Insects & Plant Diseases
Tree diseases come in many forms. Some, like the heart and root rot pathogen Ganoderma, destroy the life sustaining vascular system and heartwood which is the very structure of a tree. The fruiting body can be seen by the naked eye. Unfortunately for a tree, when this fruiting body appears, it is usually a sign of advanced damage to the tree. Any landscape tree showing this symptom should be evaluated for hazard status.
Others, like a canker growing beneath the bark in the sapwood of a tree, may be initially noticed as bleeding on a tree trunk or branch. The extent of damage can be seen by cutting away at the bark layer. These symptoms are common of oak root fungus (Armillaria mellea) and Phytophthora species.
Oak root fungus disease is common on coast live oak trees that are growing in an environment which is being watered in summer months. Fungus thrives in warm moist environments. Lawns and high water use plants growing in the root zones of these tree are a problem.
Some insects can cause serious damage if left untreated. Boring insects, such as the clearwing moth, ambrosia beetle and other species of beetles, bore into trees to construct galleries for reproduction. Although one may only see minor amounts of sawdust and frass coming from the trunk of a tree, inside the tree these insects may be doing irreversible damage.
Beetle galleries can be very extensive. The damage is caused because these beetles bore into the phloem layer of the tree, through the cambium, and into the xylem. When this happens the tree is effectively girdled, usually dies and may fail catastrophically.
Sucking insects such as aphids, scale and whitefly, penetrate leaf surfaces with their mouthparts to feed on phloem. Problems arise if disease or virus is vectored.
Treatment for Insect Damage
There is a treatment to control these beetles. Permethryn, which is a synthetic pyrethroid, can be sprayed onto the trunk of the tree. This material is persistent for several months. The timing of the sprays is important as these insects have a time in their lifecycle when they exit the tree and fly to other stressed trees. When the insect exits the gallery it can come in contact with the insecticide, thus killing it. An arboriculture or pest control company with a qualified applicator’s license can apply this material.
Diseased and Insect-Infested Trees
The effectiveness of this treatment depends on how extensively the tree is already girdled before treatment, and the timing of the sprays. We have succesfully treated Sudden Oak Death infected trees that have these beetles and Phytophthora ramorum. Again, it depends on the timing and extent of previous damage as to the effectiveness of treatment. The good news is that in many cases, it does work.
It is important to note that if you are trying to treat a tree for Sudden Oak Death and your tree has beetles, they must be eliminated before injections of potassium phosphonate can be an effective treatment.