Potato blight
Potato blight, or Phytophthora infestans, spreads from the stems quite rapidly to the tubers and also to your neighbor's allotment.
Image 1. Brown spots will appear in the leaves and if the blight has spread far, all of the foliage will darken. [3.]
Image 2. If the blight has reached the tubers, the potato is inedible. [2.]
Do the following
- Cut down the stems as soon as you notice brown spots in the foliage.
- Take the stems and tubers to mixed waste container at your home. It is also possible to put them into the compost, well covered, as long as you remember that the soil produced in that compost can not be used to grow potatoes or tomatoes. It is absolutely forbidden to throw the stems or potatoes in the forest or bushes next to the allotment area. Same rule applies to all gardening waste.
- If you manage to remove the infected stems in time, the blight may not infect the tubers and they will be edible. You can let the tubers remain in the ground and use them as needed.
- It is not necessary to remove all of the stems, if some of them do not have the brown spots. Check the foliage regularly and maintain it.
Prevention
- Choose a blight-resisting potato variety. Popular varieties (Annabelle, Timo) are not very blight-resistant, but their crop yield is usually sufficient before getting the infection. Colomba, Record, Matilda ja Rosamunda are some of the more blight-resistant varieties.
- Use inspected seed potatoes. Do not use food potatoes from the grocery store.
- Practice crop rotation: do not plant potatoes in the same spot every year.
- Plant well sprouted potatoes early, and keep space between the potato plants. This way they have enough time to grow big tubers without having to water them, and before potato blight spreads to the area.
- Do not water the potato plants unless the weather is very dry, and even then with precision. Watering and humidity increase the risk for the development of the blight.
- Do not fertilize too much. Over-fertilizing will make the plants grow thick stems, which contract the blight easier.
- Remove weeds and keep the potatoes well covered in soil. Removing the weeds and having the potatoes planted in high ridges will reduce the effects of the blight. When the tubers are well covered, they are better protected from the blight spores, as long as the infected stems are cut down and properly disposed of.