The Disease Triangle. Susceptible host plant Pathogen Favorable climate Time. Time. Host Plant

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1 Plant Diseases

2 The Disease Triangle Susceptible host plant Pathogen Favorable climate Time Time Host Plant

3 Diseases and Pathogens Can be spread or transmitted to other plants Caused by biotic or living organisms called pathogens - fungi - bacteria - viruses - nematodes - phytoplasmas - parasitic plants

4 Vector Means by which a pathogen is spread Vector can also be wind, rain splash, insects, humans, soil, and pruning tools Example: elm bark beetles spread the fungus that causes Dutch elm disease, so the beetles are the vector of the disease

5 Types of Disease Symptoms Blight Leaf spot Mosaic Stunting Marginal necrosis Distortion Wilt Canker Gall Rot Witches Brooming

6 Blight Large dead areas on leaves, shoots or flowers

7 Leaf Spots Small, discolored areas on foliage

8 Mosaic Patches of yellow and green tissue on a leaf

9 Stunting Abnormally small size of plant or plant part

10 Marginal necrosis Brown, dead tissue around the edges of leaves

11 Distortion Twisting or abnormally shaped leaves and shoots

12 Wilt Flaccid, limp condition of leaves or shoots resulting from water deficiency

13 Canker Localized, often sunken, dead area on a twig, branch, or stem

14 Gall Abnormal swelling of a portion of a branch, leaf, root or bud, a tumor

15 Rot Tissue breakdown or decay

16 Witches brooming Twig growth resulting from a lack of apical dominance causing side shoots to elongate equally, forming a dense cluster or broom-like mass of twigs

17 Fungal pathogens Fungi (sing. fungus) Cause the majority of plant diseases Rots, cankers, leaf spots, blights, blotches, and wilt diseases Spread by insects, wind, rain, pruning tools, infested plant tissue, soil Need water for disease development Most fruiting bodies are tiny and look like black pepper to the naked eye Spores emerge from the fruiting bodies

18 Fungal Diseases Apple scab Powdery mildew Black spot on rose Leaf curl and leaf blister Cedar rusts (apple, hawthorn, quince) Anthracnose (sycamore, ash, oak) Guignardia leaf blotch Cankers (Thyronectria, Nectria, Botryosphaeria) Black knot Volutella

19 Apple scab Most common crabapple disease Begins as olive-green leaf spots with fuzzy edges Leaves eventually turn yellow and fall off Also infects fruit Very common in wet springs

20 Powdery mildew Affects many woody and herbaceous plants, including vegetables Common during periods of warm days and cool, wet nights More severe when air circulation is poor Look for white to gray powdery appearance on leaves May affect winter hardiness

21 Black spot of rose Affects rose species Symptoms - black spots with fringed margins on usually the upper leaf surface Infected leaves turn yellow and drop from the plant

22 Leaf Curl or Leaf Blister (Taphrina) Fungus that causes blister-like distortion of leaves Hosts include: Peach (Peach leaf curl) Oaks (Oak leaf blister) Plums (Plum pockets) All caused by Taphrina fungus respective to their host

23 Oak leaf blister Peach leaf curl Plum pockets

24 Oak leaf blister Leaves form blisters that are at first yellow to gray, become red or brown, leaves may drop prematurely Not usually a significant problem May lose leaves in serious infection Fungus overwinters in bud scales Spores germinate in spring as buds break

25 Three kinds of cedar rusts Cedar apple rust Junipers and crabapple or apple leaves Cedar hawthorn rust Junipers and hawthorn leaves Cedar quince rust Junipers and fruits and twigs of rose family plants, especially hawthorns

26 Cedar apple rust Forms large galls on junipers which grow orange tendrils in spring rains Spores are released as tendrils dry Infection causes spots on apple leaves Spores are released from spots Spores landing on juniper twigs can cause galls

27 Cedar Hawthorn Rust Forms smaller galls on junipers which grow orange tendrils in spring rains

28 Cedar Quince Rust Does not form galls on junipers, but lives in trunk and twigs Forms gelatinous masses in spring rains which release spores

29 Anthracnose A term used to designate diseases caused by morphologically similar fungi Some anthracnose diseases are only leaf diseases and some also attack twigs Common hosts are sycamores, maples, oaks, and ash

30 Sycamore Anthracnose American sycamore is host Common fungal disease in cool, wet weather Kills leaves, buds, shoots and one year old twigs, causes witches brooming Trees leaf out a second time, but pay a price in energy

31 Ash Anthracnose Symptoms: large irregular tan to brown lesions that form on expanding leaflets Leaves become distorted Damage is aesthetic Disease overwinters in fallen leaves In spring, spores are blown onto newly emerging leaves

32 Oak Anthracnose Can show three different patterns depending on when leaves were infected When infected early, young leaves brown and shrivel When infected later, large irregular dead areas on distorted leaves When infected late, small necrotic spots on leaves

33 Guignardia leaf blotch Common on horse chestnuts and buckeyes Brown leaf blotches with a yellow border Can see black pepper-like fruiting bodies

34 Canker Diseases Causes dieback and wilting Cankers form on infected bark and sapwood beneath canker becomes discolored brown Disease is more severe on stressed plants Usually a chronic problem

35 Thyronectria canker Most common canker disease on honey locusts Cankers girdle branches and cause branches to die Fruiting bodies form at the junction of living tissue and dead twigs More common on trees suffering from drought stress

36 Nectria canker Perennial canker disease of many hardwoods Destroys cambium No chemical control Avoid wounding trees Keep trees healthy

37 Botryosphaeria canker Common fungal canker disease on many trees and shrubs Common hosts: apple, ash, crabapple, dogwood, elm, holly, honeylocust, linden, maple, mountain ash, oak, pine, redbud, rhododendron, and sycamore

38 Volutella on Boxwood Fungal canker disease which causes stem dieback Damage looks similar to winter injury

39 Black knot Serious fungal disease of plums and cherries Can stunt or kill tree Causes dark fungal galls, which eventually girdle branch, killing it

40 Vascular diseases (wilt diseases) Verticillium wilt Dutch elm disease Oak wilt Pine wilt

41 Verticillium wilt Soilborne disease that affects over 300 plants Acute or chronic problem Fungus produces toxins that causes tyloses to plug up xylem Streaking seen under bark Usually not seen until middle of summer

42 Dutch elm disease Begin seeing new infection symptoms starting in June Initially flags are seen caused by production of tyloses Flags enlarge and spread throughout the tree Streaking under bark Trees eventually die

43 Oak wilt Fungal disease Similar action to Dutch elm disease Tree wards off fungus by forming tyloses which plugs xylem Branches wilt Streaking under the bark

44 Red oak group Red oaks more susceptible than white oaks Symptoms usually appear in late spring, early summer Leaves turn bronze and fall off tree in summer Kills red oaks within 4 6 weeks Spread by beetles, root grafts White oak group Leaves become straw colored from the leaf tip, but remain attached to branches Infection occurs in crown Branch die back occurs Usually takes several years to tree to die White oak group may temporarily wall-off the fungus

45 Bacteria (sing. Bacterium) Microscopic organisms Require a vector and natural opening or wound to penetrate plant tissue Spread by wind, rain, insects, pruning tools Cause leaf spots, rots, bacterial galls, wilts and cankers

46 Bacterial Diseases Bacterial blight of lilac Crown gall Wetwood and slime flux Fireblight Bacterial leaf scorch

47 Bacterial blight of lilac Leaves develop brown spots or blotches, often with yellow haloes, which coalesce and may eventually turn the entire leaf brown Shoots and flowers may turn brown and limp, flower buds turn black Prevalent in rainy seasons or with frequent overhead irrigation when tissues are succulent

48 Crown gall Bacterial disease that causes tumor-like growths on lower stem near the soil line Gall can girdle stem and kill all growth above it Many hosts, especially common on ground cover Euonymus Bacteria survive in soil

49 Wetwood or slime flux Common bacterial disease on many trees, especially elms and poplars Liquid seeps out of the tree, frequently at tree crotches There is no satisfactory control for wetwood

50 Fire blight Bacterial disease of plants in the Rose family Serious disease that can kill trees Spread by pollinators, wind, rain, pruning tools Leaves remain on the tree, look like they were scorched by fire Sometimes see characteristic shepherd s crook Can see bacterial oozing in wet weather

51 Bacterial Leaf Scorch Marginal necrosis, usually with yellow edge Most hardwoods are effected Has not been detected at TMA Also looks like environmental scorch

52 Viruses (sing. Virus) Sub-microscopic particles that cannot be seen with standard microscopes Must be in a host cell to reproduce Cause stunting, curling, and twisting or odd coloring Spread by insects, plant propagation, and seeds

53 Viruses Wide range of host plants, especially on roses and ash trees Yellow mottling and yellow or white ringspots and line patterns are typical symptoms. Sometimes also see poor vigor, stunting or reduced leaf size. Need serological testing to confirm viruses Transmitted via aphids and leafhoppers No cure

54 Nematodes Microscopic roundworms Found in soil and plant tissue May be vectored by insects Pinewood nematode is the cause of pine wilt disease

55 Pine wilt Most common in Scots pine, but found in all pines (extremely rare in white pines) Caused by pine wilt nematode, which is vectored by the pine sawyer beetle First symptom is gray green needles which progress rapidly to yellow, then brown Trees die in less than one season Occurs midsummer to late fall or late winter to spring

56 Foliar nematodes Angular leaf spots Columbine, begonia, Cyclamen, Gerbera, Hibiscus, geranium, Brunnera, Hellebore

57 Phytoplasmas Microscopic pathogens Cause growth distortion, stunting, witches brooming, and yellowing Cause yellows diseases (Ash and elm) Found only in phloem Vectored by phloem feeding insects such as leafhoppers Electron microscopy of cross-section of gladiolus phloem tissue infected with phytoplasma. Numerous phytoplasma bodies are apparent in the upper sieve elements. The sieve element in the lower left-hand corner is apparently free of phytoplasma bodies. x6000. Courtesy of Assunta Bertaccini.

58 Ash Yellows Symptoms Elm

59 Common Conifer Diseases Needle diseases more serious than leaf spots because evergreens cannot refoliate Dothistroma needle blight Rhizosphaera needle blight Diplodia (i.e. Sphaeropsis) tip blight Phomopsis Cytospora Canker

60 Dothistroma needle blight Affects Austrian and ponderosa pines Red and Scots are resistant Begins with brown spots and bands on needles, eventually needle turns brown with base remaining green Fungal spores are released during wet weather any time during the growing season from May to October

61 Rhizosphaera Needle Cast Common on stressed blue spruce Likes warm, wet weather Infects new growth, but they do not show symptoms until fall or early spring One year old needles fall off, can see fruiting bodies in rows on needle

62 Identified in 2006 Stigmina Similar symptoms as Rhizosphaera Photos by Justin Knott Photos by Jim Walla

63 Diplodia tip blight (i.e. Sphaeropsis) Common fungal disease of stressed pines Common on Austrian, Scots, mugo, and red pines Disfiguring disease that kills new shoots New needles are stunted, twisted, and killed Sometimes see resin exudation Starts on lower branches

64 Phomopsis Fungal disease of junipers Causes tip blight of branches, only new growth is effected Initially starts as yellow spots, progresses into shoots Tips become light green and then reddish brown, eventually gray

65 Cytospora canker Common fungal disease of spruces, especially Colorado and Norway Affects older trees (at least 15 years old and 20 feet tall) In spring, needles turn purple, brown and fall off Kills older branches and progresses upwards More common on stressed trees

66 Root Rot Infections Symptoms Uniform canopy dieback, leaf drooping, almost like drought stress, brown or black roots, sloughing roots Fungal pathogens Phytophthora, Pythium, Armillaria, and Rhizoctonia Bacterial soft rot Due to excess moisture Soil will smell acrid and sour

67 Above-ground Root Rot Symptoms

68 Below-ground Root Rot Symptoms

69 Fungal decay Mushrooms at the base of the tree Conks on the stem Mycelial mats found under sloughing bark Sometimes sunken or darkened areas on the stem conk : a shelf-like, typically hardened basidiocarp of a wood decaying fungus, usually a polypore (Ganoderma applanatum).

70 Bacterial Soft Rot Found in areas with excessive moisture Soil will smell acrid, pungent, and swampy Bark of dying roots will easily slough off and dying roots will be discolored tan-brown Fine roots will be black (dead) Canopy will have symptoms of water stress, dieback, and wilt Plants recover when water is removed

71 Armillaria root rot Common landscape disease on 700 plant species Kills roots and lower trunk Above ground symptoms are similar to other diseases early fall color leaf drop, stunted or yellow leaves, dieback Can infest fast or slow Look for white, fan-shaped mycelia under the bark on major roots and at base of trunk

72 Information for Diagnosis Need a good history of the problem Host plant (name, accession number) Weather conditions (day, week, or month) Type of care given (herbicide use, mulching, pruning) Condition of surrounding plants (turf, wet areas, competing plants, surrounding symptomatic plants) Soil moisture

73 Family, genus, species, and cultivar, if possible What are the environmental requirements for the plant? Are these needs being met? Each plant has its growing conditions that it thrives in Water, nutrients, soil ph, sunlight Determine the age of the tree Identify the plant

74 Identify the plant Each plant has its own set of common diseases, insect problems and cultural needs Biotic: fungi, bacteria, viruses, phytoplasmas, insects Abiotic: pollution, mechanical damage, poor planting space, environmental Establish what a healthy plant would look like Seasonal variation, weather Herbicide damage Tilia platyphyllos 'Laciniata'

75 What is normal for the plant? What is perfectly healthy for one species may be a symptom of a serious problem for a different species Resin on bristlecone pine Pine needle scale

76 What s the plant s history When was the plant put in the ground? Was it planted correctly? Has anything changed around the plant? What sort of care has it received in the past? Consider fertilization, mulching, pesticide spray program Check the depth and location of the mulch

77 Abnormal symptoms

78 Look for Patterns Are other plants in the vicinity affected? Non-uniform damage patterns Uniform damage patterns

79 Non-uniform patterns Random branches on a plant Usually caused by living factors Insects or pathogens Specific symptoms and signs Limited to a one or a few hosts Plants within a family or genera Initially do not see wide-spread damage Takes time to multiply and spread

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81 Uniform damage patterns All leaves of a certain age affected Are there symptoms of dieback and re-sprouting? Damage seen over a wide area Neighborhood, city, street, yard Usually caused by nonliving factors Frost, drought, flooding, chemicals, construction Multiple plant species may be involved

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83 What is the environmental history? Winter temperatures Late frost Hail storms Water Drowning and drought have similar symptoms Sources of water Exposure to sun Cold damage on thin-leaved hostas

84 Environmental observations Includes soil characteristics Construction fill, soil type, clay content, soil moisture, ph Construction history, grade changes Identify surrounding plants Competition or allelopathies Growth restrictions May have originated at planting Sources of abiotic stress Salt, exhaust, mechanical damage, stem-girdling roots

85 Define the abnormality Try to determine the primary problem and plant part where the initial damage occurred Sometimes there is more than one problem

86 Time Development of Damage Pattern Observe the development of the pattern Direction of dieback Damage caused by living organisms are progressive and spread with time Damage caused by nonliving organisms are not progressive and do not spread with time and usually effect several species in the area

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