Control.—Disk under old fallen leaves in the early spring before the leafbuds begin to swell. This practice covers the leaves with soil and prevents the discharge of spores into the air, thereby controlling primary infection of new leaves. In seasons when heavy rains make early spring disking impossible, downy spot disease can be controlled by spraying the trees as indicated in the spray schedule on [page 4].
BUNCH DISEASE
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.
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.