Question
All the information I read tells me lichens are harmless but when my trees didn't havelichens they seeme healthy now that lichens have started growing on them they apear to be getting weaker and sicklier. Is it possible to get rid of them?

Answer
The lichens are not causing the sickness of the tree. Something else is stressing the trees. I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good.
No products are labeled for lichen control, but copper fungicides labeled for ball moss, or the home remedy of baking soda (sodium bicarbonate) for ball moss control (label pending) are detrimental. In pecan orchards, the fungicides used for scab and downy spot control reduce lichen numbers due to their effects on the fungal partners in lichens.   Both should be ok and control the lichens.