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Extension > Garden > Yard and Garden > Fruit > Pest management in the home strawberry patch > Black root rot

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Black root rot

Rhizoctonia fragaria, Pythium spp., Fusarium spp.

Strawberry black root rot (BRR) is the most common root disease in Minnesota. This disease is a complex problem involving several different pathogens along with a variety of plant stresses. It is common in older strawberry patches or patches stressed by poor growing conditions like soil compaction or poor drainage. The condition is aggravated by root feeding nematodes (soil borne microscopic worms) and winter injury. Plants infected with BRR decline overtime, producing significantly lower yields than uninfected plants.

Identification

black-root-rot

Above ground plant showing BRR symptoms

P. Fiserh, Berry Crop Specialist, OMAFRA

The first symptoms of BRR are often missed. Infected plants have poor growth and produce fewer and smaller fruit. As the disease becomes more severe, plants are clearly stunted. Plants may wilt and the edges of leaves turn brown or ha a 'scorched' appearance. Plants continue to decline and often die after the high stress of fruit production. In larger patches, disease often starts in low lying areas or areas with poor drainage. Each year the area of infected plants expands.

Plants displaying the above symptoms should be carefully dug up and washed, keeping intact as much of the root system as possible. A healthy plant will have young roots that are creamy white with multiple fine root hairs and older roots will have a dark brown to black woody outside layer but a white interior. Plants with BRR are often described as 'rat tail' because most of the finer feeder roots are rotted away leaving only the thick anchor roots. The remaining young roots have random gray to reddish brown sunken blotches. These lesions can expand to cover large areas of the root. The infected roots are soft and mushy. When touched, the outer layer often falls away, leaving only a thin strand from the core of the root.

Important biology

One or more of the black root rot pathogens are commonly found in soils. Disease develops when plants are stressed by drought, water-logged soils, winter injury, poor nutrition, and root feeding by lesion nematodes (Pratylenchus penetrans) or insects. Pythium spp., Rhizoctonia spp., and Fusarium spp. are root rotting fungi that infect and rot roots of stressed strawberry plants. This complex interaction of root rotting pathogens, environmental factors and other pests is known as black root rot. Root tips and young feeder roots may be completely rotten and fall off. Infection in older roots is limited to the outer tissues of the root; leaving a white core that is unaffected. The disease commonly occurs in fields with a long history of strawberries where the pathogenic fungi have had significant time to build-up their numbers.

Management

Prevention of black root rot is based on good site selection and proper plant care.

Fungicides

There are no pesticides registered for use by home gardeners that are effective in controlling BRR.


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