How to Prevent Blight on Tomato Plants

Some tomato plants are resistant to blight pathogens.

Late blight can wipe out an entire tomato crop. Caused by the fungus Phytophthora infestans, blight affects tomatoes, potatoes and other plants in the tomato family. The fungus overwinters in living plant tissue, such as potato tubers, then reinfects other plants come summer. Blight spreads by spores. Foliage develops brown or yellows lesions and the fruit stops growing and becomes discolored. Infected plants must be destroyed, but it is often too late and the disease has already spread to neighboring plants. Preventing blight is the best defense for your tomato crop.

Things You'll Need

• Fungicide

Instructions

1. Inspect areas of the garden where potatoes grew the previous year, along with any compost piles potato tubers may have wound up in. Pull up and destroy any volunteer plants in these areas in spring, as late blight may have overwintered in the tuber.

2. Rotate your tomato crop each year. Plant in a bed or an area of the bed where neither potatoes nor tomatoes have grown for the last two years.

3. Plant blight-resistant tomato varieties. Legend and Plum Regal are two resistant types. Check with your county extension office for blight-resistant varieties that grow well in your area.

4. Treat plants with a fungicide if blight is suspected in your area. Use a treatment containing chlorothalonil, copper sulfate or copper hydroxide, advises the University of Massachusetts Extension. Apply the fungicide at the rate recommended on the package.

Tips & Warnings

• Late blight does not overwinter on garden stakes, seeds or in garden soil that freezes completely over the winter months.

• Early blight is similar to late blight, but most modern hybrid tomatoes are resistant to this disease.

References

• University of Massachusetts Extension: Preventing Late Blight in Gardens
• Cornell Cooperative Extension: Avoiding Late Blight: Beware of Last Year's Crops