▪ Uniform – generally abiotic ▪ Random – generally biotic
Observation of Patterns
Scattered symptom distribution
Photo: R. Billings, Texas Forest Service,
crops
Plant Problem Diagnosis Steps
3. Investigate symptom progression.
▪ Biotic disease – symptoms progress and nearby plants become infected.
▪ Abiotic disease – generally a lack of symptom progression. Does not spread. ▪ Exception – nutritional symptoms progress slowly.
Loblolly pine killed by southern pine beetle
Random pattern of damage
Observation of Patterns
Symptoms distributed in a large area. Damage pattern is uniform.
▪ Pests – insects or mammals feeding on or damaging plants
Plant Problem Diagnosis Steps
2. Consult literature resources for possible diseases and disorders.
植物病害的诊断
Plant Problem Diagnosis
Diagnosis –process used for the identification of problems.
Tools:
▪ Plant sciences, especially plant pathology and entomology
▪ Indexes listing hosts and their pathogens
▪ Websites providing information ▪ Books with background info and
host/pathogen lists ▪ Compendia for information on specific
7. Review environmental conditions.
▪ Temperature extremes ▪ Drought or excess rain ▪ Soil type and conditions
8. Check host specificity – many hosts
may mean an abiotic problem
Plant Problem Diagnosis Steps
4. Ask questions
✓ When was the problem noticed? ✓ Was the damage sudden or gradual? ✓ How old are affected plants? ✓ Percentage of plants affected? ✓ What is the degree of injury?
▪ Recognize healthy plant appearance.
▪ What’s normal for specific plant? ▪ Compare with healthy plants of same genus,
species and cultivar.
Plant Problem Diagnosis Steps
Plant Problem Diagnosis Steps
9. Check for symptoms and signs.
1. Consider the Possible Agents:
▪ Abiotic – non-living agent
▪ Damage from chemicals, weather, mechanical
▪ Nutritional problems
▪ Biotic – living agent
▪ Pathogens - parasitic microorganisms that cause diseases
▪ Arts of investigation and detective work
Preliminary Considerationant
▪ Proper plant identification is critical.
▪ Scientific vs. common names ▪ Variety or cultivar
Plant Problem Diagnosis Steps
5. Observe patterns.
▪ Determine prevalence of problem ▪ Large area/All plants – generally abiotic
▪ Scattered, localized – generally biotic ▪ Check for distribution of symptoms
Used by permission of M. Williamson
Cotton field with chemical damage
Plant Problem Diagnosis Steps
6. Review cultural practices.
▪ Proper planting technique ▪ Fertilizer and pesticide application ▪ Irrigation frequency