Compost for Management of Plant Pathogens and Weed Seeds

Compost for Management of Plant Pathogens and Weed Seeds

Summary

We propose to demonstrate that compost, properly made, will kill disease early blight inoculum and weed seeds during the composting process, and that the resultant compost can be used to suppress early blight in the field. Both weed seeds and plant pathogens present economic and management challenges to growers, and low-input methods for addressing these challenges will help to further advance sustainable farming practices. Compost was prepared in 2010: 1) manure similar to what farmers create (‘compost’ but not to recipe), 2) proper recipe with hay, 3) proper recipe with softwood, and 4) proper recipe with hardwood. In 2011, each treatment will be applied to existing cropping patterns on farm using treatments as mulch. Crops will be monitored throughout the growing season for disease onset, incidence and severity of early blight and any other diseases that develop. Differences in disease incidence or severity that occur among different compost types will be quantified.

Objectives/Performance Targets

• 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.
  Pathogen and weed seed bags were removed from each of 12 piles at three times during the compost process in 2010. We completed pathogen viability and seed germination assessment on the second half of the samples. Properly made compost appears to effectively kill the early blight pathogen and weed seeds by the time compost attains organic certification requirements.
  We will conduct a replicated field trial to demonstrate that compost will suppress early blight disease on cruciferous crops at Intervale Community Farms (Burlington, VT) and Riverside Farms (East Hardwick, VT).

Accomplishments/Milestones

On each farm, we established six treatments (4 compost types and 2 controls), replicated in a Randomized Complete Block design, blocked by row position. Experimental units were 25’meter lengths of a cropping row with a buffer strip to avoid interplot interference. Compost treatments were applied after the first cultivation at 20 tons per acre (twice the typical application rate), and spread manually to avoid transplant damage. Effectiveness of compost as a physical barrier and/or substrate for colonization of antagonistic fungi was measured by comparing the onset, incidence and severity of foliar spot diseases that occurred naturally by residential wind-blown or splash-dispersed fungi or bacteria. The three compost treatments (hay, softwood, hardwood compost with proper C:N ratio) were 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 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. Two controls were included: sterile rice hull mulch as a control to test the role of a physical barrier only and bare soil as no physical barrier. We worked with the existing cropping management plan of the farm and took precautions not to introduce any pathogens or seed.

Unforeseen challenges that we faced:
• We were unable to locate a suitable source of rice hulls until late-July, which meant that control treatment was started later than the other treatments at both farms. Therefore, our experimental design was unbalanced, with fewer replications of rice hulls.
• The Intervale Community Farm was flooded most of May, so we were not able to begin the field trial there until mid-July. We were able to collect two time points of disease before tropical storm Irene flooded the fields leading to termination of the experiment.
• At Riverside Farm, we experienced substantial variation in plant growth because the farmer was unable to provide an even spread of manure/compost at the beginning of the season. We were able to collect six time points of disease at Riverside Farm, three before and three after Tropical Storm Irene. Noticeable increases in early blight disease were observed post-storm.

Impacts and Contributions/Outcomes

• Field trials were established as demonstration plots at two locations: Intervale Community Farm (Burlington, VT) and Riverside Farm (East Hardwick, VT).
  PI Neher accepted an invitation to present the project to potential applicants for the 2011 SARE Partnership applicants. PI Neher is scheduled to present project results at the 2012 metings of both the Northeast Organic Farming Association of Vermont and Vermont Organics Recycling Summit
  Highfields Center for Composting provides informational resources (such as workshops, lectures, and technical materials) and technical services in on-farm composting to farmers throughout Vermont, the Northeast and elsewhere in the US. Highfields staff directly reaches 100-300 farmers or more per year through workshops, lectures, and other presentations, and an immeasurable number of producers at events and through media. Through these avenues Highfields staff is able to effectively communicate the results of our research and trials to the farm community.

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