Crucifer Diseases
 

Black Rot
Xanthomonas campestris pv. campestris

Found worldwide

Damage Symptoms

Black rot occurs on all cultivated crucifers and several wild species. Lesions typically begin at the leaf margin and progress inward forming V-shaped chlorotic lesions. With time the lesions begin to dry and become necrotic. Infection normally occurs through leaf pores, but it can occur any place on the leaf where insect or mechanical wounds allow for bacterial entry.

The bacterium is a vascular invader and can move systemically in the plant. Invaded vascular tissue turns black in color which can be seen as dark veins in lesions or by observing the vascular bundles in cross sections of the leaf midrib, petiole, or main stem of infected plants. Black rot infections can serve as avenues for soft rot entry.

Conditions for Development

The bacterium persists in debris from infected plants, but it does not survive in the soil after the debris has deteriorated. The bacterium can also survive on other crucifer crop and weed plants and it is seedborne. High temperatures and periods of extensive rainfall favor black rot development. The bacterium is present in guttation droplets of infected plants and can be spread among plants by people or equipment moving through the field when the plants are wet.

Control

Rotate with non-cruciferous crops to allow time for debris from the previous crucifer crop to decompose. Use pathogen-free seed produced in an arid climate with no overhead irrigation. Avoid working in the fields when the foliage is wet. Use resistant cultivars when available; black rot-resistant cabbage cultivars have been developed.