Aphid Alert 2000, No. 11, August 20

Update: Summary of virus vector situation through 20 August

Captures of winged aphids in the Aphid Alert network traps are down dramatically compared to trap captures of last week (23.1 per trap compared to 144.5). Captures of green peach aphid averaged only 0.58 per trap compared to 1.19 per trap last week. Corn leaf aphid remains the most abundant aphid at most trapping sites with the turnip aphid the next most abundant species. Most of the canola has been swathed and aphids that were common on the leaves left on the stubble last week have all but disappeared.

For the last two weeks, we noted reports of an aphid attacking soybean in Michigan, Illinois, Wisconsin and Minnesota. It has been determined that this aphid is Aphis glycines, an Asiatic soybean pest. The current populations in Minnesota are on the eastern side of the state with the heaviest populations found in Houston, Winona and Fillmore counties of SE Minnesota. We still need to collect winged individuals from these fields for positive identification, but based on density of the colonies found in the field, gross morphology of the wingless aphids (color, size, shape, etc.) we believe these aphids are indeed, Aphis glycines. How far and how rapidly this new soybean insect pest will spread is unknown and undoubtedly scientists at the Minnesota Department of Agriculture and entomologists at the University of Minnesota will be monitoring soybean fields for this aphid for the remainder of this growing season and into next year. To see a map of the current distribution of this aphid in Minnesota, go the MDA Pest Report and click on the 25 August 2000 issue.

http://www.mda.state.mn.us/pestsurvey/PestReports/PestReport.html

Many seed fields will soon be top-killed. It is important to remember to continue your aphid control program until vines are completely dead. This is especially critical on seed fields that are to be entered for recertification. Viruses can be spread by wingless aphids that are induced to move following the first application of vine desiccant. In the process of finding a new feeding site, an aphid may move from a diseased plant to a healthy plant. Our research shows that for PLRV as few as 7 days are needed to move virus from the foliage to the daughter tubers. We suspect the same is true for mosaic (PVY). Most potato fields will need two applications of desiccant to completely kill the vines. Just like late blight control, it is recommended that aphidicides be used as long as the vines remain green.

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.