Pest 8 - Borers in Cercidiphyllum

Borers are a major problem for ornamental trees. There are a wide variety of borers. Once infested, there is little that can be done to control the insects in the wood. Keeping trees as healthy as possible is the best way to prevent borer damage. Trees that are old, drought stressed, or over watered, or otherwise unthrifty are most likely to be successfully attacked by borers. Borers always attack at joins of branches. The activity of borers encourages fungal disease, general weakening and eventual destruction of that part of the tree. 

Most of the borers encountered are beetles but some are caterpillars of clearwinged or other moths and others are primitive wasps. Pictured below is the frass (collection of excreta, thread, dead material), which acts as a protective, cushioning covering over the hole of the borer insect. The plant affected is a Cercidiphyllum japonicum (Katsura Tree), a deciduous tree found in the Japanese garden area of the Royal Botanic Gardens. 

An attempt can be made to treat borers by applying methylated spirits via a straw down the hole and sealing the entrance with putty. 

On a neighbouring Katsura tree, there is also a preying mantis egg case or ootheca. 

ref : University of Idaho website, pers. comm. Marcus Ragus