Certified Arborist Test Tree Diagnosis and Treatment 1 — Questions and Answers
Question 1: Which symptom pattern most reliably distinguishes oak wilt from other causes of rapid crown decline in red oaks?
- Interveinal chlorosis beginning on the oldest leaves and progressing inward over several seasons
- Rapid wilting and bronzing of leaves beginning at the leaf margins and progressing from branch tips toward the trunk, often killing the tree within a single growing season (Correct answer)
- Scattered branch dieback concentrated in the upper canopy with heavy fungal fruiting bodies on the bark
- Gradual thinning of the canopy over three or more years with eventual trunk decay
Correct answer: Rapid wilting and bronzing of leaves beginning at the leaf margins and progressing from branch tips toward the trunk, often killing the tree within a single growing season
Oak wilt (Bretziella fagacearum) in red oaks causes a characteristic symptom called 'flagging' — leaves bronze rapidly from the margins inward and wilt while still attached. The disease moves through root grafts and xylem so quickly that red oaks typically die within weeks to months of symptom onset, a pace that distinguishes it from slower decline causes like compaction or drought.
Question 2: An arborist observes sunken, discolored bark lesions on a stressed honeylocust with an amber, gum-like exudate at the margins. The inner bark beneath the lesion is brown and water-soaked. What is the most likely diagnosis?
- Cytospora canker, a stress-related fungal canker that invades weakened or wounded tissue (Correct answer)
- Bacterial wetwood, which causes fermentation gases to force liquid through bark fissures
- Hypoxylon canker, which produces a silvery-gray crust of fungal stromata on the bark surface
- Armillaria root rot, identified by white mycelial fans beneath the bark at the root collar
Correct answer: Cytospora canker, a stress-related fungal canker that invades weakened or wounded tissue
Cytospora canker is a common stress-related fungal disease in honeylocusts and many other species that enters through wounds or winter injury. The sunken, resin-soaked lesions with water-soaked inner bark are classic. Hypoxylon canker produces a distinctive metallic stromata crust rather than amber exudate, and Armillaria signs appear at the root collar, not mid-trunk.
Question 3: What is the primary mode of transmission for fire blight (Erwinia amylovora) from tree to tree, and which tissue type shows the pathognomonic 'shepherd's crook' symptom?
- Soil-borne root contact transmits the bacterium; shepherd's crook forms on large structural roots
- Windborne spores spread during dry conditions; shepherd's crook appears on the trunk
- Pollinating insects carry the bacterium to blossoms during wet spring weather; shepherd's crook forms on infected shoot tips (Correct answer)
- Bark beetle galleries inoculate the xylem; shepherd's crook forms on water sprouts
Correct answer: Pollinating insects carry the bacterium to blossoms during wet spring weather; shepherd's crook forms on infected shoot tips
Fire blight bacteria are spread primarily by bees and other pollinators that visit infected blossoms during warm, wet spring conditions — optimal spread occurs above 65°F with rain or high humidity. The infection moves into young shoot tissue, where the wilting and darkening of the terminal growth produces the characteristic downward curl called a shepherd's crook at the tip of the shoot.
Question 4: A mature sugar maple shows progressive dieback of branches in the upper crown combined with heavy seed production, early fall coloration, and epicormic sprouting along the lower trunk. These signs together are consistent with which condition?
- Maple decline syndrome, a multi-factorial stress condition often linked to soil compaction, drought, and foliar diseases acting together (Correct answer)
- Verticillium wilt, distinguished by the characteristic green-brown streaking visible in cross-sections of affected branches
- Asian longhorned beetle infestation, identified by the round exit holes and frass-filled galleries in the sapwood
- Hypoxylon canker, which preferentially attacks the upper crown first in sugar maple
Correct answer: Maple decline syndrome, a multi-factorial stress condition often linked to soil compaction, drought, and foliar diseases acting together
The constellation of symptoms — upper-crown dieback, heavy mast production (a stress response), early senescence, and epicormic sprouting — is the classic presentation of maple decline, a complex disorder driven by cumulative stressors such as soil compaction, road salt, drought, and repeated defoliation by pests or pathogens. No single pathogen produces this exact multi-symptom pattern, which is the key to distinguishing decline from a primary infectious disease.
Question 5: Phytophthora root rot is frequently misdiagnosed as drought stress in landscape trees. Which combination of diagnostic observations most reliably differentiates Phytophthora infection from simple moisture deficit?
- Wilting that does not recover after irrigation, discolored (reddish-brown) inner bark at the root collar, and decline symptoms that worsen in chronically wet or poorly drained soils (Correct answer)
- Yellowing of leaves beginning at the shoot tips with brown necrotic margins, and wilting that recovers fully after a single deep watering
- White mycelial fans visible under the bark at the root collar accompanied by honey-colored mushrooms at the base of the tree
- Bark splitting and sunken cankers on major scaffold branches combined with oozing liquid from trunk lenticels
Correct answer: Wilting that does not recover after irrigation, discolored (reddish-brown) inner bark at the root collar, and decline symptoms that worsen in chronically wet or poorly drained soils
Phytophthora spp. are water molds that thrive in saturated soils, so symptoms paradoxically worsen in wet conditions rather than improving with irrigation. The tell-tale sign is reddish-brown discoloration of the inner bark just at and below the soil line (the root collar), often with a distinct boundary between healthy and dead tissue. Drought stress typically improves after watering and lacks the root-collar lesion, while white mycelial fans indicate Armillaria, not Phytophthora.
Question 6: When evaluating a tree for potential Armillaria root rot, which combination of field signs provides the strongest confirmatory evidence?
- Round emergence holes approximately 3/8 inch in diameter in the bark and sawdust-like frass in bark crevices
- White, fan-shaped mycelial mats beneath the bark at the root collar, dark rhizomorphs under the soil surface, and honey-colored mushrooms clustered at the base in autumn (Correct answer)
- Resinous pitch tubes on the lower trunk with blue-stained sapwood visible in bark peel-backs
- Galls or swollen tissue at the root crown with a crumbly, tumor-like internal structure
Correct answer: White, fan-shaped mycelial mats beneath the bark at the root collar, dark rhizomorphs under the soil surface, and honey-colored mushrooms clustered at the base in autumn
Armillaria mellea and related species produce three highly diagnostic signs used together to confirm infection: flat white mycelial fans (which smell mushroom-like) between the bark and wood at the root collar; dark, shoestring-like rhizomorphs running under the bark or through the soil; and clusters of honey-colored (amber) mushrooms with a ring on the stipe fruiting at the base in late summer or fall. No other root disease produces all three signs.
Certified Arborist Test Tree Diagnosis and Treatment 1
Which symptom pattern most reliably distinguishes oak wilt from other causes of rapid crown decline in red oaks?