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Ministry of Agriculture, Food and Rural Affairs

Black Root Rot

Plant wilt due to black root rot Black root rot symptoms on roots
Click to enlarge.

Beginner

Scientific Names
Rhizoctonia fragariae, Pythium spp.

Identification

  • Fine feeder roots rot or dry up.
  • Dark lesions develop along the white roots.
  • The interior core of the roots remains white during the early stages of development, but eventually turns rusty brown.
  • The outside of the roots turn black.
  • Severely infected plants collapse.
  • Partially infected plants wilt during drought stress, berry production or periods of rapid growth, resulting in poor runner growth and small berries.

Often Confused With
Verticillium wilt
Drought stress
Red stele
White grubs
Root weevils

Period of Activity
This disease is most common in fields with a long history of strawberry production.  Symptoms of black root rot show up most severely when plants are under stress.  Plant collapse is most obvious in new plantings about 3- 4 weeks after establishment or during periods or rapid growth.  In fruiting fields, symptoms occur as the plant is beginning to fruit, or after renovation.

Scouting Notes
Black root rot should not be confused with the natural darkening of healthy roots which occurs as the roots age.  By fruiting time, most of the older roots on healthy plants have a black surface, but the core of the root is white, and healthy feeder roots are present.

When symptoms of black root rot are present, carefully dig up the plants to examine the roots.  Note the pattern of injury in the field and determine if the problem is variety specific.

Thresholds

There are no thresholds for this disease.  Avoid planting strawberries in fields where strawberries have been grown in the preceding 3-4 years.

Advanced

Scientific Names
Rhizoctonia fragariae, Pythium spp.

Black root rot is a general name for several root disorders which produce similar symptoms.  One or more may be present and the causes can vary from region to region.  Pathogens implicated in black root rot of strawberries include nematodes, Fusarium, Rhizoctonia and Pythium..  

Identification
Fine feeder roots rot or dry up and dark lesions develop along the white roots.  The interior core of the roots remains white during the early stages of development, but eventually turn rusty brown.  The outside of the roots turn black.  Severely infected plants collapse. Partially infected plants wilt during drought stress, berry production or periods of rapid growth, resulting in poor runner growth and small berries.  Black root rot occurs in patches in the field.

Often Confused With
Red stele (Plants are stunted or dying, long feeder roots show red stele when sliced.)
Verticillium wilt (Plants are stunted or dying, vascular tissue in the crown may be darkened.)
Drought stress (Plants are stunted or dying in the heat of the day but often perk up at night.)
Root weevils(Plants are stunted or dying, but roots are pruned, frass and/or larvae are present.)
White grubs (Plants are stunted or dying, roots are chopped clean about 2.5- 5 cm (1- 2 in.) below the crown. Larvae may be present.)

Biology
The soil fungi that cause black root rot are present in many soils.  These pathogens tend to build up in strawberry fields as they age.  Infection of strawberry roots is most likely when populations in the soil become very high or when soil conditions are unfavourable for root growth.  Factors which favour this disease include soil compaction, poor soil structure, low organic matter, and lack of crop rotation.  Drought, excessive soil moisture, excessive fertilizer application, high rates of Sinbar and continuous strawberry culture are stressful to plants and make them more susceptible to black root rot.

Period of Activity
This disease is most common in fields with a long history of strawberry production.  Symptoms of black root rot show up most severely when plants are under stress.  Plant collapse is most obvious in new plantings about 3- 4 weeks after establishment or during periods of rapid growth.  In fruiting fields, symptoms occur as the plant is beginning to fruit, or after renovation.

Scouting Notes
Black root rot should not be confused with the natural darkening of healthy roots which occurs as the roots age.  By fruiting time, most of the older roots on healthy plants have a black surface, but the core of the root is white, and the feeder roots are present.

When symptoms of black root rot are present, carefully dig up the plants to examine the roots.  Note the pattern of injury in the field and determine if the problem is variety specific.

Thresholds
There are no thresholds for this disease.  Avoid planting strawberries in fields where strawberries have been grown in the preceding 3- 4 years.

Management Notes

  • Plant into a well-drained soil where strawberries have not been grown for at least 4 years.
  • Incorporate cover crops the year before planting strawberries, to increase organic matter and improve soil structure.
  • Mulch plants during the winter to reduce winter injury and heaving.
  • Varieties which seem to be especially susceptible to this disease are Kent, Honeoye, Mira and Jewel.