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Oak Pests - A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury

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Inonotus hispidus

Importance -- Hispidus canker, caused by I. hispidus, appears on willow oak, Nuttall oak, white oak, and hickory. Incidence of infestation varies by area and species, but may be as high as 13 percent. Cankers lengthen about 6 inches (15 cm) yearly. The decay column length exceeds the canker length. Diseased trees are quickly converted to culls.

Identifying the Fungus (figure 49a) -- Hispidus conks are about 2 to 12 inches (5 to 30 cm) wide, spongy, stalkless, yellowish brown to red, with pores on the lower surface. Conks are produced during the summer or fall. They dry to a black mass, fall, and can usually be found around the base of infected trees.

Identifying the Injury (figure 49b) -- Hispidus cankers are large, elongate, sunken in the center and bordered by callus folds. Infected stems become spindle-shaped. A small branch stub may be found near the center of the canker where the infection started.

Biology. -- Microscopic spores are released from conks for a few weeks. They are spread by the wind, but most travel no more than 140 yards (128 m). Spores reaching dead branches on healthy trees start new infections. Conks will form after deadening or felling diseased trees.

Control -- Cut hispidus-diseased trees as soon as possible for salvage and to reduce disease spread by limiting spore dissemination to healthy trees. No suitable treatment is known for high-value trees in urban areas.

Figure 49a
Figure 49b
Figure 49. -- (a) Inonotus hispidus conk; (b) Hispidus canker.
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