We know that it seems logical to prune all of our trees in the spring; however, with oak trees, it is the worst time of the year to prune them.

 
Oak wilt is one of the most destructive tree diseases in the United States and is killing oak trees in central Texas at epidemic proportions. Oak wilt is an infectious disease caused by the fungus Ceratocystis fagacearum, which invades and disables the water-conducting system on live oaks, Shumard oaks, Spanish oaks, and other members of the red oak family. 
 
Taking preventative steps can help reduce the spread of oak wilt. Pruning at the proper time is important. The Nitidulid beetle is responsible for transmitting the disease and is most active in the early spring. AVOID pruning all oak trees between February and June. The least hazardous periods for pruning are during the coldest days in midwinter and extended hot periods in mid to late summer (July and August). All pruning cuts or wounds to oak trees including freshly cut stumps and damaged surface roots should be treated immediately with a wound or latex paint to prevent exposure to contaminated insects. 
 
Transporting unseasoned firewood from diseased red oaks is a potential means of spreading the oak wilt fungus. Diseased wood from any oak species should never be stored near healthy oak trees. It is best to purchase wood that has been thoroughly dried for at least one full year. 
 
Oak wilt can be spread in other ways also. Live oak roots can graft together underground, spreading the fungus from infected trees to healthy ones through tree sap. If there is oak wilt in an area, one method of prevention is trenching between the healthy trees and the ones with oak wilt. The 48 inch deep trench should be at least 100 feet from the trees that are showing symptoms, and filled immediately after it is dug. Severing the joined roots should prevent the fungus from spreading. 
 
Sometimes a systemic fungicide can be used to control oak wilt. The fungicide is injected into the root flares under low pressure. Trees that are symptomatic have less chance of a complete recovery. If trees have lost more than 30% of their canopy, they should not be treated. 
 
Being knowledgeable about oak wilt is a great beginning to controlling a serious problem. The goal is to reduce or prevent the loss of oaks in all of our landscapes. By protecting your trees, you are protecting your investment. Once oak wilt is identified it is costly for the homeowner as well as the entire neighborhood since every effort must be made to try and control the disease. If we were to lose our oak trees, our property values would be greatly impacted as well. A specific example of the cost for oak wilt is the homeowner in Whispering Oaks who has spent $2300 to date in trying to save trees and the Whispering Oaks HOA has obtained a quote for digging the trench to try and isolate the diseased trees for a cost of $75,000-$100,000. 
 
The city of San Antonio has Article VIII. Section 21-170 states that the provisions of this ordinance apply to any person, firm, corporation, business entity, city department, public or private utility to the extent permitted by law. Prevention and control of the spread of oak wilt requires all wounds to the trunk, limbs and root system of oak trees in the city that expose sapwood shall be painted within thirty minutes of the wound with asphaltic or exterior oil or latex base paint. Firewood from oak wilt infected trees shall not be brought into the city at anytime. (Ord. No. 97332) Section 21-171 states that it shall be unlawful for any person to engage in the business or occupation of pruning, treating, or removing trees for profit without first applying for and procuring a tree maintenance license. A tree maintenance license shall require proof of continuing education credits at a minimum of four hours per three-year licensing period. 
 
For more information including how to identify it, go to www.texasoakwilt.org