If SOD phosphite treatments are being applied by injection November 1st – December 15th, data has shown that treating every 2 years is sufficient. When preparing the injections, be sure to use the most current dosage recommendations as they have recently been updated. Current recommendations can be found at http://nature.berkeley.edu/matteolab/?page_id=2345. The new dosages are significantly more diluted than the original label dosages, yet are just as effective and cause almost no damage to the wood (the original label dosages do cause some wood damage).
If SOD phosphite treatments are being applied using a topical bark application, treat every 1 – 2 years. While data has shown that topical applications last for 18 months, fall treatments are the most effective. Therefore, in a county known to be infested, treat trees in riparian areas, within 20 miles of the coast, or within 2 miles of redwood forests every year. Treat trees in drier areas (of infested counties) every 2 years.