Catalpa
Yellowish Wood Rot
Caused by Polystictus versicolor
Fries This destructive heartwood rot of the hardy catalpa may be found wherever the trees grow The disease is not common in trees growing in the open In close stands however the limbs are killed by shading and after they break away holes are left which soon become infected by the spores of the fungus causing this rot The causal fungus is a very common saprophyte which grows everywhere on the wood of deciduous trees It may often occur as a semi parasite in the bark and sap wood of deciduous trees when they have been severely injured Otherwise the catalpa is the only tree in which this fungus is known to cause a distinctive heartwood decay.
Symptoms
The affected trees may be recognized by the holes in the trunk where the old branch stubs have rotted Insects and birds remove the decayed wood and use the hollowed out areas in the trunk for habitations In cross sections of the trunk the first indications of the decay show as pale colored areas The spring wood of the annual rings becomes reddish with small whitish areas Later both the spring and summer wood of the annual rings are similarly affected The decayed wood then becomes straw yellow and is very soft and brittle The decayed area enlarges rapidly and eventually the sapwood may be invaded The decay may extend into the branches and roots Coppice is usually affected if the wood of the stump is decayed The fruiting bodies of the causal fungus are formed where the bark is dead or on the affected wood when it is cut from the tree They are thin tough shelving structures hairy on top and marked with variable yellowish and brown shiny zones The under surface is yellowish or white and covered with small pores The fruiting structures are annual bodies but they persist through the winter and may revive and shed spores in the spring
Cause
The yellowish soft wood rot of hardy catalpa is caused by the fungus Polystictus versicolor The spores from the tubes on the under surface of the fruiting bodies are wind borne and cause infection when they lodge in branch wounds When the trees are planted close together the lower shaded branches die and remain attached to the tree for some time When they are broken off a hole is left in the trunk which serves as an excellent infection court The mycelium progresses rapidly in the wood For further details concerning the life history and control of the wood rotting fungi.
Manual of tree diseases
By William Howard Rankin
Cullarboration 