Saturday, 15 July 2006

Correlation of Land Management Practices to the Incidence of Fusarium Wilt of Tomato.

Dan O. Chellemi1, Erin N. Rosskopf1, and Jim H. Graham2. (1) USHRL, USDA-ARS, 2001 S Rock Road, Fort Pierce, FL 34945, (2) CREC, Univ of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850

In July 2000, five land management treatments were established on a commercial fresh market tomato farm with a history of significant yield reductions from soilborne pests. The five treatments were: Conventional' a continuation of annual tomato production using the same conventional methods practiced by the commercial grower except that soil fumigation with methyl bromide was replaced by fumigation with 1,3-dichloropropene-chloropicrin; Disk fallow' soil cultivated routinely to maintain plots free of vegetation; Weed fallow' soil left undisturbed and vegetation allowed to regenerate naturally; Organic production' summer and winter cover crops of Sunn Hemp and Japanese millet, respectively were combined with annual applications of poultry manure (broiler litter) and urban plant debris; and Bahiagrass pasture' establishment and maintenance of an improved stand of a perennial pasture grass. Treatments were arranged in a randomized complete block design with 6 replications and the size of each replicate plot was 0.16 ha. Tomato was cultivated following a three or four year rotation in each land management treatment (September 2003 and September 2004). Tomato was also cultivated for two consecutive years in the same soil following a three year rotation in each land management treatment. Organically-based crop production procedures, including the use of soil solarization, were adhered to in the organic land management treatment. Strip-tillage was used prepared the soil for tomato cultivation in the bahiagrass pasture treatment. Conventional tomato production practices were implemented in the other land management treatments except that soil fumigation was omitted from the disk fallow and weed fallow treatments. Treatment affects on soil quality, soilborne disease and marketable yield of tomato were assessed. Fusarium wilt, caused by Fusarium oxysporum f.sp. lycopersici Race 3, was the primary soilborne disease present when tomatoes were cultivated. Disease incidence was <3% in the organically managed plots, even when tomato was cultivated in the same location for two consecutive years. In the bahiagrass treatment, Fusarium wilt was also <3% when tomato was cultivated following a three or four year bahiagrass rotation but increased to 22% when tomato was cultivated for two consecutive years in the same soil. In the conventional treatment, Fusarium wilt of tomato ranged from 1% to 20%. In the disk fallow treatment, Fusarium wilt of tomato was 15% and 26% after three and four years, respectively of maintaining soil free of vegetation. Disease incidence was 35% when tomatoes were cultivated for two consecutive years following the disk fallow treatment. In the weed fallow treatment, disease incidence was 16% and 11% when tomato was produced following three or four years respectively of maintaining the soil in a weed fallow rotation. Fusarium wilt increased from 11% to 40% in the second consecutive year of tomato production following a weed fallow rotation. Total marketable yield of tomato were lowest in the bahiagrass treatment, intermediate in the organic treatment and weed fallow treatments and highest in the disk fallow and conventional treatments. Marketable yields declined significantly in the second year when tomato was cultivated consecutively in the same soil following the land management treatments. The largest declines were observed in the bahiagrass, disk fallow and weed fallow treatments. Early harvests (1st pick) were greatest in the organic, disk fallow and conventional treatments. The results demonstrate that undisturbed soil where plants are allowed to regenerate naturally in a weed fallow rotation or soil that is maintained free of vegetation in a disk fallow rotation is more conducive to Fusarium wilt of tomato than soil that is managed organically or maintained in a bahiagrass rotation. In contrast, Fusarium wilt of tomato is more variable in land that has been managed using conventional tomato production practices including soil fumigation. The results also demonstrated that continuous cultivation of tomato in the same location will lead to significant increases in Fusarium wilt in the bahiagrass, weed fallow and conventionally managed land systems while suppression of Fusarium was more stable in the organically managed system.

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