- 1). Walk away from a lichen-filled oak and observe the canopy. Lichens often grow in trees with declining health because the tree has a thinner canopy that allows sunlight to touch the branches and trunk. This leads owners of oak trees to blame the lichens for the tree’s declining health. If your tree has a reduced canopy, diagnosing the problem and correcting it will cause the tree to grow more foliage and the lichen will die out.
- 2). Diagnose your tree’s issue by examining the leaves, branches, bark and roots. Most oak trees in declining health will show symptoms such as spotted leaves, holes or peeling bark in the branches or trunk, fungus growing from the base, or roots that are dead and brown instead of white and succulent. Treating these problems with insecticides, fungicides or an application of fertilizer and regular watering will boost the canopy of the oak tree and kill out lichen.
- 3). Mix a foliar fungicide according to package directions and pour it into the holding tank of a sprayer with a wand applicator. Spray the foliar application over the tree’s limbs and trunk to kill the lichen. Wave the wand of the applicator over the tree using a sweeping, side-to-side motion in a grid pattern for even coverage.
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