Understanding top tomato diseases

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Tomatoes are one of the most popular plants to grow in the spring. They can be grown from seeds fairly easily or bought at just about any garden center. Choosing a variety that does well in your specific climate is important. Some varieties such as Better Boy, Celebrity and Whopper are VFN, which means they are resistant to verticillium wilt, fusarium wilt and root-knot nematodes. 

It is important to make sure tomatoes receive sufficient water during the season. The soil should be soaked 6 to 8-inches deep each time you water and the use of mulch such as wheat straw or composted leaves will conserve moisture.

Tomato diseases can be the most important limiting factor in tomato production in North Carolina. Some diseases can destroy crops within two to three weeks. More than 20 tomato diseases have been documented in North Carolina. Generally, soil-borne diseases (bacterial wilt, root-knot, and southern blight) are more common in the coastal region.

Bacterial wilt is a soil-borne, bacteria that infects the plant through the root system and will cause wilting and rapid collapse of the plant. The disease is favored by high soil temperatures and moisture. Crop rotation is not effective due to the persistence in the soil. Growers should avoid planting in affected areas.

Fusarium wilt is another soil-borne disease that has been effectively controlled in the past by using resistant varieties. The fungus will persist in the soil for several years and is transmitted by seed, transplants, soil, tomato stakes and other equipment. The fungus is destructive, causing wilt, yellowing on one side of the plant and eventually death. The only effective control is the use of Fusarium wilt-resistant varieties. This disease is often seen in association with root-knot nematode damage.

Root-knot nematodes are most prevalent in the Coastal Plains during periods of drought. It can cause severe stunting of plants and significant crop loss. Crop rotation with non-host plants such as grasses and corn reduces the population of nematodes in the soil. To identify root-knot nematodes, observe the plants root system for large root galls.

Southern Blight is a soil-borne fungus that can cause damping-off in seedlings, stem rot and death of older plants. It is favored by warm, rainy seasons you may notice brown to black stem rot near the soil line. This fungus can persist in the soil for years as well as in plant debris. Crop rotation with corn and small grains can reduce the population of the fungus in the soil.

Bacterial Spot causes spots on leaves and fruit, which can result in severe blighting and defoliation. The disease is favored by warm temperatures and heavy rainfall. The bacteria can overwinter on crop debris and can be introduced on seeds and transplants.

Septoria Leaf Spot can develop rapidly during rainy weather. The fungus is seed-borne and can overwinter on debris and on equipment. Fungal spores spread by splashing rain. The leaf will show black dots with a yellow halo.

 Lastly, there is Early Blight. It is the most common foliar disease and can occur at any time. It causes leaf spotting and blight, which progress over the season from lower leaves to upper leaves. The fungus can also affect tomato stems and fruit.