Phosphonate injection treatments to help prevent sudden oak death infection of susceptible oak species (coast live oak; California black oak, Shreve’s oak, and canyon live oak), if applied in the fall (after October 30th ), need only to be applied once every other year (biannual frequency). If your first phosphonate treatment is in the spring, then treat again in the fall (after October 30th) and then treat once every other year.
If applying phosphonate as a bark application in conjunction with the surfactant PentraBark®, then one fall treatment each year is the prescription. If you apply it the first time in the spring, apply again in the fall after October 30th and then apply again in the fall of each year (after October 30th).
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