Ask Mr. Smarty Plants

Check out this excellent link from the Royal Horticultural Society on lichens and moss on the bark of trees. Briefly, it points out that lichens and moss are non-parasitic and will not injure the plants on which they grow; however, they may be an indication of trees that have been neglected. They can be controlled to a certain extent by improving air circulation by pruning out overcrowded branches.

No doubt all the (unusual) rain we have had in Texas this year has at least contributed to this sudden upswing in the lichen population. However, as pointed out above, good plant vigor is the best defense against lichens. There are no pesticides recommended for control of lichens, and it is not recommended that they be considered, as they will more likely damage the desirable vegetation than otherwise.

Incidentally, we found another very interesting website called "General Information About Lichens and Pollution." This has more information on lichens, but adds that it has been noted by scientists that the presence of lichens may indicate that the air quality in the area is good. It's not that the lichens have anything to do with making the air cleaner, it's just that they don't thrive where the air is very polluted. So, if it's any comfort, the trees you are concerned about may be telling you that the air quality around your area is acceptable, at least to lichens.