The insects are only 2 to 2.3 mm long, but shed large amounts of a bluish/white wax. This give the illusion of ash in the air as it falls to the ground.
These aphids also produce large amounts of sticky “honeydew”. The tiny drops fall on leaves or anything below – outdoor furniture, cars, sidewalks, etc. Sooty mold fungi will then begin to grow on the sticky film. Leaves and bark will turn black. Leaves are not killed, but their ability to photosynthesis is reduced which add to tree stress if other negative conditions are present (drought, other insects, disease etc.)
their own but if you want to avoid an infestation next year, there are some preventative steps you can take:
It’s next to impossible to spray a tree for insects since obtaining good coverage is difficult in the tall canopies. However, there is an option for control: in late winter to early spring, drench the base of your tree(s) with Iimidacloprid (name brands: Merit or Bayer Advanced Tree & Shrub Insect Control). The systemic insecticide will move up into the plant and to the leaves. Aphids are chewing / sucking insects and will ingest the control.
As always, when using any chemical treatment, follow label directions and use appropriate safety precautions.
For more information go to this Extension link: http://entnemdept.ufl.edu/creatures/trees/asian_hackberry.htm
blog entry by Linda Lindquist, CMG
sources: UT Extension / Dr. Frank A. Hale/ Cornell University Extension / University of Florida Extension
photos: Steve Wilson and L.J. Bass, University of Florida