Consulting Arborists, Inc. was called by ASAP Enterprises to assess the damage to species Quescas douglasii on the property of Steve and Christine Homes because they have recently become brown and show signs of dying. The initial program was to walk the property and visually examine the trees to determine the extent of the damage and see if any other species are similarly affected. It appears that all Blue Oaks on the property, both those that are in the actual landscape and those in the surrounding forest, have been affected but no other plant species appear to be in distress. The homeowners were then questioned as to their actions to try and alleviate the issue, and they said that they have only pruned the dead branches but have not used any fungicide or other herbicide. The landscape includes irrigation lines and hardscape which has been designed in such a way that it keeps water from escaping. The hardscape also allows water to splash against the oaks. Plant Labs, Inc. was sent samples from the trees and they determined that the trees were infected with Actinopelte leaf spot disease a fungus of type Actinopelte druina. This fungus is thought to have infected the landscape trees because they are under water stress and the remaining trees because they are of the same species. The recommendation is to alter the landscape to be more native plant friendly, stop watering so much, and treat the trees by pruning the remaining dead branches and by using a copper fungicide.
Consultation Report: Homes' Blue Oaks
This report was gathered for the Homes' property as a consultation with ASAP Enterprises. The problem seemed to be that the homeowners were having some problems with the Blue Oaks which they had placed in their landscape and those that grew naturally on their property. As the Blue Oak is native to this area, there should be no problem if they are properly maintained as they are very drought resistant and will have few problems in a natural landscape. However, there is evidence that the oaks of this particular species have been turning brown prematurely in this landscape and the surrounding forest due to some pest of other cause. It has been necessary to both examine the surface issue that exist and send a sample to Plant Labs, Inc. To determine what the actual issue is. This report looks at the possible causes of the problem and what can be done to return the plants to a vigorous health.
ASAP Enterprises contacted Consulting Arborists, Inc. regarding the status of a group of Blue Oaks (Quercas douglasii) that were having some issues with browning and foliage thinning. The goal of the consultation is to determine what is happening to the trees, look at all possible causes that research and lab testing can reveal, and find solutions for the Homes' landscape. The immediate assignment entails sending a specimen to the lab to determine the extent of the problem and to determine a long-term solution that will completely eradicate the issue. It will also be necessary to give the Homes' family some idea as to the possible cost of the entire project.
Blue Oaks are native in central and northern California especially on the slopes of the Sierra Nevada mountains and the "north slope of the San Gabriel mountains" (Blue Planet, 2010). The tree is relatively short for the overall species reaching only 30 feet as a wild plant, but it can grow to 75 feet in carefully tended gardens (Sacramento Tree Foundation, 2012). The canopy grows to a breadth of from 50 to 80 feet. The reason for its short stature is that the annual rainfall in its native habitat is considered arid at only 20 to 40 inches per year (Blue Planet, 2010). The Blue Oak is grown as a member of landscapes, but it does not easily handle being overwatered as is the case with many native plants in the State of California. The dryness of the area in which the Blue Oak grows also makes it prone to forest wild fires, but the tree has natural adaptations which provide it protections. According to Blue Planet (2010);
"The blue oak has an extensive root system. It can grow through cracks in rocks to depths of 80 feet to reach ground water. Its root system allows it to survive in fire prone and arid regions. Blue oaks reproduce both through seeds and vegetatively from burnt or cut stumps. The light colored bark is thick and helps reduce fire damage."
These means of survival in an arid climate also have the detriment of making the tree vulnerable to heavy watering and irrigation (Bartlett, 1999).
Most tree genus have specific diseases and problems that are related to specific types of insects or fungi that infect and debilitate the species. Oak trees are no different. This genus seems to be particularly susceptible to different types of fungus that can affect all of the different species of the oak family. Anthracnose and Oak Wilt are probably the two most common amongst all types of oak (NASWC, 2000), but there are issues that specifically target the Blue Oak.
One study conducted by Swiecki, Bernhardt and Arnold (1991) looked at how the trees at their most vulnerable stages, seedlings and acorn, were affected by different diseases and insects. The researchers allowed common insects and fungi to infect the seedlings they planted and also examined the acorns produced by older trees. The acorns had to be on the tree to be considered because those on the ground would necessarily be more prone to fungal infestation. The group found that more problems were associated with trees that had in some way been stressed during the test that in normal growing conditions. The primary means of stress was due to too much water intake by the trees. Thus, all information relating to the Blue Oak species is that it is a hardy plant when it is provided the correct environment, but too much water or an improper growing placement is detrimental to the health of the plant.
In this particular case, not all of the Blue Oaks on the property are affected by the thinning and discoloration of the leaves. It seems that the trees that are affected are those which have been located near the house and around areas where there has been a great deal of landscaping work. Although there seems to have been some issues with other Blue Oaks in a seemingly undisturbed woodland nearby, these other trees were near the more obviously damaged trees. Another significant observation is that along with the landscaping ventures that have taken place, new irrigation has been added to the property to water non-native species that have been added to the landscape and which require a greater amount of water to survive the arid climate.
It is also important to note how the discoloration is spread and in what pattern it appears in the canopy of the affected trees. It has been noted that there is no notable pattern to the damage done to the trees; the entire canopy of those with the issue seems to have the same issue. The leaves are often entirely brown, but many have spots or tracks of brown along the veins of the leaf. This observation, and its significance will be covered in the analysis.
Finally, although the trees have been kept as a part of the landscaping, they have not be over pruned, nor have they been subjected to a great deal of insecticide or other chemical substance that could obviously cause such an issue. The trees have been allowed to grow naturally except for an occasional pruning of the dead branches that are caused by the problem. It seems that the Blue Oaks have had the best possible care and should not be having these issues due to anything that the homeowners or landscapers have done intentionally or through negligence.
Unfortunately, there is a problem and it is caused by some undo stressor to all of the Blue Oaks in the immediate vicinity. The best clue is that the oaks of other species are not having the same problem and that all the oaks of species douglasii are having the same problem. Most oak trees are susceptible to many varieties of disease whether insect infestation or fungus, but the oak, in general, is a very hardy plant. Different species of Quercas grow around the world, and though they have some differential characteristics, they all share a hardiness which allows them to live extremely long lives even under the most adverse conditions.
The problem here is that while other species of oak, in the same conditions (they all reside in the same forest), are thriving, the Blue Oaks are obviously, if not dying, then at least very stressed out. The stress is the issue here. In the study by Swiecki,…