Managing Alfalfa After Flooding
Farm Advisor, San Joaquin County
Alfalfa can withstand flooding for a limited time, depending on its growth stage, air and water temperature. Dormant varieties may withstand submersion for as long as ten to fourteen days. When actively growing, plants can usually withstand submersion for less than three to five dayswith minimum damage. During winter flooding and colder temperatures, plants survive longer due to their slowed physiological processes. Also, moving water is less harmful than standing water, containing more oxygen.
When fields have drained, inspect roots and crowns for damage caused by anaerobic (without oxygen) conditions. Roots that are soft and compress easily when squeezed may be damaged beyond investing any further time or money. If roots are beginning to release a strong odor, excessive injury has probably occurred and removal is advised.
Ten Steps to Manage Flood Damaged Alfalfa Fields
Alfalfa stands exposed to minimum flood damage can behelped with the following management suggestions:
- Caution is advised on the use of herbicides when plants are stressed. If weed control is necessary, reduce use to the lowest label rates. Avoid the use of herbicides that are foliar systemic or absorbed through the roots.
- Delay first harvest until 10% bloom or longer. This will increase carbohydrates and strengthen the root system.
- If possible, cut above the new re-growth (about four to six inches).
- Monitor and treat for weevil and aphid populations early. Stressed plants can be a preferred target and subject to increased damage by these pests.
- Silt deposits of over two to three inches will weaken the stand and may need to be re-graded and re-established in places.
- Add nitrogen fertilizer to help stimulate faster recovery of damaged roots (approximately 30 to 40 units after first harvest).
- Hold off from an irrigation until vegetative growth is substantial and allow roots time to strengthen and utilize excessive soil moisture.
- Manage your irrigation with quick shots of water. Any standing water beyond six to eight hours will only worsen the problem.
- Re-seeding of small areas in spring may be useful where alfalfa has completely died out and a new seed bed is formed. Re-seeding of alfalfa into existing stands has limited success. Interseeding alfalfa plus red clover mix may be better suited in problem areas where developing a new seed bed is not possible.
- If the alfalfa population decreases below three to four plants per squarefoot, the end may be near. Plan for a new crop!
November 5, 1999