Arborist Practice is independent and not affiliated with the International Society of Arboriculture. These are original Diagnosis and Treatment practice questions written for study. They are not real ISA exam questions, not official ISA material, and not a replacement for the current ISA exam outline or official study materials.
Start with diagnostic reasoning, not pest memorization
Free ISA Diagnosis and Treatment practice questions are useful because this domain rewards a process: observe symptoms, look for signs, read the site history, separate biotic from abiotic causes, and choose a treatment that fits the evidence. A question may mention chlorosis, dieback, cankers, frass, conks, leaf scorch, poor growth, or old insect damage. The trap is jumping straight to fertilizer, pesticide, pruning, or removal before the diagnosis supports it.
Use this set as a focused diagnostic drill. Answer all 15 questions before checking the explanations. If you miss several questions about symptom/sign wording, pest activity, disease patterns, or treatment timing, review the ISA Diagnosis and Treatment exam questions guide before returning to mixed practice.
For broader prep, use the mixed free ISA Certified Arborist practice questions. If your diagnosis misses involve soil, water, or root-zone clues, pair this page with free ISA Soil Management practice questions and the tree risk assessment exam guide.
How to take this diagnosis quiz
Treat this as a reasoning check, not a score prediction:
- Give yourself 20 minutes for all 15 questions.
- Mark each answer as confident, uncertain, or guessed.
- For every miss, label the failure: symptom vocabulary, missing sign, host clue, site history, abiotic stress, pest timing, disease pattern, or treatment overreaction.
- Review the explanation before moving to another quiz.
- Retest the weakest category, then return to mixed-domain practice.
The ISA Certified Arborist exam outline is controlled by ISA and can change. Use the official ISA Certified Arborist credential page and the exam outline PDF as the source of truth for current domain wording and exam details.
15 ISA Diagnosis and Treatment practice questions
1. Symptom vs. sign
Which observation is a sign rather than a symptom?
A. Interveinal chlorosis on new leaves
B. Wilting shoots during hot weather
C. Fungal fruiting bodies on the trunk
D. Premature fall color
Answer: C. A sign is direct evidence of a causal agent, such as fungal fruiting bodies, insect bodies, eggs, frass, galleries, spores, or bacterial ooze. Chlorosis, wilt, and early color are symptoms: tree responses that still need interpretation.
2. Biotic or abiotic pattern
Several unrelated tree and shrub species along one street show similar marginal scorch after a week of heat, reflected pavement load, and irrigation failure. No pest signs are present. Which explanation best fits the pattern?
A. A host-specific fungal disease
B. A site-related abiotic stress
C. A borer attacking every species equally
D. A pruning wound response
Answer: B. Multiple unrelated species affected at the same time points toward environmental or site stress. Heat, drought, reflected light, and irrigation failure fit an abiotic pattern better than a host-specific pest or disease.
3. Old damage
A client wants an immediate insecticide application because old leaf-miner damage is visible. Inspection finds no active larvae, no new injury, and the tree is otherwise vigorous. What is the best response?
A. Monitor and explain that old damage does not prove active infestation
B. Apply insecticide because any visible injury requires treatment
C. Fertilize heavily to replace damaged foliage
D. Remove the tree before the pest spreads
Answer: A. Treatment should match current pest identity, activity, severity, timing, and tree condition. Old damage on a vigorous tree does not automatically justify chemical control.
4. Chlorosis and pH
A pin oak shows interveinal chlorosis on new leaves. The site has alkaline soil, no visible insect signs, and normal soil moisture. What should stay high on the diagnostic list?
A. Nutrient availability affected by soil pH
B. Chewing insect damage
C. A need for crown reduction
D. Normal seasonal color change
Answer: A. Chlorosis is a symptom, not a diagnosis. On alkaline soils, nutrient availability can be limited even when nutrients are present. Soil pH, species tolerance, root function, and testing matter before recommending treatment.
5. Root-zone history
A declining tree has crown dieback after a driveway installation. The stem shows no fresh insect signs, but the root zone was compacted and several roots were cut. Why is a simple leaf-disease diagnosis weak?
A. Leaf diseases cannot occur on stressed trees
B. Root injury and compaction can cause canopy symptoms
C. Driveways always improve soil oxygen
D. Crown dieback proves a pesticide is needed
Answer: B. Root-zone disturbance can reduce water uptake, oxygen movement, and fine-root function. Diagnosis questions often hide the cause in construction history, grade change, trenching, paving, or compaction clues.
6. Pest presence
An insect is found on a declining tree. Which next step is most appropriate before recommending control?
A. Confirm identification, host relationship, damage pattern, severity, timing, and site stressors
B. Treat immediately because insect presence proves causation
C. Remove the tree because insects always indicate irreversible decline
D. Ignore the insect because all insects on trees are harmless
Answer: A. Insects can be causal, secondary, incidental, or beneficial. A treatment recommendation needs evidence that the organism fits the host, symptoms, damage pattern, severity, and timing.
7. Canker management
A branch has a localized canker with dieback beyond the affected area. The rest of the tree is vigorous, and the canker is limited to a small branch. Which response is usually most reasonable?
A. Prune the affected branch using proper cuts and reduce stress where possible
B. Top the entire tree to remove disease pressure
C. Apply fertilizer as the only treatment regardless of site conditions
D. Remove the whole tree because every canker is fatal
Answer: A. Localized branch cankers are often managed by pruning infected or dead material when appropriate and improving tree vigor. Severe pruning, automatic fertilizer, or removal without risk/extent context is usually an overreaction.
8. Root rot clues
A tree has thinning foliage, poor vigor, and mushrooms near the root collar after repeated soil saturation. Which detail makes root or buttress decay more plausible?
A. Fruiting bodies near the root collar
B. Leaves are green in spring
C. The client dislikes the species
D. The tree was not pruned last year
Answer: A. Fungal fruiting bodies are signs. Their location matters. Mushrooms or conks near roots, buttress roots, or the lower trunk can support a decay/root disease concern, especially with saturated soil and decline. Structural implications may also overlap with tree risk.
9. Herbicide or disease?
Several plants near a lawn edge show distorted new growth shortly after a nearby herbicide application. The affected plants are different species, and symptoms are strongest nearest the treated area. What should the diagnosis consider first?
A. Herbicide exposure or drift
B. A host-specific vascular wilt
C. Lack of crown cleaning
D. Normal dormancy
Answer: A. Timing, proximity, multiple species, and a gradient from the treated area support an abiotic exposure pattern. A host-specific disease would usually not affect unrelated species in the same exposure pattern.
10. Treatment timing
A pest causes predictable early-season damage, but the damaging life stage has already passed and the tree is currently stable. What is the best exam-style answer?
A. Consider monitoring and planning correctly timed management for the next susceptible period
B. Apply any pesticide immediately because the pest name is known
C. Remove healthy branches to prevent future feeding
D. Ignore the pest forever because this year is over
Answer: A. Timing matters. If the damaging life stage has passed, immediate treatment may not help. Monitoring, client education, and planning for the correct timing can be stronger than action that misses the biology of the pest.
11. Nutrient deficiency trap
A tree has sparse leaves and poor shoot growth. The site also has compacted soil, poor drainage, and a buried root flare. What is the safest diagnostic approach?
A. Evaluate root-zone limitations before assuming fertilizer is the main fix
B. Fertilize heavily because poor growth always means nutrient shortage
C. Top the tree to reduce demand
D. Diagnose from leaf size alone
Answer: A. Poor growth can come from oxygen shortage, drainage problems, compaction, planting depth, root injury, pH, or true nutrient limitations. Fertilizer is not a substitute for diagnosis.
12. Monitoring vs. removal
A tree has minor cosmetic leaf spots, no major defoliation, no dieback, and good overall vigor. What management response best matches the severity described?
A. Monitor, reduce stress, and explain the likely limited impact
B. Remove the tree immediately
C. Apply trunk injections without identifying the disease
D. Perform severe crown reduction
Answer: A. Not every visible disease symptom requires aggressive treatment. Severity, tree condition, disease cycle, site stress, and client expectations should guide management.
13. Sampling and confirmation
A question describes ambiguous wilt symptoms that could be drought stress, root injury, or a vascular disease. No signs are provided. What is often the best next step?
A. Gather more evidence through site review, inspection, and appropriate sampling or testing
B. Choose the most expensive treatment immediately
C. Assume the first disease name that matches wilt
D. Ignore site history because symptoms are enough
Answer: A. When evidence is incomplete, diagnosis may require more inspection, history, samples, lab confirmation, or monitoring. The exam often rewards knowing when the cause is not confirmed yet.
14. Integrated pest management
Which answer best describes an IPM-style response to a confirmed pest problem?
A. Identify the pest, assess host health and damage threshold, consider nonchemical options, and use targeted treatment only when justified
B. Apply the strongest broad-spectrum product first
C. Treat every tree on the property regardless of host or symptoms
D. Ignore monitoring once a pesticide is used
Answer: A. Integrated pest management is based on identification, monitoring, thresholds, timing, host condition, cultural practices, and targeted control when needed. Broad, automatic treatment is usually a weak exam answer.
15. Decay and risk overlap
A mature tree has a conk on the lower trunk and a frequently used picnic area beneath the canopy. What is the best reason this is not only a disease-identification question?
A. Decay signs may affect likelihood of failure and target consequences
B. Conks always mean the tree must be ignored
C. Picnic areas remove the need for inspection
D. Disease questions never overlap with tree risk
Answer: A. Diagnosis can identify signs of decay, but the next decision may involve risk: defect, likelihood of failure, likelihood of impact, targets, and consequences. Review tree risk assessment exam questions if this distinction is weak.
Score guide
Use your score to choose the next study action:
- 13-15 correct: Diagnosis reasoning is probably not your main leak. Review any uncertain answers, then test related weak areas such as soil, risk, or safe work practices.
- 9-12 correct: You understand the main vocabulary but still miss applied judgment. Sort misses by category and retest that category before another mixed quiz.
- 0-8 correct: Pause mixed mocks. Review symptoms vs signs, biotic vs abiotic patterns, pest activity, disease categories, site history, PHC, and treatment timing.
A short quiz cannot predict your real exam score. The useful signal is the pattern of misses. Missing three pest-timing questions is different from missing three abiotic-stress questions.
What Diagnosis and Treatment questions usually test
Diagnosis and Treatment questions usually test evidence-based restraint:
- Symptoms vs. signs: Can you tell tree response from direct evidence of a causal agent?
- Biotic vs. abiotic causes: Can you read site-wide patterns, affected species, timing, and exposure clues?
- Pest and disease reasoning: Can you connect host, plant part, sign, symptom, severity, and timing?
- Root-zone clues: Can you notice construction, compaction, saturated soil, planting depth, and pH before treating leaves?
- Treatment fit: Can you avoid automatic spraying, fertilizing, topping, or removal when the evidence does not support it?
If an answer treats a symptom as a cause, ignores site history, assumes any insect is the problem, or chooses treatment before confirming the diagnosis, be skeptical.
How to review missed diagnosis questions
For each miss, write a one-line correction:
- “I confused a symptom with a sign.”
- “I ignored that multiple unrelated species were affected.”
- “I treated old damage as active infestation.”
- “I jumped to fertilizer before checking pH, drainage, and root function.”
- “I missed the target/risk implication of decay.”
Then drill the related page: soil management practice questions for root-zone misses, tree risk assessment for decay/target misses, and the full Diagnosis and Treatment exam guide for symptom, pest, disease, and PHC reasoning.
Where Arborist Practice fits
Arborist Practice is the practice-and-feedback layer after you understand the concepts. Use focused Diagnosis and Treatment questions to expose weak patterns, then use explanations, bookmarks, the glossary, AI tutor, and study analytics to keep those misses from repeating in full timed mocks.
A practical sequence:
- Read the Diagnosis and Treatment section in your study material.
- Take this 15-question set without notes.
- Review every explanation and label the miss.
- Drill 25 to 50 focused diagnosis questions.
- Return to a full ISA Certified Arborist practice test only after the same diagnostic traps stop repeating.
FAQ
Are these real ISA Diagnosis and Treatment exam questions?
No. They are original practice questions for study. Arborist Practice does not publish real ISA exam questions and is not affiliated with ISA.
What makes Diagnosis and Treatment hard on the ISA Certified Arborist exam?
The hard part is not only pest memorization. The exam can combine symptoms, signs, host species, site history, soil conditions, timing, and treatment choices. Many wrong answers are tempting because they are active interventions that happen before the diagnosis is strong enough.
Should I study pests or abiotic stress first?
Study the diagnostic process first, then pests and diseases. If you cannot separate symptoms from signs or biotic from abiotic patterns, pest lists will not help much under exam pressure.
How many diagnosis questions should I practice?
Use enough focused questions to find repeated mistakes, then retest after review. If diagnosis is one of your weak domains, a short free set is only a start; move into focused domain practice before relying on full mixed mocks.