Free ISA Pest and Disease Diagnosis Questions and Answers — Questions and Answers
Question 1: An arborist is examining a maple tree showing dieback and chlorosis. While inspecting the trunk, the arborist finds several small, dark, mushroom-like structures growing from the bark. How would these structures be classified in a diagnosis?
- A symptom of root rot
- A sign of a fungal pathogen (Correct answer)
- An abiotic disorder indicator
- A physiological response to stress
Correct answer: A sign of a fungal pathogen
A 'sign' is the physical evidence of the damaging agent itself. In this case, the mushroom-like structures are the fruiting bodies of a fungus. 'Symptoms', such as dieback and chlorosis, are the tree's reaction to the pathogen or disorder.
Question 2: A row of linden trees planted along a newly installed sidewalk all exhibit leaf scorch and branch dieback on the side facing the street. The damage is uniform across all trees in the row. Damage on the opposite side of the trees is minimal. What is the most likely cause?
- An insect borer infestation
- A bacterial leaf spot disease
- Abiotic stress from reflected heat and/or de-icing salt (Correct answer)
- A systemic fungal wilt
Correct answer: Abiotic stress from reflected heat and/or de-icing salt
The uniform pattern of damage on one side of multiple trees strongly suggests an abiotic (non-living) factor. Reflected heat from pavement and the potential for de-icing salt spray are common environmental stressors in such locations. Biotic issues (insects/diseases) are typically more random in their initial distribution.
Question 3: For a biotic disease to develop in a tree, three components must be present, often referred to as the "disease triangle." Which of the following correctly lists these three components?
- A susceptible host, a virulent pathogen, and a conducive environment (Correct answer)
- An insect vector, a weakened host, and high humidity
- A nutrient deficiency, a virulent pathogen, and compacted soil
- A susceptible host, a mechanical injury, and a secondary pest
Correct answer: A susceptible host, a virulent pathogen, and a conducive environment
The disease triangle is a fundamental concept in plant pathology. It states that a disease will only occur if there is a host plant that is susceptible to the disease, a pathogen capable of causing the disease (virulent), and an environment favorable for the pathogen's development and infection.
Question 4: Upon inspecting a birch tree, an arborist notices several D-shaped exit holes in the bark of the trunk and larger branches. This specific sign is a key diagnostic feature for which type of insect?
- Aphids
- Scale insects
- Flatheaded borers (Correct answer)
- Tent caterpillars
Correct answer: Flatheaded borers
Flatheaded borers, such as the bronze birch borer and emerald ash borer, create characteristic D-shaped exit holes as the adult beetle emerges from the tree. This is a highly reliable diagnostic feature that distinguishes them from other wood-boring insects, which typically create round or oval holes.
Question 5: The fungal pathogen responsible for Dutch elm disease (*Ophiostoma* spp.) is primarily spread over long distances and introduced to new, healthy trees by which vector?
- Root-to-root grafts with neighboring infected trees
- Splashing rain carrying spores to fresh wounds
- Wind carrying spores from dead elms
- Native and European elm bark beetles (Correct answer)
Correct answer: Native and European elm bark beetles
Elm bark beetles are the primary vectors for Dutch elm disease. As new adult beetles emerge from infected wood, they carry the fungal spores and introduce the pathogen into healthy elms when they feed. While root grafts can transmit the disease between adjacent trees, the beetles are responsible for long-distance spread and introducing the disease to new areas.
Question 6: An arborist is assessing a large white oak in mid-summer. The client reports that leaves are browning and dropping prematurely. The arborist observes that the damage is most severe on the lower and inner branches, and the browning on the leaves is irregular and concentrated along the veins. What is the most likely diagnosis?
- Oak wilt
- Anthracnose (Correct answer)
- Bacterial leaf scorch
- Iron chlorosis
Correct answer: Anthracnose
Anthracnose on oaks typically develops in cool, wet spring weather and affects the lower and inner canopy most severely, where humidity is highest. The symptom of browning along the veins is also characteristic. Oak wilt, a much more serious disease, usually causes symptoms to appear at the top of the tree first and progress downward.
