Twice in 2002–03 landowners harvesting merchantable pines accidentally triggered outbreaks of the California fivespined ips (Ips paraconfusus) by creating piles of green slash at the wrong time of the year. Fresh slash is the preferred breeding material of Ips and it allows beetle populations to increase to levels where they attack and kill standing green trees. In one case young pines were killed at a distance of almost a mile from the original Ips infested slash piles. Two years of drought in the Willamette Valley also contributed to the observed tree mortality by weakening tree resistance to bark beetle attack.
There are at least two generations of Ips per year in the Valley. In the spring, over wintering beetles seek out fresh slash, wind thrown trees or snow breakage as breeding material It is the generation of beetles emerging from this slash in mid-June through October that can attack and kill standing green trees.
Management strategies that avoid accumulations of fresh pine slash at certain times of the year and encourage removal or treatment of storm damaged trees are the only proven approaches to preventing Ips damage. By the time the crowns of Valley pine have turned orange, it is too late for preventative measures and the outbreak, that typically lasts only a year, is already over. Here are some management recommendations that can prevent outbreaks and minimize Ips problems:
- Avoid creating fresh pine slash with a diameter > 3” between January and the end of July. This includes large branches and treetops.
- Any storm breakage > 3” in diameter, including branches, should be salvaged, chipped, or cut to small pieces and scattered in openings so it dries rapidly. If large amounts of broken tops and large branches are present, an Ips outbreak can result.
- If creation of green slash is unavoidable in the January – July period, any pieces >3” in diameter should be chipped, or cut into small pieces and scattered in openings. Do not pile slash since this slows the drying process.
- Keep all fresh pine slash, logs, or firewood several yards away from living pines.
Fresh pine slash created in the August – December, the safe period, maybe infested by some Ips, but the resulting population buildup is minimal and does not result in attacks on standing trees.
If your neighbors have Valley pine, it is important to talk to them about the risk involved in creating pine slash at the wrong time of the year. An Ips outbreak created by your neighbor may kill your trees as well as his.