Aphid Alert 2003, No. 7, August 1

Aphid flight activity was much increased across the Northern Great Plains last week. Turnip aphid was the species most abundantly represented in Minnesota and North Dakota trap catches. Turnip aphid is reported in the literature to be capable of acquiring and transmitting PVY, but its vector efficiency is believed to be quite low. Canola is the principal host plant for turnip aphid in our region. Canola is likewise a favored host of green peach aphid. The sudden spike in turnip aphid flight during the past week likely reflects that canola is maturing and becoming a less suitable aphid host. Perhaps for the same reason, captures of green peach aphid are also on the increase. Other aphid species showing increases during the past week included sunflower aphid, corn leaf aphid and English grain aphid. Bird cherry-oat aphid numbers continued to decline for the third week. Most of the region's small grain cereals are near maturity and no longer suitable hosts for the various species of "cereal" aphids. At Gully, we caught many Hayhurstia atriplicus, a species of no economic consequence, but common on lambsquarter. This common weed, like redroot pigweed, wild mustard, and common mallow, is a green peach aphid host. In the Northern Great Plains, invasion of potato fields by green peach aphid tends to peak the first week of August. This pattern has occurred consistently during the nine years we've operated the Aphid Alert network. These mid-summer green peach aphid flights appear to be associated with the deteriorating suitability of other crops and weed hosts. Spring flights, on the other hand, tend to be associated with wind events (low level jets) and are assumed to represent long distance transport (migration) from more southerly locations where the species overwintered.

Growers should be aware that there was much aphid flight activity across the Northern Great Plains last week. Aphid flight activity tends to peak in the early morning and near dusk. Aphids are not strong fliers so most directed flight occurs when there is little air movement. Potato aphids have been abundant on potato in our region since early spring. Considerable potato colonization by green peach aphid occurred last week. We also are seeing colonization by buckthorn aphid and melon (cotton) aphid. From this time on, seed potato growers should monitor their seed lots regularly paying particular attention to any field margins adjacent to fallow.

In last week's Aphid Alert, we reported initiation of a large-scale University of Minnesota demonstration/research project to evaluate possible benefits of targeting the year's first insecticide [Monitor (methamidophos)] spray treatment for green peach aphid along field margins. Twenty six of the 30 fields growers had volunteered for use in the experiment met our criteria for selection. Pretreatment counts were made in each field to establish within field distributions of colonizing aphids. Field margins, usually just headlands, were then sprayed by airplane. Usually, only a single pass was made on each border. Initial inspection of the data suggests that aphid distributions conformed to our expectations with most found within 10-20 yds of field margins. Almost all of the aphids found in field interiors were potato aphid or less commonly buckthorn aphid. Our timing appears to have been near optimal with respect to green peach aphid. Posttreatment sampling will continue next week. We also want to take this opportunity to thank the growers participating in this project.

Aphid Alert: a research/outreach program providing region-wide virus vector surveillance to the Northern Great Plains potato industry.