June 15, 2004 | General


BioCycle June 2004, Vol. 45, No. 6, p. 32
Field experiments this summer will compare disease control impacts on plants from applications of aerated and nonaerated compost tea.
Sarah Kelley

IN RECENT YEARS, water-based compost extracts – commonly known as compost teas – have attracted increasing attention from growers and researchers. Field trials, laboratory tests and grower testimonials suggest that these substances have the potential to suppress plant diseases, particularly fungal infections.
To obtain more data on the efficacy of aerated compost tea (ACT) for disease control, field experiments on a Long Island, New York farm are being conducted by a nonprofit organization called Earth Pledge which promotes sustainable technologies. The project is a collaborative effort that includes Earth Pledge based in New York City; Stephen Storch, founder of Natural Science Organics in Water Mill, New York; and Dr. Margaret McGrath, plant pathologist at Cornell University’s Long Island Horticultural Research and Extension Center in Riverhead, New York. The initial phase of the project is funded by a grant from the Organic Farming Research Foundation (OFRF) in Santa Cruz, California.
Researchers attribute the disease suppression effect to the diverse microorganisms and soluble nutrients found in compost tea. Microorganisms in the tea are thought to fight disease by competing with pathogens for colonization sites and nutrient supplies, secreting antibiotic or antifungal substances, or directly parasitizing pathogens, while soluble nutrients improve plant health and bolster natural defense mechanisms. Because fungal diseases are among the most difficult pest problems to control with nonchemical methods (Weltzien 1991), compost teas offer important potential advances in biological controls for agricultural systems.
Research on compost teas began in the mid-1980’s, but results from controlled field trials are still scarce and those that exist are often conflicting. To further confuse the issue, there are two different “schools” of compost tea making: a nonaerated method that results in largely anaerobic conditions during tea production and an aerated method that deliberately aerates the mixture. In his February, 2003 BioCycle article, Steve Scheuerell at Oregon State University uses the terms nonaerated compost tea (NCT) and aerated compost tea (ACT) for these methods; these terms will be employed here.
Weltzien and Ketterer (1986) published the first experimental results using water-based compost extracts applied to above-ground plant parts, and Weltzien continued to be a pioneer in this area through the 1990’s. These researchers employed NCT; as a result, studies during this period focused almost exclusively on the nonaerated method. However, in recent years attention has shifted to ACT, which can be prepared in two to three days, as opposed to up to two weeks steeping time for NCT. Shorter production time is a significant advantage for ACT, enabling growers to respond more quickly to weather forecasts or other indications of disease outbreak. ACT production also is reported to create less odor than NCT, and some researchers have suggested that ACT reduces the risk of contamination by human pathogens.
ACT technology has also come to dominate the commercial market for compost tea brewing devices. However, neither increased interest from growers nor increased commercial availability of ACT technology has inspired additional research on ACT. As Scheuerell (2003) notes, research has shown that a variety of foliar plant pathogens and/or diseases have been suppressed by applications of NCT, while considerably fewer controlled studies have examined ACT. Given the level of interest in ACT, there is a need for practical research results to determine whether the current emphasis on ACT is justified and will result in concrete benefits for growers.
Our trial is sited on a two-acre parcel of land in Water Mill, New York. The plot has been uncultivated for the past two years. Stephen Storch has mowed the plot regularly for the past two growing seasons, and has applied compost tea approximately once a month.
Our experimental design has two variables: Soil amendment — Added at the beginning of the season with ground basalt; No soil amendment — Four different spray treatments with known or reputed fungicidal activity; Compost tea produced by the ACT method; A water spray as a control. We will replicate each treatment combination four times in a randomized complete block design.
We chose pumpkins as a test crop because of their extreme susceptibility to fungal diseases, especially powdery mildew (Sphaerotheca fuliginea). Dr. McGrath has conducted extensive research on disease control in cucurbits, and notes that powdery mildew has affected pumpkins every year she has worked with them. Currently, growers are heavily dependent on fungicides to control powdery mildew and other pumpkin diseases. As McGrath (2003) reports, development of resistance to strobilurin fungicides is already a documented problem in New York State. In addition, Suffolk County’s sandy porous soils increase the risk of chemical runoff and contamination of Long Island’s fragile aquifer system. These environmental concerns, combined with demand for nonchemical alternatives for the pick-your-own pumpkin market, increase the need for research results on alternative disease control methods such as compost tea.
Our trial will also test two other emerging technologies. Silica sprays are a technique utilized by organic and biodynamic practitioners that has begun attracting wider recognition in the scientific literature. Quarles (2003) notes that recent research has confirmed that silica sprays can protect cucumbers against damping-off, and has been effective in cucumbers, grapes, and squash against powdery mildew. The basalt soil amendment we will investigate contains high levels of magnesium, calcium, and iron. Few studies have examined basalt dusts, but some positive effects on soil fertility and crop yields have been observed. It is known that microbial action enhances the release and turnover rates of soil nutrients (Marschner 1995), so synergistic effects could occur between the basalt dust and compost tea treatments. We will investigate this possibility through statistical analysis of the interaction between the soil amendment treatments and the spray treatments.
We began preparation for our experiment in March. Stephen Storch has mowed and disked the plots and continues to spray them with compost tea every two weeks. We have also taken baseline soil samples and compost tea samples, which we will continue throughout the experiment. The basalt soil treatment will be incorporated on May 15, and pumpkins will be seeded on June 15. Spray treatments will begin as soon as seedlings emerge and continue once a week through the end of August.
Harvest will occur in late September. Data analyzed will include: Percent disease incidence in pumpkins, possibly subdivided by disease type depending on test results; Total weight of pumpkin fruits from each test plot; and Data about number of marketable fruits and extent of disease damage.
Sarah Kelley is coordinator of Earth Pledge’s Farm To Table Initiative (
Marschner, H. 1995. Mineral Nutrition of Higher Plants. London: Academic Press.
McGrath, M.T. 2003. Occurrence of Strobilurin resistance and impact on managing powdery mildew of cucurbits. Cornell University Vegetable M.D. Online.
Quarles, W. 2003. Least-Toxic Controls of Plant Diseases. Brooklyn Botanic Garden.
Scheuerell, S. 2003. Understanding how compost teas can control disease. BioCycle, 44(2):20-30.
Weltzien, H.C. 1991. Biocontrol of Foliar Fungal Disease with Compost Extracts. In J.H. Andrews and S. S. Hirano (eds.), Microbial Ecology of Leaves. New York: Springer Verlag. pp. 430-450.
Weltzien, H.C. and N. Ketterer. 1986. Control of downy mildew, Plasmopara viticola (de Bary) Berlese et de Toni, on Grapevine Leaves through water extracts form composted organic wastes. Journal of Phytopathology, 116: 186-188.
IN SPRING 2003, we started making compost solution at the Central Park Conservancy with one 55-gallon aerobic brewer using our leaf and wood chip compost. Since then, we’ve purchased two more brewers and expanded the program quite a bit.
For our composting program, leaves are raked up in the park and brought to our three-acre site where they are windrowed and turned periodically. Approximately 3,000 cubic yards of compost are managed at a given time. Wood chips generated by tree work in the park are collected in a separate pile and allowed to compost.
Concerning tea applications, we have 12 acres of lawn receiving solution as well as dozens of trees and ornamentals including tulip beds. The compost solution program is integral to meeting our goals for building soil health and promoting stress-free, vigorous plants. It is too soon, however, to tell how well the program has been performing. We are applying the solution with a long-term outlook and want to measure results over multiple years before drawing any conclusions. It requires careful monitoring, which we do through our Integrated Pest Management program, and complex biological soil analysis that we have done through an outside laboratory. – Matthew Brown
Matthew Brown is with the Central Park Conservancy’s Soil and Water Health Lab in New York City.

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