Certified Arborist Test Diagnosis and Treatment 3

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?

Accepted Answer

Fire blight caused by the bacterium Erwinia amylovora

Answer

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?

Accepted Answer

Dutch elm disease caused by Ophiostoma novo-ulmi

Answer

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?

Accepted Answer

Phytophthora root rot and collar rot

Answer

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?

Accepted Answer

Identify and control the sucking insect pest that is producing honeydew

Answer

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?

Accepted Answer

Girdling root; carefully sever or remove the offending root

Answer

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.

Certified Arborist Test Practice Test

Certified Arborist Test Practice Test

Certified Arborist Test Diagnosis and Treatment 3