Biological Control of Foliar Diseases and Fruit Rots of Tomato
Composts have long been known to improve soil fertility and suppress plant diseases. More recently, it has been shown that components of composts improve the ability of plants to resist disease caused by root and foliar pathogens. The objectives of this study were to: 1) develop consistently high quality, disease suppressive composts inducing systemic resistance (ISR/SAR) to disease, utilizing farm and locally produced wastes, 2) develop a compost-amended potting mix consistently inducing ISR/SAR in tomato transplants, and 3) assess the ability of selected composts in comparative farming systems to reduce foliar and fruit diseases of tomato.
A radish bacterial leaf spot bioassay was developed as a rapid and efficient method for assessing the ability of composts to induce resistance. Incorporation of composted pine bark (CPB) into planting mixes reduced bacterial spot severity of tomatoes in initial greenhouse tests, but not in field trials. Batch-to-batch variation between composts in ability to induce resistance was observed, which may explain this discrepancy. Compost water extracts prepared from various sources of composts also were effective as topical sprays for bacterial spot control in greenhouse tests, but were not effective in the field.
Several biocontrol agents have been identified that when inoculated into the CPB mix, induce systemic resistance in radish and tomato to bacterial spot. Active microorganisms include Trichoderma hamatum 382 and several strains of Bacillus spp. Combinations of these microorganisms have been identified that also suppress Pythium and Rhizoctonia damping-off of seedlings. Both are important diseases of transplants that are difficult to control in organic peat mixes. These novel compost-amended plug mixes have yet to be tested under field conditions.
Field trials utilizing composted yard wastes and composted cow manure (conventional processing tomato production) and composted cannery wastes (organic tomato production) were conducted at the Ohio Agricultural Research and Development Center (OARDC) and at Hirzel Farms, Luckey, Ohio, respectively. In the organic production trial, yields were increased 27 percent and 42 percent in 1997 and 1998, respectively, for plants grown in compost-amended soil. Low rates of compost (10-12 tons/ac) were as effective as high rates (20-24 tons/ac). 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 the conventional trial, 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 production 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.
Results of the studies conducted during this project have been communicated to scientist and grower audiences through publications, oral presentations and posters. Presentations were made at: 1) the Tomato Disease Workshops in 1997 (Indianapolis, Ind.) and 1998 (East Lansing, Mich.), a meeting for pathologists, growers and other industry representatives; 2) the annual meeting of the American Phytopathological Society in 1997 (Rochester) and 1998 (Las Vegas, Nev.), 3) a four-state SARE Conference, Bryan, Ohio, February 1998; 4) the OEFFA Annual Conference (March 1998) in Wilmington, Ohio, to organic farmers; and 5) a meeting of the OSU/OARDC Organic Farming Initiative meeting, December 1998, to scientists and stakeholder organic farmers.
We plan to publish the results of this work in refereed journals during 1999. We will also develop fact sheet(s) for growers describing the main points of this research and potential applications for tomato production on their farms. This work will also be communicated to organic growers through the Organic Farming Initiative, an interdisciplinary initiative involving OSU researchers and growers that has recently been established at OSU-OARDC.
North Central Region 1998 Annual Report.