Q. I believe I have crustose growing on my rock pillar columns (white crytal like hairs) how do I kill it? Terry Johnson – Lacey, WA
A. I believe you are describing crustose lichen. Lichens are a symbiotic organism that pairs up a species of algae (or cyanobacteria) and a species of fungus. The various combinations make up the different types of lichen. These lichen grow in a very thin layer on all kinds of surfaces including tree trunks, boulders, rocks, as well as statues, columns and pillars (as is in your case). This is in contrast to the fruticose lichen, which are branching and often hang off of their substrate. Fruticose lichens are usually an indicator of air pollution since many varieties die off when exposed, but the crustose lichen is more resistant than other types of lichen. The crustose lichen is of particular concern to conservators of stonework and statues since the structures that hold the lichen to the surface are small enough to get into small cracks and fissures and eventually cause some deterioration. Their metabolic processes can also create acidic conditions, which can be detrimental to many types of stonework. This is a gradual process but when you are a conservator you are thinking about long-term preservation. I know that copper sulfate is effective on lichen but it can stain some kinds of stonework. There are other treatments of which I would be hesitant to recommend to a do-it-yourself homeowner. The other issue is that even if you kill off the existing crustose algae and clean them off this does not change the conditions that will allow future growth from re-colonization. There are often treatments that can protect the stone from future attacks like coating them in epoxy resins. I would suggest hiring a professional that works in this area to help you with your specific situation.