While most mosses and lichens are not in themselves harmful to your apple trees, they can hide the presence of mites and other microorganisms that can be potentially damaging--not to mention detracting from the overall aesthetic quality of your trees. Getting rid of this moss and lichen can be quite challenging at times, with the best method being to apply a copper sulfate solution to the tree to remove the moss and lichen. Caution is strongly advised when undertaking this task, as copper sulfate can be harmful to you.
Choose the proper time for spraying. Spray apple trees in the fall, just after the end of the harvest. Choose a dry period with no chance of rain in the forecast for at least 3 days. This will help prevent the spread of the dangerous chemicals you will be using.
Put on protective gear before getting started. Copper sulfate can be harmful if it comes in contact with exposed skin. Make sure to wear protective clothing--long sleeves, long pants and enclosed shoes--and don protective eyewear, chemical-resistant gloves and a disposable breathing mask.
Read the instruction sheet that comes with the copper sulfate. As a rule, it takes 1/2 pound of copper sulfate per 100 gallons of water to kill mosses and lichens on apple trees. Be sure not to use more copper sulfate than the directions require.
Mix the ingredients together in the spray tank. Fill the spray tank to the halfway point with water and then add the required portion of copper sulfate to the spray tank. Add additional water to the spray tank to fill it to approximately three-quarters full.
Add the amount of spreader stick as directed on the instruction sheet that accompanied the copper sulfate. Add 3 to 5 pounds of hydrated lime to the spray tank, as directed on the instruction sheet, and then top the spray tank off with water. Your copper sulfate solution is now ready for use.
Turn on the agitator and let it run for approximately 2 minutes before you begin spraying. Keep the agitator running during the entire time you are spraying. Spray the apple trees thoroughly in long, even strokes.