Tomato Disease Identification Guide for Southeast Farms

Tomatoes are the most disease-prone vegetable most Southeast farms grow. Warm nights, high humidity, and 25–30 inches of rain during the fruiting window mean you will see disease every year — the question is whether you catch it early enough to spray or rogue before the block loses pack-out.

This is a field-ID guide, not a spray guide. For chemical recommendations, follow your state extension IPM guide.

Foliar diseases

• Early blight (Alternaria). Bulls-eye lesions on the oldest leaves first, working up the plant. Appears after first fruit set and after rain. Expect it — don't let it climb past the second truss before you act.
• Late blight (Phytophthora). Water-soaked greasy lesions on leaves and stems, white fuzz on the underside in wet mornings. Moves through a block in 3–5 days. Rare in the Southeast but catastrophic when it arrives.
• Septoria leaf spot. Tiny gray-centered spots with a black margin, only on foliage, lower leaves first. Common in wet Junes.
• Bacterial spot / speck. Small dark angular lesions on leaves AND fruit. Fruit lesions kill pack-out even at low incidence.

Wilts and soil-borne

• Fusarium wilt. One side of the plant wilts first; vascular tissue browns when you cut the stem. Race-specific — check resistance letters (F1, F2, F3) on your seed.
• Verticillium wilt. Similar wilt pattern, cooler-soil onset, V-shaped yellowing on lower leaves. Persists in soil 7+ years — rotate away.
• Bacterial wilt (Ralstonia). Sudden collapse with green foliage. Cut stem into water: milky streaming is diagnostic. Rogue plants immediately.
• Southern blight (Sclerotium). White fungal mat at the soil line with mustard-seed sclerotia. Loves hot wet mulch.

Virus

• Tomato spotted wilt virus (TSWV). Bronze ringspots on fruit, stunted tops, transmitted by thrips. Once symptomatic, the plant does not recover — rogue it.
• Tomato yellow leaf curl virus (TYLCV). Whitefly-vectored, upward leaf cupping and yellow margins. Increasingly common in coastal FL/GA.

What to do this week

Scout twice a week from first flower to final harvest. Walk every block — drive-bys miss early lesions. Keep a paper or app log of first observation for every disease each year; that history is what tells you which varieties and blocks to retire.

Pair this with a working 4-year crop rotation — half of the soil-borne pressure above disappears on a real rotation.