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Plant Diseases. Terms Abiotic plant disease—caused by unfavorable growing conditions. Biotic plant disease —caused by plant pathogens. Pathogen- an infectious,

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Presentation on theme: "Plant Diseases. Terms Abiotic plant disease—caused by unfavorable growing conditions. Biotic plant disease —caused by plant pathogens. Pathogen- an infectious,"— Presentation transcript:

1 Plant Diseases

2 Terms Abiotic plant disease—caused by unfavorable growing conditions. Biotic plant disease —caused by plant pathogens. Pathogen- an infectious, biological agent such as a virus, bacteria or fungus that causes disease to its host.

3 Introduction Plant disease—a harmful change in the growth of a plant.

4 Abiotic Plant Diseases Not caused by pathogens Caused by unfavorable growing conditions –Improper light –Temperature extremes –Mechanical injury Abiotic diseases lead to stress that can increase susceptibility to damage from insects or pathogenic diseases Most abiotic plant diseases are avoidable

5 Biotic Plant Diseases Plant disease triangle Causal agents: –Fungi –Bacteria –Viruses, etc.

6 Causal Agents (Pathogens) Fungi –Most turf and ornamental disease are caused by fungi –Do not produce their own food –Reproduce by forming spores Spread –Some by water –Some by wind –Mechanical/animal –Infected plants

7 Causal Agents (Pathogens) Bacteria –Single celled microbes –Enter plants through injuries or natural openings Spread –Some by water –Some by wind –Some in soil –Mechanical/animal –Infected plants

8 Causal Agents (Viruses) Viruses –Smaller than cells---multiply in cells –Often spread –Infected plants must be removed---no cures Spread –Mechanical---e.g. contaminated equipment –Contact between plants –Sucking insects

9 Susceptible Host Plants Ornamental plants vary in disease resistance Susceptibility increases with stress Symptoms of decline –Late flowering or leaf emergence –Smaller leaf size –Less shoot growth –Excessive water spouts

10 END

11 Important Plant Diseases-Turf Brown Patch Symptoms –Irregular brown areas inches to feet wide –Grass leaves turn olive green then wilt, turn light brown, and die. –Stems and crowns can also be infected Causes –All grasses susceptible –Caused by Rhizoctonia solani, reside in soil

12 Important Plant Diseases-Turf Brown Patch Favorable conditions –Excess thatch –High temperatures (75-90 degrees) Control Aerate Water to 4-6 inches depth when needed Avoid excess nitrogen

13 Important Plant Diseases-Turf Dollar Spot Symptoms –Small, bleached out or straw-colored spots –Seldom larger than 2 inches in close-mowed turf –On taller grass (1-3 inches) spots can be 3-6 inches in diameter –Spots can merge together –Does not kill the grass plants Causes –Caused by fungi – indicates Nitrogen deficiency

14 Important Plant Diseases-Turf Leaf Spot Favorable conditions –Nitrogen deficiency –Warm days with cool nights –High humidity Control –Adequate nitrogen and potassium –Water in the morning let turf dry out before dusk –Preventative fungicides –Curative fungicides

15 Important Plant Diseases-Turf Leaf Spot Symptoms –Start as small, dark purple or black spots –Become oval spots with buff centers and purple margins Causes –Primary cause--- fungus Bipolaris sorokinianum

16 Important Plant Diseases-Turf Leaf Spot Favorable conditions –Dry periods alternating with cloudy, wet weather Control –Avoid over-lush turf –Mow so that no more than 1/3 of the leaf blades are cut –Resistant cultivars

17 Important Plant Diseases-Turf Melting-Out Symptoms –Circular to elongated, purplish or brownish spots –General e.g. spread throughout the grass Causes –Melting-out is the summer phase of leaf spot –Brent grass, fescues, ryegrass and burmudagrass---fungus Bipolaris sorokinianum

18 Important Plant Diseases-Turf Melting-Out Control –Reduce shade –Mow at recommended heights –Improve soil aeration

19 Important Plant Diseases-Turf Necrotic Ring Spot Symptoms –Begins as scattered light green patches 2-6 inches in diameter –Patches enlarge and fade to tan, may become sunken. Streaks or crescents 1-3 or more feet in diameter –Patches can increase over the years Causes –Fungus Leptosphaeria korrae –Formerly called fusarium blight

20 Important Plant Diseases-Turf Necrotic Ring Spot Favorable conditions –Cool or mild periods followed by dry, hot conditions –Widespread disease of Kentucky and annual bluegrass that is intensively managed---follows stress Control –Good cultural practices: aeration, drainage, balance of fertilizers, water in the morning –Resistant cultivars –Systemic fungicides

21 Important Plant Diseases-Turf Pink Snow Mold Symptoms –Appears first as snow melts –Round, water-soaked spots 1-3 inches in diameter Causes –Fungi Fusarium nivale or Microdochium nivale –These fungi inactive in warm dry conditions

22 Important Plant Diseases-Turf Pink Snow Mold Favorable conditions –High humidity and temperatures around 40 degrees Control –Adequate, balanced fertilizer –Reduce shade –Aeration –Drainage

23 Important Plant Diseases-Turf Powdery Mildew on Turf Symptoms –Thin, white powdery coating –Lives primarily on outer surfaces Causes –Fungi Fusarium nivale or Microdochium nivale –These fungi inactive in warm dry conditions

24 Important Plant Diseases-Turf Powdery Mildew on Turf Favorable conditions –Cool (55-70 degrees) cloudy weather –Important disease on Kentucky bluegrasses during extended periods of low light, especially in areas with poor air circulation Control –Include shade tolerant cultivars in seed mixtures –Prune trees and shrubs to permit light to reach turf –Deep, infrequent watering

25 Important Plant Diseases-Turf Rust Symptoms –Begins as light green or yellow flecks becomes –Reddish brown to orange (spores) Causes –Puccinia species

26 Important Plant Diseases-Turf Rust Favorable conditions –Cool to warm, moist weather –Dew or condensed moisture on plants for 12 hours Control –Maintain healthy growth with fertilizer and irrigation –Remove infected portions of leaves with weekly mowing –Curative fungicides

27 Important Plant Diseases-Turf Slime Molds Symptoms –Slimy masses 1 inch to 2 feet in diameter –Shades of grays and yellow –Easily removable Causes –Non parasitic on turf---feed on organic matter

28 Important Plant Diseases-Turf Slime Molds Favorable conditions –Warm, moist weather and high humidity –Spread by winds, water, equipment Control –Will disappear but can rake or hose-off

29 Important Plant Diseases-Turf Stripe Smut Symptoms –Long, black stripes (pustules) –Grass leaves curl, become shredded and die –From a distance appears clumpy and patchy –Plants die when hot weather occurs Causes –Fungus Ustilago striformis often contaminates turf seed –Can remain dormant for 3 years in soil

30 Important Plant Diseases-Turf Stripe Smut Favorable conditions –Moderate temperatures (50-65 degrees) –Prevalent in spring and fall –Occurs on other grasses but more common on bluegrasses Control –Resistant cultivars of bluegrass –Seed treatment with fungicides –Dystemic curative fungicides

31 Important Plant Diseases-Turf Fairy Ring Symptoms –Circular or semi-circular dark green band on turf (released nitrogen from breakdown of organic matter in soil) –Mushrooms will often develop around edge after wet weather Causes –Several fungi –Occurs in areas with high levels of organic material e.g. thatch

32 Important Plant Diseases-Turf Fairy Ring Favorable conditions –Presence of high concentrations of organic matter e.g. tree stumps, roots, construction lumber Control –Remove excess organic matter –Antagonist strains for heavy infestations

33 Important Plant Diseases-Turf Pythium Blight Symptoms –Large areas can die in hours when conditions favoring pythium blight occur –Round to irregular, dark and water-soaked, greasy or slimy –Sunken patches 6-12 inches wide –Reddish brown areas fade to tan and die Causes –Several species of Pythium fungi

34 Important Plant Diseases-Turf Pythium Blight Favorable conditions –Temperatures degrees with 90% RH (relative humidity) and warm nights (.70 degrees) for most Pythium but some thrive in cool weather –Waterlogged soils with heavy thatch –Excess nitrogen Control –Improve drainage –Systemic fungicide prior to hot, humid weather

35 Important Plant Diseases-Turf Summer Patch Symptoms –Bluish-green patches become wilted then die –Patches become circular or crescent-shaped. Causes –Several species of Pythium fungi

36 Important Plant Diseases-Turf Summer Patch Favorable conditions –Usually occurs when a wet period follows hot, dry weather –Frequent or excessive watering Control –Before planting new turf remove stumps and construction material –Avoid mowing or walking on wet turf –Apply systemic fungicides when temperatures reach 70 degrees

37 Important Plant Diseases-Ornamentals Anthracnose Symptoms –Leaf buds do not emerge in spring –Defoliation from progressive death of mature leaf tissue along leaf midrib or veins Causes –Anthracnose in many common tree species –Transitional disease, intermediate between a leaf and stem disease caused by fungi (genus Gnomonia)

38 Important Plant Diseases-Ornamentals Anthracnose Favorable conditions –Disease begins in late winter or early spring during periods of warm weather –Splashing of spores during warm. Wet weather spreads the disease Control –Fungicide application on leaves and buds during emergence –Cultural practices including avoiding planting species that are especially susceptible, maintaining adequate irrigation and fertilization

39 Important Plant Diseases-Ornamentals Cytospora Canker Symptoms –Affects poplar and willow –Circular or irregular cankers first appear as brown, sunken areas on younger trees –Cankers often start at wound openings Causes –Fungus Cytospora chrysosperma

40 Important Plant Diseases-Ornamentals Cytospora Canker Favorable conditions –Fungus is opportunistic, infects weakened or wounded tissues –Spread by splashing rain, wind Control –Remove dead and dying branches –Clean pruning tools –Fertilize –Deep water (10-12 inches) –No fungicides are available

41 Important Plant Diseases-Ornamentals Dutch Elm Disease Symptoms –Leaves brown and curl---usually drop early –Large elms may die over 2 or more years Causes –Fungus Ceratocysitus ulmi –Infects elms and closely related plants –Transmitted by: Elm bark beetles Root grafts with adjacent trees Pruning tools

42 Important Plant Diseases-Ornamentals Dutch Elm Disease Control –Plant cultivars with superior resistance (Siberian and Chinese) –Water and fertilize –Spray with appropriate insecticide in late winter/early spring before the buds swell (requires special training and equipment) –Systemic injections –Halt transmission through root grafts (see oak wilt procedures)

43 Important Plant Diseases-Ornamentals Fire Blight Symptoms –Infected flowers first appear water-soaked –Leaves and stems then appear brown or black as though scorched by fire Causes/favorable conditions –Bacterium Erwinia amylovora overwinters in plant tissues and emerges when temps reach 65 degrees –Spread by insects, wind, water, hail

44 Important Plant Diseases-Ornamentals Fire Blight Control –Plant resistant varieties of apple, crabapple, and pear where available –Good cultural practices (fertility, watering, drainage) –Prune in dormant season and disinfect tools between cuts with 70% rubbing alcohol solution –6 inches of mulch around susceptible tress reduces chance of infection

45 Important Plant Diseases-Ornamentals Fungus Leaf Spot Symptoms –Difficult to diagnose from anthracnose –Variable spot colors and shapes Causes –Wide variety of fungi

46 Important Plant Diseases-Ornamentals Fungus Leaf Spot Favorable conditions –Cool weather, light rains, high humidity –Crowded plantings Control –Preventive measures usually not needed –Good culture –Remove fallen leaves and branches –Proper spacing

47 Important Plant Diseases-Ornamentals Juniper Twig Blight Symptoms –In spring tips of twigs and branches turn light green then brown –Usually affects branches less than 1/3 inch diameter –Spores emerge during wet weather in spring and early summer Causes –Fungus Phomopsis juniperova Controls –Cultural practices –Provide ventilation in shaded areas –Fungicides every 2 weeks early spring to fall

48 Important Plant Diseases-Ornamentals Oak Wilt Causes –Fungus Ceratocytis fagacearum –Spread by beetles from infected plants on their bodies f Root grafts

49 Important Plant Diseases-Ornamentals Oak Wilt Symptoms –Impairs water conduction from roots to branches and leaves –Trees wilt from the top down and leaves wilt from the tips to the base –Fallen leaves have brown tips and green along the main vein

50 Important Plant Diseases-Ornamentals Oak Wilt Favorable conditions Control –Avoid pruning wounding) from April 15 to July 1 st if wound occurs during that time cover with tree wound dressing or latex paint---this is the critical period of beetle movement –Isolate infected trees---preventing root grafts--- trenching machine or vibratory plow (cut to feet deep) –Red and black oaks most susceptible –Reduce spore quantity---cover pruned wood, debark branches that are 3 inches and over (fungus mats below bark)

51 Important Plant Diseases-Ornamentals Rust Symptoms –Bright orange, yellow, chocolate brown or black pustules Causes –Several fungi Control –Alternate hosts e.g. junipers and cedars one year,--- apple, crabapple, hawthorne, mountain ash the next –Disease free plants –Prune infested tissue

52 Important Plant Diseases-Ornamentals Scab Symptoms – Apple scab develops as circular lesions during leaf expansion in spring. Color progresses from dark green to black –Fruit can be infected at any time during development Cause –Fungus Fusicladium saliciperdum

53 Important Plant Diseases-Ornamentals Scab Favorable conditions –Apple scab overwinters on leaf litter –Wet weather during bud break spreads spores –Cool, wet conditions Control –Plant resistant varieties when available –Prune out diseased tissue –3-4 applications of fungicides at 10 day intervals starting just before bud break

54 Important Plant Diseases-Ornamentals Sphaeropsis Blight (Diplodia Tip Blight) Symptoms –On new, emerging needles browning occurs near the base of the needle and progress to the tip. Ooze forms –Infection spread to twigs and die back to the next whorl –Begins with lower branches and progresses up the tree over successive years –In severe cases the tree dies Causes –Fungus Sphaeropsis sainea

55 Important Plant Diseases-Ornamentals Sphaeropsis Blight (Diplodia Tip Blight) Control –Removal of infected branches –Balanced fertilizers in spring –Adequate watering

56 Important Plant Diseases-Ornamentals Phytopthora Symptoms –Variable, may be slow decline or rapid death during dry weather –Root and crown root –Symptoms may include chlorosis, sparse foliage, reduced sized foliage in trees and shrubs Causes –Fungi from the genus Phytopthora soilborne

57 Important Plant Diseases-Ornamentals Phytopthora Favorable conditions –High occurrence in areas with high soil moisture and low fertility Control –Plant in well drained soil –Allow plants to dry out between irrigation –Systemic fungicides

58 Important Plant Diseases-Ornamentals Verticillium Symptoms –Especially common on maples but can occur on several landscape trees and shrubs –Usually the leaves on the entire plant or all the leaves on one side of the plant suddenly wilt –Dieback –May progress through several years Causes –Fungi from genus Verticillium –Soilborne and spread by contamination

59 Important Plant Diseases-Ornamentals Verticillium Control –Plant disease-free nursery stock –Avoid wounding and contaminated tools –Avoid excess nitrogen –Replace infected plant with resistant varieties or immune species

60 Important Plant Diseases-Ornamentals Powdery Mildew Symptoms –White, powdery spots that grow to cover the entire surface –Young plants most vulnerable, especially in shade –Dwarfing, distortion, yellowing. –Leaves may drop Causes –Over 1000 species of fungi primarily Microsphaera and Odium

61 Important Plant Diseases-Ornamentals Powdery Mildew Favorable conditions –Shade –Areas with poor air circulation –Easily spread by splashing water Control –Prune affect parts –Select plants for resistance –Because powdery mildew are usually external they can be controlled ---curative fungicides


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