CHIPPEWA FALLS, Wis. — As the calendar flips to May, the snow has finally melted and air temperatures are becoming close to normal in northwest Wisconsin. Although spring growth of alfalfa is behind normal, stand evaluations are a way for farmers make sensible management decisions about fields.
Did plants suffer winterkill? As spring green up occurs, healthy plants will have growth occurring from the crown along with a firm, white taproot. Plants that suffered winterkill will have no spring growth and possibly a crown that has frost heaved above the soil surface. Taproots will also be brown and mushy. Rotate any fields when 50% or more of the stand has suffered winterkill.
Did plants suffer winter injury? Healthy plants will have even growth across the whole field along with a firm, white taproot. Alfalfa plants suffering from winter injury will have uneven growth around the crown of the plant, uneven height of stems, and roots with brown discoloration. Plants with 50% or more of a discolored root will probably die during the growing season. Rotate fields when a majority of plants has suffered this level of damage.
What is the potential productivity of this field? First year stands should have a minimum of 12 plants/ft2 while stands over 1 year old should have at least 6 plants/ft2 (40 stems/ft2 ). If possible, rotate stands that do not meet the densities above.
The late start to the growing season will also influence other forage management decisions.
How does late planting impact corn for silage? From mid-May to mid-June, the potential for yield and quality losses in corn steadily increases. To minimize these losses:
- Prioritize corn planting over alfalfa seeding
- Consider no-till to minimize trips across fields
- Switch to short season hybrids after May 20
How should I manage alfalfa if I harvest using my typical cutting schedule? In 2018, farmers who cut alfalfa based on the calendar will be harvesting first crop at an earlier maturity:
- Recognize immature alfalfa will have higher Relative Feed Values
- Let second or third crop mature to early or mid-bloom
- Make sure stands have adequate pH and potassium levels
- Don’t harvest after Labor Day to allow buildup of root reserves for the fall
One final note, the Midwest Forage Association and local Wisconsin forage councils are conducting a formal Aphanomyces race survey of alfalfa fields. We are looking for soil samples from alfalfa fields that are suspected to be suffering from Aphanomyces root rot. Roots and stems of Aphanomyces infected seedlings initially appear gray and water- soaked, and then turn brown. In established stands, Aphanomyces reduces yield due to poor root growth and less nodulation resulting in plants that are slow growing in the spring and rebound slowly after harvests. Please contact your local forage council or Damon Smith (damon.smith@wisc.edu) if you suspect fields containing Aphanomyces.
— UW-Extension
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