Viruliferous aphid damage during specific growth stages of dry peas

The pea aphid, Acyrthosiphon pisum, vectors two economically important viruses to commercial dry peas, Pisum sativum, in the Palouse region of northern Idaho and eastern Washington: Bean Leaf Roll Virus (BLRV) and Pea Enation Mosaic Virus (PEMV). We conducted field experiments during the summer of 2009 and 2010 to quantify the relationship between the date of virus inoculation and crop seed yield. Our ultimate goal was to derive guidelines producers could use to make insecticide-use decisions to manage viruliferous aphids. We infested ‘Aragorn’ dry pea plants with three viruliferous aphids for a 72-hr inoculation access period using small clip cages to encage aphids from insectary colonies positive for either BLRV or PEMV. Field infestations began 10-days after plant emergence and continued approximately every third day until crop maturity. Ten replicates consisting of 10-plants each were inoculated with either BLRV or PEMV each date. Seed yield was measured by hand-harvesting plants at crop maturity. The best-fit statistical model for the 2009 experiment was y=-0.0003x2 + 0.0297x + 0.3328 (n=2800, r2=.423), where y is relative seed yield and x is the days after emergence on which plants were inoculated. This model predicts up to 20% yield loss if plants are colonized by viruliferous aphids within 4-weeks of plant emergence, but inconsequential losses of no more than 5% if viruliferous aphids colonize plants afterwards.