Aphid Alert 2002, No. 2, July 12
Aphid Situation, July 12
No green peach aphid have yet been captured in 2002 in traps at any location in the Aphid Alert Network. However, potatoes are abundantly colonized by green peach aphid at Rosemount (25 mi south of St. Paul campus of the University of Minnesota) as of June 30. Spring 2002 has now seen six major wind events (low level jets) likely to have brought green peach aphid to the Northern Great Plains. We encourage potato growers, especially seed potato producers, to closely monitor their fields and apply effective aphicides at first detection of green peach aphid colonization. Some buckthorn aphid and potato aphid have been captured at Manitoba locations. Low numbers of bird cherry-oat aphid have been caught at some locations in Minnesota and North Dakota. Previous observations suggest that bird cherry-oat aphid is an important PVY vector in the Northern Great Plains. Turnip aphid colonies are developing on canola and wild mustard. Turnip aphid has been implicated as PVY vector.
Weather Conditions and Late Blight
Heavy rains occurred through the Northern Great Plains region mid-week with some areas receiving as much as 9 inches. In many locations soils were already saturated and the resulting surface flooding damaged crops, especially potatoes. The rains significantly increased the risk of late blight. Many locations have already exceeded the threshold severity value of 15. Growers need to be proactive in their fungicide treatment programs. No late blight has been reported yet in 2002 in Minnesota or North Dakota, but growers can anticipate its occurrence within the next week or two. Forty fields have been reported with late blight in Wisconsin.
Potato late blight status reports
This is the second issue of Aphid Alert 2002. This newsletter is intended to alert seed potato producers in the Northern Great Plains to flight activity by aphid species that are 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 is updated as additional data becomes available. To become an e-mail subscriber send us an e-mail message with the word "subscribe" in subject line. If you have no interest in receiving this newsletter by e-mail, please reply with the word "unsubscribe" in the subject line. Some e-mail subscribers may not wish to receive messages containing graphics. If so, reply with the the words "no graphics" in the subject line.
Minnesota locations: aphid captures during the week ending July 12
North Dakota locations: aphid captures during the week ending July 12
Manitoba locations: aphid captures during week ending July 12 (see Manitoba Agriculture and Food Website)
Wisconsin, South Dakota and Nebraska locations: aphid captures during the week ending July 12
Figure: Trap locations in the Aphid Alert network in 2002
6th Wind Event of 2002
Figure: Back trajectories of July 6 wind event (low level jet) that could have brought migratory insects to the Northern Great Plains. This was the sixth such event of this growing season. The first event occurred May 21-23 and was of 36 h duration (see Aphid Alert 2002, no. 1), the second occurred June 8-10 and was of 42 h duration (Fig. 2), the third occurred June 18-19 and was of 24 h duration, the fourth was June 21-23 and was of 45 h duration, and the most recent was June 29-30 and was of 36 h duration
Predicting potato seed lot rejections
We have used data collected in previous years of the Aphid Alert project to develop tentative models of the relationship between the incidence of seed lot rejections the previous year and current season aphid pressure.
Figure: The percent of seed seed potato lots rejected for excess PLRV in the winter grow-out is correlated with the percent of seed lots rejected the previous year times log10 mean cumulative capture per trap of green peach aphid (Myzus persicae).
Figure: The percent of seed seed potato lots rejected for excess PVY in the winter grow-out is correlated with the percent of seed lots rejected the previous year times log10 mean cumulative capture per trap of green peach aphid (Myzus persicae) + bird cherry oat aphid Rhopalosiphum padi).