Tomato plants are susceptible to several diseases that can reduce yield and plant health. Proper identification and management are critical for maintaining a productive garden.
Early Blight
Caused by the fungus Alternaria solani, early blight appears as brown spots with concentric rings on lower leaves. Symptoms worsen in damp conditions. Prevention strategies include:
– Rotating crops annually
– Spacing plants 24-36 inches apart
– Using stakes or cages to elevate foliage
– Applying thick mulch to prevent water splashing
– Pruning lower leaves immediately upon detection
– Using copper-based fungicides (with caution due to soil toxicity risks)
– Planting resistant varieties like ‘Defiant’ or ‘Mountain Magic’
Fusarium Wilt
This soil-borne fungus (Fusarium oxysporum) causes yellowing and wilting starting at the plant’s midsection. Management includes:
– Crop rotation every 4 years
– Using resistant varieties
– Growing susceptible plants in containerized soil
– Avoiding overwatering
Late Blight
The water mold Phytophthora infestans causes rapid leaf decay in cool, wet conditions. Control measures:
– Avoiding hoop houses (high humidity risk)
– Planting resistant varieties like ‘Iron Lady’
– Destroying infected potato tubers and nightshade weeds
– Monitoring for thrips (vector for tomato spotted wilt)
Nematodes
Root-knot nematodes (Meloidogyne spp.) cause stunted growth and yellowing. Mitigation:
– Using French marigold cover crops (‘Tangerine’ or ‘Nema-Gone’)
– Solarizing soil with clear plastic in summer
– Rotating crops with non-nightshade plants
Tomato Spotted Wilt
Transmitted by thrips, this virus causes leaf distortion and fruit necrosis. Controls:
– Planting resistant varieties
– Using reflective mulches to deter thrips
– Introducing natural predators like minute pirate bugs
– Monitoring with yellow/blue sticky traps in greenhouses
Verticillium Wilt
This fungal disease (Verticillium albo-atrum) causes V-shaped yellowing on leaves. Management:
– Planting resistant varieties
– Rotating nightshade crops every 4 years
– Applying mulch and maintaining consistent watering
Disease Resistance Codes
Seed catalogs use abbreviations to denote resistance:
– EB: Early blight
– F/F1/F2/F3: Fusarium wilt
– LB: Late blight
– N: Nematodes
– TSWV/TSW/SWV: Tomato spotted wilt
– V: Verticillium wilt
Use the Tomato Chooser App to filter varieties by disease resistance and other traits.