CWC Technology Brief

COMMERCIAL DEVELOPMENT OF DISEASE-SUPPRESSIVE COMPOST

Purpose

To determine the feasibility of developing a value-added product for the nursery industry through the introduction of beneficial microorganisms into composted yard debris.

General Description

Natural compost and compost amended with beneficial microorganisms was evaluated in greenhouse bioassays for ability to suppress diseases of pea caused by Fusarium solani, and Rhizoctonia solani; and a disease of radish caused by Pythium ultimum. A supplemental study, funded in part by the Weyerhaeuser Company, involved bioassays for the suppression of diseases of Douglas Fir caused by Species specific to conifers, Fusarium oxysporum and Pythium ultimum. The nine to fifteen week old compost was treated with Biological Disease Control Agents (BDCAs) using a water suspension sprayed onto the compost during screening. The treated compost was stored in the curing area of the compost facility and evaluated over a 12 week period. All inoculations were made during the normal operation of the compost facility using routine composting equipment, in order to evaluate the feasibility of this approach in a commercial facility.

Pre-selected, Peninsu-Lab (PL) BDCAs with known suppressive properties were used for the first fifteen inoculations, and BDCAs isolated from natural compost showing suppressive properties, were used for the last nine inoculations. PL BDCAs used consisted of two fungi, Trichoderma hamatum and T. harzianum, and two bacteria Pseudomonas fluorescens and Acinetobacter spp. Four fungal isolates from the suppressive compost piles were all Trichoderma-like. Various combinations of the above were used in the inoculations.

More than two dozen chemical, physical, microbial, and bioassay analyses were conducted on over 580 samples collected from the compost piles. Over 100 greenhouse suppressive assays were also carried out on the test compost piles.

The results of this study clearly demonstrated that unamended yard debris compost produced at this facility is naturally suppressive to the three pathogens studied. The addition of selected BDCAs to the compost increased its suppressive nature, in some cases providing 100% disease control. This demonstration is even more impressive considering the fact that the BDCAs could not be introduced into the compost stream during the ideal time, at onset of the mesophyllic phase. Due to a severe windstorm in the region, the compost facility was flooded with storm debris, which necessitated deviating from the original plan of BDCA introduction during cooling of freshly completed compost. The compost inoculated in this study had been stored unscreened for several weeks prior to screening and inoculation with the BDCAs.

The chemical, physical and microbial evaluations performed on the compost in conjunction with the suppressive assays, provided the basis for establishing a quality assurance (QA) protocol for the development of a plant disease suppressive compost (PDSC). This information supplied to the end user of the product would be an objective assurance of a consistent, quality product. This study also revealed certain precautions that are needed to ensure a good quality product.

Production of BDCAs for use in creating a PDSC would cost less than $1.00/m3 of compost using current technology. Introduction of BDCAs into compost on a commercial scale would require only a 30 L sprayer with spray nozzles mounted over the feed conveyer belt of the trommel screen. The only additional labor at the compost facility would involve the set up and monitoring of the sprayer during the application.

This project was extremely successful in demonstrating the feasibility of producing a PDSC in a commercial yard debris composting facility. Additionally, naturally occurring BDCAs have been isolated from the compost and their suppressive nature demonstrated when reintroduced into the compost. The production of a PDSC can be carried out in a cost effective manner, resulting in a high value-added product for the nursery and other plant production industries.

This technology brief was prepared by the Clean Washington Center's Technology Assistance for Business Program.

Report Dated: October 1994

Fact Sheet Update: October 1994