The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
If algae, lichens and moss are considered unsightly, they can be controlled to some extent by improving air circulation; prune out overcrowded branches and cut back overhanging vegetation. Following this, try to stimulate new growth by feeding, mulching, watering and applying a foliar feed. Once an affected plant regains vigour, badly affected shoots can be pruned out. Control is not necessary on tree trunks.
There are no chemical controls for algae, lichens and moss on plants.