Stefan Buczacki solves your plot problems
Robert Crerar, Methven, Perth and Kinross
Stefan says: This does look unsightly and I can understand why you're concerned and also why you call it a fungus, but you're only half right. The growth isn't a fungus but a lichen. It's a very widespread and common species, especially on lawns, called dog lichen. And I say you're half-right because lichens are biologically unique – they're double organisms, comprising a fungus and an alga growing in close association.
Many species occur on all types of garden habitat, including lawns, but they're especially common on old walls, roofs and tree trunks. Although often attractive in these places, they can be unsightly when they grow on ornamental shrubs. This often happens on azaleas, heathers and rhododendrons, especially on shaded sites and in moist areas like the far west of the British Isles and on poor soil. They usually form either a grey-green, crust-like or a leafy covering to the bark, or scaly or woolly growths on twigs and branches.
On lawns, lichens are generally an indicator that the lawn isn't growing well for whatever reason; perhaps it's on poorly draining, or conversely, too freely draining soil, possibly it's shaded, and almost certainly in need of feeding. A moss killer/weed killer fertiliser mixture will certainly help eradicate the lichen. But you really need to identify why it’s growing in the first place and then correct the growing conditions (where you can). Lichens are slow growing and this is why they're only likely to be seen on long-lived plants such as woody perennials and on lawns. Although enormous cloaks of lichens cover trees in the wetter,
western parts of Britain, they're not generally harmful, although their development is probably greater on trees that aren't growing well, for whatever reason.
Lichens are highly sensitive indicators of environmental pollution. Generally speaking, the more woolly or leafy the lichen species, the less polluted is the prevailing atmosphere. They can often be brushed off sturdy plants but care is needed not to damage the underlying bark and the best solution is generally to feed the affected host plant.