Freeze Damage to Alfalfa

Freeze damaged alfalfa leaves — Light freeze (27 to 31 degrees) in 2015 caused this leaf damage

With warm weather the first week of April and the current cold spell, questions about freeze damage to alfalfa will be on the rise. Friend, Plymouth, and Beatrice reached 86, 87, and 89 degrees respectively on April 7. In Lincoln, a record high was set for the day of April 7 (87 degrees) and a record low for April 10 (17 degrees). Other low temperatures in the area on April 10 were York at 16 degrees, Hebron at 20 degrees, Beatrice at 20 degrees. The National Weather Service in Omaha in response to these temperature extremes, called it a “weather whiplash”.

The air temperature (4 to 6 ft above the surface), near surface air temperature (6 to 12 inches above the surface for alfalfa this time of year), soil temperature, length of freezing conditions, and local topography among other factors including the alfalfa growth stage all influence the extent of damage to alfalfa during an early morning freeze event. We do know the potential damage to alfalfa is correlated with the amount of spring growth (i.e. more growth, more risk). Established alfalfa was about 6” tall prior to the freeze on April 10 in this area. Before reading the general guidelines on temperature below, due to the complexity I mentioned it is best to look at the response of the alfalfa plant itself to determine freeze damage. I strongly encourage you to wait several frost/freeze free days before assessing damage.

New seedlings (first trifoliolate or less) this early in the spring handle low temperatures (low 20s) better than one often thinks due to natural seedling cold tolerance and being close to the warmer soil. Seedlings from emergence to the second trifoliolate leaf stage are more cold tolerant than later growth stages. Companion crops would help new alfalfa seedlings survive under colder or longer periods of exposure. When seedlings lose all trifoliolates (leaves) and look discolored, they will not likely regrow.

For established alfalfa, it will outgrow the damage from a light freeze (27 – 31° F). Observable damage from a light freeze is the loss of several sets of trifoliolate leaves down the stem and some slight curling of the stem. Buds or growing points will continue to grow as normal. A majority of the terminal buds should still look green and alive 2 to 3 days after the freeze event. In terms of management, there is no need to do anything under these conditions. Under moderate (26-27° F) and hard freezes (26° F and colder) additional damage can occur. Moderate freeze damage will kill the upper part of the stem and terminal buds. Regrowth must occur from lower axillary buds on the stem or from new crown buds. Growth and first cutting will be slightly delayed. A hard freeze causes leaf, buds, and stem tissue death and plants will regrow from crown buds and first cutting will be delayed. There may need to be some management actions taken after a hard freeze (cutting, grazing, shredding, no action).

Numerous factors influence how much alfalfa damage will occur from a spring freeze. It is best to wait several freeze-free days before assessing the final damage. To learn more about alfalfa management or actions to take as result of freeze damage, visit https://croptechcafe.org to find guidance, additional articles and resources. Know your crop, know you tech, know your bottom line.