Rhizoctonia black scurf - Gardening at USask - College of Agriculture and Bioresources (2024)
Rhizoctonia spp.
Often referred to as “dirt that won’t wash off”, Rhizoctonia is a fungal disease of potatoes. The disease is caused by a fungus in the soil that grows on the surface causing irregular hard small black spots of the potato tuber. The incidence of the diseasetends to be higher in the weeks following planting when the weather is cold and wet, when plant growth is slower relative to the growth of the fungus.
The spots look unsightly, but have no effect on the inside flesh of the tuber. The potato is edible and the spots can be easily peeled off before cooking.
Symptoms:
Small hard, black spots on the potato skin.
Reddish-brown to brown lesions may develop on sprouts, stolons and young stems.
Secondary symptoms include a mat of white to graymycellium at the base of the stem that can be easily rubbed off.
In severe infections, leaves may roll upward and be reddish in colour.
Control:
Rotate where you grow potatoes so that they are not grown in the same place for at least three years to avoid a build-up of the disease.
Purchase certified seed every year.
Adding 3 - 5 cm of organic matter to the soil such as compost, which tends to reduce black scurf.
Plant later in spring andmore shallowly than you would normally into warm soil (above 8°C). This speeds up emergence of the plant and reduces the risk of stem canker.
Harvest as soon as the crop is mature as the severity of symptoms increases rapidly once the tops begin to die back.
Remove all debris from garden after harvest as the fungus over-winters on infected plant material. Debris can be hot-composted.
Howard, R. J., Seaman, W. L., & Garland, J. A. (Eds.). (2002). Diseases and pests of vegetable crops in Canada. Vancouver, British Columbia: The Canadian Phytopathological Society and the Entomological Society of Canada.
Rhizoctonia solani is a fungal disease causing stem canker, damping off, black scurf, skin netting and tuber growth distortions. Black scurf can be soil and seed borne and survives a long time in soil and on volunteers or crop debris. There is no significant proliferation during storage.
Seed treatments with fluodioxinil or a mixture of thiophanate-methyl and mancozeb are effective against the spreading of a variety of fungal diseases, among them black scurf. In-furrow treatments at planting with fluotanil or azoxystrobin also help to control the progression of the fungus.
If you have ever had lots of little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, then you have seen black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani.
Rhizoctonia can't be eliminated, but it can be suppressed to the point where it doesn't cause significant yield loss. The most effective method of reducing disease pressure is cultivation, which breaks up the rhizoctonia 'web'– a network of filaments in the top 10 cm of the soil.
Irrigation and leaf wetness management is an important part of controlling Rhizoctonia diseases. Fungicide applications can be necessary if leaf wetness and soil moisture cannot be adequately managed (for instance, as a result of rain or high humidity).
Black scurf, or sclerotia, can be minimized by harvesting soon after vines are killed. Sclerotia begin to form on tubers as vines senesce and become larger and more numerous over time. Therefore, harvesting tubers as soon as possible after skin set reduces tuber scurf significantly.
By Leah Brickley and Emily Saladino for Food Network Kitchen
Sometimes called eyes, these frilly growths can look worrisome but are entirely natural. Sprouted potatoes are safe to eat, too; just remove the eyes and check the rest of the potatoes for freshness.
These spots are called, appropriately, internal black discoloration; and are bruising that occurs from the potatoes lying against each other for an extended period, as they would after several months in storage. The moldy looking spots are a condition that can develop from the bruises, called fusarium.
Stem canker and black scurf of the potato are the two common names for the same disease due to Rhizoctonia solani, a soil-borne fungus. Black scurf refers to the presence of small to large, dark black dots on the tuber surface, which correspond to sclerotia, i.e. survival stage of R.solani.
Black scurf is a fungal disease producing hard, black growths on the surface of tubers that can be rubbed off. Although unsightly it is not destructive, but infected seed potatoes can lead to plants with stem cankers.
Abstract. Rhizoctonia solani is a most widely recognized strong saprophyte with a great diversity of host plants. It is a first ever case of extensive human mycosis caused by Rhizoctonia solani in a 65-year-old diabetic and hypertensive farmer, with a history of head injury caused by fall of mud wall.
Introduction: My name is Kerri Lueilwitz, I am a courageous, gentle, quaint, thankful, outstanding, brave, vast person who loves writing and wants to share my knowledge and understanding with you.
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