Damaged Alfalfa” by Stephen Barnhart, and a May 2008 newsletter article by Dr. Dan Undersander and Krishona Martinson, University of Wisconsin Extension.