Ten Steps to Manage
    Damaged Alfalfa Fields

     Marsha Campbell Mathews
    Farm Advisor

    Here are some tips on salvaging water-damaged alfalfa stands from Mick Canevari, Farm Advisor in San Joaquin County.

    There has been significant damage to most alfalfa fields this past winter and spring. What started out to be a rain-welcomed winter has turned into a disaster for many crops, including alfalfa. Many calls have come into the Extension office asking: What is the problem? Which disease? What to do?

    We all know that the problem was excessive amounts of rainfall. Actually, most fields were in reasonably good to fair condition in February. All the rain in March with saturated soils and standing water for days in fields caused an anaerobic state; that being a condition where the oxygen between soil particles was displaced by water. Plants, like people, require oxygen to remain healthy and grow. Under long periods of flooding and plants trying to grow in oxygen depleted soils, they will quickly suffocate and die.

    Roots and crowns completely rot and when removed from the soil, have a putrid odor and soft or mushy tissue. This is not phytophthora root rot or other fungi that cause crown rot. However, this condition of damaged roots can quickly give way to such diseases.

    10 Steps to Manage Water Damaged Alfalfa Fields:

    1. Cut winter growth as soon as soil conditions allow.
    2. If possible, cut above new regrowth - 3"-5" height.
    3. Hold off from irrigation until regrowth is substantial. Allow damaged plants to develop new bud growth and utilize soil moisture.
    4. Manage your irrigation with quick shots of water. Avoid long irrigation sets.
    5. Maintain tail water drainage. (Any standing water beyond 6-8 hrs. will be the final bullet.)
    6. Try and delay the second cutting as long as possible (10-30% bloom; this will help the plant recover).
    7. Add nitrogen fertilizer to help stimulate growth. (Approximately 30-40 units until plants recover. Not a recommended practice in healthy fields.)
    8. Control high populations of insects and weeds to maintain alfalfa health. Avoid systemic or soil active pesticides which could cause injury to already stressed plants.
    9. Try and reseed small areas that completely died out. Perennial clovers or alfalfa are better than the weeds that will take over.
    10. If plant population decreases below 4-5 plants per sq. ft. the end may be near. Plan for a new crop.


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    November 5, 1999