Theses and Dissertations Collection

Potato industry in Washington State, which generates $4.6 billion economic impact and 23,500 jobs, susceptible to outbreaks of numerous pests. Two such pests are Beet leafhopper (BLH), which causes a disease called "purple top" via Beet Leafhopper Transmitted Virescence Agent (BLTVA) and Green peach aphids (GPA) which vectors Potato leaf roll virus (PLRV). This thesis examines how BLH and GPA affect potato yields in the Columbia Basin of Washington. In addition, this thesis also examines how pest populations are correlated with weather conditions and with potatoes planted acreage. Endogeneity of pest populations is examined using two and three stage least squares regressions (2SLS and 3SLS), And results from two estimation methods, Seeming Unrelated Regression (SUR) and Ordinary Least Squares (OLS) are reported.

The regression results show that due to increase in the peak of BLH population by 1 per plant, potatoes yields decrease by 9.26 cwt/acre. Peak GPA numbers display a positive, but statistically not as significant, correlation with yields perhaps due a common correlate like weather. Acreage has a significant, correlation with yields perhaps due a common correlate like weather. Acreage has a significant effect on BLH population but not on GPA population. Although acreage does not have a direct effect on yields, it appears to have an indirect effect via BLH-increase in acreage increase BLH numbers which in turn reduce yields. The effects of temperature and precipitation on the population of BLH and GPA vary throughout the growing season. Finally, no direct evidence of pest population endogeneity is detected and system estimation of SUR produce more significant coefficients than equation by equation OLS estimation.