The effectiveness of crop rotation on management of Verticillium wilt over time
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2019 Elsevier Ltd The objective of this research was to determine the effectiveness of using grain crops in rotation with cotton in managing Verticillium wilt of cotton over a 10-year period. The circular shaped field (52 ha) was divided into six equal sized wedges and cotton or grain crops (sorghum, corn, wheat) were rotated from 2001 to 2018, with some wedges having cotton more frequently and others rotated with grain crops more frequently. Verticillium wilt, which is caused by Verticillium dahliae, was first seen in the field in 2007. Verticillium wilt incidence increased as long-term cotton (host) frequency (HF) increased during 20082010 and 20122014, but wilt incidence was unaffected by HF in 20162018. Grain crops planted in rotation with cotton in one of the two previous years reduced wilt incidence in rotated cotton relative to continuous cotton in 20082010, but either had no affect or increased wilt incidence in rotated cotton in 20122014 and 20162018, relative to continuous cotton. Verticillium dahliae microsclerotia density (MS/cm3 soil)1/2 increased with increasing HF for all three time periods. Three consecutive years of cotton increased MS1/2 relative to rotated cotton in 20082010 and 20122014, but either did not affect MS1/2 or negatively affected MS1/2 density by 20162018 (relative to rotated cotton). Yield, adjusted each year to a 0 to 1 scale, decreased with increasing HF in all three time periods. Yield decreased with three consecutive years of cotton relative to rotated cotton in 20082010 and was unaffected by rotated cotton in 20122014 and 20162018. Crop rotation with nonhosts for management of Verticillium wilt, initially (first four years) was very effective at reducing MS, wilt incidence, and increasing yield. However, 911 years after the initial Verticillium wilt symptoms occurred, short-term crop rotation no longer reduced Verticillium wilt incidence, reduced microsclerotia density, or increased cotton yield.
