Compost for Management of Plant Pathogens and Weed Seeds

View the project final report

• 2010 annual report
• 2011 annual report

Commodities

• Vegetables: beans, broccoli, carrots, cauliflower, tomatoes, brussel sprouts

Practices

• Crop Production: biological inoculants, nutrient cycling, organic fertilizers
• Education and Training: demonstration, farmer to farmer, on-farm/ranch research
• Natural Resources/Environment: biodiversity, soil stabilization
• Pest Management: biological control, competition, compost extracts, cultural control, weed ecology
• Production Systems: organic agriculture, integrated crop and livestock systems
• Soil Management: organic matter, soil microbiology, soil quality/health
• Sustainable Communities: local and regional food systems

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.

The project consists of two parts:

Part 1) Make compost and test pathogen and weed seed viability (season 1)Known quantities of early blight infested plant material and crab grass seeds (Digitaria sanguinalis) will be placed into two types of bags, one with a mesh and the other sealed in plastic. The mesh bag will test the effect of heat and biota and the sealed bag will test the effect of heat alone. These bags will be placed into compost piles of different recipes that are aerated similarly:

1) raw manure ‘composted’ without proper recipe as a grower would typically do,
2) proper recipe with softwood and/or hay,
3) proper recipe with hardwood; and
4) proper recipe with hardwood and infested plants from farmer fields. Bags will be removed over a time series and analyzed for viability of the early blight pathogen and seed germination. The four sampling times will be i) before composting, ii) end of peak temperature period, iii) half way through curing, and iv) end of curing phase.

Part 2) Field demonstration of disease suppression properties of compost (season 2). On each farm, we will establish six treatments (4 compost types and 2 controls), replicated in a Randomized Complete Block design, blocked by row position.

Experimental units will be 2 meter lengths of a cropping row with a buffer strip to avoid interplot interference. Effectiveness of compost as a physical barrier and/or substrate for colonization of antagonistic fungi will be measured by comparing the onset, incidence and severity of early blight and other occurring diseases for three compost treatments and three controls.

The three compost treatments will be tested for their relative ability to suppress disease by a combination of a physical barrier mulch and antagonistic fungi or bacteria acting as biological control agents. Hardwoods (recipe 4) are known to be substrates that attract colonization of biological control fungi such as Trichoderma during the curing phase of compost. With proper curing, we hypothesize that this treatment will offer both a physical barrier to spore splashing from soil to plant, and provide antagonistic fungi.

We will include two controls: sterile rice hull mulch as a control to test the role of a physical barrier only and bare soil as no physical barrier. We will work with the existing cropping management plan of the farm and take precautions not to introduce any pathogens or seed.