Q: How long does Alamo treatment protect an oak tree?
A: Alamo treatment lasts a couple of years. If you treat the trees at the proper time, when the trees are within 100 ft of known disease, which is just before the disease reaches the trees, then the disease comes along, and the tree remains alive. If the disease is still active in the immediate area after two years, then you would re-treat the trees.
Trees should only need to be treated twice, because after a four year period, the disease should have moved through and out of the area. This is the same principle as a fire burning toward your house. You hose your house down, and the fire burns past your house because you have protected it, and then the fire is gone. There is no need to keep hosing your house down once the fire has moved past it. This principle also applies to Alamo treatment once oak wilt has moved out of the immediate area.
Treatment of the trees on your property is a judgment call. If you treat every tree on your property, then it is difficult to judge the progression of the disease. Robert Edmonson prefers treating just the significant trees, leaving the others as indicators to monitor the progression of the disease through the property in order to determine whether or not you need to treat again two years later.
Some contractors will send you a flyer every two years telling you that it is time to retreat your trees. It is not automatically necessary to re-treat your trees every two years. It depends on the rate of progression of the disease on your property.