The effect of an alternate weed host, hairy nightshade, Solanum sarrachoides (Sendtner) on green peach aphid distribution and Potato leafroll virus incidence in potato fields of the Pacific Northwest

Hairy nightshade, Solanum sarrachoides (Sendtner) is an annual solanaceous weed prevalent in potato farmlands of the Pacific Northwest. S. sarrachoides is also a reservoir for Potato leafroll virus (PLRV) and its most important vector, the green peach aphid, Myzus persicae (Sulzer). Green peach aphids prefer S. sarrachoides than potato, Solanum tuberosum (L.), and produce more nymphs on S. sarrachoides than on potato. Increased green peach aphid preference for S. sarrachoides and greater fecundity on this plant could lead to overcrowding and movement toward neighboring potato plants. To test our hypothesis, field trials were conducted at Kimberly, Idaho during the summers of 2003 and 2004. A row of S. sarrachoides seedlings was planted in the middle of potato plots and naturally occurring green peach aphid populations were monitored weekly on potato plots with and without S. sarrachoides. More aphids were consistently found on S sarrachoides plants than on potato plants. More aphids were found on potato plants in plots with S. sarrachoides plants than without S. sarrachoides. Targeted insecticide applications on S. sarrachoides rows alone reduced the number of aphids on potato plants in those plots, suggesting that insecticide sprays prevented aphid movement from S. sarrachoides to potato. Testing of potato tuber sprouts 90 days after harvest by double antibody sandwich ELISA indicated a greater PLRV infection rate on plots with S. sarrachoides than plots without S. sarrachoides. Therefore, the presence of S. sarrachoides in potato plots will likely increase aphid populations and PLRV incidence on neighboring potato plants.

► Solanum sarrachoides plants had more aphids than adjacent potato plants.
► Aphid densities on potato plants increased when S. sarrachoides plants were present.
► PLRV incidence in potato plants increased when S. sarrachoides plants were present.