A Canker on a Forest Pansy Tree

Identification

• Cankers on “Forest Pansy" redbuds result from infection by the Botryosphaeria ribis var. chromongena fungus. The fungus is one of several Botryosphaeria canker strains affecting more than 170 commonly grown shrubs and trees, according to the Purdue University Extension. Its effects are most noticeable on older, environmentally stressed redbuds.

Fungal Life Cycle

• The dormant Botryosphaeria fungus overwinters in "Forest Pansy's" foliage and bark as spore-bearing structures called pycnidia or pseudothecia. Spore production resumes with the arrival of rainy spring weather when spore-contaminated insects, water, wind or tools spread the disease. It enters the redbud through natural openings, such as the pores on the undersides of its leaves, or through pruning cuts, insect damage or bark wounds. Trees suffering from drought stress are especially vulnerable to Botryosphaeria infection.

Symptoms

• A "Forest Pansy" redbud stricken with Botryosphaeria develops cankers, sunken and sometimes-dark lesions covered with rough bark. Ranging from insignificant to very large, they're often bordered with rings of raised, callused tissue. Their bark may crack to reveal the tree's fluid-transporting xylem, or slough off and fall to the ground. On canker-girdled branches, the leaves' healthy purple-green color fades to reddish-brown as the lack of moisture wilts and eventually kills them. These wilted, discolored terminal leaves often serve as the first indication of the Botryosphaeria infection. Peeling back the cankered bark exposes diseased, brown or reddish-brown instead of healthy, creamy-white wood. If the cankers spread to the trunk, the tree may die.

Preventing Canker Disease

• Drought stress and bark wounds raise "Forest Pansy's" risk of contracting Botryosphaeria canker. Watering whenever the top 3 to 4 inches of soil are dry to the touch keeps the tree hydrated during drought. A 2- to 2 1/2-inch layer of mulch spread over the root zone beginning several inches from the tree retains soil moisture without encouraging fungal buildup around the trunk. The mulch also discourages weeds and grass, so you won't expose the tree to mowing or trimming wounds.

Managing Existing Canker Infection

• Fungicides are ineffective against Botryosphaeria cankers. To manage an existing infection, prune diseased twigs and branches back to healthy, creamy-white wood. In most cases, cutting back to 6 or 8 inches below the lowest canker is sufficient. Prune in late winter before "Forest Pansy's" flower buds emerge, disinfecting your tools with a rag dipped in denatured alcohol between cuts and destroying the infected debris.