Efficacy of Four Soil Treatments Against Fusarium oxysporum f. sp. vasinfectum Race 4 on Cotton

Bennett, R. S., Spurgeon, D. W., DeTar, W. R., Gerik, J. S., Hutmacher, R. B., and Hanson, B. D. 2011. Efficacy of four soil treatments against Fusarium oxysporum f. sp. vasinfectum race 4 on cotton. Plant Dis. 95:967-976. Fusarium wilt, caused by race 4 of Fusarium oxysporum f. sp. vasinfectum, is a critically important disease problem in California cotton (Pima, Gossypium barbadense; Upland, G. hirsutum). Because few cultivars with resistance to race 4 are available, alternative management strategies for this disease are needed. Four soil treatments (50:50 methyl-bromide + chloropicrin as a positive control; 60:40 chloropicrin + 1,3-dichloropropene; 6 weeks of solarization; and metam-sodium) were evaluated for efficacy against race 4 in a naturally infested, heavy clay soil. Treatments were evaluated based on plant mortality, height, number of mainstem nodes, vascular discoloration ratings, and soil counts of F. oxysporum. Two cultivars each of Pima and Upland cotton varying in resistance to race 4 were used. Plant mortality was lowest in methyl-bromide + chloropicrin, solarization, and chloropicrin + 1,3-dichloropropene treatments, and highest in the nontreated and metam-sodium treatments. Although most plant mortality occurred within 5 weeks after planting, substantial mortality of the susceptible Pima cultivar DP 744 accumulated for up to 10 weeks. Seven to eight weeks after planting, plants in methyl-bromide + chloropicrin and chloropicrin + 1,3-dichloropropene treatments were taller and had more mainstem nodes than in other treatments. Vascular discoloration was reduced in methyl-bromide + chloropicrin and solarization treatments compared with the nontreated control, metamsodium, and chloropicrin + 1,3-dichloropropene treatments. Soil counts of F. oxysporum were significantly reduced only in the methylbromide + chloropicrin, chloropicrin + 1,3-dichloropropene, and solarization treatments. Six weeks of solarization and 60:40 chloropicrin + 1,3-dichloropropene (295 liters a.i./ha) proved effective for reducing Fusarium wilt of cotton in heavy clay soil. Fusarium wilt, caused by race 4 of Fusarium oxysporum Schltd.:Fr. f. sp. vasinfectum (Atk.) W.C. Snyd. & H.N. Hans., has become a major disease of cotton (Gossypium spp.) in California. Race 4 was first detected in this state in 2001, when severe loss to Fusarium wilt was observed in a field with clay loam soil. Races 1 and 2 of F. oxysporum f. sp. vasinfectum were known to be present in California (20), but Fusarium wilt caused by these races generally occurs in sandy or sandy loam soils infested with root-knot nematodes, Meloidogyne incognita (Kofoid & White) Chitwood (8,12,17). Previously, race 4 had been found only in Asia (1,10,23,32). Since its discovery in California, race 4 has spread to most cotton production areas in the San Joaquin Valley. Availability of economically practical options for managing Fusarium wilt of cotton (7) is limited. Fusarium wilt caused by nematode-associated races of F. oxysporum f. sp. vasinfectum may be managed by minimizing populations of the root-knot nematode through soil fumigation, crop rotation, and use of nematode-resistant cultivars (19,24,29). The ability of root-knot nematodes to affect crops rotated with cotton (24,31) provides additional incentive for managing nematode populations. However, management of Fusarium wilt caused by races not associated with nematodes, such as race 4 and the Australian genotypes of F. oxysporum f. sp. vasinfectum, is more difficult. In California, host resistance has been the primary tactic for managing race 4 despite the limited number of cultivars with useful levels of resistance (16,34). In 2008, nearly three-quarters of the Pima (G. barbadense L.) production in California was planted to a single cultivar with race 4 resistance (Phytogen 800, Dow AgroSciences) (35). Although Phytogen 800 and a recently released race 4–resistant cultivar, Phytogen 805RF, are widely planted in California, resistance in both cultivars to race 4 is incomplete. Fields planted with Phytogen 800 and 805RF occasionally exhibit significant plant loss to Fusarium wilt (R. B. Hutmacher and R. S. Bennett, unpublished data). Most other commercial Pima cultivars are highly susceptible to race 4 and increase soilborne inoculum if planted (15). To date, Upland (G. hirsutum L.) cultivars have demonstrated only moderate resistance to race 4 (16). While host resistance is the most economical strategy for managing Fusarium wilt of cotton, the limited selection of resistant cultivars indicates the need for other management options. Chemigation (3) and solarization (soil heating under transparent plastic film) (4,21) to reduce soilborne inoculum are usually considered too costly for cotton production. However, use of these approaches may be warranted in small disease hotspots to prevent further spread of inoculum, especially if the benefits persist over multiple seasons or reduce weeds or disease in rotation crops. Relatively costly fumigants, such as methyl-bromide, chloropicrin, and 1,3-dichloropropene, have been widely used to manage Fusarium wilt and other soilborne diseases in high-value crops (5,13,14,26). In California, metam-sodium and 6 weeks of solarization were evaluated individually and in combination for controlling Fusarium wilt of cotton (3). Ben-Yephet and colleagues found that neither of two rates of metam-sodium (151 and 303 Corresponding author: R. S. Bennett, E-mail: [email protected] Current address of B. D. Hanson: Department of Plant Sciences, University of California, Davis 95616. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. The U.S. Department of Agriculture is an equal opportunity provider and employer. *The e-Xtra logo stands for “electronic extra” and indicates that one supplementary table and one supplementary figure are available online. Accepted for publication 14 March 2011. doi:10.1094 / PDIS-09-10-0696 This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2011. e-Xtra*