Q.
We have a Curly Willow tree that is being eaten by small,
shiny black bugs. They are chewing holes in the tree leaves. What are they and what can I spray to control
them?
A. Those shiny black bugs are likely imported willow leaf
beetles (Plagiodera versicolora). Adults and larvae feed on the
leaves of most willow (Salix) species, as well as Lombardy poplar (Populus
nigra 'Italica') and cottonwood (Populus deltoides). Large
populations of these beetles can cause significant damage to host
trees, but they are not considered life threatening.
Imported willow leaf beetles overwinter as adults under loose bark
and in protected crevices of host trees. The shiny, black- to
greenish-blue-colored beetles emerge in spring as host trees begin
to leaf out. They feed by chewing holes in the leaves, consuming
leaf veins as well as tissue. After feeding briefly, adult females
lay masses of small, pale yellow eggs on the undersides of the
leaves. The black larvae hatch in a few days, and begin to feed by
skeletonizing the undersides of the leaves. This means the insects
consume the tissue on the underside of the leaves, but not the leaf
veins. As the larvae mature, they also feed on the upper side of the
leaves. Larvae pupate in three to four weeks. Insects undergo a
complete transformation, from larvae to adult, during pupation.
During that time, they do not actively feed, nor or they as
susceptible to control as they are as larvae. We see two or three
generations of imported willow leaf beetles annually.
As is often the case with insects that produce multiple generations
a year, it is most beneficial to obtain good control of the first
generation. That way the second and third generations are much
smaller, easier to control, and cause less damage to the tree.
BioNeem (azadirachtin); Sevin (carbaryl); horticultural oil (larvae
only); pyrethrins and piperonyl butoxide; and Captain Jack’s Dead
Bug Brew (spinosad) are labeled to control imported willow leaf
beetle.
If your tree is very large, you should hire a certified arborist to
spray it for you. They have the training and equipment to spray the
tree thoroughly and safely.
To find a certified arborist near you, log on
to the
International Society of Arboriculture's website at
and enter your zip code.
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