The oak pit scale is a non-native oak pest introduced in the United States from Europe, now well-established in California. As a lumberjack consultant, I have observed how this pest population grows in many parts of Sonoma County, in particular in the Sonoma Valley, and may increase in other areas of the bay range. While not a new pest, both the number of trees affected and the severity of infections increased.
The oak hole scale is a small sucking insect that creates donut-shaped crust baking on the bark of branches and small branches. All our native oaks can be the host of this insect, but the scale of oak pits seems to be the most common on the oak of the valley, Quercus lobata , and this tree, on which I observed the most significant damage. Blue Oak, Quercus douglasii , and white oak hybrids can also be severely infected.
When the scale of the oak pit is present on a branch or a small branch, feeding them may cause the affected part to die. When the twigs die in the summer, the leaves that are present also die, but they do not fall in the fall like healthy leaves. However, I also see similar symptoms on oaks with numerous small branches caused by Diplodia quericna , another fungal disease.
In winter, potentially infected oaks in the valley are easy to spot, because they often have crown areas that still retain brown dead leaves. I have seen isolated valley oaks, so heavily infected with the pocket of an oak that they show signs of strong decay.
Clients are often called the belief that oaks are still, but upon inspection, I discover that the main reason for the dying is the scale of oak pits. If left untreated, these oaks may continue to decline.
The good news is that this pest can be easily controlled. There are systemic insecticides that, when applied to the soil or through body injections, will kill an oak hole. The treatment may take several years to ensure complete control, and before the tree shows signs of recovery, when dead and damaged branches and branches are replaced.
Although it may seem easy to diagnose this pest, it is not always that easy. Many other pests and diseases have similar signs and symptoms that can cause oak declination. In addition, there is a human activity that can lead to a decrease in the tree. Any stress factor that weakens a tree can make it more susceptible to pests and diseases.
When there is a scale of oak pits on the tree, it may not mean that this is the main reason for the decline. It is important to get an accurate diagnosis and determine all the factors affecting the health of the tree, before starting treatment. Incorrect diagnosis can lead to a partial or complete inability to control the problem, as well as unnecessarily introducing potentially toxic chemicals into the environment.
For more information about this pest and treatment options, see University of California IPM Pest. Note: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7470.html
Sherby Sanborn Consulting Arborist, April 2, 2012
