1. Field Diagnosis of Plant Problems
Adapted from Dr. James L. Green (USDA CSREES, Washington, DC, USA)
‘Diagnosing Plant Problems’ and…

2. A Systematic Approach to Diagnosing Plant Damage

3. Field Diagnostic Equipment
Knife, handlens, pruners, trowel, hatchet, saw, insect net, forceps
Camera, GPS, binoculars
Packaging materials
Reference (images, pressed specimens, dried specimens, spore prints, etc)
Laboratory analysis (bags, vials, labels, cooler, etc.)
Forms for site and history information
Field testing kits (pathogens, soil)
Field references

4. Collecting Samples for Lab Analysis - Tips
Photograph plant(s) and site
Collect a range of symptoms
Set labeled samples in plastic or paper bags (as determined by type of sample) and keep in cooler/refrigerator
Do not add water or wet paper towels
Press several leaves between stiff pieces of paper
Carefully pack fleshy items
Mail early in the week

5. Five Diagnostic Steps DETERMINE THAT A ‘REAL’ PROBLEM EXISTS
Know Plant Identification and Characteristics
Normal Appearance
Abnormal Appearance
LOOK FOR PATTERNS
Uniform vs. Non-uniform Patterns
DETERMINE TIME-DEVELOPMENT
DETERMINE CAUSES OF PLANT DAMAGE
SYNTHESIZE INFORMATION
Probable cause / Management recommendation

6. 1. DETERMINE THAT ‘REAL’ PROBLEM EXISTS – Identify Plant Species and Expected Characteristics
Normal Appearance: What does this specific plant species (cultivar) or plant part look like—remember it may vary by season and location
Abnormal Appearance: There is only a ‘problem’ if plant’s appearance is abnormal for this time of year and this plant part
SYMPTOMS - Changes in growth or appearance of the plant in response to damaging factor
SIGNS - Evidence of the damaging factor

7. NORMAL PLANT STRUCTURES
Lenticels
Leaf hairs, leaf color, leaf drop
Bark patterns, bark color
Bud scale scars
Fruit/seed
. . .

8. Normal Abnormal *Triazine herbicide damage (left top)
*Natural leaf variegation on Aphelandra *Mosaic virus on palm
Abnormal

9. Left: Normal genetic varigation on Acuba-leaf croton
Abnormal
Left: Normal genetic varigation on Acuba-leaf croton
Above: Zinc chloride spray droplet drift on tomato
Normal

10. Phytophthora cinnamomi
Normal? Abnormal?
Phytophthora cinnamomi

11. Symptom: Galls Cause: ???? Root Knot Nematode—lettuce--Columbia
Galls- Inga, Bolvia
Symptom: Galls Cause: ????

12. NORMAL - ABNORMAL Leaf Drop from Evergreens
NORMAL - If drop is confined to leaves 2 or more years of age, it is a normal response. Drop will be more concentrated and apparent when the plant is exposed to environmental (nonliving) stress conditions, such as drought.
ABNORMAL - If current year’s new leaves fall, it is a problem. Drop of current year’s leaves may result from pathogen or insect attack, from chemical deficiencies and toxicities, and from environmental extremes.
NORMAL
ABNORMAL

14. ‘SYMPTOMS’ of the Causal Agent
‘Symptoms’ are changes in the appearance or growth of the plant itself in response causal agents
Wilting
Something missing

15. ‘SIGNS’ of the Causal Agent
Signs are evidence of the actual damaging organism
-Insect, mite, pathogen life stages, excrement, cast skins, etc.
-A non-uniform, expanding damage pattern

16. Symptoms
Signs
Rhododendron Lace Bug (Stephanitis rhododendri) damage - Byther et al. 1996

17. Inchworm (Geometridae) - Byther et al. 1996
Symptom OR Sign?
Inchworm (Geometridae) - Byther et al. 1996

18. Symptoms OR Signs?
Adult lacebugs and black tar spots on lower surface of leaf - Antonelli, et al. 1984

19. Eggs of the Leaf Beatle = SIGN

20. Symptom OR Sign?
Rust - Byther et al. 1996

21. 2. LOOK for PATTERNS Non-uniform Patterns *Suggest living causes
*Suggest non-living causes

22. Damage Patterns: Pattern in the ‘plant community’
On more than one plant?
On more than one plant species?
Pattern on ‘individual plant’
On entire plant or only on certain plant parts?
On certain age of growth?
On certain exposures/sites (wind, sun, low, steep, etc.)
Pattern on ‘individual plant part’

23. Uniform Patterns of Damage
Seldom expand over time
Suggests non-living factors as the cause
Usually caused by:
Mechanical Damage
Environmental Occurrences
Chemical Damage

24. Non-Uniform Patterns of Damage
Usually expand over time
Suggests living factors as the cause
Possible reasons for non-uniform patterns:
Spotty introduction of causal agent
Microenvironment favors development
Vector movement
Specific vector feeding habits
Movement to new ‘food’ sites; population increases and migration with time; life cycles

25. Pattern in Plant Community

26. Damage Patterns: Uniform -nonliving vs Nonuniform -living
Pattern in the ‘plant community’
On more than one plant?
On more than one plant species?

27. A B C D E F

28. Spray Drift – Contact Herbicide

29. Casoron runoff

30. Fertilizer Stripes

32. Patterns on Plant Canopy
A. ENTIRE OR MAJOR PORTION OF TOP IS DYING. If a major portion of the top dies suspect a problem with the roots. ALSO, LOOK FOR DAMAGING FACTORS AT THE JUNCTION OF NORMAL AND ABNORMAL PLANT TISSUE
GRADUAL DECLINE
Suggests living organisms
SUDDEN DECLINE
Suggests non-living factors such as temperature extremes affecting plant

33. Patterns on Plant Canopy
B. SINGLE BRANCH IS DYING. If scattered damage occurs in plant canopy, suspect foliar or aerial factor, not usually a root problem
GRADUAL DEATH OF BRANCH
Suspect living organism such as canker pathogen
SUDDEN DEATH OF BRANCH
Suspect non-living factor

35. Shoot Dieback . . .
Shoot dieback caused by non-living factors is sudden
Look for a clear line between living and dead tissue.
Shoot dieback caused by living factors is gradual
Look for missing plant tissue (shrunken stem, or canker), retention of dead leaves, and SIGNS!
NON-living
Living

36. Phytophthora ramorum on Rhododendron Diffuse Edge
Phytophthora ramorum
on Rhododendron
Diffuse Edge

37. Rhabdocline, a foliar fungus, on Fir

38. Canker

39. Aphid cast skins

40. Puckered leaf growth = SYMPTOM
NONuniform pattern = SIGN of Living Factor
Puckered leaf growth = SYMPTOM
Aphid cast skins = SIGN

41. Look at Patterns on Individual Plant Parts

44. Leaf Damage Patterns: Fungal Leaf Spots
Spots usually vary in size, generally round, occasionally elongate especially on stems
Spots usually not limited by leaf veins
Zones of different color or texture may develop giving the spot a bull's eye effect
Look for SIGNS!

45. Fungal Leaf Spots

46. Leaf Damage Patterns: Bacterial Leaf Spots
Bacterial leaf spots are often angular because they are initially limited by the leaf veins
Tissue may first appear oily or water-soaked when fresh, but on drying often becomes translucent and papery tan
Chlorotic halo’s common

47. Leaf Damage Patterns: Chemical Uptake
Injury from chemicals entering root or leaf tissue usually results in scorching (necrosis) of leaf margins and interveinal areas.
If uptake of toxic chemical is to fully expanded leaf, toxicity is marginal and interveinal - if to non-expanded leaf, toxicity occurs in veins.

49. Leaf Damage Patterns: Chemical--Foliar Contact
Spots are usually uniformly and evenly distributed over the leaf surface, and generally will be of uniform size
Color is usually uniform across the spot
The margin between affected and healthy tissue is usually sharp
Injury pattern does not spread with time or move to previously undamaged plants

50. Page 17

51. 3. Delineate Time Development of Damage Pattern
Progressive spread with time to other areas is characteristic of ‘living factors’
Damage that occurs but does NOT spread and usually has a clear line of demarcation indicates ‘non-living factors’
However, intensification where damage initially occurred, but with no spreading or new damage is also characteristic of ‘non-living factors’

52. ABIOTIC Causes of Plant Disease
NON-Living agents:
Mechanical Factors
Improper pruning, branch rub, cultivator damage
Physical/Environmental Factors
Temperature Extremes
Light Extremes
Oxygen and Moisture Extremes
Wind, Hail, Lightning
Chemical Factors
Pesticides, Pollution, Nutrient Disorders, Allelopathy

53. Intensification over a short period of time

54. 4. Determine Causes of Plant Damage
Distinguish among:
Living Factors
Non-living Factors
Ask Questions
Get site history
Get owner’s description of problem
Check References/Authorities
Laboratory Analysis

55. BIOTIC Causes of Plant Disease
Living agents:
Pathogens
Fungi, bacteria, nematodes, phytoplasmas, viruses
Insects and Mites
Animals
LOOK for signs along with symptoms!

57. Coconut Palm
Lightning Damage

58. Review Five Diagnostic Steps
DETERMINE THAT A ‘REAL’ PROBLEM EXISTS
Plant Identification and Characteristics
Normal Appearance
Abnormal Appearance - SYMPTOMS – SIGNS
LOOK FOR PATTERNS in community and on individual plant - Uniform vs. Non-uniform Patterns
TIME-DEVELOPMENT of the damage pattern
DETERMINE CAUSE(S)
SYNTHESIZE INFORMATION TO DETERMINE PROBABLE CAUSE
Make management recommendation