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Protecting your trees from Mountain Pine Beetle - what
works, what doesn't.
With Mountain pine beetle populations on the rise, many homeowners
would like to protect their trees from being killed. There are many
products out there that claim to protect trees from mountain pine
beetle, and some of them have more science and field-testing backing
them than others. Colorado State Forest Service Entomologist Ingrid
Aguayo investigated these different products, and came up with some
thoughts that are summarized below.
Pheromones are a hot topic right now. These are
essentially powerful scents that insects use to communicate. One
is an antiaggregation pheromone called verbenone, which acts to
tell other beetles that "this tree is full." Research on this has
shown that it works pretty well while beetle populations are low.
However, the pheromones don't kill the beetle - they merely divert
them to a neighboring property where the populations will continue
to build. When populations increase (epidemic levels), the synthetic
material is not able to 'mask' the communication system of the beetle,
and it loses efficacy. Additionally, research has shown mixed results
on the use of these pheromones in a natural forest setting. Verbenone
is commercially available, and registered in Colorado; landowners
should have their property assessed by a professional forester before
deciding to use verbenone. It is not a "silver bullet", but it may
temporarily help in an area where the beetle populations have not
built up. It should be used in conjunction with an aggressive plan
of searching out and treating infested trees.
Tree injections have also received a certain
amount of media attention. With this system, a systemic insecticide
called emamectin benzoate (EB) is injected into the trunks of trees.
While EB has been shown to be effective in protecting ash trees
from emerald ash borer infestation in the eastern U.S, EB is not
registered for use against mountain pine beetle and cannot currently
be used for this purpose on a commercial basis. Further, there are
no research reports available that demonstrate that injecting pine
trees with EB (or even any other insecticide) will protect trees
from pine beetle infestation. The reason for this is that pine beetle
larvae feed in the phloem tissue of the tree, and there is limited
movement of the insecticide to the phloem area. Preliminary results
of research carried out with EB in conifers against mountain pine
beetle by CSU show treated trees have become infested.
The only mechanism for protecting trees that consistently showed
effectiveness on the Western Slope was to spray trees. Because there
are environmental consequences to spraying, landowners will have
to weigh their options. If you do decide to spray, choose only a
few high value trees, and get a certified applicator to spray. It
will need to be done each year for as long as the epidemic lasts
(10 years or more). Spraying should occur on a dry day in May or
June before the beetles fly; call the contractor as soon as possible
to get on their list. You can look in the phone book under "tree
services" to find a qualified applicator.
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