Evaluation of Beet Leafhopper Transmitted Virescence Agent Damage in the Columbia Basin

Abstract

Potato purple top disease is caused by a phytoplas- ma known as Beet Leafhopper Transmitted Virescence Agent (BLTVA), which is vectored by the beet leafhopper (BLH, Circulifer tenellus Baker). Previous studies determined that BLTVA can cause significant reductions in yield and tuber quality; however, quantifying the damage caused by BLTVA and the insect vector has been challenging. In 2009-2011, potato plants at different growth stages were exposed to vary- ing densities of BLH in a screen house located at the Hermiston Agricultural Research and Extension Center in Hermiston, OR. The densities of potentially infective BLH were one BLH per plant (low), two BLH per plant (medium), and five BLH per plant (high). Releases occurred at the following growth stages: vegetative, tuber initiation, tuber bulking, and maturation. The treatments were arranged in a randomized complete block design with three replications per treatment. Disease incidence was monitored weekly and yield was assessed. When all 3 years were combined, we found that increasing rates of disease incidence correlated with decreas- ing yields. We also found that greater yield losses were ob- served with later BLH release times. With both correlations, differences between years were a strong contributing factor. There was a mean decrease in yield of 0-12 % at a density of oneBLH per plant,6-19% attwoBLH per plant,and 6-20% for five BLH per plant. These general trends in yield loss suggest that economically relevant damage may occur at levelsas low as one or two potentially infective BLH per plant in the Columbia Basin.