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University
of Rhode Island GreenShare Factsheets
Diseases
of Crucifers: Clubroot
Clubroot
is a worldwide problem of temperate climates in the production
of cruciferous vegetables such as cabbage, broccoli, cauliflower,
radishes,
kale, brussels sprouts and turnips, as well as field crops such
as mustard and rape. The disease was known as early as the
13th
century in England where it was called "finger and toe" disease
because of the shape of infected roots. The
most striking symptom of clubroot is an abnormal enlargement of
the root system, with clubs often thickest at the center, tapering
spindle-like towards the ends. In radishes, clubroot causes distorted
swellings on the base of the bulb and along the tap root. In severe
cases, entire plantings are destroyed. Clubroot-infected plants
often wilt on sunny days and permanent wilting may accompany advanced
decay of infected roots. Severe stunting may be evident if infection
occurs early and the disease progresses rapidly. The malformed and
greatly enlarged roots are the key symptom of this disease.
Clubroot is caused by the soil-borne fungus Plasmodiophora brassicae,
which only infects plants in the crucifer family. It infects susceptible
host plants through root hairs. Once in the tissue, it stimulates
abnormal growth of affected parts, resulting in a swollen club.
Infection is favored by excess soil moisture and low pH, although
it can occur over a wide range of conditions. Once a plant is infected,
numerous resistant spores of the fungus are produced in the "clubbed" tissues.
As these tissues decay, spores are released into the soil where
they can remain infectious for at least 10 years. Contaminated
soil moved by wind or water can serve as a source of infestation
of nearby fields, causing outbreaks of disease in areas where susceptible
crops are planted for the first time. Numerous races of the pathogen
have been identified. Clubroot
is a very difficult disease to manage, and heavily infested areas
may have to be abandoned for future crucifer production. Some control
may be achieved with the following measures:
• A good crop rotation program, growing crucifers on the same
soil no more than every third or fourth year, is essential to retard
development of a large population of spores on land not already
heavily infested.
• Remove weeds in the crucifer (Brassicaceae) family.
• Since clubroot is favored by a low pH, liming soil to pH
7.2 or above may be helpful. Raising soil pH too high, however,
may interfere with the growth of succeeding crops other than crucifers.
Calcitic lime is usually preferable to dolomitic lime, except for
soils low in magnesium, where dolomitic lime is more effective.
In course-textured soils, increasing the pH can result in boron
deficiency. This may be alleviated by application of boron in transplant
water or as a foliar spray.
• With transplanted crops, the use of pathogen-free seedbeds
and uninfected plants is essential to prevent introduction of the
disease.
• Application of an appropriate fungicide in transplant
water prior to planting may help to reduce disease development.
• Clean and disinfect all machinery before moving it
from infested to non-infested land.
• Some resistant cultivars are available. However, plant
resistance has not been very useful in clubroot control because
of rapid development of new races of the fungus.
• Grow your own transplants to ensure that the disease does
not enter from infested areas on new plants. Adapted
from Sally A. Miller, Randall C. Rowe and Richard M. Riedel, Ohio
State University Extension, 2000
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are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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