CROWN GALL
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.
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.
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.