University of Illinois Extension

University of Illinois Extension

Hort Answers

Bacterial Disease

Bacterial Leaf Spot
Pseudomonas spp. & Xanthomonas spp.

Bacterial leaf spot on coneflower.
Bacterial leaf spot on coneflower.
3 (1 = rare 5 = annual)
3 (1 = very little damage 5 = plants killed)
Heuchera sp. (Coral Bells) & Echinacea sp. (Coneflower) and other plants.

Plants Affected
Pseudomonas causes "reddish" brown spots that may cause the leaf to distort. Xanthomonas causes small brown angular to circular spots with yellow halos. In some plants these bacteria can cause dead spots in foliage and or fruit and sometimes cankers in stems.

Life Cycle
The bacteria overwinters in dead plant material, but does not survive for long in water or soil. Bacteria are weak pathogens and need a natural opening (stomates and lenticels) or an injury (mechanical, insect or another disease) to infect.

Never work on plants or in the garden while plants are wet since the "bruising" and other mechanical injury helps to spread diseases. Bacteria are not controlled with fungicides. There are no bactericides available to gardeners that control these bacteria. Sanitation is the main control for these leaf spots.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic