1. What’s Wrong With Your Plants and Why?
Biotic vs. Abiotic Problems
Plants can be injured and damaged by biotic (living) and abiotic (non-living) agents.
Based solely on symptoms, however, determining whether the condition is caused by a biotic or an abiotic agent can be challenging. In many cases, a proper diagnosis of abiotic diseases requires thorough examination of the site, knowledge of relevant past and present environmental conditions, in-depth knowledge of plant species biology, site management history, and an orderly series of tests to determine possible causes.
I’ll discuss some general characteristics that can help to differentiate between biotic and abiotic stresses.
Tony Glover
Regional Extension Agent

2. Diagnosis Can Be Tricky Without All The Facts

3. Abiotic vs. Biotic Problems
Abiotic – non-living agent (non-infectious).
Extreme temperatures
Excess or deficient water, light or nutrients
Soil compaction, soil grade changes
Damage from cultural practices: herbicides, fertilizers, pruning, mulching
Abiotic agents or factors include environmental conditions such as extreme temperatures; excess or deficient water, light or nutrients; soil compaction; and abnormal conditions such as drought, flooding and/or adverse cultural practices.
Most abiotic diseases cause generalized symptoms such as wilting, yellowing, thinning and the development of smaller than normal leaves, limited root growth or slow growth.

4. Abiotic vs. Biotic Problems
Biotic – living agent (infectious).
Pathogens - parasitic microorganisms that cause disease (fungi, bacteria, viruses, phytoplasma)
Pests – insects, mites, nematodes or mammals feeding on or damaging plants.
Abiotic agents or factors include environmental conditions such as extreme temperatures; excess or deficient water, light or nutrients; soil compaction; and abnormal conditions such as drought, flooding and/or adverse cultural practices.

5. Abiotic vs. Biotic Problems
Symptom Progression
Biotic disease – symptoms progress and nearby plants become infected.
Abiotic disease – generally a lack of symptom progression. Does not spread.
Exception – nutritional deficiency symptoms progress slowly.
The progression of symptoms is one of the most important characteristics associated with problems caused by biotic or living agents.
Diseases often exhibit both primary and secondary symptom. For example, decayed tree roots primary symptom and yellowing leaves due to damaged roots are secondary symptom. Secondary invaders in later stage of disease can also complicate diagnosis.
Look for lack of symptom progression with abiotic diseases. For example, in the case of herbicide damage, initial symptoms of 2,4-D injury include leaf deformation may initially be similar to infectious agent like a virus. However, herbicide injury the symptoms appear suddenly and new leaves may be free of symptoms indicating a lack of progression
Abiotic disease – Herbicide Injury

6. What’s Wrong? Biotic or Abiotic
Diseases are the exception, rather than the rule. Because diseases are difficult to diagnose it is often faster to rule out the involvement of other factors than to verify the presence of disease. It is important to rule out the possibility of abiotic disease problems and one of the best times to do this is during the site visit. Ruling out abiotic problems can be challenging.
But where do you start?
What’s Wrong?
Biotic or Abiotic

7. Steps in Problem Diagnosis
Know the Plant
Inspect the Site and Look for Patterns
Look for Symptoms or Signs
Examine cultural practices and weather conditions
Identify Potential Causes
Consult Resources and Reach Diagnosis

8. Steps in Problem Diagnosis
Know the Plant
Identify the species and cultivar affected
Know what problems commonly affect the species. For example:
Red Maple – Phyllosticta Leaf Spot, gloomy scale
Flowering Dogwood – Powdery Mildew, spot anthracnose

9. Steps in Problem Diagnosis
Know the Plant
What’s normal for specific plant?
Fall Needle Drop on White Pine

10. Steps in Problem Diagnosis
Know the Plant
Look at the Whole Plant (foliage, stems, branches, leaves, and roots)
Note the color, size, and thickness of the foliage
Check the trunk and branches
Examine the Roots

11. Check the Trunk and Branches
Look for wounds, cankers, exit holes and other clues
Pitch Tubes on Bark, Southern Pine Beetle

12. Check the Trunk and Branches
Sapsucker damage to sugar maple
Don’t mistake sapsucker damage for borer exit holes

15. Check the Trunk and Branches But…

16. Girdling Roots

17. Girdling Injury

18. Planted too deep

19. Deep Planting or Covered Later
Check for flare at base of trunk

20. Girdling Roots
Girdling roots are a common problem with trees that are planted too deep

21. Too Much Mulch Over The Root Ball
Problems caused by too much mulch
Keeps trunk tissue wet
Can increase rodent damage
Mulch can intercept rain and irrigation
Can keep poorly drained soils too wet
Can encourage surface roots
Can encourage development of stem girdling roots
Too much mulch was placed over the root ball. This keeps trunk tissue wet, can increase rodent damage on the buried portion of the trunk, can intercept rain and irrigation meant for the roots, can keep poorly drained soils too wet, can encourage surface roots, and can encourage development of stem girdling roots.

22. Planted too deep
Old root system has died

23. Steps in Problem Diagnosis
Inspect the Site and Look For Patterns
Determine prevalence of problem.
Large area, all plants – generally abiotic.
Scattered, localized – generally biotic.
Check for distribution of symptoms.
Uniform – generally abiotic.
Random – generally biotic.
Are the symptoms/patterns related to geography? (soil, low spot, etc)
Is the damage limited to one type of plant?
Multiple plant species - often abiotic
One species – often biotic

24. Observation of Field Patterns Abiotic Problem
Symptoms distributed in a large area. Damage pattern is uniform.
Gas leak from building

25. Observation of Patterns Random vs. Uniform
Leaf Spot (Fungal)
Marginal Leaf Scorch

26. Observation of Field Patterns Random vs. Uniform
Boxwood Phytophthora Root Rot
Oak Nutrient Deficiency

27. Observation of Field Patterns Random vs. Uniform
Random Patches
Uniform Stripes
Bermuda spring dead spot
Fertilizer application problems

28. Steps in Problem Diagnosis
Know the Plant
Inspect the Site and Look for Patterns
Look for Symptoms and/or Signs
Examine Cultural Practices and Weather Conditions
Identify Potential Causes
Consult Resources and Reach Diagnosis
Examine injured parts and list the symptoms. Is injured part chlorotic, necrotic, discolored or distorted? Are the symptoms in patches, yellowing, leaf spots?

29. Look for Symptoms and/or Signs
Symptoms - plant reactions or alterations of a plant’s appearance due to a disease or disorder.
Signs - actual presence of the pathogen, it’s parts or by-products seen on a diseased host plant.

30. Symptoms

31. Signs
Visible or physical presence of a pathogen or pest. Signs - visible presence of the pathogen, it’s parts or by-products seen on a diseased host plant

32. Steps in Problem Diagnosis
Know the Plant
Inspect the Site and Look for Patterns
Look for Symptoms and/or Signs
Examine Cultural Practices and Weather Conditions
Identify Potential Causes
Consult Resources and Reach Diagnosis
Examine injured parts and list the symptoms. Is injured part chlorotic, necrotic, discolored or distorted? Are the symptoms in patches, yellowing, leaf spots?

33. Steps in Problem Diagnosis
Examine Cultural Practices and Weather Conditions
Ask questions - Collect as much background information as possible
When was the problem noticed?
Was the damage sudden or gradual?
Has the problem spread?
How old are affected plants?
What cultural practices have been performed recently? Herbicide Sprays?

34. Hail Damage

35. Steps in Problem Diagnosis
Identify Potential Causes
Consult Resources and Reach Diagnosis
Get Laboratory Assistance
Take samples (plant, soil)
Don’t forget pictures
Synthesize Information and Identify potential causes
When you have finished collecting information about the turfgrass and site, identify potential causes.
Test likely causes and consult resources. Submit samples to agricultural or plant disease lab, soils labs; use literature and resources to reach diagnosis.

36. Most Common Diseases of 2009 Ornamentals
Phytophthora Root and Crown Rot
Boxwood, Juniper, Hydangea, Leyland Cypress, Pansy, Petunia,
Fungal Leaf Spots (Oak Leaf Blister, Anthracnose, and other leaf spots)
Armillaria Root Rot
Oakleaf Hydrangea, Cotoneaster
Pythium Root Rot
Pansy and other flowers
Powdery Mildew
Dogwood, Crape Myrtle, Rose
Botryosphaeria Canker /Dieback
Leyland Cypress, Japanese Maple, Cleyera
Bacterial Leaf Spots
Basil, Begonia, Oakleaf Hydrangea, English Ivy
Azalea Leaf Gall
Sooty Mold
Various Trees and Shrubs (Hackberry Woolly Aphid)

38. Diseases Caused by Phytophthora
Some of the most economically important and damaging diseases on woody plants in the Southeast, USA, and worldwide
The name Phytophthora derives from Greek and literally means “plant destroyer.”
Cause problems annually
Notorious Phytophthora diseases include rhododendron root rot, sudden oak death, and potato late blight.
Particularly serious in or following “wet” years
Diseases often are associated with wet or saturated soils

40. Phytophthora 101 Phytophthora species resemble fungi but are not.
They are most closely related to aquatic organisms, such as brown algae and diatoms.
Phytophthora organisms are often referred to as ‘water molds’ because they do need water to complete their life cycle.
This group of organisms produces swimming spores .

41. Disease Cycle: Phytophthora Root Rot

42. Some Trees and Shrubs Attacked
Abies – fir
Acer – maple
Arbutus – madrone
Betula – birch
Buxus – boxwood
Camellia – C. japonica
Castanea – chestnut
Cedrus – cedar
Cercis – redbud
Chamaecyparis - false cypress
Citrus - orange, lemon, etc.
Cornus – dogwood
Cryptomeria -Japanese cedar
Cupressus - cypress
Elaeagnus
Eucalyptus
Fagus – beech
Ficus - fig
Forsythia
Ilex - holly
Juglans—walnut
Juniperus –juniper
Kalmia – laurel
Malus - apple

43. More Trees & Shrubs Attacked...
Pieris – andromeda
Pinus – pine
Platanus – sycamore
Prunus - cherry, plum, etc.
Pseudotsuga - Douglas fir
Pyrus - pear
Quercus – oak
Rhododendron - rhododendron, azalea
Robinia – locust
Rosa - rose
Rubus - raspberry
Syringa - lilac
Taxus - yew
Thuja - arborvitae
Tsuga - hemlock
Vaccinium - blueberry
Viburnum -arrowwood
Ulmus – elm

44. Phytophthora as Pathogens of Woody Plants
They can attack all parts of the plant
Blight & dieback on shoots & foliage —uncommon
Cankers on stems & trunk —e.g., “bleeding” cankers – occasionally
Root & crown rots — most common

45. Symptoms—Above Ground
Appear after roots are diseased
Chlorosis & yellowing of the foliage
very slight at first, then becoming obvious
Stunted growth
Overall wilting & decline
Cankers - orange/red/brown discoloration
on stems and trunk
distinct margin between healthy & diseased tissues
Plant death

46. Phytophthora Foliage Blight

47. Trunk and Stem Cankers “bleeding” cankers - maple

48. Trunk and Stem Cankers “bleeding” cankers - Oak
Slide 28.
The next few slides show what P. ramorum cankers look like compared to cankers caused by other fungi or insects. On the left is a photo of the outer bark, showing the bleeding canker caused by P. ramorum. On the right is the same tree with the outer bark removed to reveal the inner bark under the bleeding.
outer bark
inner bark
Photo: Bruce Moltzen, Missouri Department of Conservation

49. Symptoms—Below Ground
Must expose roots for examination
this usually requires digging!
need to know what healthy roots look like!
Reduced root volume/lack of feeder roots
Roots discolored - red, brown, dark brown
healthy roots are white or off-white
Cortex sloughing/root rot
Cankers on root crown
may move up stem above ground

50. Boxwood - Cortex sloughing/root rot

51. Phytophthora Root Rot on Boxwood

52. Phytophthora Root Rot on Shore Juniper

53. Field Diagnosis
Above-ground symptoms alone usually are not diagnostic—merely indicate vascular dysfunction
Therefore, look below ground at roots & crown
Together, these may be diagnostic
Other pathogens also can cause root rot
Armillaria, Fusarium, Sclerotium, Thielaviopsis, etc.
and sometimes Pythium spp., especially on boxwood

54. Fungal Leaf Spot Diseases
Typically have tan to gray centers surrounded by a darker border
Fungal fruiting structures (pycnidia, spores, etc.) can be seen within the leaf spot
Defoliation is common
Fungi survive on fallen leaves
Prolonged leaf wetness, high humidity and poor air circulation increase disease development
Spores are spread by wind and water-splashing, but can also be spread by insects, on clothes, tools, and hands

55. Japanese Maple Phyllosticta Leaf Spot

56. Defoliation due to Entomosporium leaf spot disease - Indian Hawthorn
Less water stays on this protected area

57. Oak Leaf Blister
Common fungal disease on oaks, especially red oaks (s. red and water oak)
Disease favored by cool, wet springs
Symptoms appear in late spring as yellow, blister­like, circular, raised areas

58. Oak Leaf Blister Spots become dull brown with age
As leaves mature, become resistant to infection
Affects appearance not tree health
Fungicides not needed, but one application of chlorothalonil or mancozeb before budbreak will control disease

59. Anthracnose - Red Maple

60. Cercospora Leaf Spot – Crape Myrtle

61. Cercospora Leaf Spot

62. Cercospora Leaf Spot - Dogwood

63. Boston Ivy Leaf Spot
The fungus Guignardia bidwellii f. sp. parthenocissi causes distinct, angular, tan, spots to form on Boston ivy leaves in the spring and summer. A dark brown halo or margin along the edge of the spot is usually present. Within the tan areas, small black dots (fungal fruiting structures where new spores develop) can be observed soon after the spot reaches full size. Branch dieback occurs if the disease is very severe.

64. Armillaria Root Rot

65. Armillaria Root Rot – Oakleaf Hydrangea

66. Armillaria Root Rot - Oakleaf Hydrangea

67. Armillaria Root Rot -Oak

68. Armillaria Root Rot - Rose
White fungal growth under bark
Drainage?
Irrigation? Death by watering hose?
No fungicides for control
Resistant plants best replacement option

69. Bacterial Leaf Spots
Plant wetness, high humidity and warmer temperatures favor disease development
Bacterial cells spread by water splashing, tools, hands, or insects
No Fruiting structures in spots
Many controlled with copper fungicides (Kocide)
Oak Leaf Hydrangea
Angular leaf spots running along veins

70. Bacterial Leaf Spots
‘water soaked spots’
English Ivy
Hydrangea

71. Sooty Mold
Common name for group of black-colored fungi that grow on honeydew on plants and other surfaces
Fungal growth gives appearance of being covered with a layer of soot
Honeydew produced by aphids, mealybugs, soft scales, whiteflies
Control sooty molds by controlling the honeydew producing insect. Drenches with Merit or Safari for hackberry aphids (early spring)
Sooty mold on crape myrtle

72. Asian Woolly Hackberry Aphid
Multicolored Asian lady beetle pupa

73. Azalea Leaf Gall Occurs in cool, moist springs
Spores for next year’s infection are released when leaf galls turn white
Prune infected leaves
Leaves, and occasionally flower buds, become deformed, developing pink or white, soft fleshy growths called galls.

74. Camellia Leaf Gall
Leaves, and occasionally flower buds, become deformed, developing pink or white, soft fleshy growths called galls.
Spores for next year’s infection are released when backside of leaves turn
white
Camellia leaf gall early symptoms and last
year’s infected leaves

75. Leaf Gall Control
Remove galls and destroy before they turn white with spores
Disease most severe when foliage becomes wet during leaf expansion in spring.
Avoid planting in heavy shade
Avoid wetting foliage in spring
If the disease was severe in previous years and galls were too numerous to pick, apply a fungicide before new leaves and flowers emerge.
Applications can stop when leaves become full size
Bayleton. Apply first spray as new leaves and flowers appear. Repeat 2-3 times at 10-day intervals.
Problem: Some leaves have red or yellow spots. Other leaves, and occasionally flower buds, become deformed, developing pink or white, soft fleshy growths called galls.
Remove galls by hand. Apply first spray as new leaves appear. Repeat 2-3 times at 10-day intervals. Plant Azaleas resistant to leaf gall

76. Powdery Mildew Common disease on dogwood and other plants
Looks like baby powder
Use Resistant Cultivars:
Cherokee Brave, Karen’s Appl. Blush, Kay’s Appl. Mist, Jean’s Appl. Snow
Start sprays at first sign of disease (early May)
Fungicides:
Heritage
Spectricide Immunox
Fertilome Systemic Fungicide
Fertilome Halt Systemic Fungicide
Powdery mildew will reduce growth
Once leaves are white fungicides are of little value

77. Too late for fungicides

78. Spot Anthracnose
Small reddish spots on bracts and leaves, trees in sun
Rake leaves in fall
Heritage, Daconil, Mancozeb, Halt, Immunox
Spray before budbreak, after bract fall, and one month later, and September after new flower buds form
Heritage, Daconil, Dithane/Protect, 3336, Eagle
Heritage, Daconil, Dithane/Protect, 3336, Eagle

79. Dogwood Anthracnose Different disease than spot anthracnose
Spots with reddish or purple borders
Spots enlarge over time
Leaf, twig blights, cankers, can kill tree
Blighted leaves remain attached through winter
Resistant Cultivar ‘Appalachian Spring’

80. Hydrangea – Leaf Spot
Several fungi cause leaf spots on hydrangea – Cercospora, Corynespora, Colletotrichum
Often in combination with powdery mildew
Adequate plant spacing for good air circulation
Avoid watering late in the day
Remove fallen leaves
Apply fungicide at first sign of disease:
Heritage, Daconil*, Immunox Mancozeb*, Fertilome Systemic Fungicide
* Poor control of powdery mildew, but good leaf spot control
Ultra-fine Spray Oil

81. Leyland Cypress Problems

82. Botryosphaeria Canker
J. Woodward - UGA

83. Botryosphaeria Canker
UGA
J. L. Williams-Woodward - UGA

84. Control of Canker Diseases
Difficult to control once infection has occurred
Prevent canker diseases by proper establishment and care:
Plant in well drained soils
adequate plant spacing
Irrigate plants to prevent drought stress, mulch plants
Remove branches with cankers. Trace the dead wood back to the base of the canker and prune at bud or branch fork. Prune 4-6 inches below canker.
Sterilize pruning tools frequently
Avoid canker susceptible plants
Fungicides are of little value

85. Thank You