Wednesday, June 23, 2010

Pest of the Week: Black Rot

Photo Courtesy of the University of Illinois Extension Integrated Pest Management

Black Rot (Xanthomonas campestris pv. campestris)
On Cole Crops (examples: broccoli, cauliflower, Brussels sprouts, cabbage)

Life Cycle: Black Rot infects many Crucifer crops and weeds. The cycle can begin with infected plant debris left in the field (more common in warmer climates), infected seed, or infected weeds on field edges. Transmission within a crop occurs from machinery, tools, hands, wind, or rain. The disease can enter plants through wounds on leaves and roots, specialized pores called hydathodes, and insect damage sites. Bacteria grow fast within the plant, clogging the vascular system. This diagnostic characteristic of the disease is displayed as black veins and black vascular tissue in a cross section of the stem. Black Rot favors warm, wet weather and symptoms are readily observed under such conditions. A seedling or plant may still be infected when there is cooler weather present, but symptoms may not be expressed.

Plants Affected: Broccoli, cauliflower, cabbage, Brussels sprouts, and cruciferous weeds are susceptible to Black Rot. Radishes are less susceptible to Black Rot than other crucifer crops.

Symptoms: Seedlings wilt, turn yellowish, and may eventually die. More mature leaves will show V-shaped lesions that start at the margin and taper to a point farther into the leaf tissue. Leaf lesions will enlarge and turn yellow. As the disease progresses, veins may or may not turn black. The plant will drop lower leaves to expose a discolored (yellowing) stem with a tuft of leaves at the end. Cabbage heads will often be misshapen or stunted. Cauliflower leaves may have tiny black spots when Black Rot is present.

Control: Healthy plants fight disease more readily than compromised ones. Maintain seedling health by following a proper nutrient and watering program, using disease-free growing media, disease-free seed, and regularly scouting for and roguing out weak or diseased seedlings. Please read the Cabbage culture box in Johnny’s paper catalog or the Growing Information tab for any Cabbage product on the Johnny’s website for more detailed information on this and other Crucifer diseases. Keep damage in the field to a minimum by removing plant debris at the end of the season so the disease doesn’t overwinter. Remove Crucifer weeds from field edges. Work soil and plants when dry. Wet weather perpetuates disease by making it easy for bacterium to spread. Rotate out of Crucifer crops for at least two to three years in a field. Spray Champ® WG Copper Fungicide (#9778) as a preventative if Black Rot presence is suspected. Read all product labels in full and follow label instructions as specified for that particular product.

Resources:
http://urbanext.illinois.edu/hortanswers/detailproblem.cfm?PathogenID=133
http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg16.htm
http://www.aces.edu/pubs/docs/A/ANR-0937/ANR-0937.pdf
http://vegetablemdonline.ppath.cornell.edu/factsheets/Crucifers_BR.htm

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