That depends. Some moss killers have iron as the active ingredient and some use fatty acids. Lichens grow in damp, cool spots and prefer acid conditions so a moss killer that changes that will slow down lichen. Please note that lichens do not kill your lawn or plants. They simply grow where nothing else can survive. Improve your drainage, fertilize and renovate the lawn with topsoil and new seed if lichen is the problem. Keep growing, Marianne Binetti