Spots on tree trunks just lichen
Q. We have a large red maple tree in our yard. There are white spots on the trunk and limbs. Looks like someone put dabs of white paint on it. Is this a disease? First year we noticed it and we have enjoyed it for many, many years. Rolly Opsahl - University Place, WA
A. It does not sound like a disease. It does sound like lichens have colonized your tree. Lichen are what I have heard referred to as farming fungi. There are many species of fungi that “go into business” with various species of algae or cyanobacteria both of which can produce energy from sunlight, which the fungi cannot. The fungi provide the support and protection for these organisms, which allows them to grow in what would be inhospitable places without the fungi’s help (e.g., rocks and tree bark). The fungi receives energy in the form of sugars in return. Scientists still debate on the level of coercion that the fungi exert on their business partner. This is why some do not call this arrangement symbiosis. The crustose lichen are a group of lichen that are particularly thin and can often look like paint dabs as you have described.