Aphid Alert 2003, No. 5, July 18
Potato insect update for the Northern Great Plains, week ending July 18
Aphid flight activity throughout the Northern Great Plains continued to be light during the last week. Bird cherry-oat aphid captures declined from the previous week, but again this was the species most abundantly represented in our trap captures. Soybean aphid populations are building rapidly on soybean throughout Minnesota and the Red River Valley. This aphid can reach very high densities on soybean and has a great propensity to produce winged adults when crowded. Previous experience suggests that soybean aphid tends to be underrepresented in our trap captures. Soybean aphid does not colonize potato, but we have shown that it can acquire and transmit PVY. Buckthorn aphid continues to be commonly represented in the trap captures from Manitoba. In Minnesota and North Dakota, potato aphid was captured at most locations and is a common colonizer on potato throughout the region. Only one green peach aphid was captured during the past week.
Potato leafhopper continues to be the insect pest of greatest immediate concern to Northern Great Plains potato growers. Some growers have reported potato leafhopper pressure above the economic threshold even after the application of foliar insecticides. Potato leafhopper management is discussed in Aphid Alert No. 3, July 3.
Colorado potato beetle remains a control concern for some growers, particularly in more northerly locations. In southern and central Minnesota the first summer generation of larvae have finished feeding and most have entered the soil to pupate. The summer adults have not yet emerged. Results from the 2003 University of Minnesota insecticide efficacy trials targeting Colorado potato beetle are summarized in the following tables. Three experiments were conducted:
Expt. 1. Systemic insecticides applied at planting or hilling
Expt. 2. Systemic insecticides applied at planting but with varying seed piece row spacing
Expt. 3. Foliar insecticides applied when late instar (3rd and 4th) larvae first appear
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 Situation
High relative humidity and locally heavy rainfall drove up Late Blight disease severity values across much of the Northern Great Plains during the past several days. Highest severity values are reported in U.S. counties on either side of the Red River of the North and in the Carman/Morden/Winkler region of Manitoba. Most locations have reached the threshold where Late Blight fungicides should be applied on a routine schedule. Spray intervals should be shortened in periods of rapid increase in disease severity value accumulation. The only confirmed case of Late Blight to date has been from Carberry, Manitoba (July 10).
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 fifth 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.