Freeze effects on forage crops
(Producer Questions prior to 2009)
Updated information: Effects of a Freeze on Forages (October 2015)
How long after a hard freeze do I have to wait before I can start to graze alfalfa with my cow herd?
First, look at the plants instead of the thermometer. Plants turning black or plants wilting and starting to dry are basically done for the year. If there is enough to economically mechanically harvest, do it as soon as possible to salvage leaves, which will start to fall off soon as they dry. For grazing, wait 4 or 5 days after the killing freeze to reduce bloat hazard. The higher the proportion of alfalfa that starts to dry from the freeze, the safer the grazing. If plants show little or no signs of wilting and drying, follow management plan as if no freeze had occurred. Don't expect much more growth but active, green plants can continue to accumulate nutrient reserves in the roots and crowns for winterizing.
We had a spring freeze on our wheat fields, what quality of hay will this wheat make to feed cows? The heads of the wheat will not fill out due to freeze.
The effect of a hard freeze on wheat that has headed out will have little effect on the hay quality and is mostly related to the stage of growth at the time of the freeze. There may be some kernels that try to fill and it is also possible that some reserve or secondary tillers will try to grow (but not many). Disease will also impact the wheat right now. I would suggest going ahead and cutting for hay now. I would guess that crude protein content would be in the range of 10 to 14 percent.
What effect does freezing have on sudex, millet hay etc. still standing in the field as far as nitrates are concerned? Can I cut it right after freezing or should it stand awhile?
Nitrates are not reduced due to freezing. If the plant has been stressed during the growing season, then the nitrates will be located in the lower part of the stalk. There may be some additional accumulation at the base of the plant after a freeze because of the disruption in plant growth as a result of the freeze. So if you suspect nitrates, set the mower height to 6 to 8 inches instead of cutting close to the ground.
Some of the sudan and sudex may also have prussic acid and prussic is typically higher after a freeze. Prussic acid will decrease after a freeze. In a grazing situation, usually we recommend to wait 7 days after a hard freeze before allowing cattle to graze these plants.