CATS Southwest Pest and Disease 2 — Questions and Answers
Question 1: Which fungal pathogen causes the 'witches' broom' symptom commonly observed on hackberry trees in the Southwest?
- Phytophthora ramorum
- Eriophyid mite and powdery mildew complex (Correct answer)
- Cytospora canker
- Armillaria mellea
Correct answer: Eriophyid mite and powdery mildew complex
Hackberry witches' broom is caused by a combination of eriophyid mites and powdery mildew (Sphaerotheca phytoptophila) acting together.
Question 2: The Emerald Ash Borer (EAB) has been detected moving into New Mexico. Which ash species native to the Rio Grande riparian corridor is most at risk?
- Fraxinus pennsylvanica (green ash)
- Fraxinus velutina (Arizona ash) (Correct answer)
- Fraxinus americana (white ash)
- Fraxinus latifolia (Oregon ash)
Correct answer: Fraxinus velutina (Arizona ash)
Fraxinus velutina (Arizona/velvet ash) is the native ash of the Southwest's riparian areas and is highly susceptible to EAB.
Question 3: A homeowner reports that their cottonwood tree has yellowing leaves with dark spots and premature defoliation each summer. The most likely cause is:
- Iron chlorosis
- Marssonina leaf spot (Correct answer)
- Septoria canker
- Cytospora blight
Correct answer: Marssonina leaf spot
Marssonina leaf spot (Marssonina populi) is a common fungal disease of cottonwoods causing dark spots and early leaf drop in the Southwest.
Question 4: Zimmerman pine moth larvae cause the most damage to ponderosa pines in the Southwest by:
- Mining needles in fascicles
- Girdling branches at crotch unions with pitch masses (Correct answer)
- Boring through the root collar
- Feeding on pollen cones
Correct answer: Girdling branches at crotch unions with pitch masses
Zimmerman pine moth (Dioryctria zimmermani) larvae bore into branch crotches and the main stem, producing large pitch masses that can girdle branches.
Question 5: Which soil condition in Albuquerque's urban landscape most predisposes trees to Phytophthora root rot?
- Sandy, well-drained caliche-free soil
- Poorly drained, heavy clay or compacted soil with overwatering (Correct answer)
- Highly alkaline soil above pH 9.0
- Extremely dry, drought-stressed soil
Correct answer: Poorly drained, heavy clay or compacted soil with overwatering
Phytophthora thrives in waterlogged, oxygen-depleted soils, making poorly drained compacted soils with excess irrigation the primary risk factor.
Question 6: The Piñon engraver beetle (Ips confusus) is best described as a:
- Primary pest that attacks healthy vigorous piñons
- Secondary pest that primarily attacks stressed or weakened piñons (Correct answer)
- Defoliator that feeds on piñon needles
- Gall-forming insect that distorts piñon shoots
Correct answer: Secondary pest that primarily attacks stressed or weakened piñons
Ips confusus is a secondary bark beetle that primarily colonizes drought-stressed, weakened, or recently dead piñon pines.
Question 7: Fire blight (Erwinia amylovora) on ornamental crabapple or pear in the Southwest is best managed during the growing season by:
- Applying systemic fungicides to the root zone
- Pruning 8–12 inches below visible infection with sanitized tools (Correct answer)
- Injecting oxytetracycline into the trunk
- Applying copper bactericide after bloom only
Correct answer: Pruning 8–12 inches below visible infection with sanitized tools
Pruning well below the visible shepherd's crook infection margin with sterilized pruners is the primary in-season management tactic for fire blight.
CATS Southwest Pest and Disease 2
Which fungal pathogen causes the 'witches' broom' symptom commonly observed on hackberry trees in the Southwest?