ISSUE 15 August 9, 2001
SUNFLOWER INSECTS TO WATCH
Red Sunflower Seed Weevil: Reports from South Dakota and south central North Dakota indicate that seed weevil numbers are up. Field scouting for the red sunflower seed weevil in oilseed sunflower should begin when half the plants in the field are beginning to show yellow ray petals. The NDSU Crop and Pest Report, no. 13, July 26, gives tables for determining if you have an economic population of seed weevils in oilseed sunflower.
For confection sunflower, scouting and treatment decisions should be made earlier to prevent early infestation. A second treatment may be necessary to control reinfestation. The threshold for confection sunflower is about one weevil per plant.
Banded Sunflower Moth: We continue to see banded sunflower moth in sunflower fields and staging in grassy margins along fields. A treatment guideline of 1 moth per 2 plants when scouting at dusk has been used.
Gary Brewer, Entomologist
POTATO APHID ALERT UPDATES
U of Minnesota researchers continue to monitor aphid activity with emphasis on potato virus vectors. You can review their reports at:
Following are excerpts from the August 3 report:
We have completed our eighth week of aphid trapping for 2001. We still can only report the capture of one lone green peach aphid (last week at Baker). The same situation exists in Scotland. The July 22 Scottish Aphid Bulletin reports "The summer goes by but still the aphids in Scotland refuse to fly. " In view of the low level of potato aphid activity, and the low level of activity of other aphid species that vector non-persistent viruses, aphid monitoring in Scotland was ended for 2001 as of July 31. In the northern U.S., the 2001 growing season has had few wind events favorable for the long-distant transport of green peach aphids to the northern Great Plains. We are finding green peach aphid and turnip aphid, Lipaphis erysimi, on canola and other brassicas, but numbers are low compared to the past three years. Corn leaf aphid, Rhopalosiphum maidis, has been the most abundant aphid in our trap collections. The total of aphids other than green peach aphid captured in 2001 is less than on the same date in 2000. The species complex is different between the years with many more corn leaf aphid and fewer turnip aphid in 2001.
This year is shaping up to be a repeat of 1993, when there was essentially no green peach aphid flight activity all summer. Still, we urge caution. Much virus infected seed was planted this spring by commercial growers. We have to assume that even with low vector numbers the risk of virus spread to seed fields remains high. Since July 23, we have observed a 5-fold increase in green peach aphid numbers on canola. We expect green peach aphid flight activity will pick up with the onset of canola harvest. Thus, growers should scout their fields frequently (at least twice a week), especially on field margins and corners, to detect colonization. Remember that green peach aphid favors the underside of lower leaves of the plant. Focus scouting on the lower third of the potato plant. When green peach aphid densities reach the threshold of 3 wingless green peach aphids per 100 leaves insecticides should be applied to prevent the spread of PLRV. However, the most effective method to reduce spread of both PVY and PLRV spread is to kill the vines as early as feasible.
Dr. Ted Radcliffe
University of Minnesota
Aphid Alert 2001