In early September of this year I noticed creamy white blotches on the trunks of a twin black oak with trunk diameters of eight to ten inches.
The trees are located on a neighbors property. Upon closer examination I also discovered small dark spots near the top and in the center of the individual blotches. They covered the entire trunk of the trees from the top of the main trunk to near the bottom. See pictures below. Watch Full Movie Online Streaming Online and DownloadOne can clearly see the creamy white substance that looks almost like an inverse tear drop and a dark spot near the top.
Since I have never witnessed such a problem on an oak in all the years living in the San Bernardino Mountains, I took photos and immediately reported my observation to the Cal Fire forester responsible for the San Bernardino Unit. His preliminary diagnosis was that the tree had become infested with the Western Oak Bark Beetle (Pseudopityophthorus pubipennis). The about 2mm long Western Oak Bark Beetle is a California native.
However, its natural habitat are the low elevation mountain ranges close to the coast line. During the past years it has infected large patches of Coastal Live Oaks and decimated the stands of these old growth trees by introducing a fungus into the trees. This fungus, (Geosmithia pallida) causes the trees to bleed a whitish and foamy canker. It is also pathogenic to the tress because it eventually moves into the sapwood.
The picture above shows a close-up of an infected area. The substance spreads over the exterior of the bark with the sap the tree bleeds through the tube the beetle drilled into the bark.
The picture below is another close-up showing the canker development directly in and around the tube drilled by the beetle.
Considering this beetle’s natural habitat is at low elevations and near the coast, the question how did this beetle find its way up to Lake Arrowhead arises. One possible answer is an accidental introduction by a tree contractor from down the hill doing fire hazard compliance work on two vacant properties just on the other side of an access road. Larvae and even the beetle could have travelled on equipment and in tarps and found the black oaks to be the closest target.
At this time Cal Fire, in close cooperation with U.C. Riversides renowned entomology department are growing cultures of the fungus samples that were taken mid October to determine if it is the same fungus that is killing coastal live oaks in various regions of California or if this is a new species.
If any readers notice wet spots on black oaks on their properties or nearby, please contact me right away at (909) 744-8634 or at email@example.com – I will visit the tree(s) and forward any pertinent information on to the unit forester of Cal Fire.
– Beverly O. Voelkelt