Friday, October 19, 2012


Some Thoughts and Considerations
            Rory Lewandowski, Extension Educator Wayne County and Crossroads EERA
  We have had some frost over the past week and one question that comes up is the use of alfalfa and/or grass hayfields following a frost.  Management after a frost depends upon several factors.  Was there a frost or a killing freeze? Is the hayfield a legume or a grass stand? What are the needs and goals of the hayfield’s owner.
Temperature is a consideration.  A frost may burn the top of the plant, but growth will still continue from the green, unburned leaf area.  A killing freeze for alfalfa is generally defined as a temperature in the 24 to 25 degree F range over a period of at least 4 hours.   After a killing freeze, alfalfa is done growing and the plant can be cut for mechanical harvest, grazed, or left to overwinter.
          This year, because of the drought, livestock producers need all the forage they can get so many livestock owners are cutting hay fields regardless of the calendar or weather forecast.  Alfalfa is the forage we generally hear a lot about regarding fall management.  One reason for that is because alfalfa regrows by mobilizing and using carbohydrate root reserves to produce new leaf growth after a cutting.  At some point, there is enough new leaf area that sugars manufactured by photosynthesis meet the plants growth needs plus have surplus to put back into root reserves.   If management during the growing season has left low levels of root reserves and now the plant is cut in the late fall, burns more reserves to start growth, but the growing season ends before the plant can grow enough leaves to restore those root reserves, then there is risk of the plant dying over the winter.  The reason the recommendation is made to not cut alfalfa between about mid-September until a killing frost is to protect those plant root reserves.
          So, does this mean that all the alfalfa we have seen around the state that has been cut before a killing frost is going to die over the winter?  No, while some stands will be hurt by this management, other stands will not, or only be impacted in a minimal way.  That is because there are other factors that play a role in determining winter kill.  Factors that affect winter kill include cutting date in the fall which I have mentioned, but there is less winter kill risk when a fall cutting is taken on a young vs. an old alfalfa stand, and less risk when the stand is planted on a well-drained site.  In addition soil fertility is important.  Stands that have maintained good soil fertility, especially soil potassium levels and that have kept soil pH close to that 6.8 level have reduced risk of winter kill.  Finally growers who use improved genetic varieties with good disease resistance and over wintering levels have reduced risk.
          Sometimes the question is asked if too much top growth can lead to smothering over the winter.  In alfalfa this is not an issue because the leaves will dry up following a killing freeze, become brittle and drop off the plant.   The stem that remains standing is not a concern for smothering the stand.  Tall grass plants however can mat down.  This mat can provide a habitat favorable for disease development that could thin out the stand.  For this reason, it is recommended that a grass hay field with tall growth be cut or grazed before winter. 
          With our shorter days and cooler temperatures it becomes very difficult to get a cut legume or grass to dry down enough to bale as a dry forage.  Wrapping wilted forage or harvesting as baleage is the best mechanical option.  Grazing a hayfield is usually a more economical option as compared to mechanical harvest.  Use of temporary electric fencing can facilitate the grazing use of a hayfield.  While forages such as alfalfa, clovers and cool-season perennial grasses do not produce toxic compounds after a frost, bloat can be a concern when alfalfa or clovers are grazed after a frost. 
          The risk of bloat is higher one to two days after a killing frost and when livestock are grazing a pure or mostly pure legume stand.  The safest management practice is to wait a few days after a killing frost before grazing pure legume stands.   At that point the forage will begin to dry from the frost damage.  If animals are not accustomed to grazing high legume content stands, it is a good idea to feed some dry hay before turning into the legume field, or move animals into the legume field in the late morning or early afternoon after they have been grazing another pasture so that they are not entering with an empty rumen.