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Title: Efficacy of four soil treatments against Fusarium oxysporum f. sp. vasinfectum race 4 on cotton

item Bennett, Rebecca
item Spurgeon, Dale
item DETAR, WILLIAM - Retired ARS Employee
item Gerik, James
item HUTMACHER, ROBERT - University Of California
item HANSON, BRADLEY - University Of California

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2011
Publication Date: 7/15/2011
Citation: Bennett, R., Spurgeon, D.W., Detar, W.R., Gerik, J.S., Hutmacher, R.B., Hanson, B.D. 2011. Efficacy of four soil treatments against Fusarium oxysporum f. sp. vasinfectum Race 4 on cotton. Plant Disease. 95:967-976.

Interpretive Summary: A relatively new strain (race 4) of a plant wilting disease called Fusarium wilt has become an important problem for California cotton growers. Cotton growers may manage this disease by planting varieties that are resistant to race 4, but few resistant varieties are currently available. Soil treatments, either chemicals applied to soil or solarization (soil heating from sunlight through a plastic cover), may be useful methods for managing this disease. We compared solarization and three chemical preparations to a non-treated control for managing race 4 of Fusarium wilt. Results showed that plants in the methyl-bromide + chloropicrin, chloropicrin + 1,3-dichloropropene, and solarization treatments had the best survival and the fewest signs of root and stem injury. These treatments were also best at reducing Fusarium spores in the soil. Plants in the metam-sodium and the non-treated control had poor survival and greater root and stem injury. Plants in the methyl-bromide + chloropicrin, and chloropicrin + 1,3-dichloropropene treatments, were also larger than plants in the solarization, metam-sodium, and non-treated control. Although the methyl-bromide + chloropicrin treatment was highly effective, methyl-bromide is environmentally undesirable and its use is being phased out. Results from solarization and chloropicrin + 1,3-dichloropropene treatments indicate these may be used to manage Fusarium wilt in cotton caused by race 4.

Technical Abstract: Fusarium wilt caused by race 4 of Fusarium oxysporum f. sp. vasinfectum is a critically important disease problem in California cotton (Gossypium spp.). Because few cultivars with resistance to race 4 are available, management alternatives for this disease are needed. Four soil treatments (50:50 methyl-bromide + chloropicrin, as a positive control; 60:40 chloropicrin + 1,3-dichloropropene; six 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 Fusarium spp. Two cultivars each of Pima and Upland, 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 non-treated 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 non-treated control, metam-sodium, and chloropicrin + 1,3-dichloropropene treatments. Soil counts of Fusarium spp. were significantly reduced only in the methyl-bromide + 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 high levels of race 4 inoculum in heavy clay soil.