Aphid Alert 2003, No. 4, July 11
Potato insect update for the Northern Great Plains, week ending July 10
Aphid flight activity remained light throughout the Northern Great Plains in the week ending July 10. Again, the species most commonly caught in our traps was bird cherry-oat aphid. Highest numbers of bird cherry-oat aphid were captured in traps at Karlstad and Williams. Flight activity of this species is expected to increase as small grains ripen. Bird cherry-oat aphid does not colonize potato, but is an efficient vector of PVY. Turnip aphid was also commonly represented in the captures. Turnip aphid, like green peach aphid, reproduces abundantly on canola, but unlike green peach aphid, does not appear to be of importance in transmission of any potato virus. Potato aphids have been abundant colonizers of potato this spring. To date we have only captured one green peach aphid, this week at Climax, MN, but green peach aphid apterae are found in low numbers on weed hosts, e.g., common mallow and redroot pigweed. Further to the south, at Rosemount, MN, green peach aphid are already well established on potato. We anticipate green peach aphid flight activity in the Northern Great Plains will remain light for the next 2-3 weeks and then peak in early August.
Adult potato leafhoppers remain abundant in potato fields throughout the region. Some growers have reported potatoes showing "hopperburn." For information about potato leafhopper thresholds and insecticidal alternatives readers are referred to the July 3 issue of Aphid Alert.
Potato leafhopper nymph and adult. Adult insect is about 1/8 inch long. Nymphs run sideways when threatened (e.g., if you place your finger beside them). Thresholds for insecticidal treatment are 1 adult per sweep (18 inch insect net) or when abundance of nymphs exceeds 1 to 1.5 per compound leaf.
Minnesota-North Dakota Aphid Data, week ending July 7
Manitoba Aphid Data, week ending July 10
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 Warning
Minnesota issued Late Blight alerts (July 10) for the Crookston, Foxhome, Grand Rapids, Humboldt, Little Falls, and Stephen areas. Alerts were previously issued for Alexandria, Brooten, Karlstad, Morris, Perham, Sabin, and Williams. In North Dakota, Late Blight Disease Severity Threshold (July 10) exceed 15 at Cando, Eldred MN, Hillsboro, Linton, Northwood, Oakes, Robinson, Sabin MN, Stephen MN, St. Thomas, and Warren MN. To date, there have been no reports of Late Blight in Minnesota or North Dakota. Most Manitoba stations are still below the Manitoba Disease Severity threshold (18) for late blight, but threshold has been reached (July 10) in in portions of the Carman/Morden/Winkler region, and the Treherne, Holland and Cypress River areas. Manitoba's first case of late blight was confirmed (July 10) near Carberry. The recent wet weather over the Northern Great Plains is expected to be replaced by warm, clear weather today (July 11) and over the weekend. However, it is strongly recommended that you scout your fields on a regular basis and maintain a regimented fungicidal spray program to prevent the development and possible spread of late blight in your area.
Potato late blight status reports
Guide to the Field Identification of Wingless Aphids on Potato
|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)|
This is the fourth 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.