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POTATO INVESTIGATIONS LABORATORY
Mimeo Report POL 71-3
SUGGESTED CONTROL MEASURES FOR BLACK ROT OF CABBAGE
D. P. Weingartner, Asst. Plant Pathologist
Black rot of cabbage, which was severe during the 1969-70 growing season, is a
perennial problem in the Hastings area. Black rot is caused by a microscopic
bacterium called Xanthomonas campestris. The bacterium not only infects cabbage
but also infects plants related to cabbage such as cauliflower, rutabaga, turnips,
collards, rape, black mustard, chinese cabbage, and certain weeds. Infected
seeds, cabbages and other infected host plants, and infested soil can harbor the
bacteria. Blowing and splashing rains, irrigation water, moving machinery or
other means of moving droplets of water can spread the disease rapidly from plant
to plant. Black rot cost Florida growers thousands of dollars during the 1969-,7
season. Late season cabbages were particularly hard hit. Many questions about
black rot have been asked by concerned growers. Hopefully this report will help
answer most questions.
ANSWERS TO MOST FREQUENT QUESTIONS ASKED ABOUT BLACK ROT OF CABBAGE:
1. Is hot water treatment of seeds effective? Yes. According to all available
evidence, black rot can be eliminated from contaminated seed by holding seeds
at 1220F for 25 minutes. It is critical that all seeds in a lot being treated
be held at 122 -10F for the full 25 minute period.
2. Can hot water treatment reduce viability of seeds? Yes. Germination of old
or weak seed can be reduced by treatment. Reductions in germination of new,
vigorous seed is usually negligible. Small samples of all seed lots should
be pretested to determine effects of hot water treatment on germination.
3. Following hot water treatment, should seeds be treated with a fungicide?
Yes. Fungicides such as thiram should be used to dust seeds following
treatment. Such treatment reduces damping off.
4. In 1969-70, was black rot introduced into the Hastings area on seeds hot
water treated by seed companies? It is not known for certain. It was
possible to trace each incidence of black rot in the Hastings area to other
sources than the seed.
5. Can black rot be carried on transplants even though the seedlings look healthy
and vigorous? Yes. Seedlings infected with black rot are often symptomless.
6. If I buy transplants, do I run a risk of buying black rot as well? Yes. If
transplants are being purchased make certain that they were grown from hot
water treated seeds on new land, sterilized seed beds, or land cropped to
noncrucifers for several years.
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7. Can black rot be transmitted via cow manure? Possibly. There have been
several outbreaks of black rot in cabbage fields following deposition of
manure from cattle which were fed cabbages infected with black rot.
8. Can collard greens or other plants related to cabbages be infected with
black rot? Yes. In faci black rot was observed on collards in July 1970.
Such infected plants could provide bacteria for infection of early field or
seed bed cabbages.
9. Can black rot spread rapidly? Yes. During blowing rains black rot can spread
throughout a field even though only a few plants were initially infected.
10. Will roguing out plants infected with black rot reduce the final incidence of
the disease? Only if all plants with symptoms are rogued before any spread
has occurred. If symptoms appear following heavy rains, chances are that
roguing will have little effect on the final number of plants infected with
11. Is black rot a serious problem in areas where cabbage seeds are produced?
No. Black rot depends on rain for rapid and wide spread dissemination.
Seeds are produced in areas of Washington and California where rains are
12. Are some varieties of cabbage resistant to black rot? No. All varieties of
cabbage currently available are, to some degree, susceptible to black rot.
A few varieties, however, appear to be less severely affected than others
under Florida growing conditions.
13. Are there chemical sprays available for controlling black rot? No.
14. Can black rot bacteria survive in the soil? Yes. Black rot bacteria can
survive for a period in plant debris found in soil. The exact length of
time black rot bacteria can survive in soil is not known. In Florida,
evidence suggests that it is safe to plant cabbages on "black rot soil"
12 14 months after the last infected plants were disked under.
15. Can black rot be spread by machinery and irrigation water? Yes. Drops of
water brushed from infected plants by passing machinery can spread black rot
16. Will black rot be serious during the 1970-71 season? It is impossible to say.
Weather conditions and availability of bacteria for spreading the disease will
determine its severity. The disease will be severe if we have frequent, heavy
blowing rains. It will probably occur only in localized areas if it is a
POL 71-3 Page 2
SUMMARY OF MEASURES FOR CONTROLLING BLACK ROT:
1. Plant only hot water treated seed.
2. Use new land or land cropped to noncrucifers for 2 3 years for seed beds.
3. Use transplants grown from hot water treated seed on black rot free soil.
4. Do not plant cabbage or cabbage related crops on land with black rot for
12 14 months.
5. Wait until rain or dew has dried before moving machinery through fields with
black rot. Always work first those areas where black rot is least severe.
6. Machinery used in fields with black rot should be disinfected with steam,
dilute clorox, etc. before entering noninfested fields.
7. When buying transplants make certain they have been grown following the
precautions listed above.
8. Disk under collards, mustard greens, etc. 6 8 months before planting
current season's cabbage seed beds or field cabbage.
POL 71-3 Page 3