Thursday, May 22, 2014

Bark Beetles, Drought and Monterey Pines

Many of the older Monterey Pines on the golf course are showing stress this year.  Some of the stress is drought related, as the rainfall never amounted to enough to deeply water the trees. And as the older trees become stressed, it provides an opportunity for the bark beetles to invade.  The trees' defense mechanism is their sticky sap, which normally stops the beetle larvae from advancing.  But as the trees age, they produce less sap and the beetles gain the advantage.

This has been an ongoing problem in the Monterey Forest, and to a lesser extent here.  Below are some photos showing the effects of the stress and the beetles, and a close up of the frass (sawdust) produced by the beetle larvae while tunneling.  The tunnels under the bark are very problematic.  Once the tunnels become extensive, they girdle the tree, preventing nutrients from reaching the root system.  Then, with a dysfunctional root system, the tree canopy dries and the tree perishes.

Unfortunately, treatments have proved ineffective, as the beetle larvae are protected by the tree's bark.  Injections have shown promise, but have not solved the problem.  The best recommendations are to keep the trees as healthy as possible, and plant replacement trees that are naturally resistant.