Although the cause of bunch disease is not known, evidence indicates it
is an infectious disease, which suggests that the causal agent may be a
virus.
Trees affected with bunch disease show the bunching symptom, which is
due to excessive growth of slender succulent twigs from lateral buds
that normally remain dormant. In moderately affected trees one or
several branches will show the “bunch” growth symptom. Bunching in
severely affected trees may involve all main branches which produce
thick masses of sucker-like growth and few, if any, nuts.
Observations indicate that the Stuart variety is the most resistant to
bunch disease.
[Illustration: Figure 4. Rosette die-back symptoms of pecan tree
showing severe zinc deficiency.]
_Control._—There is no known effective control for bunch disease. Early
detection of the first symptom of bunch and pruning out of the affected
branch may prevent spread of the disease throughout the tree. When the
tree is severely affected, and limbs are involved, the tree should be
destroyed to protect nearby healthy trees from infection.
For propagation purposes, all bud or scion wood should be taken only
from bunch disease-free trees.