Agriculture: Almond Pest Management Guidelines

Crown Gall

Symptoms and Signs

Rough, abnormal galls on roots or trunk are the typical symptom of this disease. Galls are soft and spongy, and 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.

Management

To help prevent crown gall

  • purchase trees from a reputable nursery and
  • carefully handle trees 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 tumefaciens (formerly A. radiobacter) K-84, which produces an antibiotic that can reduce or eliminate infection. 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 the K-84 strain have been reported. Their occurrence is not widespread, but failure to control crown gall with these materials should be reported to cooperative extension advisors and industry representatives.

Eradication involves removal of existing galls and topical application of Gallex. Carefully follow label instructions for exposing crown and roots and removing large galls.

Most peach-almond hybrid rootstocks are very susceptible to crown gall, and are more susceptible than Nemaguard rootstocks. Lovell peach is also very susceptible.

Common name Amount per acre REI‡ PHI‡
(Example trade name) (hours) (days)
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
 
A. AGROBACTERIUM TUMEFACIENS (formerly A. RADIOBACTER) K-84#
  (Galltrol) Label rates See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): A biological fungicide.
  COMMENTS: Preventive preplant treatment only.
 
B. GALLEX
    Label rates See label See label
  COMMENTS: For removal of existing galls, apply winter through spring.
# Acceptable for use on organically grown produce.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode-of-action group number.
Text Updated: 08/17
Treatment Table Updated: 08/17