Diagnosis and Treatment 2 Flashcards

A mature sugar maple (Acer saccharum) shows wilting and yellowing of leaves on one side of the crown. When you cut through a branch on the affected side, you notice an olive-brown to greenish-gray streaking in the sapwood. What is the most likely diagnosis?

Answer: Verticillium wilt

Verticillium wilt, caused by the soil-borne fungi Verticillium dahliae or V. albo-atrum, characteristically causes asymmetric crown decline and produces a distinctive olive-brown to greenish-gray vascular streaking when infected wood is cut in cross-section. This discoloration in the sapwood is a definitive diagnostic feature.

You observe a young crabapple tree in early spring with water-soaked blossoms that quickly turn brown and collapse, remaining attached to the branch. The infected shoots have a curved, 'shepherd's crook' appearance. What is the most likely cause?

Answer: Fire blight (Erwinia amylovora)

Fire blight, caused by the bacterium Erwinia amylovora, causes the characteristic 'shepherd's crook' symptom in which infected shoot tips wilt and curl downward. The blossoms turn brown and remain on the tree, which is a key diagnostic sign, especially during cool, wet spring conditions.

A client's Norway spruce (Picea abies) displays browning needles that begin on the lower branches and progress upward over several seasons. Closer inspection reveals small, dark, pimple-like fruiting bodies on the dead needles. What is the most likely diagnosis?

Answer: Rhizosphaera needle cast

Rhizosphaera needle cast, caused by the fungus Rhizosphaera kalkhoffii, is a common fungal disease of spruce trees. It causes needles to turn purplish-brown and drop, progressing from the bottom of the tree upward. The diagnostic indicator is rows of small, black, pimple-like fruiting bodies (pycnidia) visible in the stomatal rows of infected needles.

While treating a tree wound, an arborist discovers that the cambium tissue at the wound margin is brown and dry rather than white and moist. What does this finding indicate when planning treatment?

Answer: The wound edges are dead, and the tree has failed to initiate the CODIT response in that area

Healthy, active cambium tissue is white, cream-colored, and moist. Brown, dry cambium at the wound margin indicates the tissue is dead and that the tree has not successfully initiated wound closure (CODIT) in that zone. This finding is important because it signals the wound boundary is non-viable and may require removal of dead tissue before treatment or assessment for further decline.

An arborist is asked to evaluate a declining ornamental pear tree. The client reports noticing a foul-smelling, wet, dark-colored liquid oozing from a crack in the trunk during hot summer months. This liquid stains the bark and sometimes has a slightly alcoholic odor. What condition does this describe?

Answer: Bacterial wetwood (slime flux)

Bacterial wetwood, also called slime flux, is caused by anaerobic bacteria that ferment sap within the heartwood or sapwood, producing gases under pressure that force a foul-smelling, slimy liquid out through cracks or wounds. The characteristic sour or mildly alcoholic odor distinguishes it from other types of trunk oozing.

A homeowner's established dogwood tree (Cornus florida) shows small, tan-colored spots with purple halos on the leaves, and the leaf tips and margins are beginning to die. The tree has been watered with an overhead irrigation system. What cultural change should the arborist recommend as part of an IPM approach?

Answer: Switch to drip or soaker hose irrigation to keep foliage dry and reduce fungal spread

The symptoms—tan spots with purple halos on dogwood leaves—are characteristic of Spot Anthracnose or Cercospora leaf spot, both of which are fungal diseases spread by moisture on leaf surfaces. Switching from overhead irrigation to drip or soaker hose irrigation eliminates prolonged leaf wetness, which is a primary driver of fungal spread. This is a classic cultural control recommendation within an IPM framework.