Question
Thank you for taking the time to answer my question. I have searched the web, went to several garden businesses, and went to the library for help on this matter.I have 3 Poplar trees in my front yard which face west. One of the trees is flourishing. The other two are not. They have yellow leaves with black spots and are not growing at all. They are all located with each other and receive the same insecticide treatments and mineral treatments. I would really love to keep them. Any ideas on what is going on?

Answer
I am sorry your question got misplaced so I am late answering it. It sounds like a leaf spot fungus not an insect problem so insecticides will do not good.


There are several different fungi that cause leaf spot, including septoria and marssonina. The spores of the fungi are borne on drops of water, which includes rain splashing from the leaves of one tree to another, or water blown on the wind from one leaf to another. Both fungi can also overwinter on fallen leaves, only to arise in the spring to infect nearby trees.

These diseases first appear as spots on the leaves, giving rise to the name. The spots can be brown, grey or even two-colored. Eventually, the spots merge and the leaf withers, or the spots fall out, leaving holes in the leaves. The fungi can also spread to the twigs and branches, causing cankers to form. Cankers are dark, sunken, cracked areas in the wood. If they encircle the branch, the branch may die.

Prune away infected branches to control the spread of the disease. A preventative fungicidal treatment may also help, but it is difficult to stop possibly infected water from getting on your popular hybrid trees. Cleaning up fallen leaves and twigs can help. While unsightly, leaf spot does not usually kill the tree.


Here is a web link with pictures that may help in identifying the fungi and their treatment. Most leaf spots do not kill the tree but cause premature leaf drop.


http://www.ext.colostate.edu/pubs/garden/02920.html