|I have a cottonwood in my backyard. About 2 yrs ago half of the tree died, while the other part lived. Its now a great shade tree, but has a minor drawback... the dead part has attracted black bumble bees which have burrowed into it. The leaves attract black wasps. We love the tree for the shade, but dont want to cut it down. Are there any solutions?
|We normally do not recommend the use of wound dressings for trees but I think the tree in your yard will benefit from an application of the black tarry substance to discourage the insect activity. You'll want to wait until this winter when the hornets/bumblebees are not active to apply the wound dressing. Carefully paint it on the damaged limbs/trunk where the activity has been in the past. Sealing the wood and the bark will exclude the insects and provide a physical barrier. You'll want to watch the tree for bee activity next spring. If you see them hanging around, hose them off with a strong stream of water from the hose. If you repeat each time you see them hanging around, you'll eventually discourage them from nesting and they will go elsewhere.
I suspect the wasps are attracted to the canopy because there are insects feeding on the leaves. When colonies of aphids or other sucking insects are present, bees, wasps and ants are attracted to the honeydew they excrete. If you can control the insect pests, the wasps will go away. On large trees the best control method is the use of a soil drench systemic. Merit or Bayer Advanced Tree and Shrub Insect Control or two products to consider using.