Assessment and treatment of Actinopelte leaf spot disease in blue oaks

Consultation Report

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Consultation Report: Homes' Blue Oaks

Observations

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

Introduction

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.

Background

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.

Observations

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.

Discussion

The report from Plant Labs, Inc. describes a disease that can easily be countered through an aggressive program. It is possible that this fungus could spread to healthy oaks of other species and even other trees of common type. The area has recently been plagued with sudden oak death, a disease that is caused by a similar "pathogen" which girdles trees and causes them to die very quickly (Protect Your Oaks, 2009). Although this issue is not as serious as that, it is reminder that fungi can cause very large problems if the issue is not dealt with swiftly.

One of the immediate issues also is that although the other oaks are not infected as of yet, they could easily become infected if they are subjected to some stressful situation such as a drought or other condition that makes for a more tenuous environment. The dying crowns of the trees could spread to these other species.

Conclusions

The immediate conclusion is that the Homes' need to make a decision about the type of program that they wish to conduct to bring the trees back to their healthy best. It is apparent that the problem has something to do with the growth cycle of the single oak species and that the owners need to focus on the root cause there. It is also obvious that this is a fungus that is very specific, right now, to this one species of oak, but that it could spread to the other species in the genus that are included in the forest because they are so genetically similar. The homeowners need to decide between saving their trees and sacrificing elements of their landscape or sacrificing the trees.

The main issue here seems to be the water that is provided for the garden as a whole. Plants native to this region do not require the amount of water that some of the non-native species do. The landscape includes trees that need to be watered more frequently, so they have to be in a watering program that allows them to procure the appropriate amount of water. Unfortunately, this means that the Blue Oaks are water stressed and are then susceptible to the fungus and the problems that the Homes' see occurring in their landscape. It would be simple to reduce the amount of water used, but this could prove detrimental to the garden as a whole.

Another area that was discovered is the fact that the root ball of some of the trees are partially or completely covered. A tree, like any other plant or animal needs a means by which it takes in a requisite amount of air. Trees generally do this through the roots that are exposed above the ground. That is why Cypress trees that grow in the southern swamps have such large "knees" that grow above the level of the swamp. Although the tree needs an exorbitant amount of water to survive, it still needs air to provide nutrients needed for survival. The same can be said of the Blue Oaks in the Homes' landscape. With the root ball completely covered, the trees are not able to breathe properly so they are further stressed above that caused by the excess amount of water. It is imperative that the trees be allowed to both breathe and have the proper low amount of water necessary for survival.

Recommendations

The landscape, the way it is currently constructed, is the main issue. The dirt and mulch which surrounds each tree needs to be reduced so that they are able to breathe properly. The landscape also allows for too much water to be left standing around the base of the trees so that they are receiving too much an becoming stressed. The Homes' need to have their landscapers funnel water away from native plants so that they receive the correct amount of water for their species. It may also be necessary to reimagine the entire landscape to be completely comprised of native species that do not need the amount of water that has been provided previously.

To bring the trees back to a healthy life, they first need to be pruned of all dead material which has the taint of the active fungus. This needs to occur during the months when the trees are dormant (preferably the winter) so that they are not unnecessarily shocked and stressed by the exercise. In the Spring when the buds first arrive on the trees, they need to be treated with a copper fungicide (NASWC, 2000). This should be applied to the trees at least twice. Once when the buds are new, then again after the leaves are half grown. A third application can also be made two weeks after this second application. The fungicide should kill the fungus, but it could easily return if the antecedents of its growth are not addressed by the arborist.