Compost Tea for Disease Management in Horticultural Crops

2003 Annual Report for LNE03-181

Project Type: Research and Education
Funds awarded in 2003: $147,956.00
Projected End Date: 12/31/2006
Matching Non-Federal Funds: $6,933.00
Region: Northeast
State: Pennsylvania
Project Leader:
Paul Hepperly
The Rodale Institute

Compost Tea for Disease Management in Horticultural Crops


The goals of this project are: 1) to evaluate aerated compost tea (CT) as a disease suppression tool and plant health stimulant in horticultural crops, 2) to educate potential users on production and application methods, and 3) to inform users about specific applications in which CT is most useful.

Field trials at The Rodale Institute®, in conjunction with experiments at three collaborating vineyards, provided data for the evaluation of CT’s disease suppression efficacy. General information about compost and CT, along with research results, are being outreached through multiple outlets, including farmer-targeted field days. Information from this project is distributed to a wide variety of people including farmers, growers, landscapers, extension agents, researchers, and the general public.

Objectives/Performance Targets

1) Of the 30,000 people exposed to and 120 people engaged in this SARE project, 50 farmers will adopt CT practices for their operations within two years of the experiments.

2) 15 vineyard managers will incorporate CT into their management practices within one year of the field day. Ten will permanently adopt CT and serve as a model for other sustainable vineyards.

3) At least 10 extension agents will permanently incorporate CT practices into their recommendations upon reviewing our research and attending our field days. They will be able to easily provide CT production and application information, research results, and contact information for equipment and ingredient suppliers.


As with many new projects, some of our anticipated milestones have not yet been reached, while other important achievements have already been accomplished. In our proposal only one identified milestone should have been reached at this point in time. This milestone and beneficiary action was “CT information is posted on the New Farm website. Interested farmers visit site, read info, complete survey and explore compost tea at home.” This milestone was scheduled to be reached in May 2003, but instead will occur in January 2004. However, we have already provided information at three different field days through presentations and the distribution of information resources.

Information generated from this project was presented at different workshops at several field days including:

1) “Compost Tea: How to and What for?” at the “Transitioning to Organic Vegetable Production in South Jersey” field day hosted by The Muth Family Farm in cooperation with Rutgers Cooperative Extension, Northeast Organic Network, and Northeast Organic Farming Association New Jersey, and The Rodale Institute®. This event, held in Williamstown, NJ on June 20, 2003, drew an audience of approximately 50 farmers.

2) “Use of Compost Tea in an Organic System” at the “Organic Production Methods Field Day” in Bivalve, Maryland was hosted by Provident Organic Farm and sponsored by the University of Maryland Cooperative Extension, Peninsula Horticulture Society, and the Maryland Coastal Bays Program. This event was held on August 13, 2003 and attracted approximately 45 farmers.

3) “Compost Tea Making” session was part of the “Compost in the Vineyard Workshop and Field Day”, hosted by Pennsylvania State University (PSU) at the Fruit Research and Extension Center in Biglerville, Pennsylvania. Approximately 70 vineyard owners, growers, and researchers attended this event on October 14, 2003.

Impacts and Contributions/Outcomes

As part of our project, and a pathway to reaching our performance targets, specific experiments were established to test anecdotal evidence that CT may be an effective tool to manage plant pathogens. Three crops (wine grapes, potatoes, and pumpkins) were chosen to evaluate the effect of CT on the overall health of the crops. To date we have had mixed results in the various experiments.

Grape Trials:

During the first nine months, we conducted trials at three vineyards to evaluate the potential of CT as a preventative tool for disease suppression. Dr. James Travis, PSU plant pathologist, collaborated with the experimental design, pathogen identification, and management decisions. All of the experimental sites received well above average rainfall during the growing season, making environmental conditions extremely favorable for pathogen growth and high disease pressure. Vineyard trials were designed with three treatments: compost tea (CT), fungicide (F), and non-treated (NT). Grape vines were monitored for black rot (Guignardia bidwellii), powdery mildew (Uncinula necator), downy mildew (Plasmopara viticola), and gray mold (Botrytis cinerea). Compost tea clearly affected disease incidence and severity in these trials. We observed approximately 50% suppression of powdery mildew on Chardonnay and Chambourcin grape clusters at two vineyards. Levels of gray mold in the CT treatment appeared to be consistently less than both the NT and F treatments. These differences were not always statistically significantly. Levels of downy mildew in the CT treatments were found to be elevated above both the NT and F treatments. Please refer to Appendix 1 for detailed information on disease evaluations. Due to high disease pressure, fungicides were used effectively to control black rot and downy mildew in all plots at these vineyards in late June and early July.

Graph 1. Percent Control of Powdery Mildew on Grape Clusters at Two Pennsylvania Vineyards in 2003. Uppercase letters in paired bars indicate significant difference (p=0.05, DNMRT, ANOVA). (Please view hard copy, available on request from Northeast SARE)

In a conventional vineyard, CT could be used to suppress powdery mildew, thus reducing the need or number of fungicide applications for powdery mildew control. Although other fungicide applications may be needed to control black rot and other pathogens that CT does not suppress, the grower would be able to reduce the total number of fungicide applications by using CT. Based on this information, an effective disease management program could be designed for a certified organic wine-grape vineyard in the Northeast. In both conventional and organic vineyards, disease management could be improved greatly by selecting cultivars with disease resistance and/or tolerance.

Pumpkin Trial:

Pumpkins were chosen as a test crop due to the fact that many farmers in the area struggle with powdery mildew. Powdery mildew on pumpkins is caused by two different fungi, Erysiphe cichoracearum and Sphaerotheca fuliginea. No difference was found in the incidence or severity of pumpkin powdery mildew in our CT treated and non-treated plots. As part of this trial we also evaluated a number of different powdery mildew resistant / tolerant pumpkin varieties from Cornell University. A portion of these tolerant varieties did show reduced levels of powdery mildew. Based on our experience this past year, CT alone does not seem to be a viable tool to suppress powdery mildew on pumpkins at this point.

Potato Trial and Yields:

The potato trial was designed with three treatments: compost tea (CT), nutrient solution (NS), and non-treated (NT). This trial did not produce any information on disease suppression, due to lack of overall disease incidence, but plant stimulation was measured. In all of our experiments, we did not inoculate with specific plant pathogens, and instead relied upon natural pathogen populations in our systems to infect our plants. Unlike our pumpkin and grape trials, we did not observe any significant disease epidemics in our potato trial. Robert Leiby, PSU Lehigh County Extension Agent specializing in potato production, observed the experiment on numerous occasions and provided insect identification confirmation.

In addition to disease observations, we tested for crop nutrients, quality, and yield differences among the treatments. Weekly applications of CT were shown to increase marketable yields, reduce the number of cull potatoes, and increase nutrient levels in tuber tissue.

Graph 2. Marketable Yields Across Treatments 2003 Potato Trial at The Rodale Institute® in Kutztown, PA (Please view hard copy)

Potatoes were categorized and graded using USDA standards according to the Agricultural Marketing Service Fresh Product Branch regulations. These grading standards include appearance, internal defects, injury, disease, and size criteria. The US Extra No. 1 grade potatoes are more than 2¼ inches in diameter or 5 ounces in weight. The US No. 1 grade potatoes are more than 1⅞ inches in diameter, but less than 2¼ inches in diameter. The CT treatment increase in marketable yields (US Extra No.1 and US No.1) was approximately 5% due to the nutrient effect, approximately 14% related to the biological effect, and approximately 19% from the combined nutrient and biological effect.

Overall, the CT treatment yielded 7.8% and 3.9% more total tuber biomass than the NS and NT treatments, respectively. This increase in total tuber biomass was not statistically significant. However, potatoes in the CT treatment were consistently larger and of better quality. In the US Extra No.1 grade, the CT treatment yielded 29.93% more by weight and 17.78% more in count compared to the NS treatment, with the average CT potato being 11% heavier. Compost tea potatoes were also 33.26% more by weight and 23.72% more in count compared to the NT treatment, with the average CT potato being 7.13% heavier. In the US No. 1 grade, the CT treatment yielded 6.57% more by weight, 8.1% more in count compared to the NS treatment; and 13.23% more by weight, 11% more in count than the NT treatment.

Leaf and Tuber Nutrient Analyses:

Potato leaf and tuber samples were collected and analyzed for nutrient content. Potatoes from all treatments were low in K, Ca, Zn, and B, based on potato leaf tissue analyses. In Graph 3, the CT potato leaf tissue percent increase in nutrients over the NT is presented. Potato leaf samples from CT treatments showed a 1 to 11% increase in Mn, B, N, Ca, Cu, and Zn above NT samples.

Graph 3. Percent Increase of Leaf Tissue Nutrients 2003 Potato Trial at The Rodale Institute® in Kutztown, PA (Please view hard copy)

In Graph 4, the CT potato tuber percent increase in nutrient content over the NT is presented. Potato tuber samples from CT treatments showed a 10 – 1744% increase in Mn, K, N, and Fe. Although nutrient differences between treatments were less in the leaf tissue analysis report, these nutrients were greatly concentrated in tuber tissue in the CT treatment, thus differentiating the treatments on a greater scale.

Graph 4. Percent Increase of Tuber Nutrients 2003 Potato Trial at The Rodale Institute® in Kutztown, PA (Please view hard copy)


The results from this trial indicate that the use of CT in potato production systems may prove to be a profit enhancing practice by increasing tuber quantity and quality. In Graph 5, we present the potential gross profit increase related to the yield increase from nutrient and CT effect. Usually a 3 to 1 increase in profit to expense is needed for farmer adoption of new technologies.

Graph 5. Gross Profit Increase over Standard Practice 2003 Potato Trial at The Rodale Institute in Kutztown, PA (Please view hard copy)

Soil Foodweb Analyses:

In all of the trials, we tested the CT being used for biological properties including total and active bacterial and fungal biomass. We also tested for microbial colonization of the leaf surfaces in all crops to ensure proper coverage following foliar applications of CT. These tests were preformed at the Soil Foodweb laboratory (SFI) in Port Jefferson Station, New York. The results of these tests indicated that adequate levels of bacteria and fungi were present in the CT. Leaf organism assays were also conducted on leaf samples in all treatments. Results from leaf organism assays indicate that leaves from plots sprayed with CT did have what SFI considers adequate microbial coverage as suggested on the leaf organism report, “We have found that a minimum of 60 to 80% coverage (sum of both bacterial and fungal coverage) can prevent disease significantly.”

Overall Conclusions:

Overall, the ability of CT to suppress plant pathogens is very complex and should be viewed on a crop- and pathogen-specific level. Based on information generated from this project, CT could be considered as part of a comprehensive disease control program in certain crops with disease from specific pathogens.

Although the project is less than half complete, a conservative informal estimate of five people have adopted the use of CT as a result of this project to date. Vineyard managers would be more eager to initiate CT use if results from the experiments indicated that there were comparable levels of disease suppression to conventional fungicides in the trials that have been conducted thus far. Extension agents may be the last group of individuals to accept CT as an effective, recommendable disease suppression tool, due to the extensive experimentation that must be done before any new technique can be recommended.

A great deal of information was obtained from this project during the first season and we will be making various adjustments to the experiments in order to optimize results. We are working closely with Paul Wagner from SFI in order to improve the quality of the CT that we will use for experiments in 2004. Dr. Travis is currently evaluating various management strategies for downy mildew and other pathogens that would be compatible with CT. Compost is being applied to experimental areas in the fall to improve microbial populations in the soil, a practice that could not have been done during the first year. Other improvements will be made as more information about CT comes to light.