Assessment of irrigation as a method of managing potato early dying

Pre- and posttuber initiation irrigation treatments were evaluated for their impact on development of potato early dying symptoms in Russet Burbank potatoes grown in field microplots in northcentral Oregon. Irrigation treatments were in a factorial arrangement of three pre- and three posttuber initiation regimes across six inoculum densities of Verticillium dahliae. Microplots were drip-irrigated to provide deficit, moderate, or excessive amounts of irrigation water prior to tuber initiation, followed by all nine possible posttuber initiation combinations. Moderate irrigation was approximately equal to estimated consumptive use (ECU) by the plant; the deficit and excessive regimes were 50 and 150% of ECU, respectively. Differences in area under the senescence progress curve (AUSPC) values were significant (P less than or equal to 0.01) based on irrigation treatment prior to tuber initiation, whereas posttuber initiation irrigation and the interaction of pre-and posttuber initiation irrigation treatments were not significant. When plants were watered in excess of ECU prior to tuber initiation, AUSPC values were 22% higher than the deficit pretuberization treatment, regardless of the posttuber initiation treatment. Averaged across the nine irrigation treatments, AUSPC values were 2.5 times greater in soils infested with 30 cfu of V. dahliae per gram of soil than in noninfested soil. Pretuber initiation irrigation also was assessed as a method of managing potato early dying in cultivar Russet Burbank in field plots in eastern Washington and central Wisconsin. Plots were noninfested or infested with 5 and 25 or 50 cfu of V. dahliae per gram of soil. Differential irrigation treatments (deficit, moderate, or excessive) were imposed from plant emergence to tuber initiation (3-5 wk). AUSPC values were significantly lower in the deficit compared to the excessive irrigation treatment. Increases in symptoms of potato early dying were most apparent 850 degree days after planti