How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms of red stele include severe stunting, occasionally followed by death of plants. Symptoms first appear on plants located in low, poorly drained parts of the field. Affected plants become stunted as older leaves die and are replaced by smaller, younger leaves with short petioles. Young lateral roots are often completely rotted. New crown roots die from their tips back, producing a symptom called "rat tail." Splitting affected roots reveals the red stele symptom (red coloration in the core of the root above the rotted end) from which the disease gets its name.

COMMENTS ON THE DISEASE

Most infections are limited to winter and early spring in California. Optimum conditions for disease development occur when the soil is saturated and temperatures are cool. Under these conditions the pathogen produces zoospores (motile spores) that swim to the roots and infect them. Well-drained soil can minimize disease incidence and severity.

MANAGEMENT

Disease incidence and severity can be minimized by locating strawberry fields on well-drained soil, planting annually with certified transplants, fumigating the soil before planting, and using raised beds to provide optimum drainage. The use of systemic fungicides may be helpful. Avoid excessive or insufficient amounts of irrigation water. There are no commercially available California strawberry cultivars with resistance to the pathogen that causes red stele.

Cultural Control

Use raised beds and carefully managed drip irrigation; plant in noninfested soils that have good drainage. Also, use clean plant stock and consult your farm advisor about cultivar susceptibility. Soil solarization can also provide control.

Soil solarization. In warmer areas of the state, solarization has been shown to be effective for the control of soilborne pathogens and weeds. Solarization is carried out after the beds are formed and can be effective if weather conditions are ideal (30-45 days of hot weather that promotes soil temperatures of at least 122°F). The effectiveness of solarization can be increased by solarizing after incorporating the residue of a cruciferous crop, in particular broccoli or mustards, into the soil or following an application of metam sodium (40 gal/acre). For more details on how to effectively solarize soil, see Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377.

Organically Acceptable Methods

Control red stele in an organically certified crop with cultural controls.

Treatment Decisions

If drip fumigation is planned, good results have been obtained with a sequential application of chloropicrin (200 lb/acre) or 1,3-dichloropropene/chloropicrin (300 lb/acre) followed 7 days later with metam sodium (45 gal/acre) or metam potassium (37 gal/acre). Preplant dips and foliar sprays with fosetyl-aluminum or postplant ground or drip applications of mefenoxam are advisable when field history or environmental conditions suggest significant disease risk.

More information on strawberry fungicides

• Efficacy on strawberry diseases
• Treatment timing

PUBLICATION

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Diseases
S. T. Koike, UC Cooperative Extension, Monterey Co.
W. D. Gubler, Plant Pathology, UC Davis
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis

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