Introduction
In recent years it has become evident, as a result of public opinion and environmental laws, that new and safer alternatives to traditional synthetic pesticides are both desirable and mandated. Research emphasis in our Unit has therefore been on the development of alternative approaches to control pathogens and pests of ornamental crops utilizing biocontrol agents, natural plant products and reduced risk pesticides. The current focus is on utilizing these components to develop an integrated system to control soilborne pathogens without the use of pre-plant fumigation with products such as methyl bromide.

Biological control agent research has utilized naturally-occurring soil saprophytic fungi to compete with and/or destroy pathogenic soilborne fungi allowing production of marketable ornamental bedding and flowering crops.   {See details below}.

Natural products research has primarily centered on evaluation and development of extracted plant oils as alternatives to synthetic pesticides. Aspects of both direct and protectant activity have been evaluated as well as formulation of promising materials into commercially acceptable biopesticide products.   {See details below}.

This research has been accomplished through cooperative research ventures between private-sector partners and the U.S. Department of Agriculture. These ventures have resulted in over eight U.S. Patents and the development and registration of biocontol agents and natural plant products with the U.S. Environmental Protection Agency as environmentally- and applicator-friendly biopesticide products with activities against fungal pathogens, insects and spider mites.

Biological Control Agent Development

Trichoderma - Fusarium wilt of greenhouse-grown chrysanthemum, caused by Fusarium oxysporum f. sp. chrysanthemi, was chosen as the bioassay system in which to screen for a biocontrol agent capable of controlling this serious disease. Twenty-two isolates of soil fungi reported to have biocontrol potential were evaluated. The four isolates that reduced disease incidence the most were evaluated alone and in combination in a greenhouse cut mum production system that included pre-plant adjustment of soil pH to 7.2, addition of three field strains of F. oxysporum, addition of the test biocontrol strains to designated plots, and use of an all-nitrate nitrogen fertilization program. In addition to the pre-plant pH adjustment and all-nitrate nitrogen fertilization program, the control plots received a drench application of benomyl on a 14-day interval. Trichoderma viride T-1-R9 (patented), a benomyl-tolerant strain, in combination with a reduced number of benomyl drenches (two) provided the best control of Fusarium wilt.

Gliocladium - Damping-off of bedding plants caused by two common fungal pathogens, Rhizoctonia solani and Pythium ultimum, was used as the screening bioassay to identify a second biocontrol agent. Gliocladium virens GL-21 was shown to have the greatest level of activity against the combination of these two serious damping-off pathogens. GL-21 is a naturally-occurring isolate from the USDA Beltsville Agricultural Research Center which is capable of being mass fermented in liquid culture to produce a high percentage of fungal chlamydospores. Under a cooperative research and development agreement with the W. R. Grace & Co., this biocontrol agent was developed and registered by the U.S. Environmental Protection Agency as one of the first fungal biocontrol agents for use against soilborne pathogens. This biocontrol agent (originally called GlioGard) is marketed under the trade name of SoilGard® to the horticultural industry. Further research determined that SoilGard® must be applied and incorporated prior to planting to allow the dormant chlamydospores to resume growth and produce an antibiotic (gliotoxin) in the growing medium. It is this antibiotic that provides the primary activity of this biocontrol agent against soilborne pathogens.

Natural Plant Products Development

Traditional agricultural practices have utilized natural products for centuries. In recent years it has become evident, as a result of public opinion and environmental laws, that new safer alternatives to conventional synthetic pesticides are both desirable and mandated. To address this need, a number of natural products and plant extracts are being evaluated for their potential to control a variety of fungal pathogens and to develop promising candidates into commercial biopesticides.

~ Neem Oil Development

Initial research in the area of natural products and plant extracts involved extracted plant oils. Neem oil, obtained from the seeds of the tropical mahogany tree, Azadirachta indica, was developed into a commercial triple-action biopesticide product with activity against fungal pathogens, insects, and spider mites.

Private Partner Cooperation: This project was a joint venture of the W. R. Grace & Co., Horticultural Products Division, and the USDA , Floral and Nursery Plants Research Unit. Grace approached the USDA offering to provide by-products of a neem seed extraction process in order for the USDA to determine if sufficient biological activity remained in these materials to warrant development of a biopesticide. The USDA did the pest and pathogen screening which demonstrated the potential of an oil fraction. Grace contributed formulation expertise to provide compositions for evaluation.

Screening: Foliar applications of various neem by-products and formulations were made to a number of test crops both under greenhouse and outdoor conditions. Observations were made as to plant safety and the effect on several fungal pathogens, insects and mites.

Pesticidal Activity: Neem oil was shown to have good activity as a preventative treatment to protect against infection by pathogens which cause powdery mildews and rusts. Post infection activity was limited to surface pathogens such as powdery mildew. Treatment also resulted in a repellency effect on insects such as the greenhouse whitefly. Activity against spider mites was dramatic on outdoor roses treated weekly in that there was no buildup of spider mite populations even during the heat of summer. Laboratory tests later demonstrated a high level of spider mite egg mortality following direct treatment with the oil.

Formulation Development: Grace laboratories provided the formulation expertise to develop an agriculturally useable product. They also provided the national field testing network to evaluate the biopesticide for both entomology and plant pathology needs.

Products: As a result of this project, a series of products were developed by Thermo Trilogy Corp. Thermo is the base producer and labels the commercial products Triact 70 and Trilogy 70 while Green Light has the license to package a series of products for retail and homeowner use.

Marketing: In addition to Thermo and Green Light packaging, labeling, and distributing their respective products, Olympic Horticultural Products now serves as a national distributor for Thermo products in serving the commercial horticultural market.

~ Clove Oil & Other Botanicals Research
Subsequent research demonstrated that formulated clove oil could effectively reduce the population of various soilborne fungal pathogens and control diseases caused by them. Other plant extracts, for example, from Cassia, cinnamon, and Guayule are also being evaluated for their potential as biopesticides to control diseases caused by soilborne pathogens.

Clove oil patent:Under a cooperative research and development agreement with the Thermo Trilogy Corp., a patent was applied for and granted jointly to the USDA and Thermo Trilogy Corp. based on the effectiveness of clove oil as a fungicide when used as either a foliar application or soil amendment/drench. The patent covers the use of clove oil as a plant fungicide, based on the demonstration of both foliar and soilborne disease control. Research demonstrated that formulated clove oil could be added to soilless growing medium contaminated with the damping-off pathogens Pythium ultimum or Rhizoctonia solani resulting in a healthy stand of seedlings. Use of clove oil in soil-based assays with Phytophthora nicotianae effectively reduced soil populations of this pathogen and provided good disease control on seedling transplants.

Screening: Laboratory studies are being conducted to evaluate the possible activity of a number of "generally regarded as safe" (GRAS) materials. Several spices and flavorings did exhibit, in petri plate tests, inhibition of test fungal pathogens. Of these materials, clove oil appeared to have the greatest potential and was further evaluated in bioassay systems utilizing several soilborne fungal pathogens to determine the effect on soil populations of the pathogen and seedling bioassay systems to determine the ability to reduce disease.
 

Pesticidal Activity: Varying amounts of test materials were added to soils that had been previously infested with known amounts of a pathogen. The surviving population of the pathogen was monitored over time using soil dilution bioassays or pathogen recovery procedures to determine the effect of the test material. Several test materials were shown to have varying levels of activity against one or more pathogens.
 

Disease assays: Bioassays utilizing major soilborne fungal pathogens (Rhizoctonia, Pythium, Fusarium, Verticillium, Phytophthora) have been conducted and several test materials have been shown to provide seedling protection. Clove oil applied either as a pre-plant or as a drench provided protection against seedling damping-off. Pre-plant application with clove oil and several other materials also gave disease protection to crops such as chrysanthemum, melon, and vinca (periwinkle).

Other plant extracts from Cassia, cinnamon, and Guayule are being evaluated for their potential as biopesticides to control diseases caused by soilborne pathogens. It is anticipated that a combination of these biopesticides, possibly integrated with other components such as biocontrol agents, can ultimately serve as a management alternative to pre-plant fumigation in the production of ornamental crops. Cassia extract has been evaluated under a material transfer agreement as a soil treatment in several soil bioassay systems and looks to hold promise in reducing populations of the pathogens and in controlling disease on crops planted in the treated soils.

Note: This article was edited and reformatted for this web page by Ramon Jordan from two Posters prepared and presented by James Locke at our recent Floral & Nursery Plants Research Unit Open House.