Oxyporus Root Rot, Oxyporus latemarginatus (Durieu & Mont.) Donk

Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.

Importance.-Oxyporus root rot causes decay of roots and root collars in sycamore, cottonwood, and many other hardwoods in the South.

Identifying the Disease.-Few diagnostic symptoms are known for this disease. Young trees exhibit reduced annual growth, stunting, and high mortality, whereas older trees often survive several years. The fungus causes a spongy white rot of the sapwood and enlarged cankers on the outer bark.

Figure 35. - Fruiting body of Oxporus latemarginatus on a young sycamore stem.

Identifying the Fungus.-The fungus invades the sapwood of roots as well as the wood behind fire scars in the lower bole, forming white mycelial mats and dirty white to pale yellow fruiting bodies at the soil line of dying or recently killed trees. The fruiting bodies are active for one season (fig. 35). Soil around diseased roots and the root collar may become infested, forming a white crust of mycelial strands on the soil surface at the stem base.

Biology.-Oxyporus latemarginatus colonizes and survives on dead wood or roots in the soil from which it invades small feeder roots of healthy trees. It then spreads to the root collar, colonizing the outer and inner bark, cambium, and sapwood.

Control.-Trees are predisposed to attack during warm weather, especially when the soil is waterlogged, or when feeder roots are wounded mechanically or by fire. The disease can be managed by preventing fiie and mechanical wounding to roots and the lower trunk and by maintaining adequate soil drainage. Tree vigor should be maintained by watering, fertilizing, and controlling weeds. If possible, soil with infested dead wood should be removed.