Question
We have a cottonless cottonwood that has been on our property for over 20 years. It has always been fine until this last year. It started bleeding sap in the spring and still hasn't stopped. It has covered our house, our cars (although it washes off easily), our landscaping, everything. At first it was just annoying and I thought it would go away but it is spiraling out of control. The sap has attracted a variety of bees, wasps, and hornets. There are swarms of red ants; and not there are thousands of flies. What's going on?

Answer
Sounds like one of the sucking insects--aphids or scales.
These insects suck the plant juices from the plant and  excrete a sugary liquid called honeydew. This honeydew drips onto plant foliage or other structures and provides a suitable place for black sooty molds to grow. Ants often tend or care for aphids in return for the honeydew. Therefore, if ants are running over a plant, look carefully for aphids.


Probably the most common disturbance caused by aphids and scales is their never-ending production of honeydew. This sweet liquid drips onto plant foliage and stems and is soon covered with black sooty mold. Cars, sidewalks, and lawn furniture under trees with aphids are also covered with this sticky fluid. Ants, flies and wasps appreciate the sugary meal and can become a nuisance of their own. Usually a sooty black mold will grow on the honeydew. Even though plants may look bad from the growth of sooty molds, these fungi do not damage the plant tissues. Once the aphids disappear, the sooty mold often dries up and falls off the plant.

There are several insecticides that can be sprayed on the foliage to kill the aphids but on large trees it is difficult to get the spray up into the crown and cover all leaves. Another insecticide that can be used is called Bayer Advanced Tree and Shrub Insect Control Concentrate. This is applied to the soil around the tree and the roots transport the insecticide to the leaves and stems and when the aphids suck the plant juices the insects are killed. Check with your local nursery for this product. Control the insects and the sap and wasps will go away.

Here is a web link to the Bayer product if you want more information on this product.

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