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. Irr igation treatments were in a factorial arrangement of three pre- and t hree posttuber initiation regimes across six inoculum densities of Ver ticillium dahliae. Microplots were drip-irrigated to provide deficit, moderate, or excessive amounts of irrigation water prior to tuber init iation, followed by all nine possible posttuber initiation combination s. Moderate irrigation was approximately equal to estimated consumptiv e use (ECU) by the plant; the deficit and excessive regimes were 50 an d 150% of ECU, respectively. Differences in area under the senescence progress curve (AUSPC) values were significant (P less than or equal t o 0.01) based on irrigation treatment prior to tuber initiation, where as posttuber initiation irrigation and the interaction of pre- and pos ttuber initiation irrigation treatments were not significant. When pla nts were watered in excess of ECU prior to tuber initiation, AUSPC val ues were 22% higher than the deficit pretuberization treatment, regard less of the posttuber initiation treatment. Averaged across the nine i rrigation treatments, AUSPC values were 2.5 times greater in soils inf ested with 30 cfu of V. dahliae per gram of soil than in noninfested s oil. Pretuber initiation irrigation also was assessed as a method of m anaging potato early dying in cultivar Russet Burbank in field plots i n eastern Washington and central Wisconsin. Plots were noninfested or infested with 5 and 25 or 50 cfu of V. dahliae per gram of soil. Diffe rential irrigation treatments (deficit, moderate, or excessive) were i mposed from plant emergence to tuber initiation (3-5 wk). AUSPC values were significantly lower in the deficit compared to the excessive irr igation treatment. Increases in symptoms of potato early dying were mo st apparent 850 degree days after planting, when plant senescence exce eded 40%. Senescence was twice as great in infested plots as in noninf ested plots. The effect of pretuber initiation irrigation on total tub er yield was inconsistent. In Washington in 1991, tuber yield was sign ificantly (P less than or equal to 0.05) greater in the deficit compar ed to the excessive pretuber initiation treatment. In 1992, there was no effect of irrigation regime on total tuber yield. In Wisconsin, tub er yield was significantly (P less than or equal to 0.05) lower in the deficit compared to the moderate or excessive pretuber initiation irr igation regimes. Total tuber yield was significantly (P less than or e qual to 0.05) reduced as inoculum density was increased. Early season irrigation management may be a viable option to minimize losses due to potato early dying in some production areas.