Diseases of potato (
Rhizoctonia canker (black scurf)
Rhizoctonia canker (also known as black scurf) is caused by the soilborne fungus Rhizoctonia solani. Disease causes lesions or cankers on sprouts and young stems (photo 1) and development of persistent dark sclerotia (resting structures of the fungus) on the surface of tubers, hence the disease common name black scurf. Disease is most destructive when young stems are weakened or girdled and killed, resulting in delayed development and reduced yields. Severe infections may cause malformation, cracking or pitting of tubers.
Rhizoctonia solani persists as sclerotia on tubers and in the soil or as mycelium on plant debris. In moist soils the sclerotia germinate and infect sprouts and stems. The amount of fungus in the soil, the inoculum density, is dependent on rotation, and increases when potatoes are grown in close rotation.
Disease should be managed using rotations to other crops, disease free seed pieces and fungicide treated seed pieces. Mancozeb, in a suitable carrier such as a bark, and systemic fungicides such as fludioxonil (Maxim) have demonstrated efficacy for disease reduction.
More information and pictures can be found at the following web sites:
http://www.ndsu.nodak.edu/instruct/gudmesta/lateblight/basic_frame1.htm
http://www.ipm.ucdavis.edu/PMG/r607100811.html
http://www.potatonews.com
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February 10 , 2003