Re-posted from EcoIPM.org.
Update: Today while walking around the neighborhood I saw lots of migrating woolly aphids, probably woolly elm
aphid, floating through the air. They look like little white troll dolls with white tufts of ‘hair’. Species in the genus Eriosoma migrate between two hosts. Woolly apple aphids have a complicated life history. They can overwinter on the as nymphs on roots of rosaceous plants and on elm as eggs. In spring eggs hatch and eventually adults migrate from elm to rosaceous hosts. Then it seems some of these migrate down to overwinter on roots but others must migrate back to elm. It is not well understood. Woolly elm aphids (Eriosoma americanum) feed on elm leaves in spring then adults migrate to Amelanchier spp. in early summer. These may be what we are seeing now. In any case keep your eyes out for white floating tufts and try to grab one for a close look.
Woolly apple aphid (Eriosoma lanigerum) infestations on pyracantha bushes around campus. These produce cottony fluff along the branches. When you brush away the fluff (really it is wax the aphids produce) you will see hundreds of pink or grey aphids crawling around. Woolly apple aphids have been out for a month or so now but are becoming very noticeable now. Infestations for multiple years produce large leafless patches on bushes. The aphids cause galls to form on branches and branches become black from sooty mold.
Pyracantha is also host to hawthorn lace bugs which are active now. The beautiful critters cause stippling on leaves. Between the two pests, pyracantha often looks pretty bad a lot of the time. One benefit may be that I noticed hundreds of lady beetle pupae on the the infested bushes I was photographing. Soap or oil should provide some control more information from WSU and eXtension.