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Developing Management Strategies for Bacterial Canker on Tomatoes 2000

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Project Leader: Helene R. Dillard, Cornell University, NYSAES, Department of Plant Pathology, Geneva, NY 14456

Cooperators: Carol MacNeil, Extension Vegetable Area Specialist; Abby Seaman, Extension IPM Area Specialist; John Gibbons, CCE; Meg McGrath, Long Island Horticultural Research Lab

Abstract (nontechnical):

The objective of this study was to identify sources of on-farm inoculum of Clavibacter michiganensis subsp. michiganensis (CMM), the causal agent of bacterial canker of tomatoes. Two hundred ninety seven samples from inanimate (swabbing from walls, floor, wood, hoses, etc.) and animate sources (weeds, other plants, tomatoes) from 3 commercial greenhouses were tested to see if they carried the CMM pathogen. A wide variety of methods were utilized in attempts to conclusively identify the bacteria, including an agglutination kit and a commercial diagnostic testing service that used a quick ELISA test. Any bacteria isolated that were likely to be the pathogen were further tested to see if they could cause disease on tomatoes. The various isolation procedures were cumbersome, slow, expensive, and difficult to interpret since none were diagnostic alone. The disease organism is difficult to isolate, identify conclusively, and even more difficult to prove to cause disease.

The tomato transplants from one of the commercial grower’s greenhouses were subsequently planted in 2 locations. In the commercial field where bacterial canker occurred 3 years previously, moderate disease developed on the leaves and fruit starting at fruit load. Disease also occurred in transplants planted on "new" ground, as well as on tomato volunteers from an area with canker in 1999. The transplants appeared to be harboring the disease in the planted fields, but contaminated seed or overwintering debris or weeds or other crops seemed to be the source of inoculum for the volunteers. Weather is obviously a driving factor in disease development, since the disease has varied from severe, moderate, to low over three consecutive years at one location. Bacterial canker did not develop in a sample of the same transplants that were grown in a field in Geneva that did not have a history of bacterial canker. Transplants from the other 2 growers did not develop bacterial canker in the greenhouses or in the fields.

There are no highly effective chemical control measures for bacterial canker. Disease control starts with clean seed and continues with good sanitation practices in the greenhouse. This includes disinfecting surfaces in the seedling greenhouse and sanitizing any reused equipment or supplies. Bacteria may survive as an epiphyte on other plants present in a greenhouse. Epiphytes do not cause disease on plants, but will grow and multiply on non-host plants, which become an inoculation source for susceptible plants such as tomatoes. The best practice is to dedicate a greenhouse to tomato production and avoid co-mingling tomato transplants with transplants of ornamentals or other crops. Avoid damage to the tomato plants since damage from storms, wind, blowing soil, mechanical damage, handling, etc. followed by water may increase a population above threshold level and cause or promote disease. Careful management practices are key to mitigate the impact of this disease.