1. Master Gardener Training Plant Pathology Greg Church, Ph.D. County Extension Agent – Horticulture, Plant Pathologist http://collincountygardening.tamu.edu Go to http://collin-tx.tamu.edu Click Publications, then Master Gardener Training Download Plant Pathology Information

2. Outline of training UNIT 1 : History of Plant Diseases & Plant Disease Concept. UNIT 2: Causal Agents. UNIT 3: The art of diagnosis. UNIT 4: Decisions on solutions.

3. What is a Plant Disease? Plant Disease: Injurious physiological processes induced by a continuous irritation of a primary causal agent resulting in characteristic symptoms. Plant pathogen: any organism that cause a plant disease Host: plant under pathogen attack

4. Basic plant functions (left) Disease interference with those functions (right) Damage by Pathogens * from Agrios, 1997

5. Brief history of Plant Diseases Plant disease (blight and mildew) is mentioned in the bible: Deuteronomy 28:22 (approx. 2000BC) and Amos 4:9 (approx. 750BC). Romans created 2 gods for rust disease on grain: “Robigo” and “Robigus”. Albertus Magnus (1200AD) conceived that mistletoe is a parasite. Robert Hooke (1667) first to associate a fungus with a disease [teliospores of a rust fungus]. M. Tillet (1755) proved that bunt disease is contagious.

6. More recent History of Plant Pathology 1855 – Bordeaux Mixture (Millardet) 1845/1846 – Irish potato famine Early 1900s – USA: Chestnut Blight (Endothia) and Dutch Elm Disease (Ceratocystis). 2003 – Homeland security takes over APHIS (Animal Plant Health Inspection Service)

7. Module 1: Plant Disease Concept

8. CONCEPT #1: Disease triangle Three factors: PATHOGEN (disease causing agent) ENVIRONMENT HOST PLANT DISEASE

9. How do disease develop Example: Virulence of disease causing agent Favorability of the environment Susceptibility of host plant Susceptibility Aggressiveness Wet Dry Disease Occurs

10. Disease CONCEPT #2: Disease Cycle Overwintering Management Infection (Invasion, Growth, and Reproduction) Host (Inoculation, Penetration) Dissemination and Reinfection Management

11. Early Blight

12. Disease Cycle: Peach Brown Rot Overseasoning Host Infection Reinfection DiseaseDisease

13. Sign and symptoms

14. SIGN The pathogen (or parts of) can be visually observed on the host plant.

15. SYMPTOM External or internal reaction or alteration of a plant due to the disease

16. Sign or Symptom? UrediosporesTeliospores

17. Symptomology Anthracnose – Describes an appearance as dark, sunken leaf, stem, or fruit lesions. – Typically describe symptoms made by fungi Ivy- Colletotrichum euonymus Ash- Gnomoniella

18. Symptomology Blight – Characterized by general and rapid killing of leaves, flowers, or stems. Rose-Botrytis Red cedar -Phomopsis Oleander - Rhizoctonia Forsythia-Sclerotium

19. Symptomology Canker – A necrotic, often sunken lesion on a stem, branch, or twig of a plant. Sycamore-Discula Holly

20. Symptomology Chlorosis – Yellowing of normally green tissue due to chlorophyll destruction or failure of chlorophyll formation Rose-iron chlorosis

21. Symptomology Damping-off – Destruction of seedlings near soil line, resulting in seedlings falling over on the ground. – Usually used to describe a fungal disease.

22. Symptomology Dieback – Progressive death of shoots, branches, and roots generally starting at the tip. Rhododendron-PhytopthoraDouglas Fir - Phytopthora

23. Symptomology Gall – A swelling or overgrowth produced on a plant. – Gall is plant tissue Rose-Agrobacterium Azalea-Exobasidium Pine-Cronartium

24. Symptomology Gall – Root-knot nematode causes galls on roots – Meloidogyne spp. Tomato-Meloidogyne

25. Symptomology Leaf spot – A self-limiting lesion on a leaf. Photinia-Entomosporium Rose-Diplocarpon Ivy-Xanthomonas

26. Symptomology Mildew – Used to describe fuzzy growth on plants. – Typically refers to mycelium and spores of fungi that are observed. Euonymous-Oodium Crape myrtle-Erysiphe Rose-Peronospora

27. Symptomology Ringspot – Circular area of chlorosis with a green center. INSV – Impatiens Necrotic Spot Virus

28. Symptomology Rosette – Short, bunchy habit of plant growth. Rose-unknown Rose rosette (UT-Knoxville)

29. Symptomology Scab – A roughen, crust-like disease area on the surface of a plant organ. Apricot-Cladosporium

30. Symptomology Scorch – “Burning” pattern on leaf margins. – Typically would indicate “water deficiency” problems. Sycamore-Xylella Oak-Ceratocystis

31. Symptomology Shot-hole – Holes on leaves. Cherry laurel-Xanthomonas (UT –Knoxville)

32. Symptomology Stunting – Result of reduced plant growth. Cotton-Sting nematode

33. Symptomology Wilt – Loss of rigidity and drooping of plant parts generally caused by insufficient water in the plant. Azalea-Cylindrocladium Rose-Verticillium

34. Module 2:Causal Agents

35. Definitions: Biotic vs Abiotic Biotic – having a mode of life, caused or produced by living beings. Abiotic – non living agent, factors of the physical environment.

36. Causes of plant diseases BIOTIC – Fungi – Bacteria – Viruses – Nematodes – Parasitic plants ABIOTIC – Temperature – Moisture – Light – Nutrition – Chemical

37. Plant Pathogens (Biotic) Majority microscopic Fungi, bacteria, viruses, nematodes, parasitic plants, spiroplasmas * from Agrios, 1997

38. Fungal Diseases Most of the common diseases occurring on landscapes are caused by fungi. 85% of plant diseases caused by fungi. Majority of fungi are saprophytic. Characteristics of fungi – Absorb nutrients – Multi-celled – Radial growth as tubular filaments – Reproduce and survive as spores – May “overwinter” as sclerotia, rhizomorph or spores. Images from the Plant Management Network Image Collections.

39. Diagnosis of fungal diseases Presence of visible fungal structures – May be observed unaided or with magnification. Can usually be cultured on artificial media for identification – Exceptions: obligate parasite such as rust and mildew fungi.

40. Fungi Damping-off Pythium sp.

41. Fungi Alternaria Petal Blight of Rose

42. Fungi Dollar spot of turf Sclerotinia homoeocarpa

43. Fungi Blackspot of roses

44. Fungi Entomosporium leaf spots

45. Fungi Powdery mildew Rose Lilac Crape myrtle

46. Fungi Rust Apple Cedar Chrysanthemum

47. Fungi Brown patch-Rhizoctonia

48. Fungi Take-all- Gaeumannomyces

49. Bacterial diseases Characteristics of bacteria – Absorb nutrients – One-celled (prokaryote) – Reproduce by fission – Survive by dormancy

50. Diagnosis of bacterial disease Leaf lesions sometimes limited by veins (angular) Ooze or streaming from cut tissue Soft rot (fruit) has foul odor Can be culture on media – Use of selective media for identification of pathogen.

51. Bacteria Bacterial scorch

52. Bacteria Galls

53. Bacteria Blights Lilacs - Pseudomonas syringae

54. Bacteria Spots Pittosporum Tomato Ranunculus

55. Bacteria Wilts Diagnostic Crassula Zucchini

56. Bacteria Soft rot Orchid Onion Potato

57. Bacteria Scabs and Cankers Cherry Peach Watermelon Blotch

58. Viral diseases Characteristic of viruses – Sub-cellular, composed of DNA or RNA surrounded by protein coat – Replicate by “hijacking” plant DNA – Require wound to enter plant cell – Require living host – Usually transmitted by a vector

59. Viral symptoms Mosaic

60. Viral symptoms Ring spot

61. Viral symptoms Other symptoms

62. Plant Parasitic Nematodes Characteristic of nematodes – Very small animals (microscopic round worms) – Typically in the soil – Usually attack roots, sometimes foliage – Reproduces with eggs

63. Plant parasitic Stylet

64. Various shape and sizes of nematodes

65. Plant Parasitic Nematodes Root knot

66. Plant Parasitic Nematodes Lesion Nematodes Lesion Nematode damage on Rose No nematode nematode

67. Plant Parasitic Nematodes Cyst Soybean Cactus

68. Plant Parasitic Nematodes Foliar Lantana African Violet Chrysanthemum

69. Parasitic plants Characteristic of parasitic plants – Obtain all or some of their needed nutrient from other plants. – Many has little or no chlorophyll. – Cause relatively few problems when compared to other disease problems.

70. Parasitic plants

72. ABIOTIC PROBLEMS Causes of abiotic problems Physical agents Temperature moisture light extremes Chemical agents soil pH or nutrient imbalances pollutants pesticides

73. Diagnosis of Abiotic Problems Eliminate all possibilities of pathogenic attack. Know history of the plant and its culture. Know the range of growing conditions for the plant Consider symptom patterns, site characteristics, involvement of other, non-related plants.

74. Abiotic problems Water

75. Abiotic problems Temperature

76. Abiotic problems Other environmental conditions

77. Abiotic problems Soil pH and Nutrient Imbalances Boron Toxicity Zinc deficiency Virus vs. Nitrogen Deficiency

78. Sanjuan.wsu.edu

79. Abiotic problems Chemicals

80. Abiotic problems More chemicals Copper on areca palm Glyphosate on tomato

81. Abiotic problem Urban blight