Microscopic worms called nematodes are a problem for many crop producers. Nematodes, found in soil, cause significant reductions in yield and quality of produce. Feeding by nematodes damages the plant by affecting nutrient absorption and providing infection sites for a wide range of secondary plant pathogens. Root-feeding nematodes have also been found to transmit viral diseases.

Traditionally, the most common means of controlling nematodes have included soil fumigation with Telone^® and methyl bromide, and application of nonfumigant nematicides such as organophosphates and carbamates. In 1987, researchers at Abbott Laboratories discovered
DiTera^® (formerly known as ABG9008), an environmentally compatible, biological alternative to chemical nematicides for the suppression of plant nematodes.

"DiTera^® effectively controls several economically important nematode species, including root knot (Meloidogyne spp.), cyst (Heterodera/Globodera spp.), lesion (Pratylenchus spp.), stubby root (Trichodorus spp.), sting (Belonolaimus spp.), burrowing (Radopholus similis), and several others that attack various crops. It kills nematodes in the soil on contact," says Prem Warrior, manager of agricultural microbiology, Chemical and Agricultural Products Division at Abbott Laboratories, Long Grove, IL.

DiTera^®, a natural product from the hyphomycete fungus Myrothecium spp., is composed primarily of proteins, sugars, and lipids and is stable under heat and environmental rigors. "Researchers here at Abbott Laboratories, along with university researchers and university cooperative extension personnel, tested the efficacy of DiTera^® through various levels of laboratory, growth chamber, greenhouse, microplot and field studies over the past 9 years. At this point,
DiTera^® has been tested primarily on vegetable crops, including carrot, cauliflower, egg plant, and squash, though studies on perennial crops such as grapes and citrus are under way," says Warrior.

Field evaluations on carrots conducted in Bakersfield, CA, showed that root-knot nematode galls were reduced to significantly lower numbers when treated with DiTera^® at 60 pounds per acre 1 week prior to emergence, compared with untreated controls. These results were statistically comparable to the recommended dosage of methyl bromide at 200 pounds per acre. In this same experiment, methyl bromide applications gave 55 percent marketable carrots, compared to DiTera^® at 53 percent, while the untreated crop yielded only 40 percent. Typically, without adequate nematode protection, carrot yields in this major carrot-producing area can be as low as 20 percent. Several trials on carrots, cole crops, and grapes have been completed to date and the results have been very encouraging in terms of nematode control and crop yield response.

"In field tests we've conducted so far, we found that DiTera^® suppressed all plant nematode populations in the soil and roots. It has no nematicidal activity against free-living nematodes, those which feed on soil micro-organisms. Reduced numbers of nematodes in the soil and roots were noted at a use rate of 25 to 100 pounds per acre, depending on the crop, soil type, and nematode species," Warrior says. "In addition to its direct nematicidal activity on juvenile and adult nematodes, applications of DiTera^® can also possibly modify the rhizosphere microbiology. This could increase the number of natural predators, alter the carbon/nitrogen ratio of soils, and increase the levels of ammonia around the root zone of plants, resulting in overall suppression of nematodes. DiTera^® provides economic suppression comparable to nonfumigant chemical nematicides."

DiTera^® is available as spray-dried powder (average particle size 40 microns) produced by fermentation and is known as DiTera^® WP. A liquid formulation, DiTera^® ES, is an emulsifiable suspension containing 27.5 percent active ingredient. A granular product, DiTera^® G (95 percent) is under development.

DiTera^® ES is applied directly on the soil surface as a suspension in water either as a preplant treatment in the rows or at planting, emergence, or immediately after transplanting. The granular or powder formulations can be sprinkled around the root zone and incorporated into the soil either mechanically or with water prior to planting. Field evaluations at Abbott Laboratories show a single application at the recommended rate will suppress nematode populations and protect young seedlings in the soil. However, multiple applications may be required for high nematode populations and on perennial crops. DiTera^®'s effectiveness may be altered in soils with high organic matter content, especially those containing infected plant roots from previous crops. As is typical for other soil-applied products, the specific recommendations need to be based on the crop, soil type, biology of the pest, and a variety of other factors.

"At the recommended rates of application to soil, we haven't found any phytotoxicity on any of the crops we've tested. DiTera^® has the minimal re-entry interval and waiting period (4 hours) required by law for any pesticide," says Warrior. "We're still compiling data to test the compatibility of
DiTera^® with other soil pesticides and also fine-tuning effective methods to deliver this product to target sites."

After extensive evaluations on its toxicology profile, EPA exempted DiTera^® from a requirement of tolerance on all agricultural commodities and granted unconditional registration for its use on a variety of crops in the United States. Earlier this year, the product was approved for use in several states including California, Florida, and Texas, and it has been registered for use in Chile. A stability test conducted to meet EPA's requirements for product registration showed DiTera^® did not lose its nematicidal activity even after 24 months of storage at room temperature (72 °F). DiTera^® also offers the flexibility of pre- or postplant applications.

Abbott Laboratories holds U.S. patent no. 5,051,255 and several foreign patents on DiTera^®, and plans to have it available in selected agricultural markets in early 1997. Once fully developed and commercialized, it could fill a long-awaited niche in the area of environmentally compatible biorational alternatives to chemical nematicides. DiTera^® is not a replacement for methyl bromide; it is a specific nematicide that provides suppression of plant nematodes with minimal impact on the environment or other organisms.

"In combination with other pesticides, such as herbicides and fungicides, DiTera^® can be an effective component in our overall attempt to find an alternative. The scientific community is skeptical about finding a silver bullet that will replace methyl bromide. Our efforts will be targeted toward developing DiTera^® as an effective component of an integrated pest management system to improve crop productivity," says Warrior.