Scouting for disease: Bacterial leaf spot

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

Pathogen: Pseudomonas spp. and Xanthomonas spp.

Hosts include:
Astilbe, Chrysanthemum, Delphinium, Echinacea, Heuchera,
Hypericum and Rudbeckia.

Symptoms: Disease symptoms include water-soaked lesions on foliage that darken with age. Lesions may be bordered by the leaf venation.

Spread: Bacteria on the plant surface are easily spread to nearby plants by splashing water from rain and irrigation. Asymptomatic plants can serve as a source of inoculum.

Bacterial pathogens can survive and reproduce on the surface of asymptomatic plant tissues. Disease symptoms develop once the pathogen reaches high population levels on the plant surface. Sanitation is especially important. Workers should wash their hands after handling diseased plants. Foliage should not be handled when it is wet. Symptomatic plants should be destroyed. Avoid overhead irrigation or time irrigation to minimize leaf wetness. Succulent tissue is especially susceptible to infection. Most fungicides are not effective against bacteria. Copper-based products are helpful in limiting populations of surface-borne populations of bacterial pathogens.

Note: Identification information for more plant diseases is available in the field guide A Pocket Guide for IPM Scouting in Herbaceous Perennials. To order, call 517-353-6740.

Bacterial leaf spot of ivy
Xanthomonas leaf spot of ivy. Note the
water-soaked halos around leaf spots.

Bacterial leaf spot on Heuchera
Bacterial leaf spots on Heuchera.

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