The article includes tips on what to look for and how to remove affected plants. It also recommends using the fungicide chlorothalonil (a synthetic protectant that prevents disease by blocking its entry into the surface of the plant) to protect tomatoes not yet affected. Which brings is to the question of chemicals...
I looked up chlorothalonil in Jeff Gillman's The Truth About Organic Gardening. After an explanation of the difference between the three types of synthetic chemicals used for disease control (plant activators, systemics, and protectants), he lists what he sees as the benefits and drawbacks of using synthetic protecants. I'll let you decide what is the right choice for you and your garden.
BENEFITS: Few diseases have developed a great deal of resistance to protectants. Synthetic protectants tend to be quite effective at controlling disease if used properly and can generally be expected to work as well as or better than most of the organic fungicides, with less chance of damaging your crops. Also, less of these products usually needs to be applied.
DRAWBACKS: Protectants have a wide range of degrees of safety for both humans and the environment. Some are considered relatively safe and some aren't. Because they don't get into the plant's vascular system, they don't provide complete control over the disease.
Kathryn Juergens, sales and marketing associate
Information taken from The Truth About Organic Gardening