Discoloration and streaking symptoms in the sapwood.
Controls to combat this disease generally involve sanitary measures aimed at the beetles. Dead and dying elms should be burned. This eliminates the elm wood which normally serves as a breeding place for elm bark beetles and thus reduces the beetle population. In areas where most native elms are infected, other tree species or resistant elm species, such as the Chinese or Siberian elm, should be planted rather them native elms.
ELM PHLOEM NECROSIS
Elm phloem necrosis is a disease of elm, caused by a virus or virus-like organism. The disease has occurred in the United States for many years, probably as early as 1882. The pathogen is transmitted from infected to healthy trees by the adult white-banded elm leafhopper, Scaphoideus luteolus, which feeds on the leaf veins. It is now present throughout most of the central, eastern, and southern portions of the United States. The disease is known to occur on American and winged elm, but all native elms are probably susceptible to attack by the pathogen.
Foliage symptoms of elm phloem necrosis.
The earliest symptoms of the disease appear in the top of the crown, at the outer tips of the branches. Here the elm leaves suddenly wilt, turn yellow, the margins curl upward and the leaves die. Leaf-fall causes the crown to appear sparse. In large trees, the foliage symptoms may initially appear on one branch or only a portion of the crown. However, the symptoms during the advanced stage of the disease are exhibited throughout the crown. The most reliable symptom appears as a yellow to butterscotch discoloration on the inner bark surface or phloem. This symptom initially appears under the bark of large roots, later spreading to the base of the main stem and finally to the larger branches. Phloem and cambial discoloration is often found in advance of the foliage symptoms. The moderately discolored phlomen has a slight odor of wintergreen. Thus far, all trees known to be infected with the pathogen have died. Acutely infected trees, while initially appearing healthy, may wilt and die in three to four weeks.
Stem sample showing discoloration of sapwood.