Here's everything you need to know to protect your garden:
What is late blight?
It's a funguslike pathogen. Spores from infected tomato and potato plants are easily swept up in the wind and can even be carried from one state to another. To help you identify it, check these tomato blight pictures.
Where is late blight occurring?
So far this year, late blight has been confirmed in Florida, Pennsylvania, Louisiana, Maryland, Kentucky, Connecticut, New York, and, most recently, Michigan and Ohio. "I can't tell folks enough that this is a community disease that we need to manage together,” says blight expert Meg McGrath, PhD, a plant pathologist at Cornell University. "People need to regularly inspect their plants, manage the problem, and report occurrence, especially early in the season when most plantings are healthy. This way, healthy plants can be saved, which minimizes unnecessary fungicide use."
How can it be prevented organically?
Chemical farmers and gardeners apply toxic fungicides before the disease strikes as a preventive measure, but organic planters have the option of using copper sprays. The sprays approved for organic agriculture carry the Organic Materials Review Institute (OMRI) distinction on the product label. (See a list of copper spray products.)
But are organic copper sprays safe?
Not completely. There's good reason that many gardeners will take the loss instead, and pull infected plants out of the ground, bag them up, send them to the landfill, and pray for a blight-free 2011. But if you're game to try copper, know that "Copper fungicides are corrosive, they can cause irreversible eye damage, and they may cause skin sensitization reactions in some people," says McGrath. "So if you use one, be careful not to get it in your eyes, on your skin, and take care not swallow it." To keep the off your skin, wear a long-sleeved shirt and pants, chemical-resistant and waterproof gloves, shoes, and socks, and protective eyewear, advises McGrath.
Will organic copper sprays hurt other plants in the garden?
It's possible. "Gardens tend to be more diverse plantings than farms,” says McGrath. "So you should consider what other plants are close enough to receive a significant amount of fungicide when you're spraying the tomatoes." It can damage them. Organic copper sprays can also harm beneficial insects in your garden.
How often should the copper spray be applied?
McGrath says you need to spray at least once a week to maintain protection, particularly with new growth. Therefore, it's best to decide in advance if you're committed to staying on a program. "It's not worth the effort to start something you can't continue through harvest," says McGrath.
What should I do if I spot late blight in my garden?
You should inspect your garden at least once a week—and preferably more often—for the first signs of an infected plant. If you spot the telltale brown legions with fungal growth on leaves or stems, remove infected plants early. You'll reduce the number of spores that spread to your garden and to others around you. Definitely don't try to wait out the problem. Once a plant is infected, it's going to die. The longer you let it stand, the greater the risk to your other plants, and to your neighbors' plants.