Black root rot of strawberry
- Strawberry black root rot (BRR) is the most common root disease of strawberries in Minnesota.
- This disease is a complex problem involving several different pathogens along with a variety of plant stresses.
- It’s common in older strawberry patches and patches stressed by poor growing conditions like soil compaction or poor drainage.
- Young roots rot away and remaining roots have gray to reddish-brown, sunken blotches.
- Infected plants decline over time, producing significantly lower yields than uninfected plants.
- To manage this disease, choose a proper planting site and take good care of your plants.
How to identify black root rot
Above ground symptoms
- 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 have 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.
To identify root symptoms, plants displaying the above ground symptoms should be carefully dug up and washed, keeping intact as much of the root system as possible. Inspect the roots to determine if they are healthy or infected.
Healthy plant roots:
- Young roots are creamy white with many fine root hairs.
- Older roots will have a dark brown to black woody outside layer but a white interior.
Infected plant roots:
- Infected roots 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.
How black root rot survives and spreads
- A complex interaction of root rotting pathogens, environmental factors and other pests is known to cause black root rot.
- Some of the black root rot pathogens are commonly found in soils.
- Disease develops when plants are stressed.
- Commons stressors include drought, water-logged soils, winter injury, poor nutrition, 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.
- Root tips and young feeder roots may be completely rotten and fall off.
- This disease is common in fields with a long history of strawberries where the pathogens have had lots of time to multiply.
How to manage black root rot
To prevent black root rot, select a good planting site and properly care for plants.
Buy healthy plants
- At this time there are no strawberry varieties that are resistant to black root rot.
- Choose a variety that is hardy in Minnesota to reduce winter injury and stress on the plant.
- Purchase new plants from a well-known supplier.
- Roots of young strawberry plants should be white and fleshy.
Choose a good location
- For new patches, choose a location where strawberries have not been present for the past 2-4 years.
- Choose a location with good drainage or improve drainage before planting.
- Improve drainage by adding organic matter to soil and redirecting water away from the area.
- Consider planting strawberries on raised beds to improve drainage.
- Good drainage creates a soil environment less favorable to some root rotting fungi.
Amend the soil
- Add organic matter like high quality compost, peat or straw to the soil prior to planting.
- Organic matter improves drainage and encourages the growth of beneficial microorganisms in the soil.
- Use a soil test to determine what fertilizers are needed for the planting site.
Renovate patches yearly
- Renovate patches of June bearing strawberries each year after harvest to maintain a healthy, vigorously growing patch.
- To avoid winter injury, apply 4 to 6 inches of straw on top of strawberry plants in the fall after 2 to 3 frosts have passed to harden off plants.
Start new patches
- In existing patches with black root rot, consider starting with new plants in a new location.
- Do not relocate old plants to the new location because the BRR pathogens will be carried on the roots of infected plants.
There are no pesticides registered for use by home gardeners that are effective in controlling BRR.
Reviewed in 2019