Japanese maples are among the
more common hosts of the granulate ambrosia beetle (Xylosandruscrassiusculus), with
other hosts including styrax, ornamental cherry (especially Yoshino), pecan,
peach, plum, dogwood, persimmon, sweetgum, magnolia, fig, Chinese elm and
azalea. This pest is attracted not only to damaged, stressed or transplanted
trees, but to seemingly healthy trees as well. The beetle becomes active in
early March (or earlier), and the female beetles bore into trunks or branch
wood of thin-barked hardwood trees. Once a tree has been attacked, it becomes
more attractive to further attack. Often these trees are less than four inches
Visible symptoms include wilted foliage, as well as the
toothpick-like strands of boring dust (frass) that protrude from these small,
pencil-lead size holes.
infested plants should be
removed. If only a few branches are infested they may be cut out. The life
cycle takes approximately 55 days until the emergence of the next generation of
beetles, so prompt removal or burning of the wood is important. Protective
sprays on other susceptible plants may reduce their spread. Permethrin may be
used as a trunk and scaffold limb spray beginning in March ,Thoroughly wet the bark.
Multiple treatments may be needed during a season. Research indicates that
spraying the infested trunks with permethrin may cause the beetles to leave the
galleries they have already created. Since the beetles do not consume the host
plant material, dinotefuran and imidacloprid treatments are ineffective.