Compost for Management of Plant Pathogens and Weed Seeds

• 2010 annual report
• 2011 annual report

Early blight is widespread and devastating on crops within the Solanaceae, Crucifer (Brassica) and Apiaceae (carrot) families in Vermont. Sanitation is important to reduce initial inoculum and, thus, diseased material must be disposed of in a manner to destroy the pathogen. Given that the early blight pathogen has saprophytic capabilities that facilitate survival and dispersal, on site disposal techniques are avoided in favor of diverting material to the landfill. However, composting these materials on local farms has the potential to kill these pathogens and weeds, which would allow producers to reduce export of nutrients and organic matter from their operation and generate a local source of disease- and weed-free (Liebman and Davis 2000, Larney and Blackshaw 2003) potting medium. Furthermore, composted organic wastes can serve as a biological inoculant for field soils to reduce the severity of root diseases caused by plant pathogens in natural and field systems (Stone et al. 2001, Hoitink and Boehm 1999) Organic certification outlines minimum temperature requirements to kill pathogens and weed seeds. Compost made in windrows is considered suitable for organic production has an established carbon-to-nitrogen (C:N) ratio of 25-40:1 attaining temperatures of 55-77oC (131-171oF) for 15 days, during which time the pile is turned at least five times. The problem is that most farmers do not follow these recommendations. In Vermont, farms may attempt to compost manure but have insufficient carbon to develop an appropriate ratio, or do not turn the pile frequently enough to reach proper aeration and temperatures. If properly prepared, most compost naturally suppresses Pythium and Phytophthora (Chen et al. 1988, Chung et al. 1988, Harris et al. 1997). However, diseases with saprophytic phases such as Rhizoctonia (Voland and Epstein 1997) and Alternaria are more difficult to control and require accommodating the antagonist microbe during composting. Composts prepared from lignocellulosic substrates such as tree barks become colonized by Trichoderma spp. which is an effective biocontrol of Rhizoctonia (Hoitink and Boehm 1999). Trichoderma works by producing a chitinase which lyses the fungal pathogen hyphae. Populations of biocontrol agents are linked with carbohydrate content. Once carbohydrates are depleted, the microbial communities degrading them decline. The concentration of cellulose and lignin in compost determines the longevity of the suppressive effect Nitrogen and other nutrients cycled as organic matter are decomposed by soil microbes. A proper compost recipe that provides nitrogen sufficient to basic metabolism, activity and reproduction of microbes is critical to efficient production of quality soil amendment product. Hardwoods typically have a higher C:N than softwoods and straw. Frequent turning aerates piles to reach temperatures lethal to plant pathogens and weed seeds. Curing of piles allows recolonization of fungi such as Trichoderma (Hoitink and Boehm 1999). We plan to demonstrate that compost, properly made, will heat and kill disease early blight inoculum and weed seeds. Proper compost recipe involves a proper C:N, aeration to achieve temperature targets known to kill fungal pathogens (150oF) and seeds of common weeds (175 oF) of vegetable and small berry crops. Biological control strategies support organic and low input practices. Using compost as part of the management package keeps more nutrients and organic matter on the farm and saves purchase of external inputs.