Prevent blight in your tomatoes and potatoes

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A farmers’ group wants to know how they can control early and late blight in tomatoes and potatoes. We give information on the two common crop diseases that occur during the wet season. This will help farmers prevent the diseases early enough.

In organic farming, the first line of defense against diseases and even pests is to grow healthy crops by providing them enough nutrients and managing them well. A healthy crop can withstand diseases and pests. The other method is ensuring that the crops are always protected from diseases through crop rotation and use of safe inputs such as bio-pesticides and fungicides that help keep away diseases and pests. It is possible to control early and late blight if farmers can adhere to these practices. As we always advise, prevention is the best measure for an organic farmer.

Below are some of the measures that farmers can take against the two diseases:

Early blight

Seeds: Early blight is a fungal disease that is mainly transmitted through the use of diseased seedlings. Farmers should use certified, disease-free seeds. Farmers growing tomatoes can also plant resistant varieties such as Summerset F1, Zest F1.

Transmission: The fungus that causes early blight can survive and transmit the disease from one season to the next especially if residues of infected plants from the previous crop are not destroyed through burning.

This happens when the soil is dry. The spores (the microscopically small 'seeds' of a fungal disease) are formed on infected leaves of tomatoes, stems and potatoes and fruits, and can be spread by the wind and splashes of water. A combination of warm weather and rain produces serious outbreaks, particularly if plants are weak.

Planting: Do not plant consecutively tomato crops on the same land from one season to the next. Do not rotate tomatoes with related crops such as potatoes, pepper or eggplant. Prop up the tomato plants to keep them off the soil and keep tomatoes free of weeds. For potatoes, ridging from touching the soil where the disease-causing fungus can get into contact with the plants and infect them. After harvest, residues should be removed from the field or destroyed immediately.

Control: There are several plant extracts that help in controlling fungal diseases. These are:

African Marigold: Fill a drum with a half (or 3/4) full of flowering African marigold plants. Leave it to stand for 5 to 10 days. Stir regularly. Strain before use. Dilute the filtered liquid (filtrate) with water at a ratio of 1 part filtrate to 2 parts water (1:2). Add 1 teaspoonful of soap to every litre of the extract you use for application.

Garlic: Bulbs may be dried and crushed. Add water to the powder and spray.

Milk: Spray every 10 days with a mixture of 1 litre of milk to 10 or 15 litres water.

Late blight

Late blight is one of the most devastating diseases in tomatoes and potatoes especially in cooler and moist conditions. The disease can easily destroy the entire tomato or potato crop if it is not controlled on time. At first, the leaves turn brown; under humid conditions, a white dusty layer that contains the spores can be seen on the underside of the leaves.

Seeds: There are no certified disease free seeds on the market.

Transmission: When the weather conditions are cool and moist, the spores usually spread very fast. Splashes of water especially during rains can transfer the spores from one plant to the other. Wind can carry the spores over great distances, in the process transferring the disease to other crops.

Planting: If you plant tomatoes in a field after Irish potatoes, remove all potato tubers, as the ones remaining in the soil after harvest can be a source of the disease for crops, which follow. Crop rotation with crops that are not from the tomato family such as maize, beans, sukumawiki or cabbages for 3 to 4 years helps to break the disease cycle. After harvest, remove the crop residue or dig them deep into the soil, where the fungus does not survive for long.

Control: Use wider spacing. For tomatoes you can also prop up the plants to keep them off the soil. Add mulch to cover the soil and reduce splashes of water. Pruning will increase air movement, reduce humidity within the crop and thus reduce disease intensity. If you irrigate, do it in the heat of the day; this allows the crop to dry before nightfall and reduce transmission and development. In wet weather, sprays should be applied regularly to prevent the disease. Do not wait until you see the disease to start spraying as this may fail to eliminate the disease.

The following plant extracts are useful in disease prevention:

Onions: Apply 100 grammes of onion leaves in every 1 litre water used; let it stand for 4 to 7 days in a covered container before spraying.

African Marigold: Crush 100 – 200 grammes of leaves, roots or flowers. Pour on 1 litre boiling water, soak for 24 hours, add 1 litre of cold water and spray.

>>Tell us how useful this information is to your farming enterprise. Share your experience by email to [email protected], send SMS to 0715916136 or leave a comment below this article.

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