Aphid Alert 2003, No. 7, August 1

Potato insect update for the Northern Great Plains, week ending 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.

Update on University of Minnesota Crop Border Treatment Experiment

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.

Minnesota-North Dakota aphid data, week ending July 29

table showing Minnesota and North Dakota aphid data for the week ending July 29, 2003

Manitoba aphid data, week ending July 31

table showing Manitoba aphid data for the week ending July 31, 2003

Additional information on the aphid situation in Manitoba can also be found at www.gov.mb.ca/agriculture/crops/insects/index.html, and the Manitoba Agriculture and Food potato hotline at 1-800-428-6866.
Late Blight Situation

In Manitoba, scattered showers this week provided some relief from the recent heat and extended dry weather. However, these rains were generally light and did little to change risk with respect to Late Blight in the province. In North Dakota and Minnesota, rains were locally heavy, increasing the risk of Late Blight in the area bounded by Landon to Roseau in the north and Sabin to the south. Late Blight Severity values also increased rapidly during the week in the Carrington area. The Late Blight Disease Severity Threshold has been reached over much of Northern Great Plains. When conditions become favorable and inoculum is high, Late Blight can develop within a week. So far, the only known case of Late Blight this summer occurred three weeks ago near Carberry, Manitoba.

Potato late blight status reports

Guide to the Field Identification of Wingless Aphids on Potato

(click here for a PDF of the Guide)

photo of a potato aphid photo of a buckthorn aphid photo of a foxglove aphid photo of a green peach aphid photo of a cotton aphid
Potato Aphid, Macrosiphum euphorbiae (Thomas) Buckthorn Aphid, Aphis nasturii (Kaltenbach) Foxglove Aphid, Aulacorthum solani (Kaltenbach) Green Peach Aphid, Myzus persicae (Sulzer) Cotton (=melon) aphid, Aphis gossypii (Kaltenbach)

Subscriber Alert

This is the seventh issue of Aphid Alert for the 2003 growing season. This newsletter is intended to alert seed potato producers in the Northern Great Plains to flight activity by aphid species known to be potential vectors of potato viruses. We report results weekly on the WWW, by e-mail to subscribers, and by surface mail to all Minnesota and North Dakota seed potato growers. The hard copy and e-mail versions of Aphid Alert report aphid capture data available as of the date they are mailed. The WWW version will be updated as additional data becomes available. To become an e-mail subscriber to Aphid Alert 2003, send us an e-mail message with the word "subscribe" in subject line. Note that current subscribers need not resubscribe. If you have no interest in receiving this newsletter by e-mail, please reply with the word "unsubscribe" in the subject line.