What you are seeing on the branches of the tree, are not plant galls but rather scale insects. No mention is made of the type of tree involved but from the picture it appears to be a tuliptree, Liriodemdron tulipifera. The scale is probably tuliptree scale. Females of this scale give birth to first instar nymphs called crawlers in August. The crawlers insert their piercing sucking mouth parts into the tree’s vascular system beneath the bark and begin to feed on the tree’s sap. The crawlers use only a small part of the sap ingested and discharge the excess in the form of a sugary sticky fluid called honeydew. The honeydew draws bees, wasps, flies, and ants to feed on it. The honeydew can eventually be colonized by black sooty mold which causes black areas on leaves, stems, branches, and other items it drips on including patios, lawn furniture, etc. The sooty mold causes no direct harm to the tree other than potentially interfering with photosynthesis. It is primarily and aesthetic problem. The crawlers will feed on the tree sap for a short time before molting into the over wintering second nymphal instar stage. There is one generation of nymphs per year.

The sap sucking insects have a large number of enemies such as predators, parasites, and parasitoids which may be able to keep the crawlers under control. Once the crawlers stop feeding, there will be no more honeydew and the bees, etc. should leave the area. Do not use the industrial wasp killer on the bees. If the crawlers are in great numbers over a large area of the tree, there is the possibility that a substantial loss of sap could represent a serious loss of energy sources to the tree. This accumulated stress, coupled with other stress producing conditions, e.g. drought, may cause leaf yellowing and loss, branch die back, and canopy thinning. While control is not always necessary, the scabs appearing on the branch can be removed by hand by using a dish scrubber, sponge, or bathroom scrub brush. Small infected branches could also be pruned out. If the tree is large and the infestation is sever, the use of an insecticide may be warranted. There are two options to consider, if using an insecticide. One would be treating the crawlers directly. Insecticidal soaps will kill the crawlers on contact and leave no residue. These would be used from mid-August to mid-September. As they must make direct contact with the crawlers, repeat applications would likely be necessary. Insecticidal soaps would kill any bees, wasps, etc. that they contacted. Systemic insecticides could also be used. These products are applied to the soil around the base of a tree using a watering can. Therefore, there are no residues on the plant and the insecticides resides within the tree. A systemic can be use from mid-August through September to control this year’s crawlers. An application in springtime, April or May, should provide twelve months control for over winter crawlers. Two of many products that could be used are those containing imidiclopord (Bayer Tree and Shrub or Dinotefuran Ortho Tree and Shrub). A dormant or horticultural oil could be used in the spring before new growth appears. If using an insecticide, be certain to read and follow all directions printed on the label.

Sources: OSU, Penn State, Purdue, University of Kentucky.

Thank you for your help, I appreciate it and I will not kill the bees!