There are several root and crown diseases that can impact strawberry production in the upper Midwest. Diseases vary in symptomology, causal pathogens, and how they are controlled. Diagnosing crown and root rot diseases of strawberry can be challenging as above-ground symptoms often look very similar. When diagnosing the disease, consider the soil conditions, time of year that the symptoms appear, age of the planting, and the symptoms on the roots and crowns.

Red Stele (Phytophthora fragariae)

• Symptoms: Plant symptoms develop before and during the fruiting period; often appearing during bloom. The core of the root (referred to as the stele) turns brick-red in color. The main root has a ‘rat tail’ appearance due to the sparse growth of lateral roots. Aboveground symptoms include stunted plants and a bluish hue on newly emerged leaves. Symptoms can develop by the second year.
• Pathogen spread and survival: The pathogen is usually introduced on planting material. It can survive for 10-15 years in the soil.
• Conducive conditions for the pathogen: This disease is most observed following prolonged periods of saturated soils. The pathogen is favored by cool, wet springs or falls. Severe infections can lead to plant death.
• Susceptible varieties: The varieties ‘Jewel’, ‘Honeoye’, ‘Glooscap’ and ‘Kent’ are highly susceptible to red stele. The varieties ‘Earliglow’, ‘Allstar’, ‘Tribute’, and ‘Tristar’ are known to be resistant to some races of the red stele pathogen, but not all of them. Additionally, the varieties ‘Annapolis’, ‘Brunswick’, ‘Cavendish’, ‘Mesabi’, ‘Mira’, and ‘Winona’ also demonstrate resistance to red stele.
• Looks like: Outward symptoms cannot be distinguished from black root rot; you must cut through roots to look for red stele (diagnostic symptom).

Black Root Rot

• Black root rot is considered a disease complex associated with biotic and abiotic causal agents. Factors associated with this disease often vary from site to site.
  • Fungi (clay soils), Nematodes (sandy soils), freeze injury, water logging, soil compaction, herbicides, and continuous planting of berries at the same site.
  • Commonly associated pathogens: Rhizoctonia spp., Pythium spp., Fusarium spp., and several nematode species
• Symptoms: Stunted root system. Main roots have dark lesions and feeder roots are either absent or dry and brittle. Cross sections of the roots show blackened tissue, but the stele remains white. This disease can show up after 3-4 years.
• Susceptible varieties: ‘Honeoye’ and ‘Jewel’ are susceptible to black root rot. The variety ‘Dickens’ shows good tolerance in black rot sites.
• Looks like: Outward symptoms are similar to red stele disease but on black root rot infected plants the stele is white.

Verticillium Wilt (Verticillium albo-atrum)

• Symptoms: Outer leaves wilt and dry at the margins and between veins. Few new leaves emerge. Severely infected plants are susceptible to winter injury. Verticillium can show up during the first year of planting. In new plantings, dieback appears when runners form. In older plantings, outer leaves turn brown at the margins and between veins at time of harvest; younger leaves remain green.
• Pathogen survival and spread: The pathogen resides in the soil for yearsand infects vascular tissue. The fungus also has a very broad host range (over 300 plant hosts).
• Conducive conditions for the pathogen: The fungus is most active during cool weather, but symptoms appear in early summer as temperatures start to increase and fruit develops; both increase the demand for water.
• Susceptible varieties: ‘Jewel’ and ‘Kent’ are susceptible to Verticillium wilt. Varieties that show resistance or tolerance include ‘Allstar’, ‘DelMarvel’, ‘Earliglow’, and ‘Mesabi’.

Neopestalotiopsis Crown and Root Rot (Neopestalotiopsis sp.)

• Newer disease of strawberry; appears to be more prevalent in warmer strawberry production regions. The pathogen has been reported twice in Wisconsin strawberry fields.
• Symptoms: The pathogen can infect all plant tissues including leaves, fruits, crown, and roots. Infected roots will darken, and crowns turn orange-brown (necrosis). One of the most common symptoms associated with this disease is stunting or poor plant establishment after transplanting.
• Pathogen survival and spread: The fungus likely survives and overwinters in crop residues in warmer production regions (there is currently no evidence to suggest that the pathogen can tolerate the harsh winters in Wisconsin).
• Conducive conditions for the pathogen: The fungus can spread easily and rapidly in the field. Disease development is favored by extended rain events and temperatures > 50°F. Optimal temperatures for infection and spread range from 77 to 86°F. Leaf wetness is very important for infection and disease development.
• Susceptible varieties: No resistant varieties have been identified.

Management of Root & Crown Diseases

• First, get an accurate diagnosis – send samples to the UW Plant Disease Diagnostic Clinic
  • Send samples of different stages of infection.
  • Samples should include above- and belowground plant parts.
  • Make note of when symptoms appeared and the history of the site.
• Site selection – Well drained soils, avoid low spots and fields with history of disease, break up compacted soils.
• Use disease-free plants – Check plantlets for symptoms, send samples for diagnostic testing, learn what type of production practices your supplier uses.
• Use resistant and tolerant varieties and/or varieties that tolerate stress.
• Chemical management options will depend on the disease you are dealing with. There are several pre-plant options that target some (not all!) crown and root rot diseases. Studies on the role of pre-plant dips for disease management are inconsistent. Consult the label and follow the instructions. See resources below for more information on chemical management.
• Monitor your plantings –
  • Do not overwater, avoid using water from surface ponds if possible as these can be a source of pathogen inoculum.
  • Quickly address symptomatic plants by getting a diagnosis.
• Rotate a site out of strawberries to non-host crops for at least three years (specifically for black root rot and Verticillium wilt)
• Do not plant in soils recently planted to hosts of Verticillium – ex. Solanaceous plants, cucurbits, and raspberries.
• Avoiding spreading water from infected sites to non-infected sites.
• Primary inoculum (oospores) of Phytophthora (red stele pathogen) can survive in the soil and/or can come in on infected transplants.
• Get a nematode and fungal pathogen analysis for your sites.
• Prior to planting, cut into the root system of several plants to look for discoloration or symptoms of disease.
• Spores can infect through wounds, minimize wounding plants, especially when transplanting.
• Plants from cold storage are very susceptible to crown rot and can show decline within 1-month post-planting.
• Clean and disinfect field equipment – this is critical for Neopestalotiopsis prevention.
• Avoid field operations when plants are wet – this is critical for Neopestalotiopsis prevention.

Resources:

• 2023-2024 Midwest Fruit Pest Management Guide. University of Wisconsin Extension A4104.
• BioIPM Strawberry Workbook. University of Wisconsin Extension A4080.
• 2022 Organic Production and IPM Guide for Strawberries. New York State IPM publication No. 226.

This article was posted in Berries, Disease and tagged black root rot, crown diseases, disease, Leslie Holland, Neopestalotiopsis Crown and Root Rot, Red Stele, Root and Crown Diseases, root diseases, Strawberries, strawberry, Verticillium Wilt.