Question
I have a very large hackberry tree in my backyard, approx 20 feet from our back door, it is too tall to examine the leaves or branches closely.  The leaves are falling off the tree.  The leaves still on the tree are black and ready to fall.  I don't remember if the tree usually loses its leaves at this time of year or not.  I'm giving you the details of what I've done- so maybe you can tell me if I've done something to hinder the tree.  This summer I planted 3 purple fountain grass and a type of fern around it.  I also put down the black weed blocker paper around the tree and extended it out about 3 to 5 feet.  I placed large rocks at the edge of the weed block.  I put a few potted plants within 4 feet of the tree.  I also hung 2 ferns from the large branches, (the leaves of the ferns are getting a thick black coating.)  My lawn furniture has the black stuff also.  Ants (those really tiny ants) are everywhere around this tree, but no ant mounds are seen- I'm afraid to spray anything.  

I decided to make this shade garden because- the roots of this tree have always grown above ground and make it impossible for me to mow without damaging my mower.  I slit the weed block over the largest roots to expose them.

Are the roots suppose to grow above ground, very large roots that extend way out and are more prominent in the last 2 years?

Is the black weed block killing the tree?

When making the shade garden I clipped a few of the very small roots, is that wrong?

Thank you for your time.
Julena O'Con

Answer
The black is from a fungi called soot mold. It grows on honeydew produced by sucking insects like aphids or scales. The sucking insects suck the plant juices from the leaves and twigs and excrete a substance that is high in sugar content called honeydew. The ants are coming to feed on the sugar. Control the aphids and you will control the sooty mold and the ants will stop coming.

I would use a systemic insecticide and treat the tree. Systemic Insecticides. Systemic insecticides are absorbed and moved within plants. If the plant is infested with a scale species susceptible to systemic insecticide, systemics are particularly useful where it is not practical to spray because plants are large or spray may drift to unintended areas. Depending on the product, systemic insecticide may be applied by spraying foliage, injection or implantation into trunk vascular tissue, or applying on or into soil beneath trees and shrubs, where the insecticide is absorbed by roots.

A soil application of the systemic insecticide imidacloprid can provide season-long control of soft scales and certain other species such as European elm scale. Imidacloprid is not effective on armored scales and certain other species such as cottony cushion scale. Imidacloprid is available to both homeowners (Bayer Advanced Garden Tree & Shrub Insect Control) and professional applicators (Merit and others). Imidacloprid can be effective when applied to soil during late winter to early spring or before rainfall or irrigation are expected to facilitate root absorption of the insecticide. Summer application to stressed, heavily infested trees is less likely to be effective and is not recommended.

Now the other damages--The weed blocker raised the temperature around the trees root which the tree was not use to and will cause some leaf drop. The digging near the tree did damage some roots and also caused some stress to the tree and the cutting of roots  caused stress. This is the combination of aphid attact caused the leaves to turn early.

I would control the aphids first. Water the tree real good to off set the black and the digging. I would not remove the weed blocker now the tree should get use to it if you keep it watered.