Red Stele of Strawberry


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Red Stele of Strawberry

Red stele is the most serious fungal disease of strawberries grown in cool, wet soils. It has been identified in many regions of the world and commonly occurs in the northern two thirds of the United States. The disease was originally known as Lanarkshire disease because it was first reported from that area of Scotland. It has also been referred to by several other names including red core, red root rot, red stele root rot, brown stele, and black stele. The causal organism is Phytophthora fragariae C.J. Hickman. The fungus can be divided into at least seven pathogenic races. Members of the Fragaria (strawberry) genus are the only naturally infected hosts of the pathogen. The fungus overwinters as oospores in the soil and can survive in this state for several years, even in the absence of a susceptible host. Oospores germinate in late winter or early spring forming sporangia. Zoospores are liberated from the sporangia and serve as primary inoculum. They swim to the root zone, attracted to this area by root exudates. The spores encyst then germinate and penetrate the epidermis of main or lateral root tips directly. The fungus then invades the main vascular cylinder or "stele". Oospores are produced in infected tissue and may germinate under favorable conditions to form sporangia and zoospores, which allows for secondary spread of the disease. Plant to plant spread of the fungus is achieved in this manner. Spread of the pathogen over a greater area of the field or between adjacent fields occurs when infected soil or water is transported to these areas. Long distance dissemination of Phytophthora fragariae takes place through the use of infected nursery stock. The fungus is active over a temperature range of 1-25^oC, with optimum growth and sporulation occurring at the cooler end. Mycelium of Phytophthora fragariae goes dormant at 30^oC so disease progression is halted during the summer months. It may resume in the fall. While temperature is important, excess soil moisture is also a vital component in development of red stele.

Symptoms

The most characteristic symptom of this disease, as the name implies, is a red discoloration in the stele. The outer cortical tissue of infected roots may appear normal but the red discoloration is obvious when this tissue is scraped off. As the disease progresses upward in the central vascular cylinder, reddening may become evident in the crown. However, the fungus rarely grows any farther than this. Infection and discoloration are also absent in older, suberized roots. Another common underground symptom is the appearance of a rattail. Roots with this condition have no lateral roots and the remaining main root is often discolored. Multiple infection sites may be present on a given root. Older infected tissue turns brown as tissue begins to breakdown and the red coloring is harder to discern. When a mild infection takes place, the degenerated brown root tissue may be shed and replaced by new roots. These factors make it difficult to achieve an accurate visual diagnosis in the summer months. Above ground symptoms appear in low, poorly drained areas of the field and may be confused with those of winter injury or cortical root rot caused by a number of factors. Mildly infected plants may show little or no symptoms. Others may be stunted or have discolored foliage. Younger leaves are usually a dull bluish color while older leaves may be yellow, orange or red. Wilting symptoms may be evident at the time fruit is beginning to ripen. Affected plants at the margin of the infected area wilt during the hot part of the day. Infected plants may die before blossoming if the weather is dry. When wet springs prevail the plants may die gradually or survive but be unthrifty and produce few, low quality fruits.

Plant Health Management

Use disease-free nursery stock for field establishment.

Resistant Cultivars

Site Selection and Management.

Select a well drained site for field establishment of try to improve the drainage in an established field.

Fungicide Application.

Fosetyl-Al (Alliette) and metalaxyl (Ridomil) are labeled for control of red stele.

References

Agricultural Research Service, U. S. Dept. of Agriculture. 1978. Strawberry diseases. Farmer's Bull 2140. U. S. Government Printing Office, Washington, D.C. 27pp.

Anderson, H. W. 1956. Diseases of fruit crops. McGraw-Hill Book Company, Inc. New York, NY. 501 pp.

Jeffers, W.F and D. H. Scott. 1953. Red stele disease of strawberry Pages 760-765 in Plant disease, the yearbook of agriculture 1953. United States Dept. of Agriculture, House Document No. 122.

Maas, J. L., ed. 1984. Compendium of strawberry diseases. American Phytopathological Society, St. Paul, MN. 138 pp.

Milholland, R.D., cline, W. O., and Daykin, M.E. 1989. Criteria for identifying pathogenic races of Phytophthora fragariae on selected strawberry genotypes. Phytopathology 79:535-538.

Useful Links

Ohio State University

Texas A & M University

University of California - Davis

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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