Not all the sucking sounds these days are coming from the federal government and the ever increasing U.S. national debt which tipped the scale at $12.3 billion in late January.

Sucking sounds from plant parasitic nematodes in farm field soils translate into lost yields and income for farmers. The nematode’s needlelike stylet mouthpart sucks the cell contents from plant roots in vegetable and perennial crops in California’s Imperial Valley.

“Nematodes are somewhat of an unrecognized disease of plants; out of sight and out of mind,” said Donna Henderson, plant pathology advisor with the University of California Cooperative Extension, Imperial County, Holtville, Calif.

Henderson dished up the dirt on sub-surface digging nematodes during the 20th annual Fall Desert Crops Workshop in Brawley, Calif., in December.

Western Farm Press was the official workshop sponsor. Commercial sponsors included: BASF and Bayer CropScience (Platinum sponsors); Syngenta and Tessenderlo Kerley, Inc. (Gold); Dow AgroSciences, FMC Corp., and Valent (Silver); and Certis USA (Bronze).

Nematode species

Nematodes targeting Imperial Valley agricultural production include: root knot nematode, Meloidogyne spp.; needle nematode, Longidorus africanus; lesion nematode, Pratylenchus spp.; stubby root nematode, Paratrichodorus spp. and Trichodorus spp.; and the sugarbeet cyst nematode, Heterodera schachtii.

Henderson informed growers on the importance of nematode diagnosis as the first step toward management.

Root knot, lesion, needle, and stubby root nematodes have a wide host range including most agricultural crops grown for food and fiber.

The best hosts for the needle nematode include sugarbeet, snap bean, and lima bean. Carrot is a fair host. Non-hosts include cauliflower and cabbage.

The sugarbeet cyst nematode is appropriately named due to the cysts that grow on the sugarbeet root. The cysts contain female nematodes in the reproduction stage.

“It’s a common misconception that the sugarbeet cyst nematode only attacks the sugarbeet,” Henderson said. “The nematode can also infect most cole crops resulting in stunted growth. It’s best to avoid rotating a cole crop with sugarbeets if the field has a history of high sugarbeet cyst nematode levels.”

Symptoms of nematode infestations include: stunted plants in circular ‘hot spots’ or patches; reduced plant growth and yield; mid-day wilting despite adequate water; knotting, galling, or cysts on roots; plus in carrots a forked taproot can occur.

“When comparing a nematode-infested plant with a healthy plant the most common evidence of nematode damage is stunting and reduced growth,” Henderson said.

Nematodes tend to aggregate into hot spots and generally are not uniformly found throughout the field, the plant pathologist says. Random soil samples should be collected to locate the hot spots not visible to the human eye.

Soil testing is the most accurate method to identify nematode species and gain accurate population counts.

Henderson shared a chart with expected yield loss projections from the root knot nematode (M. incognita) in various vegetables grown in the Imperial Valley.

If a 250cc soil sample contains 16 root knot nematodes then a pre-plant treatment should be weighed in tomatoes. About 200 nematodes in the sample can result in a 14 percent yield loss. Remarkably, 200 root knot nematodes in a soil sample from a squash field can lead to 100 percent crop loss.

Sampling techniques

Henderson suggests the following steps for accurate nematode sampling:

• Divide the field into blocks five acres or less in size.

• Use a shovel to obtain samples in clay-type soils; a soil probe in sandier ground.

• Walk through each block and randomly collect soil samples 12-24 inches deep.

• Place all samples from a single block into one plastic bag.

• Gather up more than 250cc of soil per block.

• Label the bag with the date and your name plus the current/previous crop variety.

Nematodes are live organisms which are sensitive to heat. Leaving bagged soil samples in the back of the pickup on a hot day can kill the nematodes. Henderson suggests refrigerating samples, not freezing them, before shipment to a lab. Place an icepack in the shipping container. Contact the lab prior to determine the preferred shipping protocol.

Among the nematode analysis labs in California: Shields Entomological Services, Brawley; the California Department of Food and Agriculture’s Nematology Lab, Sacramento; and Nematode Inc., Selma.

Management

Henderson says commonly used available chemical fumigant treatments approved in California include products containing: Metam Sodium; 1,3-Dicholorpropene; a 1,3-Dicholorpropene-Choloropicrin mix; and Oxamyl.

Available natural biological products include Ditera, Melocon, or various natural oils or extracts (Neem, sesame oil, Quillaja).

Henderson is currently researching Abamectin seed treatment, natural products, and trap crops as part of a multi-faceted control strategy against the sugarbeet cyst nematode. Other management options include green manure crops, trap crops, and soil solarization and a combination of tactics. Green manure, usually a mustard plant, is usually grown for about two months and incorporated into the soil before the flowering stage. Isothiocyanates in the plant provide the fumigant control. Trap crops including marigolds release toxic chemicals from the roots when fed upon.

Growers should be careful since some green manure “brassicaceous” plants and marigolds are actually good hosts for some root knot nematode species and can actually increase parasite numbers. Soil solarization may only heat the top 12 inches of the soil, Henderson says. Nematodes at lower soil depths can move deeper into the root zone.

An alternative bio-fumigation technique is the application of seed meal or mustard meal soil amendments. Mustard seed meal is a commercial waste byproduct from defatting mustard oil from the mustard seed.

The leftover seed tissue contains high levels of glucosinolate chemicals that break down into isothiocyanate products. Henderson says selecting the right mustard seed meal is important since some types fail to provide nematode control.

Crop rotation is a management option for the sugarbeet cyst nematode in the Imperial Valley. Crucifers, sugarbeets, spinach, and some related weeds are good hosts for cyst nematodes. Growers may want to stay away from the crops depending on soil sample results. Rotation is a poor option for root knot and needle nematodes since the parasites have a large host range in the Imperial Valley.

For more information, contact Henderson at (760) 352-9474 or dhenderson@ucdavis.com.

email: cblake@farmpress.com