Compost Tea for Disease Management in Horticultural Crops

Final 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
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Project Information


The goals of this project were 1) to evaluate aerated compost tea (ACT) 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 for which ACT is most useful.

Field trials at the Rodale Institute, in conjunction with experiments at three collaborating vineyards, provided data to evaluate ACT’s disease-suppression efficacy. General information about compost and ACT, along with research results, was disseminated through several outlets, including farmer-targeted field days. Information from this project was distributed to a wide variety of people, including farmers, growers, landscapers, extension agents, researchers, and the general public.

After two years of controlled testing under moderate-to-severe disease environments, none of the vineyard participants were interested in continuing to use compost tea on their farms. With these results, our original plan of recommending and tracking adoption no longer made sense and we revised our approach accordingly. Moreover, economic analysis was premature because consistent efficacy was not proven.

We met our objectives of informing farmers, extension agents, and researchers of our results and their significance. Making farmers, extension agents, and researchers aware that this technology is not ready for use or recommendation helps prevent early adoption of a practice that will not presently pay for itself in proven efficacy. In addition, our findings also helped steer efforts toward improving ACT technology. Our research suggested that many of the claims concerning the disease suppression efficacy of compost tea are exaggerated and cannot be proven by unbiased research. This lets the farmers and the greater community know to “let the buyer beware” in regards to the claims of product manufacturers.


Composts are one of the richest sources of disease-suppressive microorganisms found in nature. These suppressive characteristics have been scientifically researched since 1973 (Nelson and Boehm, 2002; Hoitink, Stone, and Han, 1997; Zhang, Dick, and Hoitink, 1996; Brinton, 1995). The basis for these disease-suppressive characteristics is the plethora of beneficial microorganisms that are found in compost. These beneficial microorganisms have been found to activate antagonistic, antibiotic, hyper-parasitic, predatory, and competitive reactions against pathogenic microorganisms in the soil, reducing the effects of these pathogens on plants and other soil inhabitants (Nelson and Boehm, 2002; Quarels, 2002; Hoitink, Stone, and Han, 1997; Trankner and Brinton, 1997; Zhang, Dick, and Hoitink, 1996).

Compost teas (CTs) and aerated aqueous infusions of compost(ACTs), have been used successfully as a disease prevention tool in an increasing number of agricultural arenas, from conventional potato farming and viticulture to landscaping and turf management (Nelson and Boehm, 2002, Zhang et al., 1998; Trankner and Brinton, 1997). CTs have several advantages over regular compost for disease prevention. First, properly brewed ACTs contain higher counts of beneficial microorganisms than composts. Second, ACTs allow this increased number of beneficial microorganisms to be applied directly to plant foliage, as well as to the soil, in order to counteract pathogens and prevent disease on both fronts. Finally, ACTs facilitate foliar uptake of nutrients, opening another avenue to improve plant health and vigor (Ingham, 2002; Zhang et al., 1998; Brinton, 1995).

ACTs have been cited for their effectiveness in controlling powdery mildew, a disease that is spread in grapes by Uncinula necator, a parasite that can affect all parts of the grape plant. In one study, ACT made from cattle manure compost was tested against sulfur-treated and control plots of field-grown grapes, and showed positive results. The control, sulfur-treated, and ACT-treated plots showed a 65.3%, 32.2%, and 6.9% incidence of Uncinula, respectively. Horse manure based ACT also showed great effectiveness against leaf infection in the greenhouse, with 82% Uncinula infection rates in the control, 8% in the ACT treatment, and 6% in sulfur-treated groups (Trankner and Brinton, 1997).

Zhang et al., 1998, found that ACTs significantly reduced the incidence of bacterial speck caused by Pseudomonas syringae pv. maculicola KD4326 on Arabidopsis spp. grown in media that did not originally contain beneficial microorganisms. Infected plants grown in peat had necrosis on 74.8% of their leaves when treated with distilled water, 35.9% with sterilized CT, 28.1% with unaltered CT, and 19.6% with salicylic acid.

Some of the disease fighting benefits conferred by ACTs are thought to arise from induced systemic resistance (ISR) or systemic acquired resistance (SAR). These forms of resistance are generated by beneficial microorganisms, found in ACTs, that activate the production of anti-pathogenic metabolites within a plant (Zhang et al., 1998). Some beneficial microorganisms found in ACTs, such as Bacillus subtillus and Pseudomonas sp., have been isolated and sold individually as biocontrol agents (Quarles, 2002). However, a growing body of research has shown that the greatest disease suppressing benefits of ACTs arise from the synergistic interaction of microorganisms within a CT solution (Nelson and Boehm, 2002).

Many of the previously mentioned plant diseases can be controlled by a variety of agents other than CTs, including synthetic fungicides. However, due to the increased use of fungicides over the past few decades, many fungal diseases have now developed resistance to the current most popular chemicals (Trankner and Brinton, 1997). At the same time, these chemicals are becoming more expensive and harder to find in the marketplace, due to regulatory action based on increased understanding of their dangerous toxicity. These negative pressures are directing many farmers to seek alternatives to fungicides. ACTs are a viable, readily available, cost-effective alterative that deserves proper promotion and dissemination within the agricultural community.

Performance Target:
  • Of the 30,000 people exposed to and 120 people engaged in this SARE project, 50 farmers will adopt ACT practices for their operations within two years of the experiments.

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

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


Materials and methods:

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

The research portion of the project at the Institute included an investigation into CT efficacy for preventing disease in vegetable crops. The vegetable experiments were conducted at the Institute on a half-acre plot, divided into a randomized complete block design for statistical validity. The vegetable experiment consisted of three treatments: 1) CT foliar and soil drench application; 2) non-compost tea control; and 3) a no-spray control. The non-compost tea treatment served as a control to investigate the effects of solely the nutrients that were added to CT brews. Pumpkins and potatoes were chosen as test crops because both are highly profitable to producers, are very susceptible to profit reducing diseases, and are routinely sprayed with fungicides. We monitored pathogen incidence and severity in these crops, compare yields, and assessed effects of CT on plant health.

One CT brewer was used to make tea for both of the two-year experiments at the Institute. Samples of CT were sent to the Soil Foodweb Inc. (SFI) lab in New York for microbial biomass measurements. Leaf samples were also sent to determine microbial coverage on leaves, a measure that is closely correlated to effective pathogen suppression. The issue of human pathogens in CT was addressed by testing CT for E. coli.

This project also included three two-year experiments with different vineyards. Vineyard trials demonstrated and evaluated CT’s ability to reduce and prevent diseases on wine grapes when applied as a soil drench and foliar spray. All of the vineyard owners produced CT on farm, collected samples for analyses, and applied CT to grape vines. The vineyards received the following treatments: 1) CT foliar application; 2) pesticide control; 3) no spray control. Each year, CT application was initiated in mid-May and continued on a weekly basis until harvest. Weather stations were installed at two of the vineyards to monitor climatic conditions during the growing season.

Research results and discussion:

Overall, the ability of ACT to suppress plant pathogens was complex. Based on information generated from this project, ACT could be considered as part of a comprehensive disease control program in certain crops with disease from specific pathogens. However lack of observed high consistent efficacy in disease suppression suggests that ACT should not be used as a sole disease suppression tactic.

Our performance objectives were predicated on ACT practice efficacy proving out giving positive and consistent results. However, our results were mixed for ACT efficacy. As such, we altered our plan to outreach our information without any recommendation to use it. In fact, we recommended a wait-and-see approach on the use of ACT until increased efficacy and consistency could be demonstrated. Similarly, an economic analysis was not conducted as originally planned, as the practice did not pass efficacy standards for recommendation.

None of our collaborators adopted the CT practice. Vineyard managers would be more eager to initiate CT use if results from the experiments indicated that there were levels of disease suppression comparable to conventional fungicides in the trials that have been conducted thus far. Extension agents have not incorporated recommendations for the use of CT as a disease suppression tool, due to the lack of consistency in disease suppression efficacy.

Participation Summary


Educational approach:

Several field days occurred where participants observed field trials designed to test the efficacy of compost tea, and also had the compost tea production process explained in detail. Results on pumpkins, potatoes, and grapes were seen first-hand in the field in 2003 and 2004. An extension bulletin, “Compost Tea Production, Application and Benefits,” was developed and distributed to field day and conference participants (see Appendix K). A project summary poster was presented at the Northeast SARE conference in Burlington, Vermont in October 2004 (see Appendix M). Compost tea information was also posted on the website (see Appendix E and related articles, listed below).

“Compost tea research enters its second year” by Laura Sayre, (see Appendix G).

“Pennsylvania wine-grape grower pioneers sustainable vineyard management methods” by Laura Sayre, (see Appendix I).

“From table to farm” by Laura Sayre, (see Appendix J).

“E. coli-free tea” by Cara Hungerford, (see Appendix H).

A popular grower article was published in Biocycle and a scientific article was submitted for peer-review publication in Compost Science and Utilization. These and our other activities have allowed us to surpass our targeted audience with our message on ACT.

We also sent a letter on our research results to Pennsylvania cooperative extensionists and Northeast SARE (see Appendix Q). This letter, which contained a live link to the New Farm Compost Tea website, was forwarded to other interested parties. To date, we have tracked 117 visits (246 page views) to the website as a result of our outreach efforts.

Below is a comprehensive list of all publications and outreach activities associated with this project.

Ryan, M.R., Wilson D.O., Hepperly P.R., Travis J.W., and N.O. Halbrandt. 2005. Compost Tea Potential is Still Brewing. BioCycle, Vol. 46, No. 6, p. 30.

Ryan, M. R. and C. Ziegler-Ulsh. 2003. Compost Tea Production, Application, and Benefits. The Rodale Institute Extension Bulletin.

Ryan, M. R. and D. O. Wilson. The A,B,C’s of Composting and the 1,2,3’s of Compost Tea. New Jersey Vegetable Growers Annual Conference. Atlantic City, New Jersey. January 15, 2004.

Hornor, A. L. and M. R. Ryan. Nutrient Additives and Human Pathogens in Aerated Compost Tea. Northeast Organic Farming Association of New York 23rd Annual Organic Community Conference. Syracuse, NY. January, 30, 2005.

Ryan, M. R. Compost Tea Experiments in Pennsylvania and Long Island Vineyards. Pennsylvania Association of Winegrowers Annual Summer Vineyard Walk Around: Making the Shift to Sustainable Agriculture. Fairfield, PA. August 19, 2004.

Ryan, M. R. and D. O. Wilson. Benefits and Use of Compost Tea. Building Healthy Soil – Building Healthy Farms Field Day at The Rodale Institute. Kutztown, PA. July 16, 2004.

Ryan, M.R., B. Jarjour, N. Halbrendt, and P. Roth. Compost Tea Production. Compost in the Vineyard Workshop and Field Day at the PSU Fruit Research and Extension Center. Biglerville, PA. October 14, 2003.

Ryan, M. R. and D. O. Wilson. Use of Compost Tea in an Organic System. University of Maryland’s Organic Production Methods Field Day. Bivalve, Maryland. August 13, 2003.

Ryan, M. R. and D. O. Wilson. Using Compost Teas. Rutgers University Field Day: Transitioning to Organic Vegetable Production in South Jersey. Williamstown, NJ. June 13, 2003.

Additional Project Outcomes

Project outcomes:

Impacts of Results/Outcomes

We had mixed results in the various experiments.

Grape Trials (Year One 2003):

During the first nine months, we conducted trials at three vineyards to evaluate the potential of ACT as a preventative tool for disease suppression. Dr. James Travis, Pennsylvania State University 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 (ACT), 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 significant. Levels of downy mildew in the CT treatments were found to be elevated above both the NT and F treatments. 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. See Attachment A for Graph 1 showing percent control of powdery mildew on grape clusters at two Pennsylvania vineyards in 2003.

(Note to the reader: Graphs and charts referenced in this report are available in hard copy form Northeast SARE. Call 802/656-0471 or send e-mail to and eeference project LNE03-181.)

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 tolerance.

Pumpkin Trial (Year One 2003):

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 or 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 (Year One 2003):

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.

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. See Attachment B for Graph 2 showing marketable yields across treatments in the 2003 potato trial at the Rodale Institute.

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.

As in 2003, results in 2004 were mixed. Results were positive in pumpkins and no differences were noted in grapes and potatoes. This is the reverse of the results found in 2003 for the same crops.

Grape and Potato Trials (Year Two 2004):

No positive effects in health or yield were identified in 2004 at any of the four sites (three grape and one potato).

The 2004 season was very conducive to severe disease from a number of grape pathogens including those causing powdery mildew, downy mildew, gray mold, black rot, and leafspot diseases.

On potatoes, all treatments were defoliated prematurely by late blight and no differences in yield or quality measurements were detected among treatments.

Pumpkin Trials (Year Two 2004):

Powdery mildew early severity was reduced 80% (P = 0.05) for ACT compared to the nontreated control. ACT yielded more than both the nutrient treatment and nontreated by 1,700 and 5,000 lbs/acre but the difference was not statistically significant. Serenade and milk and compost tea and the same also reduced powdery mildew severity about 70 to 90%. ACT reduced both the number and size of powdery mildew colonies.

Milk and Serenade with compost tea provided over 80% control of powdery mildew and provided downy mildew control not given by ACT. Although compost tea alone was not a viable solo treatment, the ability to get excellent and broad control with biocontrol agents deserves more attention. Downy mildew was the most destructive disease in 2004 on our pumpkins.

Analysis of Combined Years (2003 and 2004):

Variable results obtained in relation to enhancing plant health. Over two years, about 60% of the time yield and/or quality was positively affected (three of five comparisons) and only in about 40% of the time was disease reduced (two of five comparisons).

In all of the trials, we tested the ACT 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 ACT. 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 ACT. Leaf organism assays were also conducted on leaf samples in all treatments. Results from leaf organism assays indicate that leaves from plots sprayed with ACT did have what SFI considered adequate as 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.”

Microbiological Analyses (Combined Years 2003 and 2004):

We found that eliminating molasses from ACT preparations effectively eliminated E. coli and enteric bacteria that were previously encountered in 2003. We found E. coli associated with ACT in 2003 and by eliminating molasses in our mixture eliminated E. coli dangers in 2004. Our collaborator, Patricia Milner USDA, corroborated our E. coli results during this last year. This substantiates fears of potential danger in ACT related to pathogenic bacteria and the precautions needed to avoid these safety pitfalls.

Farmer Adoption

While ACT cannot be viewed as a panacea for plant health, it also is not without demonstrable, if unpredictable, benefits. Because of its variable response, more work is needed before it can be recommended without reservations and with good probability of beneficial effects that are economically viable. We recommend further investigation be aimed at improving overall efficacy of biologically based management systems by combining tactics as we did with the serenade, milk, and compost tea combination. Several approaches and tactics, as part of integrated disease and health management, seem appropriate and need more development at this point.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.