ISA Pest and Disease Diagnosis Questions and Answers — Questions and Answers
Question 1: An arborist observes that several different and unrelated tree species in a parking lot island are all showing similar symptoms of marginal leaf scorch, stunted growth, and early fall color. What is the most likely cause of these symptoms?
- An insect infestation specific to one species
- A fungal leaf spot disease
- An abiotic disorder such as soil compaction or heat stress (Correct answer)
- A bacterial blight targeting a specific plant family
Correct answer: An abiotic disorder such as soil compaction or heat stress
When multiple, unrelated species in the same location exhibit the same symptoms, the cause is most likely a non-living (abiotic) factor related to the site. Biotic problems, such as insects and diseases, are typically host-specific and would not affect a wide range of different species in the same manner.
Question 2: Which of the following is a "sign" of a pest or disease, as opposed to a "symptom"?
- Wilting leaves on a branch
- Emergence holes from a wood-boring insect (Correct answer)
- Cankers forming on a stem
- Yellowing of the foliage (chlorosis)
Correct answer: Emergence holes from a wood-boring insect
A sign is the direct physical evidence of the damaging agent (pathogen or pest). Emergence holes are physical evidence left by an insect. A symptom is the plant's reaction or alteration due to the pest or disease, such as wilting, cankers, or chlorosis.
Question 3: For a biotic disease to develop in a tree, three components must be present. This concept is commonly known as the disease triangle. What are these three components?
- A susceptible host, a virulent pathogen, and a favorable environment (Correct answer)
- An insect vector, a weak host, and high humidity
- A nutrient deficiency, a pathogenic fungus, and compacted soil
- The right temperature, the right moisture, and a point of entry
Correct answer: A susceptible host, a virulent pathogen, and a favorable environment
The disease triangle is a fundamental concept in plant pathology stating that for a disease to occur, there must be a host plant that is susceptible to the disease, a pathogen capable of causing the disease, and environmental conditions favorable for disease development.
Question 4: Upon inspecting a birch tree, an arborist notices distinct D-shaped exit holes on the trunk and significant canopy dieback starting from the top down. This evidence is most characteristic of which type of insect pest?
- Aphids
- Japanese beetles
- Flatheaded borers (e.g., Bronze Birch Borer) (Correct answer)
- Tent caterpillars
Correct answer: Flatheaded borers (e.g., Bronze Birch Borer)
D-shaped exit holes are a classic diagnostic sign of metallic flatheaded borers (Family: Buprestidae), which includes the Bronze Birch Borer and Emerald Ash Borer. Aphids are sucking insects, while Japanese beetles and tent caterpillars are defoliators; none of these create D-shaped holes in the trunk.
Question 5: An arborist is called to assess a declining oak tree. At the base of the tree, near the soil line, they find a fan-shaped mat of white mycelium under the bark. The wood has a distinct mushroom-like smell. These signs are most indicative of which common root rot pathogen?
- Fire blight
- Powdery mildew
- Verticillium wilt
- Armillaria root rot (Correct answer)
Correct answer: Armillaria root rot
White, fan-shaped mycelial mats found under the bark at the root collar are a classic diagnostic sign of Armillaria root rot. Fire blight is a bacterium, powdery mildew is a surface fungus on leaves, and Verticillium wilt causes streaking in the vascular tissue; none produce mycelial fans under the bark at the base of the tree.
Question 6: Which of the following actions best represents the principle of using cultural controls within an Integrated Pest Management (IPM) program?
- Releasing predatory insects to control an aphid population
- Spraying a targeted insecticide when pest levels exceed a threshold
- Hand-picking caterpillars off a small ornamental tree
- Improving soil drainage and sanitation to reduce the likelihood of root rot diseases (Correct answer)
Correct answer: Improving soil drainage and sanitation to reduce the likelihood of root rot diseases
Cultural controls in IPM involve modifying horticultural practices and the growing environment to make it less favorable for pests. Improving soil drainage and practicing good sanitation (e.g., removing debris) are examples of cultural controls. Releasing predators is biological control, spraying is chemical control, and hand-picking is mechanical control.
ISA Pest and Disease Diagnosis Questions and Answers
An arborist observes that several different and unrelated tree species in a parking lot island are all showing similar symptoms of marginal leaf scorch, stunted growth, and early fall color.
What is the most likely cause of these symptoms?