Aphid Alert 1999, No. 3, June 29

Summer 1999: Aphid trapping data

Results reported in this issue of Aphid Alert are total captures of winged aphids and species identifications for the following locations and sampling interval end-dates. Missing locations will be incorporated in this issue of the newsletter when available.

During the past week, total aphid captures were ~25% greater than in the week previous, i.e., 20.4 aphids per location compared to 16.3 aphids per location. Bird cherry-oat aphid, Rhopalosipum padi (L.), was, for the second week, the most abundant aphid captured in the traps, but as percentage of total aphid captures, bird cherry-oat aphid declined from 53.4% to 35.3%. Green peach aphids were captured at three locations, Baker (2 aphids), Crookston (1 aphid), and Karlstad (2 aphids). Dr. Lockhart tested the green peach aphids and found that they were not carrying potato virus Y (PVY) or potato leafroll virus (PLRV).

The first aphid immigrants arriving in a potato field usually are not carrying potato viruses since they originate from host plants other than potato. If the aphid acquires virus from a potato grown from an infected tuber, they may spread that infection to nearby healthy potato plants. If the initial infection rate is low, e.g., <1%, rogueing can be effective control measure. Roguing should be done as soon as possible and the infected vines removed from the field.

Insecticides are not very effective in preventing primary virus spread, i.e., virus coming from sources outside the protected field, because no insecticide kills quickly enough to prevent transmission. Insecticides can prevent the potato colonizing aphid species, e.g., green peach aphid, potato aphid, and buckthorn aphid, from becoming established and spreading virus within the potato crop. Insecticides can reduce secondary spread, i.e., movement of the virus from an infected plant to nearby healthy plants. Insecticides tend to be more effective at preventing the spread of leafroll (PLRV) than in preventing spread of mosaic (PVY). For more discussion of chemical control of potato virus spread see Aphid Alert, No. 4, 1998.