Tomatoes are the most popular vegetable in NW Georgia gardens and also the most disease-prone. Our combination of warm temperatures, high humidity, and frequent summer storms creates ideal conditions for fungal diseases. The good news is that most tomato diseases are preventable with good cultural practices, and early identification means you can manage problems before they kill the plant.
Early blight — the most common problem
Early blight caused by Alternaria fungus is almost universal in Zone 8a tomato gardens. It appears as dark brown spots with yellow halos on the lower leaves, typically starting in June or July. The spots enlarge and the leaves yellow and drop, working progressively up the plant.
Prevention is everything with early blight. Mulch heavily to prevent soil from splashing onto lower leaves during rain. Water at the base not overhead. Remove affected leaves as soon as you spot them. Apply copper fungicide preventively every 7 to 10 days during humid weather starting in June. Choose resistant varieties — Celebrity and Mountain Fresh Plus carry early blight resistance.
Septoria leaf spot
Similar in appearance to early blight but with smaller spots that have dark borders and light centers. It spreads rapidly in wet conditions and can defoliate a plant quickly. Management is identical to early blight — copper fungicide, sanitation, and mulching.
Fusarium and verticillium wilt
These are soil-borne fungal diseases that cause sudden wilting and brown streaking inside the stem when you cut it open. There is no cure once a plant is infected. Prevent by rotating crops — never plant tomatoes in the same spot two years in a row. Choose resistant varieties — look for F and V in the variety description. Solarize soil in summer by covering it with clear plastic for 4 to 6 weeks to kill fungal spores with heat.
Blossom end rot
Dark sunken spots on the bottom of fruit. Not a disease but a calcium uptake disorder caused by inconsistent watering. The calcium is in the soil but the plant cannot absorb it when moisture levels fluctuate. Deep mulching and drip irrigation solve the root cause. Calcium sprays help marginally but fixing the watering is the real answer.
Cracking and catfacing
Cracking happens when heavy rain follows a dry period and the fruit expands too fast. Mulch and consistent watering prevent it. Catfacing — misshapen fruit with scarring — is caused by cold temperatures during fruit set. Plant after soil warms and avoid varieties prone to catfacing in cool weather.
Building a spray program
In Zone 8a a preventive fungicide program from June through September dramatically reduces disease pressure. Apply copper-based fungicide every 7 to 10 days during humid stretches. Spray in the evening to avoid burning foliage and to give the spray time to dry before morning dew. After heavy rain reapply within 24 hours — rain washes off the protective coating. Organic neem oil applied on the same schedule also provides meaningful protection.
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