Supplemental Irrigation and Cultivar Effects on Potato Tuber Diseases

Supplemental irrigation can improve potato growth and tuber yield under deficit rainfall conditions, but may also impact potato tuber diseases. The comparative effects of irrigation on tuber disease incidence were quantified on four cultivars. Surface sprinkler irrigation was applied in July and August of each year, based on tensiometer or moisture block readings, with the goal of maintaining soil water to the required treatment levels. Black scurf ( Rhizoctonia solani ), black dot (Colletotricchum coccodes ), silver scurf ( Helminthosporium solani ) and comm- on scab ( Streptomyces scabei ) diseases were quantified on potato tubers randomly sampled at harvest and stored at 7.2 C. The incidence of tuber diseases varied among irrigations and significant treatment effects ( P<0.05 ) were observed for black dot, black scurf and silver scurf diseases across years. The highest levels of black dot and black scurf disease incidences were recorded on the irrigation treatments of artificial drought and Tiaug60 in 1996 and Eaug50 and Non-irrigated check in 1997, respectively. Disease incidence differed significantly ( P<0.05 ) among cultivars and years, and was generally greater on Superior and Shepody than on Atlantic and Russet Burbank. This study showed that supplemental irrigation may selectively impact tuber disease incidence, depending on treatment and application scheduling, while varying cultivar susceptibility may increase tuber disease levels.