Daniel E. Mullins Extension Horticultural Agent Santa Rosa County Lichens Blamed for Plant Problems, But Innocent Lichens are blamed for the decline or death of many different kinds of plants. These gray-green scaly, crusty or hairy structures that cling to shrub and tree branches are innocent, as charged. Excessive lichen growth on woody plants such as azaleas, is a symptom of a problem, rather than the cause.
Lichens proliferate only on branches and twigs of plants already in decline for some other reason.
Since these same lichens are found growing on rocks, fence posts and other non-living structures, they are obviously not plant parasites. Any growing condition that results in stunted, declining plants is therefore home sweet home for lichens. When growth ceases, the requirement of a non-moving surface is met. Then, as plants lose leaves, more sunlight is allowed to strike the branches, meeting the high light requirement. In most cases, excessive lichen growth can be found where a plant is established under the wrong soil or light condition.