Shamiran Biswas

Potato blight/late blight of potato is caused by a fungal disease called Phytophthora infestens. It first affects some parts of the leaves, tips, and stems. If the relative humidity of the air is high, most of the crops in the field are affected within 2-3 days. In the morning, a white powdery fungus is visible under the affected leaves. A burnt smell is found in the affected field and it seems as if the crops in the field have been burned.

Favorable weather for the spread of the disease: Generally: Low temperatures (10-16 degrees Celsius at night and 16-23 degrees Celsius during the day) and foggy humid weather (humidity more than 90%) are favorable for the spread of this disease. If foggy weather is accompanied by drizzle, this disease becomes epidemic within 2-3 days. The disease spreads rapidly from infected to healthy plants with the help of wind, rain and irrigation water.

Symptoms of blight:

1. When the disease is attacked, light green round or variously shaped spots are first seen on the leaves at the base of the plant, which quickly turn black and the leaves rot.
2. When you go to the field in the morning, you can see white powdery bacteria under the affected leaves.
3. In cold and foggy weather, the affected plants rot quickly. In this situation, all the plants in the field may die within 2 to 3 days.
4. Potatoes affected by this disease have brown to black spots on their bodies and become unfit for consumption.

Biological remedies:

1. Disease-free seeds should be used.
2. Irrigation should be stopped as much as possible in the affected land.
3. Apply balanced fertilizers
4. Plant disease-resistant varieties.
5. Seeds should be collected from healthy plants for the next season;
6. Make seedlings from virus-resistant and healthy seeds and collect seeds only from healthy plants.
7. Regularly monitor the field.
8. Keep the garden clean.
9. Early potato cultivation, i.e. planting potatoes by November 15 or early variety cultivation, can reduce the level of this disease to a great extent.
10. The distance between rows of potatoes should be 60 cm and the distance between potatoes in each row should be 25 cm for whole seed potatoes and 15 cm for cut potatoes.
11. As soon as low temperatures, foggy weather and rain are forecast, an approved fungicide mixture of the Mancozeb group should be sprayed every 7-10 days to prevent the disease.

What to do after the disease occurs:

1. Irrigation should be stopped until the disease is controlled in the affected land.
2. As soon as the disease is seen in your own or neighboring fields, any of the approved fungicides from the following groups should be sprayed periodically at the rate given below per liter of water and the plants should be soaked well.
For example: (Mancozeb 60% + Dimethomorph 9%) - 2 grams or (Mancozeb 50% + Fenamidon 10%) - 2 grams or (Propineb 70% + Iprovelicarb) - 2 grams or (Ametoctradin 30% + Dimethomorph 22.5%) - 2 ml or (Mancozeb 64% + Cymoxanil 8%) - 2 grams or (Flumorph 10% + Mancozeb 50%) - 2 grams.
3. If foggy weather prevails for a long time and the disease is widespread, any one of the following fungicide mixtures should be mixed in each liter of water at the rate described below and sprayed every 5 days and the plants should be thoroughly soaked. (Carbendazim 50%) 1 gram.
4. If the disease outbreak is very high, the fungicide mixture should be sprayed every 3-4 days.
5. The fungicide should be sprayed well on the top and bottom of the leaves.
6. Better results can be obtained by using a power sprayer instead of a regular sprayer.
Caution: It is better not to spray fungicide on the ground when the plant is wet. And if you have to spray, then you should mix soap powder at the rate of 2 grams per liter of water. Gloves, sunglasses, mask and apron should be used while spraying fungicide. Always spray in the wind.

The writer is a, Head of Agriculture Department, Medina Tech Ltd.