B.F. Bachelor of Forestry Forest Entomology and Pathology 2 — Questions and Answers
Question 1: What is 'Dutch elm disease' and what causes it?
- A bacterial wilt spread by aphids that kills elm within weeks
- A lethal vascular wilt disease caused by the fungus Ophiostoma ulmi, spread by elm bark beetles (Correct answer)
- A root rot disease caused by Phytophthora species affecting elms in wet soils
- A defoliating disease caused by a caterpillar specific to American elm
Correct answer: A lethal vascular wilt disease caused by the fungus Ophiostoma ulmi, spread by elm bark beetles
Dutch elm disease is caused by the fungus Ophiostoma ulmi (and O. novo-ulmi), vectored by elm bark beetles, which plugs the vascular system causing wilting and death.
Question 2: What is 'heart rot' in forest trees?
- A condition where the heartwood is missing due to normal aging
- A fungal decay of the heartwood, reducing structural integrity and timber value (Correct answer)
- A root disease that causes trees to blow over in windstorms
- A nutrient deficiency symptom appearing as discoloration in the center of stems
Correct answer: A fungal decay of the heartwood, reducing structural integrity and timber value
Heart rot is decay of the heartwood caused by wood-decay fungi entering through wounds or branch stubs, reducing wood strength and commercial value.
Question 3: What is 'white pine blister rust' and which species does it primarily affect?
- A bark beetle that attacks white pine in the Great Lakes region
- A fungal disease caused by Cronartium ribicola that infects five-needled pines and requires Ribes as an alternate host (Correct answer)
- A vascular wilt disease affecting all pine species equally
- An abiotic disorder caused by cold injury in white pine plantations
Correct answer: A fungal disease caused by Cronartium ribicola that infects five-needled pines and requires Ribes as an alternate host
White pine blister rust is caused by Cronartium ribicola, a rust fungus requiring both five-needled pines and Ribes (currants and gooseberries) to complete its life cycle.
Question 4: What is the role of 'mycorrhizae' in forest tree health?
- They are pathogenic fungi that cause root rot in seedlings
- Symbiotic fungi that colonize tree roots, enhancing water and nutrient uptake in exchange for carbohydrates (Correct answer)
- Bacteria that fix nitrogen in the rhizosphere of forest trees
- Soil-dwelling insects that aerate soil around tree roots
Correct answer: Symbiotic fungi that colonize tree roots, enhancing water and nutrient uptake in exchange for carbohydrates
Mycorrhizal fungi form mutualistic associations with tree roots, greatly enhancing uptake of water, phosphorus, and other nutrients, improving tree growth and stress tolerance.
Question 5: What is 'Phytophthora root rot' and under what conditions is it most severe?
- A fungal disease most severe in dry, well-drained upland soils
- A water mold disease most severe in poorly drained or saturated soils, causing root decay and tree death (Correct answer)
- An insect-vectored pathogen that targets seedlings in nurseries only
- A soil-borne virus that reduces seedling survival in reforestation projects
Correct answer: A water mold disease most severe in poorly drained or saturated soils, causing root decay and tree death
Phytophthora root rot is caused by water mold pathogens and is most destructive in saturated or poorly drained soils where zoospores can swim to infect roots.
Question 6: What is 'canker disease' in forest trees?
- An insect-caused wound on the bark that exposes sapwood
- A localized dead area on the bark or cambium caused by fungal or bacterial pathogens (Correct answer)
- A systemic disease that affects all tissues simultaneously
- A yellowing of foliage caused by pathogen infection of roots
Correct answer: A localized dead area on the bark or cambium caused by fungal or bacterial pathogens
Canker diseases are localized dead areas in bark or cambium caused by fungal or bacterial pathogens, which can girdle branches or main stems causing dieback.
B.F. Bachelor of Forestry Forest Entomology and Pathology 2
What is 'Dutch elm disease' and what causes it?