Powdery Mildew Or Botrytis On Tomatoes Indoors

We're assuming that you're growing tomato plant indoors or in a greenhouse since it's long past the first frost in your area. There are many plants that are more tricky to grow inside. If you are a commercial grower of tomatoes in hoop houses, we suggest that you contact your cooperative extension at Cornell: http://www.cce.cornell.edu/Pages/Default.aspx

There are a couple of leaf disease for tomatoes that look like this. Powdery mildew is the first and botrytis, aka gray mold, is the second. Without a lab culture it's impossible to be sure what is wrong with your plants. Since you are growing veggies we assume you would prefer to treat organically, and you might try one of the organic fungicides asap. Look for a copper-based fungicide, or any other organic product that's labeled for both botrytis and powdery mildew. There are several on the market.

Beyond that, provide good air circulation with fans, always water in the AM, and don't handle uninfected plants after touching those with these symptoms.