Oak wilt, caused by the fungus Bretziella fagacearum, is the most destructive disease affecting red oaks, white oaks, and live oaks in Central Texas. Most of the tree mortality results from tree-to-tree spread of the pathogen through interconnected or grafted root systems, once an oak wilt center becomes established. New infection centers begin when the nitidulid beetle carry oak wilt fungal spores from infected red oaks to fresh, open wounds on healthy oaks. Wounds include any damage caused by wind, hail, vehicles, construction, wildlife or pruning. Research has shown that both oak wilt fungal mats on infected red oaks and insects that carry oak wilt spores are most prevalent in the spring.Below is a brief description of how you can reduce the risk of oak wilt fungal spread when pruning oak trees.
- Regardless of season, immediately paint all pruning cuts and other wounds to oaks. Any wound dressing or paint can be used, and all are equally effective at preventing disease transfer by masking the scent of the sap.
- Unless you hire a professional, avoid pruning or wounding oaks from February 1st through June 30th. As an exception, pruning can be conducted to:
- accommodate public safety concerns such as hazardous limbs, traffic visibility or emergency utility line clearance
- repair damaged limbs (from storms or other anomalies)
- remove limbs rubbing on a building or against other branches, or to raise low limbs over a street
- accommodate required clearance on construction sites where schedules take precedence
- remove dead branches where live tissue is not exposed
- Pruning for other reasons (general tree health, non-safety related clearance or thinning, etc.) should be conducted before February 1st or after June 30th.
- Debris from diseased red oaks should be immediately chipped, burned or buried. Other oaks are not at risk of further facilitating the disease.
The least hazardous periods for pruning are during the coldest days in winter and extended hot periods in mid to late summer. The best time to prune oaks is during late fall. Regardless of the reasons or time of year, proper pruning techniques should be used. These techniques include making proper pruning cuts and avoiding injurious practices such as topping or excessive crown thinning. As a general guideline for pruning, clean all pruning tools with 10% bleach solution or Lysol™ between sites and/or trees.