Effect of Manure Application Timing on Potato Yield, Quality, and Disease Incidence

This study was established to determine whether the timing of liquid dairy manure application prior to planting potatoes influenced potato crop performance and the occurrence and severity of common scab (Streptomyces spp.) and verticillium wilt (Verticillium dahliae). Four potato (Solanum tuberosum L.) varieties with varying levels of resistance to common scab and verticillium wilt were planted on a site treated with manure applied at 280,500 L ha(-1) to separate plot areas 18, 6, or 1 month before potato planting in each of 2 years. Total tuber yield for 2001 showed a significant interaction between time of manure application and variety, with more scab-susceptible varieties (Russet Norkotah and W-1151R) showing lower yields compared to the fertilizer control when the manure application was made 1 month before planting. In 2002, the proportion of U.S. No. 1 tubers was significantly lower when manure was applied 1 month before planting, especially for W-1151R. Tuber dry matter was significantly reduced by manure application in both years, but was not consistently related to time of manure application. Total yield was significantly decreased as common scab levels increased, and this relationship was primarily driven by the low yield/high scab levels associated with W-1151R and Russet Norkotah planted 6 or 1 month after manure application in 2001. Late-season verticillium evaluations showed highest levels in 2001 when manure was applied 1 month before planting to susceptible varieties Superior and Russet Norkotah. This experiment showed that when manure was applied immediately ahead of potato planting yields, and quality of some varieties decreased in 1 of 2 years. Therefore, it may be safer to apply manure at least 18 months prior to planting potatoes.