Black rot, caused by the bacterium Xanthomonas campestris pv. campestris, is the most common and destructive disease of the cabbage family worldwide. The bacterium is introduced to fields on infected seeds or transplants. Once present, it may survive on decomposing crop residue for up to two years, or indefinitely on weeds in the crucifer family. The black rot pathogen develops fastest during warm (80 to 86 o F), moist weather. The disease is spread quickly between plants in a row by splashing rain and gains entry through water pores at leaf margins or through wounds.
Early symptoms appear as wedge-shaped chlorotic (yellow) patches along the edge of the leaf that point toward the midrib. Veins in the discolored area darken as the interveinal tissue dies and becomes brown and brittle. Eventually the bacteria enter the vascular system of the plant and the disease becomes systemic, producing leaf drop and head rot. A crosswise cut of the stem, leaf petiole or veins will reveal a darkened ring of vascular tissue.
Damage from this disease can usually be avoided by using an integrated approach to disease management.Controls
- Most of the black rot epidemics have been introduced on infected transplants from the southern states.
- Grow your own transplants or hire someone to do it for you.
- Ask your seed company to hot water treat your crucifer seeds to kill the black rot bacteria.
- Grow transplants in a soilless mix or use a new, pasteurized or fumigated seedbed.
- Avoid planting in low, wet sites with poor soil drainage. Planting on raised beds, which provide better soil drainage, may help reduce disease spread, especially in seed beds.
- Avoid planting in fields infested with weeds in the crucifer family, which may harbor the black rot organism from previous years.
- Use different seed lots to plant several smaller seed beds rather than one large bed. Inspect seedlings for black rot symptoms frequently and rogue infected and surrounding plants immediately.
- Avoid working in fields when the foliage is wet.
- Plow cole crop fields after harvest to hasten the decomposition of crop residues.
- Use a 4 year rotation between cole crop plantings.
- If infection occurs, fixed copper or copper hydroxide applications every seven to 10 days may slow the spread of this disease in dry seasons.
- Use black rot resistant varieties.
Black Rot Resistant and Tolerant Varieties
|Black Rot Resistant Cabbage||Guardian
|Black Rot Tolerant Cabbage||Bravo
|Black Rot Tolerant Broccoli||Arcadia
|Note: Varieties considered to be tolerant will withstand less disease pressure than those considered resistant.|
|Note: One field of Rio Verde in Connecticut was observed to be severely infected with black rot. If you have problems with this variety, please contact one of the editors.|
By: Jude Boucher, Integrated Pest Management, University of Connecticut, Updated 2012.
Reprinted from: Grower, Volume 92-6
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
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