Organic specialists discuss control of diseases, weeds

Organic growers are expanding their knowledge of pest and disease control at a series of seminars presented by the Organic Fertilizer Association of California.

Managing insect pests, weeds and soil fertility in San Joaquin Valley organic crop production highlighted the one-day program held in Tulare.

A susceptible host, a conducive environment and a pathogen can combine to bring down any agricultural crop. Larry Parker of Vista-based Westbridge Agricultural Products explained that organic growers have to alter those conditions to stay in the game. Organic growers need to stimulate plants to induce systemic resistance as a way of fighting off disease, he said.

One of the stimulants used by organic growers is a seaweed extract that stimulates anti-oxidant production that will reduce fungal infections in carrot crops. Induced systemic resistance also slows colonization of plants by insects, fungi and nematodes. Research in melon crops found that increased plant vigor and avoiding plant stress goes along with disease resistance.

Organic growers should also manipulate their crop nutrients to the advantage of the plant and the disadvantage of pathogens, Parker said. The correct ratio of calcium to potassium in lettuce, he said, will lead to a healthier crop. Manganese inhibits fungal pathogens at levels necessary for plant growth. Zinc reduces aflatoxin levels in pistachios and almonds and also decreases a pathogen's ability to cause disease by keeping numbers below threshold levels.

Biological controls also have a place in organic crop production, but environmental factors such as temperature, soil pH and sunlight can affect how well they reproduce and do the job.

Compost teas are a popular nutrient source in organic production, but Parker warned that poor quality compost could be detrimental to a crop, adding weed and disease pressure.

Other factors growers can control in organic production include modifying the environment. For example, Parker said, farmers could use pruning techniques to increase airflow to a plant and decrease humidity that allows for pathogen growth. Soil additives can also increase soil pH to inhibit fungi.

His suggestions for disease control include frequent inspection of plants, not overfertilizing, employing crop rotations when possible and controlling host weed species.

Speaking on weed control in organic production, University of California Cooperative Extension farm advisor Steve Wright of Tulare and Kings counties called fertilizer management the key to weed control. Uncomposted manure is loaded with weed seeds, he said, and is frequently used in San Joaquin Valley crop production due to the proximity of dairies.

"You need to have a strategy in weed control," Wright said.

Cultivation, herbicides approved for organic use, mulching, flaming and solarization are some options open for organic production. Burying drip irrigation lines can also keep weed populations down.

Wright advised starting with clean plants, keeping weed populations down along field edges and controlling roadside weeds.

There are herbicides approved for organic use, but many are not cost effective, he said, adding that they work best on weeds when they are in the emergent stage, not mature.

No-till practices can also allow weeds to infiltrate fields, Wright said.

Julie Finzel, a UCCE livestock and rangeland farm advisor for Kern, Tulare and Kings counties, noted that targeted grazing by sheep and goats is another alternative for weed control.

Controlling seed production is the goal in targeted grazing, Finzel said. Timing of grazing should be early in the season prior to bolting.

Growers who are interested need to determine the proper timing and length of grazing to be successful in weed elimination, Finzel said. Goats are a better choice for grazing plants that may be toxic, she explained, because they have the ability to metabolize toxins better than sheep. They also can have a significant impact on targeted weeds.

(Cecilia Parsons is a reporter in Ducor. She may be contacted at ceciliaparsons8@gmail.com.)