Plant Pathology. for Master Gardeners in the Central Arizona Highlands Bob Gessner Master Gardener

Transcription

1 Plant Pathology for Master Gardeners in the Central Arizona Highlands Bob Gessner Master Gardener

2 Outline Plant Disease Basics Plant Problem Diagnosis Common Local Diseases Jeff s Plant Morgue Specimens Identifying the bodies and determining the perpetrators

3 Plant Pathology Study of Plant Diseases Host plants Pathogens Environmental factors Interactions of host, pathogen, and environment Management/control Genetics, molecular biology, mathematical modeling to predict disease outbreaks Disease Tetrahedron

4 So You Want to be Master Gardener! Common Questions the public will ask you: What s Wrong With My Plant? How Do I Fix It?

5 Does a problem really exist? How should this plant normally look?

6 Normal or Abnormal?

7 What is Disease? Disturbance of normal functioning (physiology) of plant Many causes and appearances biotic and/or abiotic agents continuum of potential causes Microbial pathogens to physical injuries improper pruning (topping) Potato Tuber Spindle Viroid With T7 bacteriophage DNA Conk microscopic fungus

8 Diseases vs. Nondisease Problems Disease Pathogenic organism, virus, or viroid Environmental cause Non disease problems Insect or mite pests Vertebrate pests including humans Weed competition

9 Non disease Problem

10 Diagnosing Plant Diseases If a problem exists, you may need to know: Plant species, maybe cultivar Plant part affected Foliar, stem, root, fruit problem Type of abnormality Symptoms Changes seen in plant (leaf spot, canker, etc.) Type of pathogen Signs (causal agent) Environmental factor, structures of pathogenic organism (fruiting body, spores, etc.) Septoria Leaf Spot of Tomato Septoria Fruiting Body

11 Diagnosing Plant Diseases Collect large enough sample so can identify: Plant, symptoms, signs Often the best answer is: I don t know but Septoria Leaf Spot on Tomato spores pycnidium mycelium

12 What is the plant?

13 Symptoms and Signs Symptoms (host plant) Expression of disease in host plant Plant response, damage Signs (pathogen) Organisms and there parts (fungi, bacteria, etc.) Viruses, viroids

14 Other useful Information needed to diagnose problem? Where is plant located? Has the plant been exposed to any extreme or unusual environmental conditions? How has the plant been cared for or neglected?

15 Precipitation in Arizona

16 Types of Plant Diseases Based on General Type of Causal Agent Biotic Diseases (Pathogens cause) Symptoms: on specific plants or plant parts Progression of symptoms invasion of tissues (infectious) Abiotic Diseases (Environmental factors cause) Symptoms: usually uniform on all plants No progression of symptoms (noninfectious) late blight Declines (Biotic and abiotic factors cause) Symptoms: usually from interchanging biotic and abiotic agents Stress initiates (drought, cold, heat, etc.) May not recognize original cause unless know history of problem Environment, fungi and insects may be involved Disease complexes leaf scorch beetle damage (Ips sp.)

17 Types of Plant Diseases Based on Plant Part Foliar Spots, anthracnose, mildew, etc. Stem Cankers, heart rot Root Wilts, rots Fruit Field, post harvest

18 Microorganisms cause most Plant Diseases

19 Causal Agents of Plant Disease Pathogenic organisms Fungi Cause 70 80% Bacteria Nematodes Parasitic plants Algae and protozoa Noncellular Pathogens Viruses Viroids

20 Fungi Come in Two Sizes Macroscopic Mushrooms, bracket fungi, puffballs, etc. Fruiting body visible, spores microscopic Microscopic Yeast, molds, zygote fungi, cytrids Fruiting body details and spores microscopic

21 Somatic (Non-reproductive) Structures do the Work! Molds Hypha (ae) Mycelium Septa Yeast Single cells Budding Fission Pseudohyphae Dimorphic fungi Valley Fever

22 Fungi in our Gardens Decomposers Organic debris Soil fertility Nutrient cycling Compost making Pathogens Plants Insects, nematodes, weeds, other fungi (biocontrol) Symbionts Mycorrhizae Lichens Endophytes

23 Fungi Grow on all Plant Parts One or more species specific for ever plant Over 100,000 species described, probably over 1 mil. exist Mildews, leaf spots, anthracnose, etc. Leaves Branches and trunk Cankers Heart rot Roots Rots Fruits and seeds Rots, spots, etc. Rust diseases Foliar Early Blight Stems cankers, galls, brooms diseases and/or Cones

24 Bacteria ~100 species cause plant diseases Pathovars (strains) specific for host cultivars Most bacterial plant pathogens Rod shaped cells All lack nuclear membrane (Prokaryotes) Order of magnitude smaller than our cells Many symptoms Galls, blights, cankers, leaf spots, etc. Xylem and phloem invading bacteria Infect vascular system Leaf scorch, plant decline, etc.. Pseudomonas syringae

25 Other Biotic Agents Nematodes Small round worms related to pin worms Root knot, cyst, dagger, etc. Stylet pierces plant cells Parasitic plants Mistletoe, dodder Dodder can transmit viruses Algae and protozoa Once only tropical Can cause Root rot Damping off Zoospores infect

26 Viruses and Viroids Potato Tuber Spindle Viroid With T7 bacteriophage DNA Viruses DNA or RNA surrounded by protein Vectors Insects» aphids, white flies, hoppers, thrips, beetles Mites, nematodes, plasmodiophorids Disease Symptoms Leaf yellowing (whole leaf or pattern of stripes or blotches) Leaf distortion (e.g. curling) Other growth distortions» stunting of the whole plant, abnormalities in flower or fruit formation Viroids Infectious single stranded RNA Inhibit plant manufacturing of proteins Causes stunting and distortion PTSV Curly Top Virus beet leafhopper CTV

27 Abiotic (Environmental) Factors Temperature Extremes Soil ph Light Moisture Excessive, insufficient Drought, flooding, wind Nutrition Deficiencies, excess Herbicides Damage Lightning Damage Air Pollution Damage Salt damage others Cold Damage Winter Drying Lightning Summer Heat Scorch Herbicide Damage (trifluralin)

28 Disease Determining Factors HOST Disease Tetrahedron PATHOGEN ENVIRONMENT TIME

29 Abiotic or Biotic Disease?

30 What are the possibilities? Abiotic problem Hail damage Biotic disease Caused leaves to drop Non disease problem Insect defoliation Tomato horn worm, blister beetles Vertebrate animal grazing Rabbits, pack rats, ground squirrels, javalina, deer, etc.

31 Vertebrate Animal Grazing Dixie Moose Sierra

32 Vertebrate Animal Grazing Sierra

33 Scientific Based Horticultural Information

34 Science Can t Solve Everything!

35 Science is not perfect but the scientific method is the best method we have for answering questions about the natural world!

36 Common Local Diseases and Pests Abiotic Diseases Can affect all types of plants Biotic Diseases and Pests Vegetables Fruit Trees Succulent perennials Trees and Shrubs Verde Valley Diseases Texas (Cotton) Root Rot Curley Top Virus

37 Tomatoes Leaf spots Septoria lycopersici, etc. Early Blight Alternaria solani Wilts Verticillium spp., Fusarium spp. Crop rotation, resistant varieties Wilt

38 Tomatoes Curly top virus Blossom end rot Ca deficiency in fruit Maintain even soil moisture Certain varieties more tolerant Diminished pollination Below 55⁰F or above 90⁰F Reduced fruit production Need bumble bees (buzz pollination) Curly top virus No control available Wilt

39 Pollenators

40 Beet Curly Top Virus Hosts» Tomatoes, beans, pepper, spinach, beets, and cucurbits» Many plant species, weeds Symptoms» Plants stunted, roots stunted, phloem necrosis, purple leaf veins» Chlorotic leaves curl up, leaf outgrowths Vector» Beet leafhopper (Circulifer tenellus) wild mustard, Russian thistle Prevention attention to planting date breeding resistance mostly unsuccessful weed and insect management destroy infected plants BCTV beet leafhopper

41 Squash Blossom end rot Blossom end rot Pollination problems Separate female and male flowers Mildews Powdery, downy Insects Squash bugs Vine borers Wildlife Lesser goldfinch Squash, rhubarb and sunflower Vine borers Moth Powdery mildew Squash bug Lesser gold finch damage on sunflower

42 Powdery Mildew Foliar diseases of many different plants Fungal species usually very specific to a plant group Prevention Resistant cultivars Early applications of specific fungicides

43 Powdery Mildew of Cucurbits Vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm Hosts Cucumbers, melons, pumpkins, squash most susceptible days after leaves unfold, after fruit initiated, dense growth, low light susceptible cultivars (lack wild cucurbit resistance genes) Pathogens Powdery mildew fungi, airborne conidia (spores) Podosphaera xanthii, Erysiphe cichoracearum (most common) Host specific, survive winter on plant debris Environmental conditions 69 80⁰F most favorable, 50 90⁰F infection range, stops at 100⁰F, 50% RH or higher, dry leaf surface favorable, wet unfavorable Time Symptoms 3 7 days after infection

44 Fruit Tree Diseases caused by Bacteria Fireblight Pears and apples other rose family hosts Twig blight Cankers may develop in limbs and trunks Crown gall Fruit trees, also grapes, roses, most plants Woody galls on the upper roots and crown Usually comes with the plant from nursery

45 Fastidious Vascular Colonizing Bacteria Introduced by vascular feeding insect vectors Leaf hoppers, plant hoppers, psyllids, squash bugs Most other bacteria use natural openings or wounds Live in phloem sieve tubes or degenerated xylem elements 1)Phytoplasmas and spiroplasmas >600 yellows diseases 2) Fastidious phloem colonizing bacteria (Ash Decline, etc.) 3) Fastidious xylem limited bacteria, Xylella fastidiosa» (Pierce s Disease of Grapes) + 75 other host plants Many plant hosts are symptomless Some FVCBs live and reproduce in insect vector

46 Ash Decline (Ash Yellows) Symptoms dead and dying branches new tufts of foliage ( witches brooms ) reduced in size emerges from lower branches previous two or three year s growth greatly reduced trees may die Host trees in Arizona Arizona ash (Fraxinus velutina) native Modesto ash (F. velutina Modesto ) Raywood ash (F. oxycarpa) possibly Pathogen bacterium (Candidatus fraxinii) invades phloem insects possibly may transmit Reference Backyard Gardener Jun 27, 2012 Ash Decline in Yavapai County

47 Succulent Perennials Diseases Agave anthracnose Phillosticta pad spot Pests Agave and yucca weevils Cochineal scale

48 Trees and Shrubs Leaves Mildews, leaf spots, anthracnose, etc. Aphids, scale, spider mites, etc. Branches and trunk Cankers Heart rot Borers Crown gall Roots Rots Root knot nematode

49 Bacterial Wetwood and Slime Flux Hosts Elms, mulberry, and other wounded trees Cause Bacteria grow in the bark and sapwood Smelly discolored liquid flows down branch or trunk Bacterial fermentation products Soil bacteria enter injury above or below soil line» Natural cracks, pruning cuts, etc. Will not kill the tree, more a nuisance Treatment Usually no treatment, wait for wound healing Pruning and drainage tubes not recommended

50 Cotton (Texas) Root Rot Hosts Many different trees, shrubs, vines and perennials (over 2,300 host plants) Pathogen Fungus Phymatotrichopsis omnivorum Distribution Southwest USA and Mexico Low desert areas and elevations up to at least 5000 ft Verde Valley but not Prescott Dead peach tree with leaves attached

51 Cotton Root Rot Symptoms and Signs Sudden wilting during the summer when temperatures are high Dead or dying foliage remain attached to plant Roots rotted and brown in color Strands of fungus grow on root Fungal mats found on soil surface

52 Cotton Root Rot Signs Dense web of hyphae covers the root root penetrated and decays strands grow through soil, infects healthy roots nearby Survives for long periods in soil resistent hyphal structures (sclerotia) No airborne spores or other reproductive structures spreads only by growth of the strands in soil

53 Infected root Cotton Root Rot Strands growing on the surface of an infected root Hyphal mat Strand as seen under the compound microscope

54 Cotton Root Rot Treatment rarely successful therefore not recommended plant immune or highly resistant species in infested areas Replanting monocots are immune use yuccas, grasses hardy palms in mild locations pines are very tolerant Dead peach tree with leaves attached

55 Hosts Cytospora Canker Aspen, cottonwood, other stressed deciduous trees Pathogen Orange spore masses develop in moist conditions Branches and trunk girdled Do not plant riparian or high elevation trees in dry habitats Fungus Cytospora chysosperma

56 Aspen Heart Rot, etc. Marssonina Leaf Spot Phellinus tremulae Leaf rust Decay in living trees Occurs throughout range Heart Rot

57 Hosts Seiridium Canker Leyland, Italian, and Monterey cypress Fungal Pathogen Seiridium cardinale Girdles twigs, branches, and trunk Foliage dies Cankers Multiple vertical cracks» Resin flows» Black spots (fruiting bodies) at edge Diagnose from characteristic spores in resin (Backyard Gardener Aug 10, 2011)

58 Local Rust Diseases

59 Comandra Blister Rust Cronartium comandrae Pinus brutia varieties Mondel, Eldarica, Eldar, Afghan, Turkish, Aleppo etc. also Ponderosa pine, Lodgepole Economically important host blisters, branch and trunk gurdling Bastard toadflax (Comandra pallida) Alternate host Hemiparasite on oak roots root parasite on oaks

60 Colorado Blue Spruce Yellow needles, needle drop High elevation tree grown on warmer and drier sites Stress from less moisture and higher temperatures

61 Galls on Manzanita Leaf Gall Aphid (Tamalia coweni) Fungal Leaf gall (Exobasidium vaccinii)

62 Potato Verticillium Wilt Hosts 300 species of dicot plants Tomatoes, potatoes, maple, etc. Soil fungi Verticillium dahliae, V. albo trum and V. V. longisporum Tomatoes

63 Plant Parasitic Nematodes Root knot nematode swellings in the roots interfere with the flow of nutrients and water Feed with stylet most vegetables, bedding plants, many trees and shrubs impossible to eradicate introduced with plants and soil

64 Parasitic Flowering Plants True Mistletoes Phoradendron spp. Common on hardwoods, also juniper, cypress, white fir Lower elevations Limited damage to host Birds distribute seed Dwarf Mistletoes Arceuthobium spp. Common on pines, cypress Higher elevations Can severely debilitate or kill host Forcibly discharge seeds (52ft) to

65 Dodder

66 Preventing Plant Diseases Plant Disease resistant species/cultivars Location Hardiness zone, sun/shade, moisture, exposure, soil type, soil ph Proper planting Hole shape/size, depth, staking, pruning Maintenance Water, fertilizer, pruning, pest management (IPM) Reduce stress Prevent damage

67 Managing Diseased Plants Identify cause Symptoms, signs, etc. Learn about pathogen/pest s life cycle Bulletins, etc. Online information Integrated Pest Management Prevent and manage disease with holistic approach Start with lowest impact treatment May be too late or no control may be available!

68 Low Impact Management Method!

69

70 Plant Disease Diagnosis or (What s wrong with my plant? And how do I fix it?) For each specimen provide the following information: 1) Is it a biotic disease, abiotic disease, insect pest problem, or not a problem? If you know the specific problem, write it in the blank. 2) What kind of plant is the host tree, shrub, grass or forb? If you know the species write in the name? 3) Are there any symptoms? If so describe. For example: blight, blue stain, borer holes, canker, gall, leaf spot, mildew, insect galleries, root rot etc. 4) Are there any signs? bacteria, fungi (fruiting bodies, mycelium, spores), insects, mites, parasitic higher plants, etc. 5) What do you think is the specific causal agent? fungus, bacterium, virus, insect, mite, nematode, parasitic higher plant, or specific abiotic factor 6) How would you manage this problem? a) wash off with a hose, b) use insecticidal soap, c) prune out the pathogen, d) spray a pesticide, e) change the cultural practices, f) some other method or g) no treatment is necessary 1) Biotic Disease, Abiotic Disease, Insect Pest, or Not Problem? 2) Type of Host Plant? 3) What Kinds of Symptoms are Present? 4) What Kinds of Signs are Present? 5) What is the Specific Causal Agent? 6) How could you Manage this Problem?

71 Types of Plant Diseases Based on: Plant part Leaves, stems, roots, and fruits Symptoms Expression of disease in host plant Leaf spots, cankers, wilts, etc. Signs Organisms (fungi, bacteria, nematodes) Viruses, viroids General Type of Causal Agent Biotic, Abiotic, and Declines Infectious, noninfectious, complex Type of Plant (Crop) Fruits, vegetables, flowers, trees, shrubs, etc. More common approach for gardeners

72 Disease Determining Factors HOST Disease Tetrahedron TIME PATHOGEN ENVIRONMENT

73 Fungi Cause 70 80% of plant diseases Leaf spots, mildews, rots, cankers, rusts, smuts, etc. Molds, mushrooms, and yeast Hyphae, mycelium, yeast cells Fruiting bodies, spores Sexual, asexual

74

75 What is the plant? Identification Species, cultivar Key out and/or match with picture resources Cultivated Plants» Western Garden Book (2012), Jones and Sacamano (2000) Native Plants Yavapai County Native & Naturalized Plants website Seed Plants of Northern Arizona W. B McDougall (1973) Field Guide to Forest & Mountain Plants of Northern Arizona J. D. Springer et al. (2009) SEINet website, USDA plants website Android app 2800 Arizona Wildflowers

76 Catclaw (Acacia greggi) Rust Dwarf Mistletoe

77 Cottonwood Heart Rot Ionotus munzii

78 Catclaw (Acacia greggi) Rust Dwarf Mistletoe

79 Rust Diseases

80 Resources for Researching Problems Online Yavapai County and Arizona Extension websites Diseases, insects, extension bulletins, etc. Extension web sites from other states Video Pruning videos http//cals.arizona.edu/yavapai/pruning/videos.html Printed Extension bulletins Identification manuals and other books Host indices problems and pathogens reported for host plant grin.gov/fungaldatabases/fungushost/fungushost.cfm Master Gardener Helpline Seek help from Expert (UA, national) University of Arizona, Plant Pathology Lab. observations, culturing Microscope (extension offices)

81 Vegetables Diseases Blossom end rot Curley top virus Powdery mildew Pollination problems Wilt Pests Aphids Blister beetles Flea beetles Grasshoppers Squash bugs Snail case bagworms Thrips Lesser gold finch

82 Cottonwood Heart Rot Ionotus munzii

83 Catclaw (Acacia greggi) Rust Dwarf Mistletoe

84 Rust Diseases

85 Rust Diseases

86 Recognition of Disease by Symptoms Expression of disease in host plant Plant response, damage by pathogen Biotic Diseases (Pathogens cause) Symptoms: on specific plants or plant parts Progression of symptoms invasion of tissues (infectious) Abiotic Diseases (Environmental factors cause) Symptoms: usually uniform on all plants No progression of symptoms (noninfectious) late blight Declines (Biotic and abiotic factors cause) Symptoms: usually from interchanging biotic and and abiotic agents Stress initiates (drought, cold, heat, etc.) May not recognize original cause unless know history of problem Disease complexes leaf scorch beetle damage (Ips sp.)

87 Pierce's Disease of Grapes Symptoms 3 15 months after initial infection of xylem Usually include: 1) scalding, progressive drying of the leaf from the margin toward the leaf petiole 2) browning of the scalded areas 3) dwarfing, wilting, or withering of part or all of the vine 4) gradual death of the root system 5) death of the vine within 3 to 48 months Leaf scorch of landscape and fruit trees Irregular marginal or interveinal necrosis expands throughout the leaf causing deformation and early defoliation Many plant hosts are symptomless

88 Pathogen Agave Anthracnose Fungus (Colletotrichum sp.) Causes leaf and crown lesions Hosts Agave parryi, etc. Wet and humid conditions Susceptible cultivars Prevention Resistant cultivars, fungicides

89 Phyllosticta Pad Spot Fungus Phyllosticta sp. Black fruiting bodies (pycnidia), active when moist Hosts Engelmann s prickly pear (Opuntia engelmanni), etc. See AZ Bulletin 1399

90 Iron Deficiency Chlorosis High soil ph, iron less available for some plants

91 Plant Selection Considerations Prescott Area Climate Dry (B) Koppen BSh and BWk Semiarid steppe to Midlaltitude desert Precipitation, RH below national average Day/night temperatures wide range Sun amount and intensity high Cool Plateau Highlands (Zone 2) Elevation 4,000 6,000 feet Winters mostly cold with drying winds Snow and frozen ground during coldest months Growing season frost free days Prescott ~ 150 ffds

92 Plant Selection Considerations Hardiness (0⁰F) USDA Zone 7, Sunset Zone 3A Low temperatures Am. Hort. Soc. Heat Zone Number of days >86 F Disease and Pest Resistance Natural, hybrid, grafted, GMO

93 Soil Type Plant Selection Considerations Texture Drainage ph Organic matter Nutrients Planting location Sun/shade exposure

94 Planting and Maintenance Problems

95 Common Helpline Calls insects PLANTS Thrips Aphids Bee swarm removal Pinyon scale Bark beetles Pitch moth Biting insects Insect identification Annual needle drop in evergreens Curley top virus Plant Identification Plant selection Weed control Plants toxic to live stock Riparian and high elevation tree problems Vegetable diseases and insects Tree and shrub diseases and insects Wildlife problems Gopher problems Plant sap on car problems OTHER Slime molds, stinkhorns, mushrooms, moldy soil Newly moved to town questions Many more

96

97 Fastidious Vascular Colonizing Bacteria Most phytopathogenic bacteria invade their host plants through natural openings or wounds FVCBs introduced by vascular feeding insect vectors Leaf hoppers, plant hoppers, psyllids, squash bugs Live in phloem sieve tubes or degenerated xylem elements 1) wall less phytoplasmas and spiroplasmas >600 diseases 2) Fastidious (walled) phloem colonizing bacteria (Ash Decline) 3) Fastidious (walled) xylem limited bacteria, Xylella fastidiosa (Pierce s Disease of Grapes) + 75 other host plants Many plant hosts are symptomless

98 Trees and Shrubs Diseases Ash decline Bacterial Wetwood and Slime Flux Cotton (Texas) root rot Cytospora canker Heart rot Nutrient deficiencies Mistletoes Broad leaf Dwarf Seiridium canker Comandra blister bust Verticillium wilt Pests Box elder bug Cypress bark beetles Elm leaf beetle Kermes scale Black aphids on conifers Oak aphids Pinyon needle scale Pine pitch moth Ponderosa pine bark beetles Snail case scale

99 What is the plant? Identification Species, cultivar Key out and/or match with picture resources Cultivated Plants» Western Garden Book (2012), Jones and Sacamano (2000) Native Plants Yavapai County Native & Naturalized Plants website Seed Plants of Northern Arizona W. B McDougall (1973) Field Guide to Forest & Mountain Plants of Northern Arizona J. D. Springer et al. (2009) SEINet website, USDA plants website Android app 2800 Arizona Wildflowers

100 Resources for Researching Problems Online Yavapai County and Arizona Extension websites Diseases, insects, extension bulletins, etc. Extension web sites from other states Video Pruning videos http//cals.arizona.edu/yavapai/pruning/videos.html Printed Extension bulletins Identification manuals and other books Host indices problems and pathogens reported for host plant grin.gov/fungaldatabases/fungushost/fungushost.cfm Master Gardener Helpline Seek help from Expert (UA, national) University of Arizona, Plant Pathology Lab. observations, culturing Microscope (extension offices)

101 Why learn about plant diseases? Diseases, Insects, and Weeds interfere with or destroy average of 36% of annual world crop production Diseases ~14% Insects ~10% Weeds ~12% Economic Loss $100 bil. annual loss in USA when include pesticide costs (Pimetel 2007) $220 bil. annual loss worldwide biotic diseases only (Agrios 2005)

102 Vegetables Diseases Blossom end rot Curley top virus Powdery mildew Pollination problems Wilt Pests Aphids Blister beetles Flea beetles Grasshoppers Squash bugs Snail case bagworms Thrips Lesser gold finch