Common Insect & Disease Problems
Common Insect and Disease Problems of Native Forest Trees in SW Oregon
Following is a list of the most common SW Oregon tree species and the major insect and disease problems that afflict them. This is NOT an exhaustive list but covers the most frequently encountered problems. Please note that many of the links below take you to other websties.
Be aware that many, if not most, sick tree problems are related to underlying stresses that reduce the tree's vigor and make it vulnerable to pathogens. Typical stresses include: Drought; competition with surrounding trees and brush for limited resources, usually soil moisture; shallow, rocky soils; south and westerly aspects; heavy clay soils; mechanical damage to tree trunks; damage from fire; sudden exposure of shade-grown trees to intense sunlight; soil compaction; trenching; backfilling over the existing soil surface; poorly drained soils; over-watering; flooding; etc. Thus, while insects or diseases may be the DIRECT cause of tree death, the UNDERLYING cause is usually related to one of these stress factors.
TREES
WOOD-DESTROYING PESTS
MORE PROBLEMS...
PONDEROSA PINE
Whole tree is dead
Western pine beetle
Mountain pine beetle
Ips beetle (pole-sized trees)
Top is dead
Ips beetle
Branch tips dead/branch dieback/"flagging"
Possible reasons for tip dieback
Western gall rust
Western pine shoot borer
Deformed branches/"witches brooms" (trees have dense clusters of deformed branches resemebling witches brooms)
Western dwarf mistletoe
Elytroderma needle blight
Spots on needles/thin foliage
Black pineleaf scale
Needle casts
Needles are eaten/webbing visible
Pine sawfly
Heavy pitch on trunk
Sequoia pitch moth
SUGAR PINE
Whole tree is dead
Mountain pine beetle
Ips beetle
White pine blister rust
Top is dead
Ips beetle
Branch flagging
White pine blister rust
DOUGLAS-FIR
Whole tree is dead
Flatheaded fir borer
Douglas-fir beetle
Laminated root rot
Blackstain root disease
Abiotic disease
Tip and branch dieback
Douglas-fir twig weevil
Phomopsis
Witches brooms (trees have dense clusters of deformed branches resemebling witches brooms)
Dwarf mistletoe
Heavy pitch on trunk
Douglas-fir pitch moth
Stem decay - conks (toadstools) on trunk
Red ring rot
INCENSE-CEDAR
Incense cedar rust
Cedar bark beetle
Incense cedar mistletoe
Pecky rot
WHITE FIR
Fir engraver
Flatheaded fir borer
Laminated root rot
Armillaria root rot
Aannosus root and butt rot
White fir dwarf mistletoe
Indian paint fungus
PACIFIC MADRONE
What's killing my madrone trees? (brief article)
Diseases of Pacific madrone (13-page article with photos)
Determining the causes of Pacific madrone dieback in urban landscapes (10-page article)
Some observations of madrone diseases (9-page article)
Fall webworm
Sudden oak death
OREGON WHITE OAK
Oak mistletoe
Armillaria root disease
Inonotus trunk rot (heart rot)
Western oak looper
Bassetia gall wasp
Oak pit scale
White pocket rot and butt rot
CALIFORNIA BLACK OAK
Armillaria root disease
Inonotus trunk rot (heart rot)
Oak mistletoe
Carpenterworm
Pit scales
Pacific oak twig girdler
California oakworm
Fruit-tree leafroller
Sudden oak death
BIG LEAF MAPLE
Armillaria root disease
Stem and butt rots
Verticilium wilt
Carpenter worm
Roundheaded borers
Why Are My Madrone Trees Dying?
12-30-03
What's wrong with the madrone trees in our area? Many southern Oregon residents have been asking themselves this question lately.
Pacific madrone (locally known as laurel) is affected by a variety of fungal diseases. Symptoms range from leaf spotting to twig dieback to death of major branches or the entire tree. Compared to healthy, vigorous trees, stressed trees are more likely to be infected and the extent of damage will be greater. Common stress factors include overwatering, poor soil drainage, soil compaction, and backfilling over the existing soil surface. All these can lead to asphyxiation of the roots and a marked increase in tree stress.
Drought often plays a role
Drought is another major stress factor. Drought stress occurs when water loss inside a tree exceeds uptake long enough to cause damage or disturb the tree's physiology. The usual result is reduced growth and increased vulnerability to a host of insect and disease problems. Although madrone and oak are adapted to the summer drought of southern Oregon's Mediterranean climate, excessively low precipitation, especially during the growing season, may result in growth losses and stress. That appears to be the case in 2001-03, as rainfall was below normal during this period. In addition, the cumulative stress of a decade of drought from the mid-80s through mid 90's may still be affecting trees.
Many stands in southwest Oregon are overstocked with trees and brush because fire has been excluded. Trees growing in these stands must compete for a limited quantity of soil moisture, which contributes to the moisture stress problem.
The influence of the flowering cycle
Madrones that flowered heavily in the year 2000 has remarkably stunted foliage in 2001. Apparently, the trees used a considerable amount of their energy reserves in flowering. Consequently, few reserves were available for growth of the next year's foliage.
Madrone leaf spot
More than half a dozen fungal organisms can cause leaf spots on madrone. Young leaves are infected by air-borne spores during wet weather, often in the spring. Trees growing in creek bottoms or valleys are most likely to be infected. Infection results in circular to irregular spots about 1/4 to 1/2 inch in diameter. A related disease produced irregularly shaped black tarlike spots on the undersides of leaves. These diseases may result in unsightly foliage but are seldom serious. They may lead to an increase in tree stress, however.
What can you do? Raking and destroying fallen leaves can help dampen the spread of spores and infection of new leaves.
Madrone root disease (Phytopthera cactorum)
This disease affects the roots and tree trunk. Cankers (areas of diseased tissue) are usually near the base of the tree but may occur further up the trunk. The infected bark is brown and the sapwood may also be discolored. Loss of foliage, and small, curled leaves are common symptoms. Infected trees often die, sometimes rapidly. Moist soil conditions favor the fungus; hence over-watered trees or trees growing in poorly drained soils are most susceptible.
The main way to avoid root disease problems to avoid overwatering. For yard trees, frequent waterings (every day or two) on flat or poorly drained ground are a recipe for trouble. While some individual madrone trees may do OK in these situations, the risk of developing root disease is much higher. Deep waterings every two weeks or so underneath the drip line but well away from the trunk may promote tree vigor during extended summer dry spells.
Madrone cankers (Natrassia and Botryosphaeria)
Branch dieback is caused by one or more canker diseases that have been increasingly evident recently. A canker disease is caused by a pathogen that kills localized patches of the tree's inner bark, resulting in the death of branches or whole trees. In madrone, entire trees or individual trunks die after exhibiting large black cankers that spiral down the stems. Alternatively, large numbers of branch tips turn yellow, foliage droops, and eventually the ends of may branches die, leaving the tree with little or no foliage. Symptoms develop rapidly, and even large trees can be severely impacted in just a couple of years. The diseases are apparently associated with temperature or moisture extremes that injure trees or warm, wet spring weather that favors infection. Trees growing at the edges of open areas, trees that receive summer irrigation, and trees growing in areas where the soil has been disturbed or compacted appear to be preferentially affected.
Cankers typically develop after a bark injury. This could be a mechanical wound or perhaps caused by sudden exposure of a branch or trunk to direct sunlight, as when a surrounding tree is removed. Vigorous trees can callus over the tissue killed by the canker.
What to do?
For landscape trees, deep, occasional watering once every two weeks near the drop-line and well away from the base of the tree should alleviate moisture stress during extreme drought conditions. Summer irrigation close to the tree trunk should be avoided because it may increase the tree's vulnerability to root disease.
The canker disease can be prevented by keeping trees free of damage and stress, and by avoiding soil disturbance, especially compaction. Once the canker disease is established in a tree, there's not much that can be done to control it. No fungicides are known to control the disease. However, if caught early, pruning and burning individual cankered branches seems worthwhile.
Sources:
Diseases of Pacific Madrone. Marianne Elliot. http://soilslab.cfr.washington.edu/madrone/ch07_el.pdf
Leaf spot of madrone. EM 2951, Washington State University Extension, April 1973.