The effects of tillage system and irrigation on Verticillium wilt and cotton yield

A large plot experiment was conducted in a field infested with Verticillium dahliae. The test area of the field was divided into three different cropping systems. Within each cropping system, the treatments were conventional tillage (CT) and reduced tillage (RT) at three irrigation rates (base rate = 1.0B designed to meet 60% of the crop evapotranspiration [ET] needs, and 50% above [1.5B] and below [0.5B] the base rate). Higher microsclerotia densities occurred with CT at the 1.5B rate than with RT at that rate, though densities were similar between tillage treatments at the 1.0B and 0.5B irrigation rates. Wilt incidence and defoliation were not affected by tillage treatment. Yield was higher with RT than CT in the area of the field with a sorghum/cotton rotation (RT lint yield = 1411 kg/ha and CT was 1261 kg/ha) and with a winter wheat/summer fallow/cotton rotation (RT lint yield = 1490 kg/ha and CT was 1306 kg/ha). The continuous cotton with a terminated wheat cover crop had no tillage differences (RT lint yield = 1422 kg/ha and CT was 1380 kg/ha for CT), but the CT treatment with this cropping system had little to no cultivation because of the terminated cover crop. Irrigation rate was more impactful than tillage treatment on Verticillium wilt. The 1.5B rate had higher densities of microsclerotia and incidence of Verticillium wilt than the 1.0B and 0.5B rates. Yield in a semi-arid environment is often a function of irrigation rate, but in a Verticillium wilt field, the severity of wilt at the high irrigation rate affected yield. The highest yield occurred with the 1.0B rate, though it was not significantly (P < 0.05) higher than the 1.5B rate. However, given the higher irrigation costs associated with the 1.5B rate, the recommendation in a Verticillium wilt field is to utilize a lower irrigation rate targeted at replacing 60% of ET and a reduced-tillage system.