Also known as Elm Phloem Necrosis, this disease infects trees native to North America, while European and Asian elms seem to be immune.  

The first symptom is the death of root hairs and tips followed by foliar wilt. Leaves will turn yellow, then brown and curl up.  Generally the tree dies a few weeks after foliar symptoms manifest themselves.  Other symptoms include yellowing of the sapwood and a wintergreen odour emanating form the bark.  The causal agent of elm yellows is a “mycoplasma-like organism” (MLO) which is classified between a virus and a bacterium.  This organism is carried from tree to tree by leafhoppers.  There is no known effective treatment for elm yellows, so disposal of infected trees is the only option.  The most effective preventative measure is controlling the leafhopper population.

In order to do this, a homeowner can utilize a pesticide such as methoxychlor emulsifiable concentrate.  Applied during the bud breaks, this chemical represents an effective control of the leafhopper.  As most chemical pesticides are poisonous, care should be taken to read the label before use.