R.D. Lumsden, Research Leader, Supervisory Plant Pathologist, J.A. Lewis, Research Soil Scientist, and D.R. Fravel, Research Plant Pathologist, Biocontrol of Plant Diseases Laboratory; and J.C. Locke, Florist and Nursery Crops Research Unit, USDA, ARS, Beltsville, MD 20705.

Scientists at the USDA, ARS, Beltsville Agricultural Research Center have responded to the need to identify and develop alternative strategies for soil fumigation, which has been done traditionally with methyl bromide, by directing several research programs to address this critical problem. A total of six permanent scientists (SY's), along with their support personnel, are currently involved in this effort. These SY's represent several disciplines: plant pathology, soil science, microbiology and nematology, providing a range of expertise related to the control of soilborne plant pathogens.

Soilborne diseases caused by pathogens such as Pythium and Rhizoctonia are constant problems in the horticultural industry and require the use of chemical fungicides, including methyl bromide. For decades, researchers and growers throughout the world have noted that while some soils tend to encourage soilborne diseases, other soils tend to suppress these same diseases. Years of research have indicated that beneficial soil microorganisms such as Gliocladium virens are responsible for this disease suppression. Yet, until now, problems with formulation inconsistency and application have prevented the commercial application of many biological organisms to control plant pathogens.

SoilGard^TM is a technological breakthrough and captures the pathogen suppressiveness of the fungus Gliocladium virens GL-21 in a convenient, stable and highly effective form. Developed in collaboration with Grace Biopesticides and the Biocontrol of Plant Diseases Laboratory of USDA, ARS in Beltsville, Maryland, SoilGard^TM is an entirely natural product consisting of spores of the fungal strain GL-21 in a granular formulation. SoilGard^TM is registered with the U.S. EPA for control of damping-off and root rot pathogens of ornamental and food crop plants growing in greenhouses, nurseries and interior gardens. The label will be expanded for use in the field. Although SoilGard^TM was first found to have activity against damping-off caused by Rhizoctonia solani and Pythium species, it has recently been found to protect row crops from Sclerotium rolfsii and possibly other host-pathogen combinations.

When incorporated into potting media, SoilGard^TM controls plant pathogens through a variety of mechanisms including parasitism, antibiosis, competition and exclusion. Gliocladium virens is known to parasitize some soil pathogens such as R. solani. The Gliocladium will actually wrap itself around the pathogen and release enzymes that destroy the pathogen's cuticle, leaving the pathogens susceptible to attack. GL-21 also produces a broad spectrum antibiotic called gliotoxin which kills many soil pathogens. Gliotoxin is not found in the SoilGard^TM formulations, but when the spores of GL-21 begin to grow in the soil, GL-21 produces the antibiotic.

SoilGard^TM represents the new generation of environmentally friendly pesticides. SoilGard^TM has a "Caution" label, but the product has essentially no mammalian toxicity. It is exempt from tolerance for use on all food crops. SoilGard^TM has the minimum re-entry interval allowed by the U.S. EPA and has a "zero day" preharvest interval.

The team at Beltsville is carrying out studies to expand the use of SoilGard^TM to determine its effectiveness in integrated pest management (IPM) and sustainable systems for replacement of methyl bromide. If successful, this product may be used immediately in applications where methyl bromide has been used routinely for control of soilborne disease problems. The team has identified several additional beneficial microorganisms for control of soilborne plant pathogens. Some of these microorganisms have been recently discovered, while others are near transfer to industry for development as commercial products.