Late Blight Management
Year 1 (2006) Summary
All farm fields were scouted for LB and any other diseases. No farms in southern and eastern OR, one farm in the Willamette Valley, and both farms in NW WA experienced LB epidemics in 2006; the differences in farm incidence are related to differences in temperature and rainfall patterns in these distinct regions – LB is more prevalent in cooler, moister environments. In addition, NW WA is a major potato growing region with high inoculum potential. Farms in LB-conducive regions use cultural methods such as wide row spacing, row orientation, irrigation management, and destruction of inoculum sources (e.g. cull piles) to manage LB. Only one farmer collaborator has ever applied copper fungicides. Disease incidence in the one farm with LB in the Willamette Valley may have been due to row-covering of an early potato planting, a narrow in-row spacing, late afternoon irrigations, and late spring rainfall. One of the WA farms intends to implement multiple prophylactic copper fungicide applications in 2007.
Year 2 (2007) Summary
Late blight occurred on only two Ospud farms in 2007, and disease onset occurred late in potato development. The Skagit Valley farmer sprayed his fields with Nordox (copper oxide), which managed the epidemic; yield was likely not affected by LB in 2007. An unmanaged late August epidemic on one Willamette Valley Farm killed the crop within 2 weeks and probably slightly reduced yield. An experiment station spray trial demonstrated that multiple prophylactic Nordox applications reduced overall disease severity by 88%. Compost tea (produced by a local wholesale blueberry grower) reduced disease severity early in the epidemic, but in this severe fall epidemic, tea would not have increased yield. However, in a spring epidemic ended by summer hot temperatures, the tea could have significantly reduced foliar damage and ultimately increased potato yield.