Aphid Alert 2000, No. 13, September 4

Update: Summary of virus vector situation through 4 September

This will be the final weekly report of Aphid Alert for the 2000 growing season. There was essentially no aphid flight activity during the week ending 4 September. Green peach aphids averaged 0.04 per trap. Other potential virus vectors averaged 2.20 per trap, all but 8 of these were corn leaf aphids. Across all sampling dates, captures of both green peach aphid and other potential virus vectors in 2000 have totalled about 1/5th of what they were in 1999. This should translate into fewer seed lot rejections for virus this winter. However, late season flights of green peach aphid remain a possibility. These aphids would probably be coming from commercial potato fields and likely to be carrying virus. Most seed potato fields have already been killed, but any green foliage still remaining should be protected with an effective aphidicide until complete vine kill is accomplished.

Acknowledgements

We want to thank the following potato growers for allowing us to operate our aphid traps on their farms during the 2000 season. Cooperating growers in Minnesota were Robert Anderson, Thomas Hoeft, Justin Dagen, Brian Halverson, Paul Imle, Jerry Larson, Scott Pieper, Rick Thompson, Peter Van Erkel, and John Wojtanowicz; in North Dakota, the Bjornstad brothers, Jim Jorde, Henry Miller, Brad Nilson, and Justin Miller (R. D. Offutt Company); in Nebraska, Troy Dagen (CSS Farms); in South Dakota, James Carter (CSS Farms); and in Wisconsin, Andy Merry.

Aphid traps were collected by the following seed potato field inspectors of the Minnesota Department of Agriculture: Dr. Willem Schrage (director), Michael Horken, Darrell Anderson, Charles Steinke, Michael Bothum, Perry Paschke, Brent Amundson; and field inspectors of the North Dakota State Seed Department: Dr. Hossien El-Nashaar (director), Michael Oosterwijk, Tom Weippert, Jerry Pohanka, Francis Longtine, and Graham Smith.

The hard copy newsletter sent by the U.S. Postal Service was printed with the help of Irene Hoff (MDA) and the Red River Valley Potato Growers Association: Duane Maatz (president), Sheyna Richards, Tammey Schwartzman, and Melinda Goodman.

Captures of winged aphids (mean number per trap), 1992-1994 & 1998-2000. Data for Minnesota and North Dakota locations in the Aphid Alert trapping network.

Fig. 1. Captures of winged green peach aphid per trap.

Fig. 2. Captures potential PVY vectors other than green peach aphid per trap.

Fig. 3. Captures of winged turnip aphid per trap.

Fig. 4. Captures of winged small grain aphids (i.e., bird cherry-oat aphid, English grain aphid and greenbug) per trap.

Fig. 5. Captures of sunflower aphid per trap.

Fig. 6. Captures of other potential PVY vectors (including potato aphid, corn leaf aphid, thistle aphid, and others) per trap.

Eight rows of NewLeaf Russet Burbank sprayed weekly with Asana. Photo taken at Rosemount in mid-August. Asana did not control green peach aphid, but eliminated natural enemies permiting aphid populations to reach such high levels they killed the vines.

Eight rows of NewLeaf Russet Burbank sprayed only twice with low rates of Dimethoate for potato leafhopper control. Photo taken at Rosemount in mid-August. Natural enemies kept green peach aphid at very low densities all year.

Comparison of green peach aphid densities in the Rosemount plots shown in pictures above and in adjacent Guthion-treated plots (not shown). This devastating insecticide-induced aphid outbreak demonstrates a possible consequence of choosing the wrong insecticide and impressive potential of natural occurring biological control when not disrupted.