OFRF funding was awarded for this project in Spring 2008 and in Spring 2007. This summary includes initial data from the first year of research.

Investigator: Eric B. Nelson, Dept. of Plant Pathology, Cornell University, Ithaca, New York
Project location: Cornell University

Summary
Plant diseases, especially soil-borne and seed infecting pathogens, are a serious issue for both greenhouse and field production of many horticultural crops. For example, Pythium aphanidermatum, the causal agent of seedling damping off, has over 50 crop hosts and is present in greenhouse and field soils. Organic growers have limited options for control of these diseases since most of the effective fumigants and seed treatments are synthetic, toxic and potentially polluting. OMRI-listed biopesticides are available as substitutes for synthetic inputs. However, the cost of developing and registering new biopesticide products with the EPA is quite high and as a result few products are available. Furthermore, many of the formulations are not consistently effective under variable field conditions. Relying on applications of a single antagonistic organism to control plant disease can reduce pesticide use if effective in the specific conditions but is in some ways an extension of the conventional pest control mentality.

Compost and vermicompost are microbiologically rich amendments that promote plant growth and can suppress plant diseases. However, the inconsistency of disease suppression prevents growers from fully harnessing this potential benefit. There remains a need for scientifically based tests that are verified in the public sphere to determine if a specific material can suppress plant diseases. This project focuses on increasing our understanding of the complex microbial mechanisms behind compost-mediated disease suppression in order to develop new techniques to predict compost suppressiveness.

The overall goal of this project is to increase the efficacy and consistency of using composted animal manures to enhance disease suppression in organic vegetable and fruit production systems. Specific objectives include:

1. To increase our understanding of how microbes present in compost and vermicompost prevent plant diseases, specifically Pythium damping off:        
   • To identify key microbial species associated with disease suppression
   • To identify potential mechanisms of disease suppression
2. To use this understanding to develop tools for predicting whether or not a compost or vermicompost will suppress Pythium damping off;
3. To document the effect of composting process (vermicompost vs. thermogenic or “hot” compost) on disease suppressive properties of the finished material.

So far, with OFRF funding, we have confirmed that:

• Vermicompost (Worm Power, an OMRI-listed product) can suppress Pythium damping off in cucumber and this observed suppression is biologically based;
  
• The composting process appears to affect disease suppressiveness as thermogenic compost made from the same starting material offered little to no protection from disease.

And we have identified a potential mechanism of disease suppression:

• Seed colonizing organisms from vermicompost interfere with the pathogen’s ability to chemically sense the presence of a seed compared to microorganisms from disease conducive materials.

This project is part of a much larger vermicompost/vermicompost tea study taking place at Cornell that involves researchers from several departments, extension staff, as well as both conventional and organic fruit and vegetable growers and nursery operations. Our vermicompost industry collaborator has been working with growers over the 2006 and 2007 seasons to develop application methods and rates for vermicompost in a variety of production systems. Several extension workshops will be held in partnership with the Cornell Waste Management Institute over the next three years where growers and researchers can share their experiences in experimenting with vermicompost.

A final report describing the results of this project is expected in December 2009.