PLANT DISEASE CONCEPTS. Guy J. Mussey Virginia Cooperative Extension

Transcription

1 PLANT DISEASE CONCEPTS Guy J. Mussey Virginia Cooperative Extension

2 DEFINITION Disease: any deviation in normal functioning of a plant caused by some type of persistent agent

3 Damage Disease Disorder

4 Persistent agent Continuum

5 More definitions Pathogen: any agent that causes disease 1. Biotic; fungus, bacteria, etc. 2. Abiotic; air pollution, environmental Symptom: characteristic signature of the pathogen and host resulting from the interaction of specific pathogens and hosts

6 And more definitions Signs - the actual causal agent of the disease such as fruiting bodies of fungal diseases Host specificity - pathogens that infect a limited number of related or unrelated hosts

7 Three Categories of Disease 1. Abiotic Plant Diseases 2. Biotic Plant Diseases 3. Decline Plant Diseases (Trees & Shrubs)

8 Comparison of Differences Symptoms Signs Host Specificity Spatial Distribution

9 Abiotic Diseases Symptoms - usually uniform in symptom expression and general distribution Signs - none Host Specificity - similar symptoms on two or more unrelated hosts Spatial Distribution - usually nonrandom

10 Biotic Diseases Symptoms - produced on specific plant parts, progressive invasion of tissues Signs - fruiting bodies and other structures Host Specificity - usually host-specific on related hosts Spatial Distribution - usually show a random but clumping distribution pattern

11 Decline Diseases Symptoms - progression of symptoms on individual plants & between plants, reduction of growth Signs - fruiting bodies and other structures Host Specificity - usually host-specific on related hosts Spatial Distribution - random distribution within a given location

12 Abiotic Agents 1. Nutrient deficiency and toxicity 2. Salt 3. Air pollution

13 Nutrient Deficiencies & Toxicities Imbalance of nutrients such as nitrogen (N), phosphorus (P), potassium (K), calcium (C), magnesium (Mg), sulfur (S) and micronutrients Symptoms range from interveinal chlorosis to discoloration of leaves to stunted growth

14 Mobile Nutrients Nitrogen Phosphorus Potassium Magnesium Zinc

15 Iron Chlorosis

16 Magnesium Deficiency

17 Nitrogen Deficiency

18 Salt 1. Chloride accumulation in leaves and growing points 2. Changes in soil structure due to sodium cations 3. Decrease in moisture availability

19 Salt Damage on Taxus

20 Biotic Agents Nematodes Viruses Bacteria Mycoplasmas Fungi

21 Nematodes Plant parasitic nematodes have spear-like mouthparts called a stylet. Stylet used to pierce root cells to suck cell contents Two groups of plant parasitic nematodes ectoparasites - feed outside root endoparasites - feed inside root

22 Nematode

23 Mode of Pathogenicity Direct injury due to feeding Produce wounds for infection Vector viruses Parasitize mycorrhizal fungi Contributing factor in decline diseases

24 Ectoparasitic Nematode

25 Symptoms of Nematode Disease Similar to nutrient deficiencies growth reduction sparse yellow foliage reduced size of foliage premature leaf drop abnormal wilting during hot, dry periods

26 Root Knot Nematodes endoparasites over 1,500 plant species parasitized produces galls on roots

27 Control of Nematodes Chemical nematocides soil sterilants Cultural crop rotation nonhost cover crops resistant varieties fallow periods between crops

28 Viruses Infectious agents composed of nucleic acid and protein obligate parasites seldom produce plant mortality enter host through slight injuries or injected by insect vectors naming based on the symptoms they produce, ex. Tobacco Mosaic Virus

29 Examples of Viral Diseases tobacco mosaic virus (TMV) tobacco ringspot virus (TRV) elm mosaic virus (EMV) apple mosaic virus (AMV) cherry leafroll virus (CLV) potato virus Y (PVY) oak mosaic virus (OMV)

30 Symptoms of Viral Diseases flower color streaks foliage ring spots and flecks necrotic lesions mosaic or mottling patterns veinal or marginal chlorosis line patterns curling and dwarfing witches brooms and rosettes

31 Tobacco Mosaic Virus on Tomato

32 Virus Disease - Veinal Chlorosis

33 Control of Viral Diseases Chemical none Cultural discard diseased plants prevention spray insecticides for vector virus free plants produced by tissue culture

34 Bacteria Produce disease by enzymatic maceration of cell walls, secretion of toxins, and interference with cell division and differentiation. Cannot actively penetrate and infect plants. Enter through wounds, natural openings and insect vectors.

35 Symptoms of Bacterial Disease Water soaking of leaves and stems followed by necrosis infection of vascular tissue produces wilting crown galls slime flux in trees

36 Water Soaking Symptom

37 Examples of Bacterial Diseases bacterial cankers leaf blights crown galls shoot blights, ie., fire blight wetwood vascular wilts

38 Crown Gall

39 Fire Blight

40 Bacterial Wetwood/Slimeflux

41 Control of Bacterial Diseases Chemical antibiotic sprays insecticidal sprays for insect vectors Cultural elimination of infected plant parts, ie., pruning quarantines soil aeration

42 Mycoplasmas prokaryotic microorganisms - no cell wall, very little known chlorosis of foliage (yellows diseases) aster yellows elm phloem necrosis produces clusters of short stems and chlorotic foliage (witches brooms) leafhoppers - vectors

43 Characteristics of Fungi mycelial growth form reproduce by spores Basic Requirements Lack of chlorophyll specific nutrient requirements oxygen free water temperature range: 32 0 to F

44 Fungi Pathogen All three factors interact to produce disease. Manipulate any one factor to control disease. Plant Environment

45 Classification Saprophytes - utilize dead substrates Obligate parasites - parasitize only living hosts Facultative parasites - attack living hosts that are weakened by other stress factors

46 Types of Fungal Diseases Foliage Diseases Rust Diseases Canker Diseases Vascular Wilt Diseases Root Rot Diseases

47 Foliage Diseases wet, cool weather usually infect lower foliage most are both parasitic and saprophytic symptoms similar to other foliage disorders

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49 Examples of Foliage Diseases Septoria leaf spot Anthracnose Powdery mildew Leaf blister Needle blight

50 Septoria Leaf Spot

51 Discula Anthracnose on Dogwood

52 Powdery Mildew

53 Oak Leaf Blister

54 Phomopsis Tip Blight

55 Control of Foliage Diseases Preventive fungicides Selection & breeding Site selection & manipulation Species selection

56 Rust Diseases Obligate parasites Require two different hosts Can infect foliage or succulent shoots Temperature & moisture sensitive

57 Examples of Rust Diseases Cedar Apple Rust White Pine Blister Rust

58 Cedar Apple Rust

59 White Pine Blister Rust

60 Control of Rust Diseases Eradication of alternate host Disease resistant varieties Fungicides Cultural controls

61 Canker Diseases Facultative parasites Infect stems and branches Annual cankers - invade wounds, usually last one year Perennial cankers - target cankers Diffuse cankers - produce toxins

62 Three Types of Cankers: Annual cankers are quickly overcome by host defenses Perennial target cankers show cycles of infection, host defense, etc. Diffuse cankers are characterized by poor to no host defense

63 Annual Cankers

64 Fusarium Canker

65 Perennial Target Cankers

66 Nectria Canker

67 Eutypella Canker

68 Diffuse Cankers

69 Chestnut Blight

70 Cytospora Canker

71 Hypoxylon Canker

72 Seiridium Canker

73 Control of Canker Diseases Keep trees healthy Sanitation - prune out limbs with canker

74 Vascular Wilt Diseases Organisms invade vessels and disrupt water movement causing wilting Invade plant through wound in stem or through roots Darkened streaks inside stems often present Rapid drooping of green leaves during hot weather

75 Examples of Wilt Diseases Dutch Elm Disease Oak wilt Verticillium wilt

76 Dutch Elm Disease

77 Oak Wilt

78 Verticillium Wilt on Maple

79 Control of Wilt Diseases Sanitation - remove and dispose of all diseased plants Do not replant in infected sight Control of insect vectors when necessary

80 Root Rot Diseases Two types: Structural root rots Absorptive (feeder) root rots Symptoms structural root rots Fruiting bodies at base of tree No obvious symptoms in canopy Trees easily windthrown

81 Examples of Root Rot Diseases Armillaria - structural Ganaderma - structural Phytophthora Pythium Fusarium

82 Ganaderma Root Rot

83 Ganaderma Root Rot on Willow

84 Phytophthora of Rhododendron

85 Pithium

86 Controls of Root Rot Diseases Maintain healthy plants Soil drenches for some types Fumigation in greenhouses and liner beds

87 Non Disease Fungal Problems Artillery Fungus (Sphaerobolus sp.) Dog Vomit Fungus

88 Artillery Fungus

89 Artillery Fungus Colonize dung or other organic matter such as wood mulch, wood benches and wood sheds Not pathogenic to plants or animals Propel sticky spore packages several feet towards light Usually a problem in Spring or Fall

90 Dog Vomit Fungus (Fuligo septica)

91 Dog Vomit Fungus Not a fungus actually a slime mold Not harmful to plants or animals Can appear overnight Colonizes decaying wood No controls necessary

92 Decline Disease Caused by the interaction of a number of interchangible, specifically ordered abiotic and biotic factors to produce a gradual general deterioration, often ending in the death of trees. Category not accepted by all forest pathologists

93 Complex declines involve three sets of factors: Predisposing factors Inciting factors Contributing factors

94 Factors of Decline Disease Predisposing factors Static, nonchanging climate, soil type, site, genetic potential result in permanent stress Inciting factors short in duration biological or physical insect defoliators, frost, drought, salt

95 Factors of Decline Disease (cont) Contributing factors produce noticeable symptoms on weakened host bark beetles, canker fungi, root rot, etc. persistent, often blamed for problem better understood as indicators of weakened host generally finishes off host

96 Death Spiral

97 An Example of a Decline Disease Maple Decline Predisposing factors roadside and urban conditions of soil compaction impeded drainage poor soil aeration heat air pollution

98 Maple Decline (cont) Inciting factors salt damage from deicing materials root damage from urban construction defoliating insects Contributing factors Armillariella mellea root rot Verticillium wilt

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