CCA Pest Diagnostics and Disease Management 2 — Questions and Answers
Question 1: Fungicide application for managing gray leaf spot in corn is most economically justified at which growth stage?
- V6
- V10
- VT to R1 (Correct answer)
- R4 to R5
Correct answer: VT to R1
Fungicide applications for gray leaf spot are most cost-effective at VT (tasseling) to R1 (silking) when disease is moving into the upper yield-determining canopy.
Question 2: Crop rotation is the most effective long-term management strategy for which soybean pest?
- Soybean rust
- Soybean cyst nematode (SCN) (Correct answer)
- Sudden death syndrome
- White mold
Correct answer: Soybean cyst nematode (SCN)
Rotating to non-host crops like corn starves SCN populations because the nematode cannot complete its life cycle without soybean roots.
Question 3: Seed treatments containing metalaxyl or mefenoxam are specifically effective against which class of plant pathogens?
- Ascomycete fungi
- Oomycetes (water molds) (Correct answer)
- Basidiomycete fungi
- Bacterial pathogens
Correct answer: Oomycetes (water molds)
Metalaxyl and mefenoxam are phenylamide fungicides that specifically inhibit oomycetes such as Pythium and Phytophthora, which cause damping-off and root rots.
Question 4: Which cultural practice best reduces white mold (Sclerotinia stem rot) pressure in soybeans?
- High seeding rates to ensure stand
- Narrow row spacing for faster canopy closure
- Wide row spacing to improve canopy airflow (Correct answer)
- Early planting before apothecia develop
Correct answer: Wide row spacing to improve canopy airflow
Wide row spacing improves air movement through the canopy, reducing humidity and slowing ascospore infection by Sclerotinia sclerotiorum.
Question 5: The economic threshold (ET) for applying a pest control measure is defined as the pest level at which:
- Crop damage first becomes visible
- The cost of treatment equals the economic value of damage prevented (Correct answer)
- 25% of plants show visible symptoms
- Yield loss exceeds 5%
Correct answer: The cost of treatment equals the economic value of damage prevented
The economic threshold is the pest density at which the projected economic loss from the pest equals the cost of the control action, making treatment economically justified.
Question 6: Which management approach is considered the foundation of integrated disease management (IDM) because it provides season-long protection with no additional input cost?
- Foliar fungicide applications
- Planting disease-resistant varieties (Correct answer)
- Crop rotation alone
- Biological seed treatments
Correct answer: Planting disease-resistant varieties
Disease-resistant varieties provide season-long protection encoded in plant genetics at no additional per-season cost, making them the cornerstone of integrated disease management.
CCA Pest Diagnostics and Disease Management 2
Fungicide application for managing gray leaf spot in corn is most economically justified at which growth stage?