COST BENEFIT ANALYSES OF USING GRAFTED WATERMELON TRANSPLANTS FOR FUSARIUM WILT DISEASE CONTROL

Research on grafted watermelon at the Lane Agricultural Research and Extension Center in Lane, Oklahoma provided data for the cost benefit analyses performed in this work. Grafting of watermelon onto resistant rootstock was found to provide effective resistance to Fusarium wilt but at an increased cost of $1,743 per hectare. The resistance of these plants to multiple soil-borne diseases provides the farmer a viable risk management strategy and an alternative to methyl bromide for disease control. Soil-borne diseases such as Fusarium wilt continue to plague watermelon growers in intensive production areas where land resources are scarce and rotation of various crops is limited. Fusarium wilt is generally observed in farmers’ fields during the latter stages of production when most of the costs have been incurred. Risk management alternatives available to the farmer have been reduced by the loss of soil fumigation chemicals such as methyl bromide. Currently, most seedless cultivars are susceptible to Fusarium wilt. It would appear that many of the present-day triploids have a similar genetic background. With triploids commanding almost 75% of the watermelon market in 2006, Fusarium wilt resistance has become a major emphasis for seed companies. A farmer planning for yields of 40,000 kg/ha would have to receive a price of $0.19/kg to breakeven with grafted plants while non-grafted plants would breakeven at $0.13/kg with the same yield. In the case where a field is known to have a history of Fusarium wilt, the probability of losing most or all of the crop after the majority of production costs have been expended forces the farmer to evaluate best alternative decisions based on costs versus probable revenues. INTRODUCTION Grafting watermelon onto other Cucurbitaceous crops for soil-borne disease and nematode control has been practiced for many years in Europe and Asia (Oda, 1999). Because of limited ability for crop rotation, the practice of grafting has provided a useful method for growing watermelons on land which would otherwise require fumigation or be abandoned. Grafting has been routinely utilized in Japan and Korea since the late 1920s for the control of Fusarium wilt (Lee, 1994). Historically, Fusarium wilt has been the greatest yield-limiting disease of watermelon worldwide. Recently, Bruton et al. (2007) stated that 75% of the United States watermelon production is at risk for Fusarium wilt. Fusarium wilt symptoms include damping-off, seedling disease, or wilt during any stage of plant development. The specific symptom that may be exhibited is dependent on environmental conditions, age of plants when infected, and the density and virulence of the pathogen population. Symptoms on mature plants typically appear following fruit-set and may appear as a dull gray-green appearance of the leaves followed by yellowing of the crown foliage, wilting during the heat of the day, and eventual death. Fusarium wilt is considered to be a vine decline disease of watermelon where vine vigor gradually deteriorates (Bruton et al., 1998). Propagules of the fungus may be spread by soil, plant debris, and farm implements. Fulton and Winston (1915) first noted that the Fusarium wilt pathogen can be carried on seeds. Several additional reports (Martyn, 1985, 1987; Proc. IV IS on Seed, Transplant and Stand Establishment