Diseases + Pests — Disease of the Month I: Volutella Blight on Pachysandra

Disease of the Month II: Botryosphaeria Canker of Dogwood

by Heather Prince

Disease of the Month: Volutella Blight on Pachysandra

Japanese pachysandra is a common groundcover throughout our area and is relatively trouble-free. However, in a cool wet spring after a volatile winter, volutella blight will often come calling. Sometimes, this fungal disease will lurk in the background on a leaf here or there before becoming established and ‘melting out’ large patches in groundcover beds. The symptoms begin as tan or brown leaf blotches that develop target-like concentric rings which continue to enlarge and eventually kill the leaf. Stem tissues beyond the canker will also wilt and die. During warm, moist weather, you’ll find pink to orange-brown spore pustules on the undersides of affected stems and leaves.

Treatment:

The disease is a stress disease, often seen on pachysandra damaged by winter injury. You may experience it after other stresses such as transplant shock, drought, excess moisture, shearing, scorch from excess sunlight, or scale infestations. First, remove and destroy all severely infected plant parts during dry weather so any spores present are not spread. Then remove any accumulated leaf debris that is holding in moisture in the area. Use pachysandra appropriately to avoid excess sun and winter winds. Periodic thinning also helps plants dry out by creating good air circulation.

Fungicide treatments are available to prevent new infections. Spray plants when new growth starts in the spring and repeat according to label directions to protect newly emerging tissues. Additional applications may be necessary during wet weather. Effective products include: chlorothalonil, thiophanate-methyl, mancozeb, and copper-based active ingredients.

Disease of the Month: Botryosphaeria Canker of Dogwood

A common disease of many woody plants, the dark, nearly black lesions of botryosphaeria canker stands out on the brightly colored stems of red and yellow twig dogwoods. The fungus invades through wounds, weak areas of the wood, and possibly through the lenticels. Look for dark sunken lesions on the stems which grow larger, encircling the twigs and killing the cambium. You’ll find the fungus’s black, pinhead-sized fruiting bodies are often embedded in the face of the lesion.

Additional resources: watered during dry periods to keep them healthy

University of Illinois Extension Service https://web.extension.illinois.edu/state/ horticulture/index.php

Treatment: Unfortunately, fungicides are not effective against botryosphaeria canker. Your best control method is to prune it out during dry weather, making sure to sanitize pruners between cuts. Drought-stressed dogwoods are particularly prone to the fungus. Make sure plants are mulched and

217-333-0519

The Morton Arboretum http://www.mortonarb.org/Plant Clinic: http://www.mortonarb.org/trees-plants/

Chicago Botanic Garden Plant Information Service: https://www.chicagobotanic.org/ plantinfoservice

847-835-0972