One of our aspen trees appears to have been sprayed with an oily substance. The surrounding rock bed was also sprayed. Can I have a leaf tested in Colorado for possible poisoning? Is there anything we can do to counteract this potential attempt to kill this tree?
Adams County Colorado trees and shrubs
There are labs that will test for the presence of herbicides. However, the tests are expensive and if you don’t know what herbicide you are looking for it can be especially expensive and impractical. There are several labs that do such testing which can be found with an internet search for “labs for herbicide testing” I don’t believe any are local.
Are you sure the trees were spared with an herbicide? Most herbicide formulations are not oily and would not leave a residue on the sidewalk. Aspens are a host for several types the sap sucking insects that excrete a sticky substance know as “honeydew”. This substance accumulates on the leave and plant on the drips onto the ground below. It can coat rocks or sidewalk under a tree in a way very similar to what you described.
Information on aphids which might lead to this: http://www.ext.colostate.edu/pubs/insect/05511.html
Scale also produces honeydew: http://www.ext.colostate.edu/pubs/insect/05513.html
If you would like to send some picture of the tree and the residue I would be happy to take a look. I would also be happy to talk through the issue with you over the phone. If the tree has been spared with an herbicide there is not a lot you can do at this point. Most herbicides could be rinsed off if you caught them quickly enough but after a few hours (quicker for some herbicides) they have already been absorbed by the plants.
Hope this helps, please feel free to send some picture or give me a call.