Appropriate use of verbenone
Verbenone is only effective in preventing mountain pine beetle attacks; there is nothing that can save a tree once it is successfully mass-attacked. Furthermore, verbenone is only effective against mountain pine beetle. Be sure to accurately identify mountain pine beetle versus western pine beetle or red turpentine beetle. Stands in which 20% or more of the trees are currently infested with mountain pine beetle may not be protected by verbenone and ultimately not worth the cost of treatment. Ideally, infested trees should be removed prior to beetle flight and before verbenone application.
Mountain pine beetle typically flies between mid-July and August in Montana therefore, verbenone should be hung by July 1st. Do not hang prior to June 15th unless you intend to do a second application later in the season otherwise, the verbenone packets will dry out and not be effective for the entire season. Remove the verbenone from the Mylar package and staple or nail the plastic pouch to the tree through the plastic edge at the top. Specific application directions are included with the product. And remember, THE LABEL IS THE LAW so apply accordingly. (For example, chemical-resistant gloves are recommended.) Packets should be placed on the northwest or northeast side of the tree to reduce evaporation of the liquid material. Hang packets within comfortable reach from the ground, approximately 4-7 feet. If there is concern about tampering (i.e. campgrounds or curious children), hang them out of reach. Packets last for only one season and will need to be replaced each year that protection is desired.
Individual trees can be protected with 2-4 packets, depending on the size. Most average trees require only 2 packets but larger trees (>24” diameter at chest height) benefit from 3-4 pouches stapled around the circumference.
Landscape-scale protection requires 20-40 packets/acre in a grid pattern throughout the stand, depending on beetle infestation of surrounding areas. Generally, if populations are high, denser application rates are recommended. Twenty pouches per acre are spaced approximately 47 feet apart; 30 pouches/acre at 38 feet; and 40 pouches/acre at 33 feet. The aim is to permeate the stand with the verbenone. If following a grid pattern, it is not absolutely necessary to hang verbenone on a host tree if only a non-host (Douglas-fir, juniper, etc.) or fencepost is available at that particular point. Landscape protection is not a long-term solution and should only be considered for 2-3 years.