Hi Amy and thanks for your question about your dahlia leaves. I see leaf miners in your pictures as well as what looks like a virus. However, if the rest of the plant is healthy, I would just pick off those leaves (especially the leaf miner tunnels) and destroy them. Plant viruses often don't kill the plant and can sometimes make the leaves more interesting. If that is enough, the plant will still make the beautiful flowers they are known for.

If the rest of the plant begins to show signs of disease or wilt, then you might want to take it out. Good job catching it early and I hope just taking off a few leaves will solve the problem.