 Some source help for hay producers.
Frost Damages Alfalfa In Upper Midwest As if alfalfa winterkill wasn't enough, severe cold hit parts of North and South Dakota, Minnesota, Wisconsin, Nebraska and other Upper Midwestern states in late April and early May. Overnight lows dipped into the teens and 20s in many areas, leaving fields of frost-damaged alfalfa in their wake.
Dan Undersander, University of Wisconsin, and Paul Peterson, University of Minnesota, have been helping hay producers evaluate frost or freeze damage levels in alfalfa fields. They provide the following guidelines for evaluating the damage. New alfalfa seedlings are somewhat tolerant of frost. Injury evaluation should take place at least three to five days after the frost or freeze event. Plants that die back to the ground are lost to the stand. If more than 20 healthy plants per acre remain, the stand will be productive. If less than 15 plants per acre remain, the stand should be overseeded or replaced. Alfalfa plants that have at least one set of surviving leaves will likely survive. Be sure to closely examine lower stems. Established alfalfa stands should be examined at least three to five days following the frost or freeze event and evaluated on the basis of three general levels of damage:
If less than 30% of stem tops show wilting or browning from frost, assume that enough healthy stems remain to allow good continued growth and first-cutting yield. There could be some yield reduction, but normal growth should return in the second crop.
If most of the stem tops show wilting or browning, and the alfalfa is less than 10" tall, do nothing, according to Undersander and Peterson. The growing point has been killed, but the alfalfa will regrow from lower buds. First cutting will be delayed, but the stand will not be significantly damaged. If the alfalfa is over 12" tall, early harvest is advised. Be sure to allow subsequent cuttings to regrow fully to promote continued stand health.
If all stems on a plant are dead, the plant should be written off. If examination reveals that fewer than five healthy plants remain per square foot, consider planting corn or another rotational crop in that field and seeding alfalfa at another location in order to avoid autotoxicity problems.
Source: Agronomy Tips From FS Newsletter.
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