This is a tomato showing signs of the fungal disease called early blight. Leaves start turning yellow with brown spots, then wither, turn brown and fall off.
By Doug Oster Pittsburgh Post-Gazette
A cool spring followed by a hot, muggy start to summer combined with plenty of rain has created the perfect storm for early blight (Alternaria solani) on tomato plants.
Symptoms include foliage that turns yellow, sometimes with brown spots, then withers and falls. Usually the problem starts at the bottom of the plant and works its way up.
Early blight isn't usually fatal to the plant, but it often sends gardeners into a panic. Before tearing out your plants, here are a few simple tips to get the disease under control:
The first step is to remove infected foliage. I hand-pick any leaves showing signs of the disease. If using pruners, disinfect them between cuts with a 10 percent bleach/90 percent water solution. It won't be long until a heathy branch emerges in its place. Don't work with the plants when they are wet. Continue to remove infected leaves through the season. They should not be added to the compost pile as the spores can easily overwinter in the cozy confines of the heap.
Be careful not to spread the disease to healthy plants. Only work on infected plants, then wash up before continuing working in the garden. The disease can also affect potatoes, peppers, eggplants and anything else from the Solanaceae family like tomatillos.
Early blight is a soil-borne disease. If plants aren't mulched, they should be. This will stop more spores from splashing up onto the foliage.
Tomatoes should be staked or caged for good air circulation. They are much more susceptible to the disease if left to ramble on the ground.
The best time to treat plants with a conventional fungicide is before signs of damage appear. Experienced gardeners will watch the weather and when humid, wet conditions are predicted, spray the plant with a fungicide. The most popular chemical control would probably be Daconil. Organic gardeners can use a copper-based fungicide. A reminder, though: Even though copper is organic, it can have a negative effect on bees, and if introduced into water it can kill fish.
Another interesting player on the scene is a biological control like Serenade, which uses Bacillus subtilis as its active ingredient. It works well once the disease has started, attacking the fungal spores and stopping them from reproducing. It's safe for the environment, too.
Regardless of which choice is made, always follow the instructions and safety warnings on the label.
When things dry out, water the plants at the base to keep the foliage dry.
Early blight is just a part of life when growing tomatoes during certain seasons. Ride it out until things get warm and dry again.