Insect and Disease Diagnosis and Treatment

Diagnosis:

Insect and disease organisms are identified by inspection of the entire tree for signs or symptoms of the problem. A sign is actual evidence of the organism such as the insect itself, diagnostic feeding or decay patterns, or fungal tissue (mycelia or fruiting bodies: conks or mushrooms); a symptom is the characteristic reaction of the tree to the pest or disease, such as branch die back, loose bark, cankers, slow growth, excessive resin or sap flow, or early leaf drop or discoloration.  To diagnose the problem we might expose the root crown with an air knife, or climb the tree to access and examine inaccessible parts. Sampling of roots, leaves, branches, or trunks (by drilling or coring) is done to describe symptoms and condition and identify damaging agents. Samples are examined in house and may be sent to the Oregon State University Plant Clinic for identification and recommendations. Some insect and disease organisms we have repeatedly observed in the middle Gorge are described below. 

Control:

Decision Process: IPM

BAC follows the widely accepted Integrated Pest Management (IPM) approach to selecting and implementing control. This minimizes the amount and the toxicity of chemicals that are applied, saving the client money and unnecessary filling of the environmental capacity to degrade the compounds. Control may be recommended based on the damage exceeding the economic damage level and the availability of an effective control strategy. The economic damage level is set in part by client tolerance for damage; the level of damage that is permanent or fatal to the tree may be significantly less, but BAC does not recommend chemical treatment for incidental damage. The least toxic and most highly selective methods are that will be effective are recommended. To increase effectiveness, recommendations for cultural control to improve the capacity for healthy growth, as well as direct control that removes infested material are typically included.

Treatment:

Chemical Control

Once it is decided that control will be done, the treatment method or methods are selected. BAC recommends chemical treatments and cultural  and direct control based on IPM. We follow and usually exceed safety requirements on the pesticide label, and prefer using systemic, long lasting products if available to increase effectiveness and reduce cost. Chemical control products might be applied as root zone soil injection, by bark or canopy sprays, or trunk injection; the method is determined by the product, season, tree health, and target organism for control.

Direct and Cultural Control

Non-chemical control options are usually suggested with each project to augment chemical control. We often combine  chemical treatment with direct control if there are infested or dying branches, limbs, or trunks on the tree, or dying fine twigs and foliage.  Infested or green host material that is removed usually must be processed, such as by chipping or wrapping in plastic, burning, or removing it off site for disposal, depending on the particular pest. We have achieved cultural control to improve health and resistance to disease and insect problems in several ways: by exposing root crowns and replacing soil with fine gravel in cases of buried root crowns or trees with root disease to improve soil atmosphere and moisture conditions; by adding wood chip mulch to improve moisture retention and increase organic matter; by injecting beneficial bacteria, slow-release nutrients, or fungi into the fine root zone to improve root growth and resistance to disease; and by thinning the crown to change its microclimate to decrease foliar fungal diseases. 

Timing

Spring or Fall is an excellent time to treat trees with systemic chemicals for controlling several of our insect and disease problems: bark beetle, pitch moth, black pine leaf scale, oak pit scale and other scale infestation, as well as sapwood stain fungi introduced by bark beetles, anthracnose fungus branch die-back in oak, and thousand canker disease in black walnut. These problems can be treated so long as conifers (evergreen trees) are active (all year except when very dry or cold), and for hardwoods (deciduous trees) as long as leaves are on the tree and mainly still green.

The systemic chemical is taken up in the sapwood from ground-based trunk injection, lower bark spray, or foliar application, and spreads throughout the tree; some are formulated to spread in the inner bark, the phloem. In Spring, it must be applied with enough lead time to spread throughout the tree before attack by insect or disease; for this reason, treatment might be best done in the Fall, if the chemical has sufficient residual effectiveness. 

Other chemicals are not systemic; these may need to be re-applied within one season after degrading or washing off, depending on the period of time within which the pest organism is treated.

Once infested or showing disease symptoms, a tree might not take up the chemical as effectively, and it will not spread to dead or dying portions of the tree.  Such trees can still be saved but will likely also require direct and cultural control, as well as several years of treatment to recover normal health.

Prevention

Prophylactic (preventative) chemical treatments get around this problem, but are usually only recommended if high insect or disease pressure  (such as damage to adjacent trees, or repeated damage every year) makes it likely that the trees under consideration for treatment will be affected. Cultural controls done alone work this way as well, and are part of good horticultural practice to encourage health.