How to Prevent and Treat Late Blight on Tomatoes
Late blight is spread by an oomycete pathogen (fungal infection) that produces millions of spores during wet seasons and quickly infects healthy plants. Not only do spores survive in infected seed and soil, once active the spores can travel great distances and infect crops in neighboring gardens or farms. Late blight generally emerges in August when weather is hot and humid and can destroy a plant in a matter of days. Once the infection is noticed, there is little that can be done to save the plant, but you may be able to prevent further spread to nearby plants.
- Difficulty:
- Moderately Challenging
Instructions
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1
Check tomato plants daily for any signs of blight. Telltale signs consist of dark lesions on the stems, particularly in joints where new growth appears. Leaves may show signs of browning beginning at the stem and working outward along the leaf. A white powdery mold may be present on either the leaves or the stems, but is common on the underside of the leaves. Lesions may appear on the tomato fruit and will appear dark and greasy.
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2
Remove any infected plants immediately and place in a plastic bag for disposal or bury to a depth of two feet to prevent the spread of disease. Do not compost or discard plants infected with blight near the garden or in areas where they may infect other farms and gardens.
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3
Spray otherwise healthy plants with a fungicide following the application schedule (generally 5 to 7 days) on the label. Active ingredients in the fungicide should include maneb, mancozeb, chlorothalonil, or fixed copper. Use a fungicide specifically labeled for late blight in tomatoes and potatoes. The fungicide works as a coating on the plants. Apply to cover all areas to prevent infection.
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4
Apply fungicide before symptoms appear for best results. If the season is unusually wet or neighboring farms and gardeners are experiencing blight, spraying early may save your garden.
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5
Prevent the spread of late blight by mulching tomatoes or using landscape fabric under them. If spores are present in the soil, heavy rains cause water to splash back to the plant and may spread late blight.
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6
Plant tomatoes at least two feet apart to allow air circulation and decrease the risk of disease. Crowded planting combined with wet weather creates the prime conditions for disease, including late blight.
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1
Tips & Warnings
Plant disease resistant varieties.
Trying to save an infected plant may spread disease to other plants.
Do not plant tomatoes in an area where either tomatoes or potatoes were grown the year before.
