{"id":1605,"date":"2026-09-11T11:25:33","date_gmt":"2026-09-11T15:25:33","guid":{"rendered":"https:\/\/site.extension.uga.edu\/fultonag\/?p=1605"},"modified":"2026-09-11T11:25:33","modified_gmt":"2026-09-11T15:25:33","slug":"reflecting-on-tomato-diseases","status":"publish","type":"post","link":"https:\/\/site.extension.uga.edu\/fultonag\/2026\/09\/reflecting-on-tomato-diseases\/","title":{"rendered":"Reflecting on Tomato Diseases"},"content":{"rendered":"\n

by Gabrielle LaTora, Agriculture and Natural Resources Agent, Fulton County Extension<\/em><\/p>\n\n\n\n

Whether your tomatoes petered out early or held on past their prime, they probably didn\u2019t look so good when you pulled them out. In our Georgia climate \u2013 hot, humid, and with irregular rainfall recently \u2013 tomatoes can struggle with diseases.<\/p>\n\n\n\n

Now is the best time to look back on your tomatoes\u2019 performance this season (while the pain and grief is still fresh) and strategize for next year. Prevention is the smartest and cheapest way to manage tomato diseases.<\/span><\/p>\n\n\n\n

Common tomato diseases we see every year<\/h1>\n\n\n\n

Early blight <\/strong>(caused by\u00a0<\/span>Alternaria solani<\/em>\u00a0fungus) \u2013 typically starts as irregular brown lesions on leaves with concentric circles, often with yellowing around the spots. Starts on oldest leaves and moves its way up the plant. The fungus likes rainy, warm conditions. Be on guard when temps are 75-85F with rain and heavy dew.<\/span><\/p>\n\n\n\n

Septoria leaf spot <\/strong>(caused by\u00a0<\/span>Septoria lycopersici<\/em>\u00a0fungus) \u2013 small, tan leaf spots with dark edges. Lesions are smaller than early blight, almost with a \u201cshothole\u201d look. Lesions start on the oldest leaves and move up. Look out for symptoms during wet and cool-ish conditions (68-77F).<\/span><\/p>\n\n\n\n

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Early blight<\/figcaption><\/figure>\n\n\n\n
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Septoria leaf spot<\/figcaption><\/figure>\n
Early blight and Septoria leaf spot symptoms can look similar. Look for concentric circles inside early blight lesions and dark margins around Septoria lesions.
Images by (L) Gerald Holmes, Cal Poly San Luis Obispo, bugwood.com; (R)\u00a0Nancy Gregory University of Delaware, bugwood.com<\/em><\/figcaption><\/figure>\n\n\n\n

Leaf mold <\/strong>(caused by\u00a0<\/span>Passalora fulva<\/em>\u00a0fungus) \u2013 irregular yellow spots on tops of leaves AND thick, fuzzy, brown fungal spores on leaf undersides. You are most likely to see this one in greenhouses or high tunnels and rarely in open field production. Likes humid conditions, temps 70-80F, and doesn\u2019t need rain, which is why we see it so often in tunnels.<\/span><\/p>\n\n\n\n

Buckeye rot <\/strong>(caused by several species of\u00a0<\/span>Phytophthora<\/em>\u00a0water molds) \u2013 you\u2019ll see buckeye rot on the fruit, where it creates brown spots with concentric rings as they get bigger. As the spots decay, white, fuzzy mold may grow. The lesions don\u2019t look rough and sunken, like late blight spots. No symptoms on leaves. Likes warm, wet weather.<\/span><\/p>\n\n\n\n

Late blight<\/strong> (caused by\u00a0<\/span>Phytophthora\u00a0<\/em>water mold) \u2013 similar to buckeye rot but will infect leaves and fruit. The lesions are kind of irregular blotches rather than distinct spots, like buckeye rot. Fruit lesions are greasy-looking and become rough and sunken. Look out during cool, wet conditions.<\/span><\/p>\n\n\n\n

Anthracnose<\/strong> (caused by\u00a0<\/span>Colletotrichum<\/em>\u00a0fungus) \u2013 small, sunken lesions on fruit that gradually expand. May develop concentric rings or salmon-colored spores during wet conditions. The fungus survives in the soil for a long time as microsclerotia and gets splashed up onto plants during rain or overhead watering.<\/span><\/p>\n\n\n\n

Fusarium wilt<\/strong> (caused by\u00a0<\/span>Fusarium oxysporum<\/em>\u00a0fungus) \u2013 this is a vascular disease that happens when soil-borne fungi infect the xylem of the plant, preventing it from taking up water. Leaves first turn yellow and start to wilt, sometimes on only one side of the plant. Eventually, leaves turn brown and the plant dies. Only infects tomatoes and can persist in the soil for years.<\/span><\/p>\n\n\n\n

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Fusarium wilt is a vascular disease that blocks up the water-conducting xylem of the plant. Look for yellowing and wilting as first symptoms. If you cut open a stem, you will see that xylem tissue turns brown.
Images by (L) Gerald Holmes, Cal Poly San Luis Obispo, bugwood.com; (R) Clemson University Extension, bugwood.com<\/em><\/figcaption><\/figure>\n\n\n\n

Southern blight<\/strong> (caused by\u00a0<\/span>Sclerotium rolfsii<\/em>\u00a0fungus) \u2013 foliar symptoms look similar to Fusarium wilt \u2013 leaves turn yellow and wilty, then brown, and die. However, Southern blight causes the base of the stem to turn brown and rot, which is pretty distinctive. Produces distinctive sclerotia that look like mustard seeds that will survive in soil for many years and infect lots of other crops. Hot weather + poorly draining soils = perfect conditions for Southern blight.<\/span><\/p>\n\n\n\n

Southern bacterial wilt <\/strong>(caused by\u00a0<\/span>Ralstonia solanacearum<\/em>\u00a0bacterium) \u2013 first you will notice the entire plant is wilty even with enough soil moisture. Leaves don\u2019t turn brown and die as quickly as Fusarium wilt and Southern blight but will eventually. Split the stem lengthwise, and you will see dark lesions inside. Infections happen when weather is hot and soils are warm and moist.<\/span><\/p>\n\n\n\n

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Southern blight sclerotia look like mustard seeds and can be found around the base of the plant. Sclerotia are hardened fungal structures that can survive in soil for many years.
Image by Gabrielle LaTora, Fulton County Extension<\/em><\/figcaption><\/figure>\n\n\n\n

8 ways to prevent diseases without chemicals<\/h2>\n\n\n\n
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  1. Avoid touching wet plants. <\/strong>Many of these pathogens move around on droplets of water. The less we disturb dew or rain on leaves, the less some diseases will spread.<\/li>\n\n\n\n
  2. Improve air flow.<\/strong> Pruning and trellising are essential to keep canopies open and get the leaves and stems off the ground. Don\u2019t space plant too tight that air can\u2019t move around them.<\/li>\n\n\n\n
  3. Keep leaves dry. <\/strong>Forget about sprinklers or sprayers and invest in drip irrigation. If you can grow under a tunnel, you will probably see fewer leaf spot diseases. Mulch or cover the ground to prevent water from hitting the soil and splashing up onto plants.<\/li>\n\n\n\n
  4. Buy resistant varieties. <\/strong>Plenty of tomato varieties have been developed through selective breeding to be resistant to common diseases. This is a major selling point for seed companies, so look closely at the variety descriptions. This is probably the easiest, cheapest, and most effective way to reduce tomato disease.<\/li>\n\n\n\n
  5. Rotate crops.<\/strong> A 3-year rotation away from nightshade crops (tomatoes, eggplants, peppers, or potatoes) is a good practice. Consider longer if you have identified Southern blight or Fusarium wilt.<\/li>\n\n\n\n
  6. Improve drainage.<\/strong> Check your soil drainage with a percolation test to see how well it drains. Add organic matter (please not sand) to improve drainage. Make sure you\u2019re not overwatering.<\/li>\n\n\n\n
  7. Dial in soil fertility. <\/strong>Make sure soil pH is between 6.0-7.0 and that you fertilize with the right amounts of nutrients. Correct pH means the plant can access nutrients\u00a0–>\u00a0nutrients make healthy plants\u00a0–>\u00a0healthy plants don\u2019t get sick as often! Make informed decisions by having the soil tested. Without tessin\u2019, you\u2019re just guessin\u2019<\/em>.<\/li>\n\n\n\n
  8. Clean up! <\/strong>Most of the pathogens that cause these diseases hang around in crop residues (dead plant parts that fall to the ground during the growing season or are left in the field) and infect new plants the next year. Get crop residues out of the field at the end of the season. Remove symptomatic plant parts when you see them to reduce inoculum. And make sure to sanitize your pruners, tools, and implements!\u00a0<\/li>\n<\/ol>\n\n\n\n

    Learn More<\/h2>\n\n\n\n