Aphid Alert 2000, No. 6, July 16

Update: Summary of virus vector situation through 18 July

Captures of winged aphids in the Aphid Alert network traps remained low during the week ending 18 July. Minnesota and North Dakota locations averaged less than 3 aphids of all species per trap and less than 0.1 green peach aphid per trap. Total aphids and green peach aphid were both about twice as abundant as they were in the previous week. Total aphid captures in the fifth week of 2000 are about 1/3 of that during the same week of 1998 and 1999 and green peach aphid captures are 1/2 that of 1998 and 1/7 that of 1999.

What are aphid populations going to do for the rest of the year? Yogi Berra observed that "Prediction is very hard, especially when it is about the future." Aphid populations are lower on cereals or canola than in 1998 and 1999. However, both crops are nearing maturity and this will cause the aphids that are there to fly. We expect an increase in aphid flight activity in the near future. There are also substantial populations of green peach aphids on wild mustard. The surface flooding that occurred in many areas drowned out much cropland permitting wild mustard and other weed hosts of green peach aphid, e.g., redroot pigweed to take over. Scouting for green peach aphid should be focused on the margins of potato fields since this is where initial colonization occurs.

Potato leafhoppers are again abundant in the Red River Valley. The adults are not abundant enough to cause direct injury, but potato fields should be scouted for the nymphs. We have shown that reduced rates (1/4X) of dimethoate or Asana will give excellent leafhopper control without flaring aphids. Aster leafhoppers are present at very high densities. Aster leafhopper does not colonize potato, but this species vectors aster yellows (the causal agent of "purple top") which has been associated with dark chips.

Captures of PVY vectors (other than green peach aphid) per trap, 1998-1999