Watch Out For A Light Frost In Alfalfa

By Karla Hernandez

Alfalfa fields are starting to grow showing good potential for this growing season. However, as for last night we were under a Freeze Warning, meaning that some crops could be damaged by a light frost or freeze. In fact, calls came into the office regarding this event already. Below are the key points to consider for both new seedling alfalfa and established stands.

New Forage Seedings and Established Stands

At emergence, alfalfa and other winter hardy forage grass and legume seedlings have a pretty decent chance of cold tolerance. Spring cold snaps however can hurt new seedlings as well. As for well-established stands, exposed tissue is susceptible to cold temperatures injury. Several hours of 25 to 27oF or lower temperatures will damage any leaf tissue and could be a problem for alfalfa growing points.
Management Suggestions

Guidelines for newly seeded alfalfa:

• New seedling alfalfa or seedlings between the 2 and 5 trifoliate leaf stage are susceptible to being killed if exposed to 26oF four or more hours (Nathan Mueller, 2014). Using companion (Oats, Orchardgrass) crops can help seedlings survive cooler temperatures for longer periods of time.
• Seedlings from emergence to the second trifoliate leaf stage tend to be more cold tolerant (Undersander et al., 2011).
• On new seedlings re-seeding with a drill into the damaged areas may be warranted.

Guidelines for established alfalfa:

• A light freeze where temperatures do not go below 27oF is likely to freeze several sets of trifoliate leaves on alfalfa tops and terminal buds, but plants will grow out of it if it gets warmer.
• A moderate freeze where temperatures go between 26 to 27oF is likely to damage the upper part of the stem and terminal buds can be killed. Usually, growth and first cutting will be delayed.