Organic alfalfa growers need early crop management

Successful organic alfalfa growers must be one step ahead of weeds and insect pests to stay in the game.

Prior to land preparation and planting, growers need to be aware of the demands of the crop and the risks of the market, more so than conventional hay growers, said University of California Cooperative Extension farm advisor Carol Frate. Speaking at an Organic/Sustainable Production conference in Tulare, Frate stressed that good stand establishment for organic alfalfa is key to acceptable yield and hay quality.

A high level of management during stand establishment is important because subsequent weed and pest control options for organic growers are limited.

"It's critical that growers pay attention to the conditions in the field," Frate said.

Hosted by the Organic Fertilizer Association of California and the Tulare-Kings chapter of the California Association of Pest Control Advisers, the one-day conference featured speakers focused on production in organic systems in the southern San Joaquin Valley.

Organic dairies' demand for hay is the primary driver for organic production. A 2013 cost study by UCCE showed that average annual yields for organic alfalfa in California range from five to 10 tons per acre with three to 10 cuttings, depending on location and alfalfa variety. Eight tons per acre over seven cuttings per year is common in the San Joaquin Valley. The UC cost study used a yield of seven tons per acre because yields from organic alfalfa can be slightly lower due to a lower level of control for insect pests and weeds.

Returns to growers will vary during the season, the report stated, depending upon the market and hay quality, with an average of about 20 percent over conventionally grown alfalfa. Based on current markets for organic hay, an estimated price of $260 per ton was used in the report to calculate returns over inputs.

According to an Agricultural Marketing Resource Center 2010 survey, California had the highest number of certified organic dairy cows in the nation.

Growers considering organic alfalfa production should select their fields carefully, Frate said, taking into consideration soil type and fertility. They should avoid fields with severe weed or rodent infestations. Field bindweed, dodder and nutsedge will make it difficult to have weed-free hay, she added.

"We need the crop to be vigorous. That is the primary tactic for combating weeds and the most difficult in organic production," Frate said.

Nutrient needs should also be assessed with soil samples and crop history. This is an important step because of the high costs of organic fertilizer. Phosphorous and potassium are the two critical nutrients needed for alfalfa and composts can vary in their percentages of those elements. Moisture percent of compost can vary greatly, Frate said, and with higher moisture, volume has to be increased to reach the desired level of nutrients. Pre-plant, compost applications should be at four tons per acre.

In established organic alfalfa, Frate said the optimum times for fertilizer applications are after the first or second cutting or when the crop is experiencing vigorous growth in the fall. Winter application will encourage weed growth, she said.

Recommended planting times for organic alfalfa in the San Joaquin Valley are based on soil and air temperatures, day length and weed windows. Frate said the September-October window is better than the January-February window because fall-planted stands will have better root development and can outcompete most winter weeds. Yields can also be higher in fall-planted fields. One of the best tools for weed control prior to planting is pre-irrigation. That allows growers to see potential weedy areas and take control steps.

The disease sclerotinia stem and crown rot is the one disadvantage to the fall planting date.

Organically grown seeds are required for certified organic production. However, if growers can document that organically grown seeds are not available, they can use non-organic seeds. Genetically engineered seeds are prohibited in organic production. Frate recommended using certified seed to avoid weeds seeds and stem nematode.

Growers should also plant the most pest- and disease-resistant varieties of alfalfa. Highly resistant varieties will have more than 50 percent of resulting plants with resistance.

Non-dormant varieties and seeding fields at a higher rate are additional weed-control tools that Frate promotes. Seeding rates at 25-30 pounds per acre will produce a denser stand and out-compete weeds, she said.

Other weed control strategies include sheep grazing after the last cutting and in established fields, over seeding with another crop. Frate said carefully managed grazing could cut down on weeds and also help with weevil management. The down side is that sheep can bring in weed seeds. Spot treatments with propane can be done in weedy areas. Overseeding with oats or clover can help with weed control during cool-weather months, but the hay quality will be affected, she said.

Management is the primary insect control strategy. Frate said that alfalfa fields contain a large diversity of insects, including many beneficials. Leaving strips of unharvested alfalfa will help maintain a population of predators and parasites.

Green chopping can help with armyworm control. Early harvest may reduce aphid populations, but there will be a decrease in yields.

Vertebrate pests—voles, gophers and squirrels—can present major problems in an organic system. This is another area best scouted prior to field selection, Frate said. Deep tillage can destroy some burrows, and removal of vegetative cover adjacent to fields is recommended. Flood irrigation helps decrease populations, as does encouraging owl and raptor populations.

Web resources for organic alfalfa production include the UC integrated pest management site at ipm.ucdavis.edu, the UC alfalfa page at alfalfa.ucdavis.edu and the National Alfalfa and Forage Alliance website www.alfalfa.org.

(Cecilia Parsons is a reporter in Ducor. She may be contacted at cparsons_8776@hotmail.com.)