Certified Arborist Test Diagnosis and Treatment 3 — Questions and Answers
Question 1: The branch tips of an ornamental pear tree (Pyrus calleryana) have wilted and turned dark brown-black, with new shoots bending over in a distinctive hook or crook shape. The discolored leaves remain firmly attached. What is the most likely diagnosis?
- Drought stress causing tip dieback
- Fire blight caused by the bacterium Erwinia amylovora (Correct answer)
- Anthracnose fungal infection
- Verticillium wilt from soil-borne fungi
Correct answer: Fire blight caused by the bacterium Erwinia amylovora
Fire blight (Erwinia amylovora) is a bacterial disease that infects new shoot growth, causing the characteristic 'shepherd's crook' wilting and a scorched appearance. Leaves remain attached because the tissue dies quickly rather than senescing normally. It commonly affects members of the Rosaceae family including pears and crabapples.
Question 2: A certified arborist inspects a mature American elm (Ulmus americana) showing yellowing and wilting confined to one side of the canopy. Cross-sections of symptomatic branches reveal olive-green to brown discoloration streaking through the outer sapwood ring. What is the most probable diagnosis?
- Iron chlorosis due to high soil pH
- Bacterial wetwood (slime flux)
- Dutch elm disease caused by Ophiostoma novo-ulmi (Correct answer)
- Armillaria root rot
Correct answer: Dutch elm disease caused by Ophiostoma novo-ulmi
Dutch elm disease (Ophiostoma novo-ulmi) is a vascular wilt disease spread by elm bark beetles. It causes one-sided or asymmetric canopy decline, and the diagnostic hallmark is olive-green to brown streaking in the sapwood when branches are cross-sectioned, reflecting fungal colonization of the xylem vessels.
Question 3: A large white oak (Quercus alba) exhibits gradual upper canopy thinning, undersized leaves, and tip dieback. The bark at the root flare appears dark, water-soaked, and slightly sunken. Symptoms are worst after an unusually wet spring. What is the most likely cause?
- Manganese deficiency from compacted soils
- Phytophthora root rot and collar rot (Correct answer)
- Gypsy moth (Lymantria dispar) repeated defoliation
- Two-lined chestnut borer infestation
Correct answer: Phytophthora root rot and collar rot
Phytophthora species are water molds that thrive in saturated soils and attack feeder roots and the root collar. The combination of decline symptoms that mimic drought stress (because roots are destroyed), dark water-soaked lesions at the base, and correlation with wet conditions is the classic Phytophthora presentation.
Question 4: An arborist notices a thick, black powdery coating covering the leaves and stems of a crape myrtle (Lagerstroemia indica). The coating wipes off easily and does not appear to penetrate leaf tissue directly. What is the most appropriate first step in managing this problem?
- Apply a broad-spectrum systemic fungicide to the root zone
- Remove and destroy all visibly affected leaves
- Identify and control the sucking insect pest that is producing honeydew (Correct answer)
- Increase irrigation frequency to rinse the coating from leaf surfaces
Correct answer: Identify and control the sucking insect pest that is producing honeydew
The black powdery coating is sooty mold, a fungus that grows on honeydew secreted by sucking insects such as aphids, scales, or whiteflies. Sooty mold is a secondary problem — treating it directly with fungicide is ineffective. Controlling the insect pest eliminates the honeydew food source and allows sooty mold to weather away on its own.
Question 5: While assessing a declining Norway maple (Acer platanoides), an arborist excavates the root flare and discovers a large-diameter root wrapping tightly around the base of the trunk just below the soil surface, visibly compressing the bark. What is this condition called, and what is the standard treatment?
- Basal canker; apply a protective fungicide drench around the root flare
- Girdling root; carefully sever or remove the offending root (Correct answer)
- Phytophthora collar rot; improve drainage and apply phosphonate fungicide
- Crown gall; surgically excise the gall tissue and sterilize tools
Correct answer: Girdling root; carefully sever or remove the offending root
A girdling root encircles the trunk or other roots and gradually strangles the vascular tissue as both structures grow in diameter, restricting water and nutrient flow. The recommended treatment is to carefully sever or remove the girdling root, ideally when the tree is young enough that the cambium compression is still reversible.
Question 6: A red maple (Acer rubrum) transplanted three weeks ago during mid-summer shows uniform wilting and scorched leaf margins on all branches simultaneously. The soil moisture is adequate, and no insects or fungal fruiting bodies are visible. What is the most likely diagnosis?
- Verticillium wilt from soil-borne pathogens
- Transplant shock due to root system loss during installation (Correct answer)
- Bronze birch borer (Agrilus anxius) larval feeding
- Bacterial leaf scorch caused by Xylella fastidiosa
Correct answer: Transplant shock due to root system loss during installation
Transplant shock occurs when the reduced root ball cannot supply sufficient water to support the existing canopy, leading to whole-canopy wilting and marginal leaf scorch despite adequate soil moisture. Mid-summer transplanting increases the risk significantly due to high evapotranspiration demand. Verticillium and leaf scorch are ruled out by the acute onset and recent transplanting history.
Certified Arborist Test Diagnosis and Treatment 3
The branch tips of an ornamental pear tree (Pyrus calleryana) have wilted and turned dark brown-black, with new shoots bending over in a distinctive hook or crook shape.
The discolored leaves remain firmly attached.
What is the most likely diagnosis?