Alfalfa Seed Production in California

 

Approximately 80 million pounds of alfalfa seed are produced each year in the United States.  California, Idaho, Oregon, Washington, and Nevada provide 85% of this production.  The balance is grown primarily in Utah, Arizona, Wyoming, and Montana.

 

Among the most important production factors that have an impact on seed yield and quality are pollination, irrigation, insects and weed infestations.  Research funded by state boards and commissions targets issues of importance to the seed industry and helps maintain its viability despite changing economics, competition from other crops, and in some cases increasingly restrictive regulatory constraints.

 

Production Practices

 

Properly timing cultural practices is the key to a successful agricultural production system. For alfalfa seed production in California, this includes:

 

• Winter irrigation to provide 40-50% of the annual water requirement

 

• Fertilization with required nutrients as determined by soil or tissue tests

 

• Application of herbicides to control problematic weeds

 

• Spring clipping to initiate the seed crop

 

• Application of insecticides to eliminate harmful pests

 

• Pollination beginning in late May or early June

 

• Crop irrigations timed to promote seed set without stressing to the point where yields are reduced

 

• Hand weeding as necessary to control noxious weeds

 

• Desiccation of the seed crop prior to harvest

 

• Harvest and destruction of crop residue including volunteer alfalfa plants resulting from the previous seed crop.

 

Irrigation

 

An essential component of alfalfa seed production is timely irrigation scheduling.  Highest seed yields are obtained when irrigation practices prevent severe plant stress and promote slow, continuous growth through the entire production period without excessive stimulation of vegetative growth.  In the Central Valley of California, alfalfa seed production requires an average of 3 acre-feet of water per year.

 

When water is available, deep soil moisture applied in the winter and early spring can partially offset summer irrigation requirements providing a buffer to avoid detrimental effects of severe moisture stress. Optimum water management for seed production requires that the grower stress the plant just enough to promote pollination, while not stressing to the point the growth and blooming stop.

 

Deciding when to terminate irrigation for the season is also critical.  Enough water is required to mature the seed, but soil moisture must be depleted prior to desiccation or the plant will not dry down adequately to prepare for harvest. With excessive late season soil moisture, direct combining becomes difficult with a large amount of seed lost in the process.

 

Insect Control

 

The most important pests in alfalfa seed fields are lygus bugs that feed on the buds, blooms, and developing seeds of alfalfa throughout the season.  Spider mites, stinkbug, and chalcid may also cause significant yield reductions in some years.

 

Insect control costs vary widely, but are typically the highest of all production costs.  Breeders have developed techniques to screen for host plant resistance, but until resistant varieties are developed, growers must rely on chemical control of pests in order to maintain economic yields.

 

Insecticides must be carefully selected and applied to kill the target insects without harming bees.  There are few chemicals registered for alfalfa seed that effectively control insect pests.  The 24(c) registration process is used to obtain valuable chemicals for use on seed crops.  In order to use these materials, growers must comply with label restrictions to insure none of the treated seed or crop residue enters the food chain.

 

Compounding the problem of rare new product registrations, effective materials can be quickly rendered ineffective when insect populations develop resistance.  Bioassay techniques can be used to evaluate resistance mechanisms and predict resistance development, which gives growers the opportunity to adjust practices to retain product effectiveness.

 

Pollination

 

Alfalfa must be cross-pollinated to maintain high forage and seed yields.  Pollinator activity can significantly affect seed yield. Irrigation, pesticide applications, and the weather can all negatively impact the pollinator.  Honeybees, leafcutter bees, alkali bees, or a combination of the above are used to pollinate alfalfa for seed production in the United States.

 

Honeybees are used almost exclusively to pollinate alfalfa for seed production throughout California.  They are inexpensive and readily available, but they are not the most enthusiastic pollinators of alfalfa.  Because of their inefficiency, it typically requires a long pollination season to set seed with honeybees. 

 

There are concerns within the seed industry about the future availability of honeybees with the anticipated arrival of Africanized honeybees. A related concern is the ability of honeybees to remain competitive in light of the high incidence of mite infestations in colonies used for commercial pollination.  To address these concerns, researchers are improving the attractiveness of alfalfa to honeybees, selecting strains of honeybees that show a propensity to collect pollen, evaluating leafcutter bees under California production systems, and developing techniques to improve the success of beekeepers when requeening established colonies.

 

Weed Control

 

Control of weeds in alfalfa seed production is essential not only to prevent competition and encourage the growth of the alfalfa, but seed for certification must meet stringent requirements for purity.

 

Weed control in alfalfa seed fields is continuous from stand establishment to the final cleaning process.  Most winter and summer annual and perennial weeds are effectively controlled by the use of herbicides registered for alfalfa.  However, chemical control is not always 100% effective and large weeding crews are often employed to remove remaining weeds from seed fields.  The few weeds that may escape and be harvested with the alfalfa seed are removed during the conditioning process.  Modern seed cleaning equipment is available to separate and remove weed seeds from alfalfa seed, although a significant quantity of alfalfa seed can be lost in the process.  Therefore, control of weeds in the field is a more efficient and less expensive practice.

 

For additional information, contact Shannon Mueller, UC Cooperative Extension, 1720 S. Maple Ave., Fresno CA  93702.  Phone:

(209) 456-7285, or Email:  scmueller@ucdavis.edu

 

 

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