Answer: Moss, algae and lichens often grow on the branches and trunks of trees and shrubs where the air is humid. I would not blame the lichens for the poor growth of your trees. They are a symptom rather than the source of trouble. Lichens are green plants (technically, a symbiotic relationship between a fungus and an alga) that manufacture their own food; therefore they're not parasitic, and are not taking nutrients from their hosts. Instead, they indicate that your trees may not be receiving enough sunlight and that air circulation is poor. You can discourage lichens from growing on trees by pruning the canopy to open the branches to more sunlight and improved air circulation. You can increase the vigor of your trees by fertilizing during the spring when they're actively growing. If your fruit trees are hedged in by other kinds of growth (shrubs, forest trees, etc.) you may do well to open up the perimeter in in the direction of prevailing winds, which will also improve air circulation.
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