How to Manage Pests
UC Pest Management Guidelines
Pathogen: Agrobacterium tumefaciens
(Reviewed 3/09, updated 3/09)
In this Guideline:
SYMPTOMS AND SIGNS
Rough, abnormal galls on roots or trunk. Galls are soft and spongy. The centers of older galls decay. Young trees become stunted; older trees often develop secondary wood rots.
COMMENTS ON THE DISEASE
The bacteria survive in gall tissue and in soil. They enter only through wounds. Crown gall is most damaging to young trees, either in the nursery or new orchard plantings. Peach-almond hybrid rootstocks are more susceptible to crown gall than Nemaguard rootstocks.
Crown gall is best prevented by purchase of trees from a reputable nursery accompanied by careful handling to avoid injury as much as possible, both during planting and during the life of the tree in the orchard. Preplant treatment is for prevention only. Galltrol is a preparation of the biological control agent Agrobacterium radiobacter-84. It is effective only as a preventive treatment and is used as a root dip or spray before heeling-in or planting. It does not eradicate existing galls. Chlorine bleach root dips or sprays are not effective as a crown gall protectant.
Strains of A. tumefaciens resistant to Galltrol and Norbac have been reported. Their occurrence is not widespread, but failure to control crown gall with these materials should be reported. Eradication involves removal of existing galls and topical application of Gallex. Carefully follow label instructions for exposing crown and roots and removing large galls.
UC IPM Pest Management Guidelines:
J. E. Adaskaveg, Plant Pathology, UC Riverside