Effect of Chemical Defoliation, Irrigation Water, and Distance From the Pivot on Late Blight Tuber Rot in Center-Pivot Irrigated Potatoes in the Columbia Basin

Chemical desiccation of potato foliage 2 to 3 weeks prior to harvesting tubers is commonly recommended to reduce late blight tuber rot. Observations in commercial fields indicate that this practice may not be needed to manage tuber rot in the semiarid environment of the Columbia Basin. Potatoes in this region are mostly grown under center pivot irrigation, and a relatively high volume of irrigation water is often delivered near the pivot in center-pivot irrigated fields. This study evaluated the effect of chemical desiccation of potato foliage on late blight tuber rot and quantified the incidence of late blight tuber rot in relation to distance from the pivot and the amount of irrigation water applied in center-pivot irrigated fields. Potato foliage was chemically desiccated or not desiccated within 41 to 76 m of the pivot of center-pivot irrigated potato fields 2 to 3 weeks before harvest in replicated plots in five field trials during 3 years. Incidence of late blight tuber rot did not differ significantly between the defoliated and nondefoliated plots in all five trials. Incidence of tuber rot significantly increased as amount of irrigation water applied increased, and was significantly greater within 30 m of the center pivot than at greater distances in two trials in 1998 and two trials in 1999. Tuber rot did not develop in a fifth trial in 2000 where a water gradient did not occur among the plots. The largest percentage of tubers infected with late blight was observed within 30 days of harvest at a storage temperature of 9°C. Chemical desiccation of potato foliage in the semiarid environment of the Columbia Basin was not beneficial in reducing late blight tuber rot, but growing potatoes within 30 m of the pivot will likely increase the number of infected tubers going into storage.