Composts for Disease Suppression

Composts have long been known to improve soil fertility and suppress plant diseases. It has also been shown that components of composts improve the ability of plants to resist disease caused by root and foliar pathogens. Foliar and fruit diseases, especially early blight, septoria leaf blight, anthracnose, bacterial spot and speck, and bacterial canker can severely reduce yield and quality of fresh market and processing tomatoes. Extensive use of fungicides is often required to manage the diseases caused by fungi. Although the disease warning system TOM-CAST is available and has been shown to reduce the use of fungicides by 50% or more, it does not benefit organic farmers due to its reliance on synthetic fungicides. Further, it is not useful for control of bacterial diseases. Additional disease management strategies must be developed to further reduce fungicide use in conventional systems and to reduce diseases and subsequent economic losses in both conventional and organic tomato production systems.

We have evaluated the effect of composts on disease development in organic and conventionally-produced processing tomatoes since 1996. Composts were obtained from commercial outlets (yard waste compost), produced at OARDC (composted cow manure) and produced in wind-rows by an organic farmer-cooperator (composted cannery waste, made from tomato cannery wastes, duck manure, municipal yard waste and reed canary grass straw). In field trials utilizing composted tomato cannery wastes, organic tomato yields were increased 27% and 42% in 1997 and 1998, respectively, for plants grown in compost-amended soil. Low rates of compost (10-12 tons/A) were as effective as high rates (20-24 tons/A). Anthracnose was significantly less in tomato fruit in compost-amended plots than in non-amended controls in 1998, a year in which the disease was very serious. Yield and quality improvements for plants grown in compost-amended plots resulted in an economic gain of approximately $300 per acre.

In conventionally produced tomatoes, composted yard wastes hastened maturity of tomatoes by at least three weeks. Bacterial spot was reduced in 1997, a year with high bacterial disease pressure, in compost amended plots compared to non-amended control plots. The incidence of anthracnose on tomato fruit was not affected by compost amendments. However, the plant activator Actigard® reduced bacterial spot incidence in both years, and plants treated with Actigard® produced fewer fruit infected with anthracnose than control plants in 1997 but not 1998. Marketable yield in 1997 was higher in Actigard®-treated plots than in the control in 1997, reflecting the reduced incidence of disease. Yield was not significantly higher in compost-amended plots compared to the control.

These results indicate that compost amendments play a valuable role in reducing disease and increasing yields in organic tomato production systems, although not in conventional systems. It is possible that organic soils may better support a microbial community playing a role in induced resistance. Nutrients provided by composts play a greater role here also. Nonetheless, bacterial disease was reduced significantly in compost-amended plots in the conventional system, so it is likely that induced resistance is also occurring at some level in this conventional soil. Early ripening of tomatoes in compost-amended soils may provide an economic advantage for processing tomatoes and potentially for fresh market tomato production. Clearly, compost amendments should continue to be studied as a means of increasing sustainability in tomato production.

By: Sally A. Miller, Associate Professor, The Ohio State University – OARDC, Department of Plant Pathology, 1680 Madison Avenue, Wooster, OH 44691, 330-263-3678.  1999,

Reviewed: T. Jude Boucher, UConn IPM, 2012

Published: Proceedings. 1999. New England Vegetable and Berry Growers Conference and Trade Show, Sturbridge, MA. p. 316-317.

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