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


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SHOESTRING ROOT ROT
Armillaria tabescens,
Armillaria mellea

Importance. -- Root rot organisms, A. tabescens and A. mellea, cause major losses throughout the United States. Windthrow of infected trees in urban and high-use areas contribute to the importance of root diseases. Additional losses occur from loss of vigor.

Identifying the Fungi (figure 59). -- In the fall, clumps of yellow mushrooms grow on the ground near the tree and occasionally on the bole several feet above the ground. Thin black strands of mycelia (rhizomorphs) are produced on the root surface which resemble black shoe laces. The mushroom has decurrent gills and produces white spores.

Identifying the Injury. -- Infected trees may have low vigor. Roots may show various degrees of decay and have rhizomorphs on the surface. Frequently, root rot is evident only on wind-thrown trees. The rate of spread in the soil is about 1 foot (0.35 m) per year.

Biology. -- The fungus can live in dead roots and stumps for many years. Rhizomorphs spread through the soil from infected roots to nearby healthy roots which they then infect. Mushrooms produce abundant spores, but they are not important in infection of living trees. The fungus is most successful on slow-growing trees.

Controls. -- Spread can be controlled by removing the infected tree. Sterilize the soil before replanting. Any cultural practices that reduce stress and increase tree vigor will prolong tree life.

Figure 59

Figure 59. -- Armillaria tabescens mushrooms on oak.
 
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