For at least the past six or seven years, Bill and I have observed attacks on pines in our garden by pine beetles. We are not certain whether these are the Western pine beetle or the Mountain pine beetle, given subtle distinctions between them.
Year-by-year, these beetles--and multiple signs of their presence--have increased. In 2015, beetles were present in Pinus sylvestris (Scots pine), Pinus thunbergii (Japanese black pine), Pinus densiflora (Japanese red pine), and Pinus mugo. Although Momiji-en is appropriately irrigated by a computer-controlled system and the pines did not lack water, the American West was in drought in 2015 and before. Consequently, pine beetle populations (and forest tree deaths) were high throughout the West.
Evidence of beetle infestations at Momiji-en were frass piles (see image below) at the base of infected trees, first showing in May and June. Once the beetles are in a tree, controlling or eliminating them is extremely difficult. Still, Bill and I were occasionally able to reach and remove individuals while probing their excavated tubes with a dissecting needle. We would then inject the tube with an insecticide in an attempt to reduce or eliminate further beetle activity there. We continued this strategy throughout the summer, with modest success.
Not wishing to be limited to our "made up" control strategies, we sought advice from our entomologist friend and former dean of the Oregon State University College of Agricultural Sciences, Sonny Ramaswamy. Sonny suggested we consider the use of a pheromone, verbenone. In Nature, beetles will emit verbenone when beetle population in a tree has reached its maximum, thereby sending a chemical "No Vacancy" signal to other beetles that prompts them to go elsewhere.
We investigated sources for verbenone and, in the process, learned more about its character and options for using it. In one form, it is applied 8 or 10 feet above the ground as a "splat" of dark, thick paste. But the form we chose was packets, each a few inches on a side, that are then stapled, one per tree--on the north side, about head height or slightly higher. The packets are put in place in May or June, or earlier if there are signs of the insects. We have purchased the packets, but not yet applied them or even opened the sealed containers in which they arrived. This photo is of the label on the container that holds 10 packets. I will add photographs later when we put the packets themselves into place on our trees. Watch this site for further reports. And keep your fingers crossed!
Here's where we obtained verbenone...