Growing tomatoes (Lycopersicon esculentum) allows you to realize your success or failure within months, providing immediate rewards for your effort. However, a tomato plant may show signs of withering or develop discolorations and necrotic spots on its leaves, thwarting your efforts. Leaf discoloration is one way to diagnose what ails your plant early so you can act quickly to fix the problem and save your plant.
Thin plants with yellowing leaves for Fusarium wilt or Verticillium wilt. Fusarium wilt starts on one side or branch of the plant. Verticillium wilt starts at the base of the plant and older leaves die first. Once infected, the plant will continue to wilt but fruit will ripen. Wilts survive in soil for several years, so rotate crops and don’t plant Solanaceae relatives such as peppers, potatoes, eggplant or squash in the same soil for at least three years.
Plant tomatoes in mounds over clay-heavy soils to avoid phytophthora root rot, a soil-borne fungus that presents as watery spots on leaves. The leaves eventually dry out and turn brown on a wilted plant. Withhold water because the plant’s roots are drowning and the phytophhora fungus is rotting them.
Remove plants showing signs of spotted strip wilt -- brown spots or stripes on the leaves. Thrips carry the virus that also affects many weeds, so keep areas close to the garden weed-free. Remove and destroy infected plants because they will not recover but will help spread the virus.
Pull up a wilting plant if its leaves yellow and then turn brown beginning at the bottom of the plant. If the roots are covered with swollen bumps, the plant has been colonized by root knot nematodes, tiny roundworms that live in the soil and burrow inside roots, destroying the plant’s ability to make its own food. Remove and destroy infected plants.
Treat plants with powdery mildew, which appears in blotchy yellow spots on leaves anywhere on the plant. Sulfur sprays may help control the fungus on young plants. In the warm, dry autumn of a Mediterranean climate, strengthen plants by supplementing rainfall to provide at least 1 inch of water per week.
Things You Will Need
- Garden spades
- Hand pruners
- Sulfur spray
- Garden gloves
- Practice prevention before foliage begins to discolor. Plant disease-resistant varieties, space plants for good air circulation, water plants with a soaker hose rather than from overhead and don’t allow debris to accumulate. Remove infected foliage after pruning plants and clean up the entire area in the fall.
- Cut infected branches back until you encounter healthy tissue -- the inside of the stem should be white.
- When pruning diseased foliage, disinfect your tools between plants as well as before pruning uninfected foliage or stems to avoid spreading infection. Mix a seven to one solution of water to household bleach or use a wipe of rubbing alcohol or hand sanitizer.
- Never add diseased plants to your compost because many pathogens can survive and even thrive in the warmth of the pile. When added to garden soil, the compost will re-enforce or spread the infection.
- Cornell University Vegetable MD Online: Tomato Disease Identification Key by Affected Plant Leaf Symptoms
- Oregon State University Cooperative Extension: Recognizing Tomato Problems
- University of California Agriculture and Natural Resources: Growing Tomatoes in the Home Garden
- University of California Agriculture and Natural Resources: Common Diseases and Other Problems in Home Garden Tomatoes
- University of California Davis Vegetable Research and Information Center: Tomatoes (Lycopersicon esculentum)
- Seiya Kawamoto/Lifesize/Getty Images