Funded by the University of Idaho Agricultural Experiment Stations, Idaho Barley Commission and Idaho Wheat Commission.

Warning!

Bird cherry-oat aphid and Rose-grass aphid numbers are rising in Aberdeen.  Bird cherry-oat aphids (formerly known as the oat-bird cherry aphids), are small (1.7mm), yellowish- green to dark green to dull black aphids, characterized by a reddish-orange spot on the back end at the base of the cornicles.  The tips of its legs, cornicles and antennae are black.  The winged form of this aphid is darker than the wingless form and the front wing presents a median vein with two forks. 

Bird cherry-oat aphids feed on the leaves, but also feed at the base of the plant, belowground, and are easily overlooked.  Colonies are often found on underside of leaves or on leaf sheaths and heads.  Bird cherry-oat aphids do not inject toxins while feeding, therefore, even though heavy infestations can develop, injury is not readily apparent and plants appear to be able to tolerate large infestations without economic yield losses. However, this aphid is the most efficient vector of several viruses including the barley yellow dwarf virus (BYDV) and the potato virus Y (PVY). Barley yellow dwarf virus can significantly damage cereal crops and cause 50-75% crop loss if all the plants become infected. This problem seems to occur with higher bird cherry oat aphid populations.  It is difficult to recommend an action threshold because the damage depends upon what percentage of the aphids is carrying the virus. This can vary greatly from year to year.  Another complicating factor in winter wheat is the fact that symptoms of the disease are sometimes ambiguous and often do not show up until spring. As a rule, dry land wheat will suffer more than irrigated crops. Because of the many factors involved, treatment decisions should be made on a case by case basis.

Rose-grass aphid samples show increased numbers in several locations. Rose grass aphids do not inject a toxin as they feed and generally cause very little injury. Since they are easily confused with the more damaging greenbug, care should be taken in identification. If you are not sure of the species, contact your University County Faculty or Entomologist before any sprays are applied.

For a complete list of registered insecticides and rates for aphid infestations look at our Insect Management Handbook chapter, freely available at:

http://pnwpest.org/pnw/insects

Samples collected week of August 6, 2006

* - Have not received samples from this site