Club Root of Crucifers

Club Root of Crucifers

Club root has a long history as a pathogen on crucifers (members of the Brassica or mustard family). The disease was first reported in Europe during the 13^th century. It is now found worldwide and has an extensive list of cultivated and weedy cruciferous hosts as well as a few ornamental flowers. Crops, which often suffer economic loss as a result of club root outbreaks, include cabbage, cauliflower, turnip and rutabaga. The disease is caused by the soil inhabiting fungus Plasmodiophora brassicae Woronin. This fungus is a myxomycete, more commonly referred to as slime molds, and exists in 9 physiological races. Initial infection occurs when primary zoospores are released into the soil. These spores invade root hairs and develop into a plasmodium. This structure is unique to the slime molds. Plasmodia are characterized as a slimy, amoeboid shaped mass of protoplasm with many nuclei. In the case of Plasmodiophora brassicae, there first function is to form zoosporangia containing 4-8 secondary zoospores. These spores are released through a pore in the host tissue at the point where the zoosporangium is attached. Secondary zoospores reinfect the host and form plasmodia. These plasmodia are capable of infecting young root tissue directly. They may also infect thickened secondary roots and underground stems via wounds. Plasmodia may penetrate several types of host cells, including those of the vascular system and stimulate enlargement (hypertrophy) and increased cell division (hyperplasia) of these cells. Plasmodia ultimately develop into resting spores within host tissue. These spores are released when infections from secondary organisms produce cracks in host tissue. Disease development is favored by acidic soils that are cool and wet. Club root can develop over a wide range of soil temperatures with an optimum of 68-77oF. The causal organism survives between seasons for several years as resting spores in soil, in plant debris and in weedy cruciferous hosts. Moving soil via equipment, workers and water spreads it. Spores can also be disseminated in manure when livestock has fed on infected culls.

Symptoms

The distinctive underground symptoms of club root have earned it the nickname "fingers and toes". These symptoms consist of swellings on the roots and occasionally on below ground stems. Swellings range from small round enlarged areas to large spindle-shaped galls. All or part of the root system may be affected. In cases of mild infection no above ground symptoms may be evident. In severe cases, nutrient absorption and water uptake are disrupted and above ground symptoms are those commonly associated with nutrient deficiencies and drought stress. Plants may show varying degrees of yellowing (chlorosis). Infected plants may also wilt during the hot part of the day. Flagging, wilting of uppermost leaves is common on young infected plants. Premature death, stunting and reduced size and quality of heads are also symptoms associated with club root.

Plant Health Management

Field Selection.

When possible, select fields with no prior history of club root for crucifer production. Fields should also be well drained and have a soil pH of 7.2 or greater.

Crop Rotation.

A 7 to 10 year rotation out of crucifers is recommended. Some researches have also found that a rotation to cereals is most effective in reducing the amount of inoculum present.

Use Disease Free Transplants.

Lime Soil to Increase pH.

This management strategy may involve large amounts of lime, for instance 1500 lb/A is necessary to increase the pH from 7.0 to 7.2. In addition, increasing soil pH may limit rotation options by directly affecting subsequent crops or by increasing the likelihood of disease development on those crops (eg. scab on potato).

Do not use tail water from infected fields on non-infected fields.

Resistant Varieties.

Limited resistance is available to commercial growers of cabbage, turnips, radishes and rutabagas. Resistance is race specific.

Fungicide Application.

PCNB is labeled for control of club root and may be soil incorporated at planting, used as a plant dip or applied in transplant water. Crops included on the label are: broccoli, Brussels sprouts, cabbage, Chinese cabbage (lightheaded varieties), cauliflower, collards, kale and mustard greens (1997).

References

Agrios, G.N. 1978. Plant Pathology, 2nd ed. Academic Press, Inc. New York, NY. 703 pp.

Sherf, A.F. and A.A. MacNab. 1986. Vegetable diseases and their control, 2nd ed. John Wiley & Sons, New York, NY. 728 pp.

Walker, J.C. 1969. Plant pathology, 3rd ed. McGraw-Hill Book Company. New York, NY. 819 pp.

Useful Links

Michigan State University

Ohio State University

University of California - Davis

University of Maine

Highlighted Area

An extensive list of susceptible hosts of club root includes the following plants: cabbage, Chinese cabbage, Brussels sprouts, turnips, wormseed mustard black mustard, tumble mustard, kohlrabi, collards, kale, broccoli cauliflower rutabaga, sea kale, radish, and rape candytuft. Plants listed as highly resistant include: winter cress, garden cress, horseradish, Shepherd's purse, wallflower, stock, dame's violet and peppergrass.

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

E-Mail Home Page