Understanding late blight
It is a fungal disease that affects foliage and fruits favoured by cool and wet conditions. There is a myth that bright affects tomatoes during rainy seasons which in actual fact it is wrong.
Late blight spreads most in tomatoes, potatoes and related crops when there are fog, mist or little rushes.
Symptoms of late blight
- The first symptom of late blight is a bending down of petioles of infected leaves.
- Leaf and stem lesions manifest as large, irregular, greenish, water-soaked patches.
- These patches enlarge and turn brown and paper-like.
- Rapid blighting of foliage may occur during moist, warm periods.
- Entire fields can develop extensive foliar and fruit damage. Fruit lesions manifest as large, firm, irregular, brownish-green blotches. Surfaces of fruit lesions are rough and greasy in appearance.
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Conditions for disease development
- Overhead irrigation in the late evenings is the major cause. The temperature difference and wetness of the leaf facilitate the spread of the fungi. If you have to use overhead irrigation, do it as early as 3-5 pm which gives the tomato leaves time to dry.
- The fungi (Phytophthora infestans)can survive on volunteer and home garden tomatoes and potatoes, in potato cull piles and on solanaceous weeds.
- Cool, wet weather favours the development of this disease. Under these conditions, the disease progresses rapidly and can destroy a mature tomato field in a few days.
- Tomatoes grown in a greenhouse are also subject to late blight infection and may progress even more rapidly in protected culture compared to the open field.
- The fungi require only high humidity to infect, whereas many other diseases additionally require leaf wetness for infection to occur.
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How do you prevent and control late blight
- I usually say blight is like cancer. Thus prevent by an early spray with both contact (Redomil gold) and systematic fungicides (score).
- Planting hybrid varieties which have a high tolerance to blight. Open-pollinated varieties are highly affected by blight than hybrids.
- Implement a late blight forecasting system in conjunction with an effective spray program to control late blight.
- Avoid planting on land that had potatoes previously as the fungi affect potatoes as well. In greenhouses maintaining lower humidity will discourage infection and disease development.
Reference:seminis
