University of Florida

Seed Treatment Research Helps Lettuce Farmers

Situation or Issue Identification

Lettuce production has stabilized in the Everglades Agricultural Area within the last four years. It has returned to economic profitability with a value of $18 million on 3,000 acres. While only 4 major growers of the crop still produce lettuce, its per acre value is high at $6,000/acre, exceeding the per acre figures for eggplant, snap bean, sweet corn, and cabbage. Therefore, it has achieved a sort of "niche" market status, and the sustainability of the small but profitable industry merits the attention of researchers at EREC.

In 1993, a severe outbreak of bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians was reported for the first time in the EAA. Losses to the industry were estimated in excess of $1.5 million. The disease has continued to plague area farmers in most winter vegetable seasons and is currently ranked by growers as one of their most serious pest problems.

Few management practices are available for management of this disease once it becomes established in the field. This pathogen is thought to be seedborne. Therefore, we have investigated novel seed treatments for management of primary inoculum. Among 5 seed treatment chemicals tested at 3 concentrations and 2 exposure times, 3 and 5% H2O2 and several doses of a copper/mancozeb mixture provided outstanding control. Percent infested seed were reduced from 100% in water-treated controls to 0 with H2O2 and 2% or less with copper/mancozeb. Seed germination was not reduced below acceptable levels. Therefore, we recommend routine treatment of lettuce seed for this pathogen.

Rationale for Research Support Resources

Growers could conceivably apply up to 15 sprays of copper/mancozeb in the field on an attempt to manage established infections of Xanthomonas campestris pv. vitians. Use of an effective seed treatment for management of primary inoculum could reduce the need for many of these pesticide sprays. This should also provide better control of this potentially devastating disease, markedly favoring sustainability of the Glades lettuce industry.

Measurable or Potential Impact in Terms of Social, Economic, and/or Environmental Factors Resulting from Expenditure of Research Support Funds

H2O2 is a safe, economically attractive alternative seed treatment that provides superior control to the 0.5% sodium hypochlorite commonly recommended. Losses of $2 million may be avoided in a typical winter vegetable season.

Collaborating Organizations/Agencies & Teaching/Research/Extension Partnerships

This work involves collaboration between the research center, county extension, the lettuce grower's advisory committee, and the seed and agricultural industry.

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Lettuce growing in a field

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