POTATO LATE BLIGHT IN THE COLUMBIA BASIN - AN ECONOMIC-ANALYSIS OF THE 1995 EPIDEMIC

The cost of managing late blight in potatoes during a severe epidemic caused by new, aggressive strains of Phytophthora infestans in the Col umbia Basin of Washington and Oregon in 1995 was documented. The mean number of fungicide applications per field varied from 5.1 to 6.3 for early- and midseason potatoes, and from 8.2 to 12.3 for late-season po tatoes in the northern and southern Columbia Basin, respectively. In 1 994, a year when late blight was not severe, the mean number of fungic ide applications per field made to early- and midseason potatoes was 2 .0; whereas late-season potatoes received a mean of 2.5 applications. The mean per acre cost of individual fungicides applied varied from $4 .90 for copper hydroxide to $36.00 for propamocarb + chlorothalonil. T otal per acre expenses (application costs plus fungicide material) for protecting the crop from late blight during 1995 ranged from $106.77 to $110.08 for early and midseason potatoes in different regions of th e Columbia Basin and from $149.30 to $226.75 for late-season potatoes in the northern and southern Columbia Basin, respectively. Approximate ly 28% of the crop was chemically desiccated before harvest as a disea se management practice for the first time in 1995, resulting in an add itional mean cost of $34.48/acre or $1.3 million for the region. Harve sted yields were 4 to 6% less than in 1994. The total cost of managing late blight in the Columbia Basin in 1995 is estimated to have approa ched $30 million.