Late blight of potato: Phytopthora infestans
- It affects leaves, stems and tubers.
- Water soaked spots appear on leaves, increase in size, turn purple brown& finally black colour
- White growth develops on under the surface of leaves.
- This spreads to petioles, rachis& stems.
- It frequently develops at nodes.
- Stem breaks at these points and the plant topples over. In tubers, purplish brown spots and spread to the entire surface on cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.
Identification of pathogen:
Mode of spread and survival:
- The infected tubers and the infected soil may serve as a source of primary infection.
- The diseased tubers are mainly responsible for the persistence of the disease from crop to crop.
- The air borne infection is caused by the sporangia.
- RH->90% , Temp.-10-25°C and Night temperature:10°C.
- Cloudness before rainfall and Rainfall at least 0.1mm and subsequent days after rainfall.
- Protective spraying with mancozeb or zineb 0.2 % should be done to prevent infection of tubers.
- Tuber contamination is minimized if injuries are avoided at harvest time and storing of visibly infected tubers before storage.
- The resistant varities recommended for cultivation are Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo and Kufri Moti.
- Destruction of the foliage few days before harvest is beneficial and this is accomplished by spraying with suitable herbicide.
- TamilNadu Agritech Portal