There are no effective systemic pesticide treatments that will kill mountain pine beetle larvae inside the tree or adults as they emerge from an infested tree. Pesticide treatments are limited to protecting trees from becoming infested. These treatments are applied to the bark to kill the adult beetles as they land on the trunk and begin to burrow into the tree. This method of protection is highly effective and if the pesticides are applied at right time, losses may be as few as one or two trees for every hundred trees treated. However, only trees that are not infested should be treated. If a tree is already infested, pesticide application will not prevent the beetles from emerging and infested other trees.
Pesticide treatments are an effective way protecting high-value pine trees from mountain pine beetle. If there is mountain pine beetle activity within several miles of the property, protecting high value trees from attack may necessary. Generally it is more effective for homeowners to hire a commercial applicator with the experience and equipment to properly treat and protect the trees. If homeowners prefer to treat their own trees, the following are some guidelines to consider.
Pesticides to use
The pesticides that are most commonly used and labeled for bark beetle control have bifienthrin (commonly sold as Onyx), carbaryl (commonly sold as Sevin) or permethrin (commonly sold as Astro) as their active ingredient. There are products containing these active ingredients that are not restricted use so may be applied by homeowners however the specific product purchased must be labeled for bark beetle control. There are garden products of these pesticides that are not formulated for bark beetles and these will be ineffective. There are also products containing these active ingredients that may only be applied by commercial applicators with appropriate pesticide certification.
When to treat
The pesticides currently available are only effective for preventing a successful attack by the mountain pine beetle. They must be applied before the beetles begin to emerge in the summer and seek new hosts. We recommend that the application be applied during the month of May. This is sufficiently early enough to ensure that the beetles may not have already attacked the tree and are now inside the bark and protected from the pesticide. The application will only be effective for that season so trees that are in an area with mountain pine beetle activity must be treated every May to continue protection. Also do not spray if there is a threat of rain within 6 hours of application.
How to apply
The bark of the trunk must be treated so that is thoroughly wetted with the pesticide just to the point of runoff, merely misting the trunk will not allow for penetration of the pesticide into the bark fissures and cracks. The pesticide should be applied completely around the trunk from the base to a point where the trunk tapers to a diameter of 3 or 4 inches. Homeowners attempting to treat their own trees should be sure that their sprayer has sufficient pressure to wet the upper trunk of their trees. A hydraulic sprayer with at least 250 psi is needed for small trees, those that are less than 25 feet tall, while 400 psi or more is required to treat tall trees, those over 50 feet.
Homeowners considering treating their own trees are cautioned to use the proper equipment and only applied pesticides that are labeled for use for this purpose. Applications must not exceed labeled rates. Homeowners should read and follow all precautions and safety recommendations provided on the pesticide container label. Homeowners may not treat trees that are not on their property unless they are a certified applicator. Contact the South Dakota Department of Agriculture Division of Agricultural Services for more information. Any treatment recommendations, including those identifying specific pesticides, are for the convenience of the reader. Pesticides mentioned in this publication are generally those that are most commonly available to the public in South Dakota and the inclusion of a product shall not be taken as an endorsement or the exclusion a criticism regarding effectiveness. Please read and follow all label instructions and the label is the final authority for a product’s use on a particular pest or plant. It is the reader’s responsibility to determine if they can legally apply any product identified in this publication.