Aphid Alert 2003, No. 14, September 19

Potato insect update for the Northern Great Plains, week ending September 19

The past week was marked by cooler temperatures and locally heavy precipitation, over the Northern Great Plains. Wheat harvest has been completed in Minnesota and most potatoes have been vine killed. Total aphid captures were down considerably from the week before, but at some locations rain may have washed aphids from the traps.

In Minnesota-North Dakota, two green peach aphids were captured, one at Karlstad, one at Walhalla. Species most abundantly represented in Minnesota and North Dakota trap captures were: corn leaf aphid (90) and bird cherry-oat aphid (29). Other potential virus vectors captured included: soybean aphid (8), sunflower aphid (6), potato aphid (4), buckthorn aphid (2), thistle aphid (1) and turnip aphid (1). Eleven other aphids were non-vectors (7) or were not identified (4).

In Manitoba, only 49 aphids were captured. Species most abundantly represented in the Manitoba trap captures were: buckthorn aphid (24), bird cherry-oat aphid (4), potato aphid (1) and not identified (20).

The cartoon (below) shows cumulative captures of winged green peach aphid as mean number per trap (Minnesota and North Dakota data only) for the years 1992-1994, and from 1998 to the present. The gold line represents cumulative mean captures per trap to date for 2003. In the years we have operated the Aphid Alert trapping network, there were two with exceptionally high green peach abundance (1998 and 1999) and two with very few green peach aphids (1993 and 2001). Green peach aphid numbers have been relatively low this summer. This year, there appears to have been greater risk of mosaic spread than of leafroll virus because of the abundant inoculum present in the crop and because the former can be spread by other aphids in addition to green peach aphid.

graph showing green peach aphid trap captures for the week ending September 18, 2003

Note that the data is plotted in this cartoon on a logarithmic scale.

The cartoon (below) shows cumulative captures of winged bird cherry-oat aphid as mean number per trap (Minnesota and North Dakota data only) for the years 1992-1994, and from 1998 to the present. The gold line represents cumulative mean captures per trap through 18 September in 2003. For the first half of the 2003 growing season, bird cherry-oat captures were at the highest level we had recorded in the nine years we have operated the Aphid Alert network. In late summer with the onset of hot dry weather, bird cherry-oat aphid captures slowed and the cumulative captures ended slightly below that of 2002. Our previous data suggests that cherry-oat aphid and green peach aphid are the principal vectors of PVY in our region. State seed potato inspectors have seen a lot of PVY (mosaic) in the field this summer. The prospects for this year's winter tests do not look good with respect to PVY.

graph showing bird cherry-oat aphid trap captures for the week ending September 18, 2003

Minnesota-North Dakota aphid data, week ending Sept. 18

table showing Minnesota aphid data for the week ending September 18, 2003

Manitoba aphid data, week ending Sept. 18

table showing Manitoba aphid data for the week ending September 18, 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

Potato late blight status reports

Update for September 18, 2003 by Philip Northover, Soils and Crops Branch, Manitoba Agriculture and Food

Any time long moisture periods on the plant occur, late blight can be a concern. Low temperatures in the recent days have reduced, but not eliminated late blight risk. While many fields have or, are currently being harvested, any fields above threshold that are not protected still run the risk of late blight. With increased risk of frosts, injury to tubers can open the door to bacteria that may degrade tubers in storage. Also, damaged tubers may lead to an increased number of culls and result in large cull piles. As mentioned at the start of the season, cull piles left over winter are ideal for providing the fungus with both means to survive the winter, and initiate new infections in the spring. Cull piles are like tubers planted earlier than the actual crop and which have no fungicide protection from Late blight. Thus, cull piles could increase the likelihood of an early season late blight outbreak for the 2004 season. Please keep this in mind when disposing of your culls.

Subscriber Alert

This is the fourteenth and final issue of Aphid Alert 2003. This newsletter is intended to alert seed potato producers in the Northern Great Plains of the U.S. and Canada to flight activity by aphid species known to be potential vectors of potato viruses. These reports are posted weekly on the WWW and sent by e-mail to subscribers and by surface mail to all Minnesota and North Dakota seed potato growers.