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.
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ERRORS: If you find
errors, typographic or factual, we would appreciate having them called to our attention so
they can be corrected. Phone: Robert Suranyi (218) 773-3346 or Ted Radcliffe (612)
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