NC State Extension Publications

Symptoms and Identification

Typical leaf spots caused by bacteria appear as water-soaked, brown to black lesions often outlined with a yellow halo. Water-soaked (or sometimes called greasy) spots often appear on the underside of the leaf first. Lesions caused by Xanthomonas on Begonia and Pelargonium are v-shaped, extending inwards from the leaf margin. Necrotic spots may be angular or somewhat round. Spots may coalesce to cause a blighted appearance in some hosts. Bacterial leaf spots can easily be confused with fungal leaf spots, so be sure to get plants diagnosed by a plant disease clinic (NCSU Plant Disease Clinic).

V-shaped lesion on Begonia

V-shaped lesion on begonia.

NCSU Plant Disease and Insect Clinic

Bacterial leaf spot on Celosia seedling

Bacterial leaf spot on Celosia seedling.

NCSU Plant Disease and Insect Clinic

Bacteria leaf spot on zinnia

Bacteria leaf spot on zinnia.

NCSU Plant Disease and Insect Clinic

Leaf spot caused by Xanthomonas sp. on poinsettia.

Leaf spot caused by Xanthomonas sp. on poinsettia.

NCSU Plant Disease and Insect Clinic

Pathogen

Bacterial leaf spots on ornamental crops are typically caused by bacteria in the genera Pseudomonas, Xanthomonas​, and Acidovorax. Some of these bacteria cause disease on a wide host range while others cause disease on specific plant genera.

Bacterial leaf spot on geranium

Bacterial leaf spot on geranium.

NCSU Plant Disease and Insect Clinic

Bacterial leaf pot on begonia

Bacterial leaf spot on begonia.

NCSU Plant Disease and Insect Clinic

Water-soaked lesions on pelargonium.

Water-soaked lesions on pelargonium.

NCSU Plant Disease and Insect Clinic

Hosts

A wide range of ornamental hosts are affected by bacterial leaf spot. Susceptible hosts include canna, begonia, marigold, tickseed, poinsettia, English ivy, geranium, chrysanthemum, petunia, vinca, salvia, zinnia, mandevilla, lavender, and gerber daisy.

Host Parts Affected

Symptoms occur on the leaves. In some hosts, Xanthomonas can be systemic.

Disease Transmission

The organism enters the plant through natural openings such as stomata or through wounds and can be transmitted by water splashing during overhead irrigation or rainfall. Seed transmission is a means of primary spread for some bacterial species. Survival in crop debris depends on the species, but can allow the bacterium to carryover to the next crop.

Favorable Environmental Conditions

Warm, humid conditions are favorable for disease development. These conditions make disease management on propagated plants under mist particularly difficult.

General Disease Management

  • If starting crop from seed, purchase certified disease-free seed only. Most reputable seed companies provide certified disease-free seed.
  • If starting crop from cuttings or plugs, use healthy plant material only and avoid diseased material.
  • Discard any diseased material and cleanse hands before proceeding with healthy material.
  • Remove and destroy symptomatic plants and adjacent plants (to remove any asymptomatic, but infected plants) to avoid spreading the bacteria.
  • Drip or ground irrigation can help prevent spread of the pathogen. Minimize the use of overhead irrigation to prevent disease.
  • Leaves should be kept as dry as possible. Watering early or at a time of day that foliage can dry quickly will help prevent disease spread.
  • Use preventative bactericides (see below) if there has been a history of disease. Apply prior to disease development.
  • Sanitize greenhouse benches, tools, pots, flats and any other equipment by removing crop and soil debris entirely, followed by treatment with a sanitizer.

Disease Management for Conventional Growers

  • Sanitation is the most important management tool for control of bacterial pathogens. Bactericides (listed below) will only provide preventative control.
Product Active ingredient Efficacy
(various) e.g., Champ, Nu-COP, CuPRO copper hydroxide Fair
Junction copper hydroxide + mancozeb Fair
Camelot O copper octanoate Fair
Cuprofix copper sulfate Fair
Phyton 27 or 35 copper sulfate pentahydrate Fair
Agri-Mycin streptomycin sulfate Fair
Alliette WDG, Areca fosetyl-Al Poor to fair
(various) e.g., K-Phite, Fosphite mono- and di- potassium salts of phosphorous acid Poor to fair
Cease Bacillus subtilis QST 713 strain Poor to fair

Acknowledgements

This disease factsheet was prepared by the Meadows Plant Pathology Lab.

Funding for updating this fact sheet comes from the United States Department of Agriculture (USDA)-National Instiute of Food and Agriculture (NIFA) (2017-70006-27141).

Thank you to Mike Munster, NC State Plant Disease and Insect Clinic, for kindly reviewing and improving this disease factsheet.

Authors

Extension Associate, Vegetable and Herbaceous Ornamental Pathology
Entomology & Plant Pathology
Research Assistant
Entomology & Plant Pathology

Publication date: Jan. 14, 2019

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.