Aphid Alert 2002, No. 10, September 6

Aphid Situation in Week Ending September 6

Aphid flight activity was comparatively light in the week ending September 5. Mean captures per trap of both green peach aphid and bird cherry-oat aphid were down 75% compared to the week previous. The abundance of green peach aphid colonizing potato appeared to be in sharp decline with a high incidence of infection by entomopathogenic fungi. Turnip aphid was locally abundant. Most potatoes in the Red River Valley of Minnesota and North Dakota have been vine-killed. Spring 2002 was marked by an unusual frequency of wind events (low level jets) seemingly perfect for the transport of winged aphids from their overwintering sites in the south. Green peach aphid populations in the northern great plains were more abundant in 2002 than in 2000 and 2001, the latter a year of exceptionally low green peach aphid numbers, but well short of the large populations that occurred in 1998 and 1999. It appeared that 2002 did not provide especially favorable conditions for the local increase of green peach aphid populations once established on their secondary hosts. On the other hand, bird cherry-oat aphid and other aphids of small grains were very abundant in 2002. That does not bode well with respect to PVY spread because cereal aphids have been implicated as important PVY vectors in our region. The situation should be better with respect to PLRV since green peach aphid is believed to be the only vector of consequence in our area. While green peach aphid were moderately abundant, we had the good fortune of having very little PLRV inoculum present. We expect an increase in PLRV over the levels of 2001, but are optimistic that seed lot rejections for this virus should not be excessively high in this year's winter grow-outs.

Weather Conditions and Late Blight

Unwanted precipitation again soaked much of the northern region this past week. The high humidity and cool evenings provide idea conditions for the spread of potato late blight. Therefore, the risk of late blight continues to be very high throughout much of southern Manitoba, eastern North Dakota and northwestern Minnesota. In Manitoba, late blight has been confirmed in the Carberry and Portage areas and was also reported from the Winkler area. In northwestern Minnesota, late blight has been confirmed in several locations. In areas where late blight is present, growers should consider using Acrobat (a co-formulation of dimethomorph and mancozeb), Omega (fluazinam) or Gavel (zoxamide) as their fungicide. If late blight is found in your field, infected plants must be destroyed immediately. Dead vines do not support late blight, but you should continue to spray green vines and partially dead vines with fungicide to protect against tuber infection. It is essential to continue fungicide application until vine kill to limit tuber infection, but especially for growers planning to green dig. Late season blight and rain can result in severe tuber infection and high risk of total loss in storage. A 7-day spray schedule is recommended in all areas.

graphic showing estimated precipitation in inches from August 30 to September 5 2002

Potato late blight status reports

Subscriber Alert

This is the tenth issue and final issue of Aphid Alert for the 2002 growing season. This newsletter was 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 have reported 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 updated as additional data becomes available. We anticipate that aphid sampling will continue for another two to three weeks. 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. 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: mean aphid captures per trap during the week ending September 6

table showing Minnesota aphid capture data for the week ending September 6, 2002

North Dakota locations: mean aphid captures per trap during the week ending September 6

table showing North Dakota aphid capture data for the week ending September 6, 2002

Manitoba locations: mean aphid captures per trap during week ending September 6 (see Manitoba Agriculture and Food Website)

table showing Manitoba aphid capture data for the week ending September 6, 2002

Note: Glenboro trap location discontinued

Wisconsin, South Dakota and Nebraska locations: mean aphid captures per trap during the week ending September 6

table showing Wisconsin, South Dakota, and Nebraska aphid capture data for the week ending September 6, 2002

Figure: Trap locations in the Aphid Alert network in 2002

illustrated map of the upper midwest showing trap locations in the Aphid Alert network in 2002

Figure: Cumulative captures of green peach aphid (per trap), 1992-1994, and 1998-2001. Three distinctly different seasonal patterns of green peach aphid abundance have been observed. In 1998 and 1999 green peach aphid were abundant with total captures approximately an order of magnitude greater (10X) than that of 1992, 1993 and 1994, and two orders of magnitude greater (100X) than that of 1993 and 2001. For the Minnesota and North Dakota seed potato industry, low green peach aphid pressure in 1994 coincided with the end of a multi-year PVY epidemic and the low green peach aphid pressure of 2001 coincided with the end of a multi-year epidemic of PLRV. During the week ending September 6, green peach aphid flight activity increased 80% over the previous week, but overall, 2002 has been a year of only moderate green peach aphid pressure.

graph showing green peach aphid trap captures for 1992-1994 and 1998-2001, plus the week ending September 5, 2002

Figure: Cumulative captures of bird cherry-oat aphid (per trap), 1992-1994, and 1998-2001. This aphid comes off wheat and other cereals. The species is typically abundant in the Northern Great Plains. In our area, green peach aphid and bird cherry-oat aphid appear to be the two most important vectors of PVY. Lowest abundance of bird cherry-oat aphid during the years the Aphid Alert network has operated was in 1994, which, coupled with low green peach aphid pressure, coincided with the end of a multi-year epidemic of PVY. Bird cherry-oat aphid flight activity has been higher in 2002 than in previous years of the Aphid Alert network.

graph showing bird cherry-oat aphid trap captures for 1992-1994 and 1998-2001, plus the week ending September 5, 2002

Figure: Cumulative captures of bird cherry-oat aphid and green peach aphid (per trap), 1992-1994, and 1998-2001. These two aphids have been implicated as the primary vectors of PVY in the Northern Great Plains (see Aphid Alert 2002, no. 2). Other potential vectors of PVY, e.g., greenbug and turnip aphid, are also abundant this year.

graph showing bird cherry-oat and green peach aphid trap captures for 1992-1994 and 1998-2001, plus the week ending September 5, 2002

Acknowledgements

  1. Project Personnel: Robert Suranyi, Ted Radcliffe, Dave Ragsdale, Ian MacRae, Matt Carroll, Min Zhu
  2. Minnesota potato growers: Robert Anderson, Thomas Hoeft, Justin Dagen, Brian Halverson, Paul Imle, Jerry Larson, Scott Pieper, Peter Van Erkel
  3. North Dakota potato growers: Tom Bjornstad, Tom and Corrie Enander, Jim Jorde, Janet Knodel (NDSU), Henry Miller, Brad Nilson, Steve O'Neil
  4. Nebraska potato grower: Troy Dagen
  5. South Dakota potato grower: James Carter
  6. Wisconsin State Seed Farm: Andy Merry

Aphid traps were collected by the following seed potato field inspectors of the Minnesota Department of Agriculture: Willem Schrage (director), Michael Horken, Darrell Anderson, Charles Steinke, Michael Bothum, Perry Paschke, and field inspectors of the North Dakota State Seed Department: Michael Oosterwijk, Tom Weippert, Francis Longtine, Bob Dietrich, Graham Smith, Randy Sass, and John Oby

The printed newsletter was posted with the help of Irene Hoff and the Red River Valley Potato Growers Association: Duane Maatz, President

Summer help sorting aphid traps: Judd Jasmer, Adam Tunseth, Nick Glimsdahl