Crown gall disease, caused by the bacterium _Agrobacterium tumefaciens_
(E. F. and Town.) Conn., often is damaging to pecan trees. Nursery trees
as well as trees in bearing pecan orchards are susceptible to the
disease.
[Illustration: Figure 2. Brown leaf spot diseased pecan leaflet
showing typical symptoms. Lesions are circular to irregular in
shape.]
The development of galls is confined primarily to larger roots near the
base of the tree trunk, although small roots may become infected and
galls develop on them. The smaller galls are under the soil surface and
cannot be detected unless the soil is carefully removed from around the
roots, Figure 3. Large galls, often 10 to 18 inches in diameter, develop
on larger roots and may protrude well above the surface of the soil.
[Illustration: Figure 3. Crown gall disease symptoms on young
infected pecan tree.]
Galls on nursery trees develop at or below the soil surface on the
taproot and larger secondary roots.
_Control._—All infected nursery trees should be dug and immediately
burned. Crown gall-diseased orchard trees sometimes can be saved by
digging the soil from around large roots and removing the exposed galls.
Where galls were removed, the damaged root surfaces should be painted
with a creosote-coal tar mixture (one part creosote to three parts coal
tar) to prevent spread of the disease[9]. Cultivation of the soil around
the trunk base of infected trees should be avoided to prevent root
wounds and spreading of the crown gall pathogen.