Texas Root Rot
Phymatotrichum omnivorum (Shear) Dug.
J. D. Solomon, F. I. McCracken, R. L. Anderson, R. Lewis, Jr., F.L. Oliveria, T.H. Filer, and P.J. Barry
Importance – Phymatotrichum omnivorum can cause root rot on many dicotyledonous plants in the Southwest. Oaks planted on old farm fields in reforestation projects or in subdivisions may become infected.
Identifying the Fungus – During warm, wet periods, the spore mat may grow on the soil surface. Infected root surfaces are covered by a fluffy, yellowish mycelium that penetrates the cortex. Microscopic examinations show distinct cross-shaped hyphae by which identification of the fungus can be made.
Identifying the Injury – Diseased trees have a thin crown, top dieback and poor vigor. The disease is more readily detectable on young, newly established seedlings that may wilt and die suddenly.
Biology – The fungus is soil-borne and persists in the soil as sclerotia for many years. Infection occurs when mycelial strands cover the root and enter between the epidermal cells. The spores produced on the mature mats rarely germinate, and their function in the spread of the disease is uncertain.
Controls – Use soil amendments to increase soil acidity. The fungus is not a serious pathogen in acid soils. The use of resistant plants, such as monocotyledons, is recommended in areas that have a history of the disease.
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