Aphid Alert 2000, No. 10, August 13

Update: Summary of virus vector situation through 13 August

Captures of winged aphids in the Aphid Alert network traps were roughly double that of last week (144.5 per trap compared to 74.3). Captures of green peach aphid averaged 1.19 per trap compared to 0.55 per trap last week. Some locations in North Dakota averaged 3.0 green peach aphids per trap. Turnip aphid numbers also increased about 4.5-fold (to a mean of 19 per trap). Green peach aphid and turnip aphid are commonly found in large numbers on canola. Most canola has been swathed, but late planted fields still host high numbers of green peach aphid and most of the immatures will develop into winged adults. Corn leaf aphid remains very abundant in many locations, but this species is not important as a PVY vector.

Last week, we noted reports of an aphid attacking soybean in Michigan and Illinois. It since has been determined that this aphid is Aphis glycines, an Asiatic soybean pest. This unwanted immigrant is very similar in appearance to Aphis gossypii (melon or cotton aphid). Aphis glycines is native to northern China and Siberia so it unlikely to be limited by cold winter temperatures. We suspect that Aphis glycines will prove capable of transmitting PVY. That might reduce the value of soybean as a crop border for protection of elite potato seed lots from PVY, but small grains have proven effective as crop borders even though they host aphids capable of vectoring PVY. A problem would only exist if the there was some virus already present in the field you were trying to protect.

We continue to hear reports or grower dissatisfaction with the aphid control obtained using Fulfill (pymetrozine). Performance seems most problematic when low volume applications are made, especially with those applied by air. There is some suspicion that potato aphid may be more difficult to control that green peach aphid. In our insecticide efficacy trials at Rosemount, we have had good success with this product against both ot these aphids. We have tested the product under extreme green peach aphid pressure giving us considerable confidence in that data; typically we get >98% control. In our experiments, potato aphid pressure has been too low to severely test the product, but we are getting >90% control. Fulfill kills aphids very slowly (5-7 days may be required before the insect dies), but feeding activity ceases almost immediately. However, it may be that if application does not penetrate the canopy that UL light may reduce the effective life of the product.

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.