Hi, I had planted native plant Coreopsis lanceolata this spring. It developed some disease so the leaves became kind of gray/white. The new growth did not have that color, but most of the leaves did. It still bloomed well. Is this some fungal infection? How could I prevent this from happening next year? I was expecting native plants to be more resistant to diseases. Thank you in advance.
It looks like your coreopsis has been infected with powdery mildew, which is not uncommon.
And because it is so common, many gardeners have asked us about this problem! Here is a detailed answer we provided to one (with a link to a second response, too). Powdery mildew.
With this advice, you should be able to avoid or at least manage the problem next year.