Tree Health

Individual Trees Growing Around the Home

Madrone Canker

Trees growing around the home provide a lot of benefits – shade, beauty, habitat, and more. Healthy yard trees generally have full crowns, abundant foliage, and lack signs and symptoms of insect pests and diseases. Indicators of poor health include “puny” growth, unseasonal loss of foliage, spots or holes on the leaves, dead patches on branches or in the foliage, and shriveled leaves. Some problems may be serious and others may resolve on their own.

Trees with damage, rot or serious lean can be extremely hazardous. Potential indicators of hazardous trees include:

  • Large dead branches or hanging, broken limbs
  • Rot in the trunk or major branches
  • Mushrooms growing at the base of the tree (this can be a sign of root disease)
  • Cracks or splits in the wood
  • Severe lean
  • Conks or toadstools on the trunk (these are indicators of internal rot)
  • Trees that have been topped or otherwise heavily pruned in the past, or whose roots have been damaged by trenching or compaction

If you suspect that your tree(s) are unhealthy, it’s wise to address the matter as soon as possible – not just for the sake of the tree, but for the sake of you, your family and your home.

Consider hiring an Arborist (a person who practices arboriculture, or the care and maintenance of individual trees) when you see a tree in need of assistance. You can find Certified Arborists through the American Society of Consulting Arborists Referral Directory or the International Society of Arboriculture’s Find a Tree Care Service. An Arborist is also the person to call when you are building a home or driveway near trees, need a tree pruned correctly, or need a tree removed that is standing near your home.  For more information about tree identification visit this Tree Identification Site.

Forest and Woodland Health

Drought stress killed these Douglas-fir
Photo courtesy of Oregon Department of Forestry

Woodland health is an overall condition, and many healthy woodlands contain some dead or dying trees. Some would even argue that a woodland must have at least a few dead trees to be “healthy” because so many animal residents of the forest depend on them for food or shelter, and because dead trees and logs are important for nutrient cycling. However, it’s natural for a woodland owner to get concerned when a lot of trees in their “back-40” start dying.

Many, if not most, sick tree problems are related to underlying stresses that reduce the tree’s vigor and make it vulnerable to pathogens.

When woodpeckers chip off the bark, it’s often a sign of bark beetle attack

Typical stresses include:

  • Drought
  • Competition with surrounding trees and brush for limited resources, usually soil moisture
  • Shallow, rocky soils or heavy clay soils, which are bone dry in the summer
  • South and westerly aspects, which tend to be hot and dry
  • Mechanical damage to tree trunks or damage from fire
  • Sudden exposure of shade-grown trees to intense sunlight
  • Soil compaction, damage to large roots from trenching, and backfilling over the existing soil surface
  • Over-watering and/or flooding, especially on poorly drained soils.

So while insects or diseases may be the DIRECT cause of tree death, the UNDERLYING cause is often related to one of these stress factors.

Diagnosing the Problem

A key to accurate diagnosis is knowing what kind of tree is involved. Many insect and disease problems are host-specific, i.e., they affect one or a few closely related species, and not others. Know your host! If your tree identification skills need work, OSU’s Trees of the Pacific Northwest website is a great place to start.

Common Insect & Disease Pests of Trees in SW Oregon

Bark beetles are small insects that pack a big wallop! They probably kill more conifer trees than any other forest pest in the region. Bark beetles bore into the trunks of host trees. They lay eggs, which turn into larvae, which then

Bark Beetle tunnel marks

in the sugar-rich inner bark of the tree. This disrupts the flow of sugars from the leaves to the roots, ultimately killing the tree. Some bark beetles also carry a fungus which plugs up the water-conducting tissues inside the tree, hastening its death. Each species of bark beetle is hosted by only one or a closely related group of species, like ponderosa pine and sugar pine.

Bark beetles generally attack trees that are already under significant stress from overcrowding, drought, or other factors. During outbreaks, however, populations can build to very high levelsand kill apparently healthy trees. Fortunately, this rarely happens in SW Oregon since our mixed species forests don’t provide enough hosts of any one species to build beetle populations to outbreak levels.

Bark Beetle Outbreak

Signs and symptoms of successful bark beetle attack include foliage fading from green to yellow to rust color, boring dust in bark crevices, pitch tubes (see below) on the trunk, and woodpecker feeding on the trunk which is knocking off chunks of bark. Once a tree is successfully attacked, there is nothing you can do to save it. Prevention is the best cure – keep trees vigorous and healthy, especially through thinning to reduce tree densities and give them more growing space. See the links below for more information about bark beetles.

Pitch tubes
Wood beetle boring dust

Wood boring beetle dust is larger than bark beetles and more often seen, since their larvae are often found in firewood or dead trees. The vast majority of wood borers do not kill trees, despite their sometimes fearsome appearance. They primarily invade dead trees or stumps and help recycle the wood by tunneling around in it and carrying decay fungi. The major exception to this rule is the flathead fir borer, a beetle that is responsible for killing more Douglas-fir trees than any other insect in the region. This borer acts very much like a bark beetle and tends to attack trees that are already stressed or in decline.

Defoliating insects are among the most visible tree pests in southwestern Oregon. Periodic outbreaks of the fall webworm and oak looper result in the partial or even complete defoliation of hardwood trees like oaks and madrone, making them appear dead and raising much public alarm. However, these trees are seldom killed. There are a number of other defoliators of both hardwoods and conifers in the region. None are serious threats to tree health, despite their sometimes dramatic appearance.

Patch of trees killed by armillaria root disease

Root diseases are diseases of the site, caused by fungi and generally spread via root to root contact. Typically, conifer root diseases occur in pockets ranging from a fraction of an acre to many acres in size. Trees in the pockets may show a range of symptoms, from death of trees in the center of the pocket to visible growth losses on the pocket’s edges. Major conifer root diseases include laminated root rot, armillaria, annosus, and blackstain. Hardwoods also host some root diseases. One of the most common is armillaria, which is frequently associated with over-watering yard trees, especially oaks and madrone.

Douglas-fir infected with dwarf mistletoe. Note “witch’s brooms” on lower branches

There is a wide range of fungi that damage conifer and hardwood trees in SW Oregon. One of the most serious is white pine blister rust, an introduced disease that kills white, sugar, and other five-needled pine species. Sphaeropsis tip blight and western gall rust are two diseases that cause tip dieback in ponderosa pine, but seldom kill trees outright. Various “canker” fungi damage Douglas-fir, causing branch and top dieback and sometimes killing trees. Madrone trees are host to a range of fungi, some which affect the trunks and can kill branches and even entire trees, and some of which causing spotting on the leaves.

Mistletoe is a parasitic plant commonly found in oak trees. It can cause growth loss and dieback of branches but isn’t necessarily a threat to healthy trees. Dwarf mistletoes are found in conifer trees. They cause serious growth losses and often result in the eventual death of the tree.

Abiotic diseases or stresses also damage or kill trees, or predispose them to insect or disease problems. Abiotic simply means non-living – so abiotic stresses are things like drought and soil compaction.

Resources

The OSU Extension website has an extensive list of common insect and disease problems of native conifer and hardwood species in southwestern Oregon, organized by host species. The OSU Extension Master Gardener plant clinic may be able to help diagnose tree health problems, especially if a sample is brought in. Call 541-776-7371 for plant clinic hours. The OSU Extension Forester may also be able to provide help with diagnosis and possible remedies.

ODF Oregon Forest Pest Detectors(Oregon Department of Forestry). Great info on some of our most common pests.

Forest & Grassland Health On-line catalog of western forest insects and diseases. Many links to fact sheets and other information about tree health problems.

Special thanks to Forestry Images for use of images on this page.