Question
I live in Alpine,Utah, zone 6B and this October morning I noticed what would look like snow flakes on the underside of the leaves of my tri color beech. As the temperature is 51 degrees F, and it had not snowed, I suspected possible frost, however no other trees had frost. Upon touching the substance, it felt somewhat sticky. I had not noticed this in years past; (the tree has been in the same location for 6 years). Is this normal or is it possibly a disease? If a disease, with what should I treat the tree?

Answer
Sounds like Wooly beech Aphids.
Pale yellow, sap-feeding aphids, which are covered by fluffy white fibres, form dense colonies on young shoots and the undersides of leaves. Winged aphids, which have a bluish-white appearance when in flight, fly from infested plants in midsummer in search of other beech trees. These winged aphids are sometimes mistaken for another type of pest, known as whitefly, but whitefly do not infest beech trees and hedges in Britain.

The foliage becomes sticky with the honeydew that is excreted by the aphids and can develop sooty moulds. In heavy attacks the foliage at shoot tips is distorted and leaves may dry up.

The woolly beech aphid gets its name because the body is covered with waxy wool-like filaments. These aphids are gregarious and tend to congregate primarily on the undersides of leaves. Often large numbers of the molting or cast 搒kins?will be attached to leaf hairs, which gives the leaf a whitish appearance. The woolly beech aphid has piercing-sucking mouthparts, which are used to remove plant fluids. However, woolly beech aphid is not considered an economic pest because beech trees, especially large specimen types, can sustain large populations without suffering any injury. Large populations of woolly beech aphid can, however, produce tremendous amounts of honeydew, a clear, sticky liquid that may attract wasps, ants, or yellowjackets. In addition, the honeydew serves as an excellent growing medium for black sooty mold fungi. Black sooty mold fungi can detract from the aesthetic appearance of a beech tree and most importantly can reduce the production of food via photosynthesis by blocking the entry of light.

I would spray the foliage with an insecticide called Orthene. You will need to spray all the foliage and try to get the spray on the underside. This will kill the aphids present now. Then next Spring treat the tree with an insecticide called Bayer Advanced tree and Shrub Insect control. This is applied to the soil around the tree and the roots will carry it to the foliage and when the insects feed they are killed. It will protect the tree for the entire season. Here is a web link to this product. Both insecticide can be found at your local garden type store. The soil applied Bayer product will not work well this late in the season since soon the tree will start to shut down for the winter and not move material up the tree.

http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect