Apple Scab Presentation

Apple ScabDisease

aPlant

Pathology Presentation

byLisa K. Schlag30 November 2006

Apple Scab: IntroductionFor centuries, apple scab has been a disease problem plaguing

susceptible species and cultivars in the Malus genus.

A painting by Italian artist Michelangelo Merisi Caravaggio, Basket of Fruit, 1596, depicts scab-infected apples.

Apple Scab: Introduction

A painting by American artist James Peale, Fruit Still Life with Chinese Export Basket, 1824, depicts scab-infected apples.

Apple Scab: IntroductionApple scab, caused by the fungus Venturia inaequalis, is still

one of the most serious and economically important diseases of susceptible species and cultivars in the Malus genus that

exists worldwide.

In the United States, it is especially severe in the northeastern and north central states where cool, moist spring and summer weather favors the causal fungal pathogen.

significant defoliation for 2-3 years causes a general weakening or loss of vigor that could result in:

♦ increased winter injury; and

♦ susceptibility to secondary diseases and insects.

Disease losses attributable to apple scab if scab control measures are not taken

reduction in amount and quality of marketable appleharvest.poor fruit bud development for next year.


http://ohioline.osu.edu/hyg-fact/3000/3003.html

Est. Production Value losses if control measures are not taken


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OH Ttl PV of Apple Crop (inmillions)

14.858 no data 20.296 18.76 24.66 27.4

Ttl PV less 70% disease loss (inmillions)

4.457 no data 6.088 5.628 7.398 7.289

1999 2000 2001 2002 2003 2004(est.)

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Disease losses attributable to apple scab if scab control measures are not taken

reduction in crabapples aesthetic appeal and wildlife valuecaused by premature defoliation and fruit drop.


www.apsnet..org

V. inaequalis is an Ascomycetes sac fungus producing both sexual and asexual spores

ascospores are sexual spores that initiate one primary cycle of apple scab disease annually♦inaequalis named for unequal-

sized brown “footprint”shapedtwo-celled sporesconidia are asexual spores that initiate one or more secondary cycle(s) of apple scab disease annually♦ cycle name Spilocaea pomi

www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/F7a.jpg

Apple Scab: Disease CyclePathogen

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V. inaequalis belongs to the group of pathogenic fungi known as hemitrophes

parasitic phase is spent as mycelium and spores onliving tissue penetrating only the cuticle and staying between cuticle and epidermal cells.


www.agf.gov.bc.ca/cropprot/tflpm/applescb.htm

V. inaequalis belongs to the group of pathogenic fungi known as hemitrophes

saprophytic phase overwinters as psuedothecia initialpenetrating dead leaf tissue of fallen debris.


(Wilcox, 2001)

♦ Dormant ◊ before growth starts in spring

♦ Green Tip (Early April)◊ when buds start to break, showing green color of new

leaves♦ Tight Cluster - buds short-stem’d & closely pack’d (End of April)♦ Pink (Early May)

◊ when flower buds start showing color of petals♦ Bloom (Mid-May)

◊ when flower buds open♦ Petal Fall (Mid- to Late May)

◊ when flowers drop their petals♦ First, second, and third cover

◊ 10-14 days after petal fall (End of May)◊ 10-14 days after first cover (Early June)◊ 10-14 days after second cover (End of June)

Apple Scab: Disease CycleGrowth Stages of Northern Ohio Malus sp.

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Movement of fungal pathogen V. inaequalis is passivemoisture must be present to induce expulsion of ascospores from psuedothecia

♦ ascospores disseminated by splashing rain and wind

♦ few spores mature at green tip with maturity progressing slowly until tight cluster

♦ discharge usually peaks between stages pink through bloom, and nearly all discharged within 2-4 weeks after petal fall

conidia disseminated by rain, washed or splashed, and/or wind

Apple Scab: Disease CycleDissemination

Primary inoculum♦ ascospores forcibly released by asci into air

when mature pseudothecia become thoroughly wet during spring rain

♦ discharged over a 5-9 week period◊ starting at bud break (green tip) and peaking

from pink to petal fall stages

Secondary inoculum♦ conidia arise from primary and secondary lesions

when humidity levels are at least 60-70%♦ discharged over growing season

◊ throughout remainder of growing season

Apple Scab: Disease CycleInoculation

V. inaequalis is a nonobligate hemitrophe

direct penetration

♦ascospores and conidia develop fine hyphae which directly pierces cuticle and grows in a subcuticular position between cuticle and epidermal cells

◊ fungus may degrade and use cuticle as well as some host cell wall and pectic materials for nutrients

◊ once leaves fall to ground, mycelium penetrates tissue below existing lesions

does not always lead to infection

Apple Scab: Disease CyclePenetration

V. inaequalis spores require a film of water on plant tissue for a specific period of temperature-dependent time to germinate

and infect susceptible Malus sp. hosts

infections affected by age of leaves and fruit

♦ leaves most susceptible 1-5 days after unfolding

♦ fruit most susceptible until 3-4 weeks after petal fall

♦ leaves and fruit become less susceptible with maturity

Primary scab infection

♦ occurs from bud break until 2-4 weeks past petal fall

Secondary scab infection(s)

♦ can occur several times during growing season when suitable conditions prevail

Apple Scab: Disease CycleInfection

Apple Scab: Disease CycleInfection -- Revised Mills Table

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Fº Cº Wetting Period (hr)2

79 26 11.3 --

77 25 8 --

75 24 6.1 --

73-63 23-17 6 9-10

61 16 6.1 9-10

59-57 14-15 7 12-13

55 13 8 14

54 12 8.3 14

52 11 9 15

50 10 11 16

48 9 12.2 17

46 8 13.4 17

44 7 15.4 17

43 6 18 17

40 5 21.2 --

39 4 27.8 --

37 3 29.6 --

35 2 34.7 --

34 1 40.5 --

IncubationPeriod (days)3

Apple Scab: Disease CycleInfection -- Revised Mills Table

Mills Curves

♦ 1944, first attempt at using forecasting to help growers time applications of sulphur dusts

♦ relates hours of leaf wetting and temperature during wetting period to scab infection

Revised Mills Table – reflects most up to date information♦ shorter times for infection by ascospores and conidia♦does not rate severity of infection periods◊ rating severity on wetness duration misleading◊ other factors important – suceptibility; inoculum level

♦ day vs night ascospores◊ over 95% of ascospores not released until after sunrise◊ conidia not affected by light or darkness

www.nysaes.cornell.edu/pp/extension/tfabp/mills.shtml

Primary scab cycle♦ by late winter or early spring, each

mature, flask-shaped pseudothecia produces 50-100 asci with each ascicontaining 8 ascospores

◊ first ascospores become mature about bud break

♦ within 9-17 days of primary infection, ascospore lesions produce conidiophores which bear 10,000’s+ of potentially infectious secondary scab spores called conidia

These produce, produce, produce… additional conidiaphores and conidia in fall, V. inaequalis colonizes tissues beneath former scab lesions producing pseudothecia during dormant season

Apple Scab: Disease CycleGrowth & Reproduction

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Secondary scab cycle♦ conidia form olive-green to

brown, velvety textured scab lesions that push up through the cuticle

♦ can continue throughout the spring, summer, and autumn

♦ in autumn, V. inaequaliscolonizes tissues beneath former scab lesions producing pseudothecia initial during dormant season

Apple Scab: Disease CycleGrowth & Reproduction

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Apple Scab: Disease CyclePrimary scab cycle

Secondary scab cycle

Polycycl

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Disease

(Agrios, 2005)

In Spring, symptomatic spots (lesions) are most noticeable on leaves and fruit; however, symptoms of V. inaequalis infection can also appear on:

♦ petioles;

♦ pedicels;

♦ apple blossoms;

♦ bud scales; and

♦ young twigs/shoots

Apple Scab: SymptomsSusceptible Plant Parts

In spring, first spots (lesions) usually located on lower surface of expanding leaves

Apple Scab: SymptomsLower Leaf Surface

(Wilcox, 2001)

Lesions progress to olive-green to brown coloration and velvety texture. As fungal growth stops the lesion margins

change from feathery, indistinct to distinct

Apple Scab: SymptomsUpper Leaf Surface

www.uni-kl.de/FB-Biologie/AG-Hahn/Research/venturia%20engl.html

Scab sheet is a condition whereentire leaf surface is coveredwith apple scab disease

Apple Scab: SymptomsUpper Leaf Surface

later yellowing stage

www.ppdl.purdue.edu/ppdl/weeklypics/Weekly_Picture6-10-02-1.html, Gail Ruhl

circular, necrotic olive-green or brown colored warty lesions with distinct margins on fruit infected early in development

Apple Scab: SymptomsFruit

fruit infected late in season small black spots of “pinpoint” scab noticeable after harvest apples in storage

www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/photo2-9.jpg

Small, dark green lesions on pedicel before, during, or after bloom

www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/AppleScabPedicel.jpg

Apple Scab: SymptomsPedicel just after Petal Fall

Natural♦ disease-resistant Malus sp. cultivars ♦ biological♦ environment

Cultural♦ sanitation♦ pruning♦ growing practices

Chemical♦ protectant (protective) fungicides♦ post-infection (suppressant) fungicides

Integrated Pest Management

Apple Scab: Disease ControlTreatments

create environment unfavorable for pathogen

Apple Scab: Disease ControlTreatments

Flail mower chopping leaf debris Airblast sprayer applying fungicides

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Plant disease-resistant Malus sp.cultivars♦ best means of managing apple scab on crabapples♦ fresh market apples not as popular♦ disease resistancy may be temporary

◊ through sexual reproduction, V. inaequalis can overcome resistance

biological♦ New Zealand -- yucca extract prevents germination of

fungus and had curative effect ♦ antagonistic fungi may decrease ascospore

production -- viable option in futureenvironment♦ humidity < 60% and drier weather conditions

Apple Scab: Disease ControlNatural

top varieties of fresh market apples grown in Ohio1 vary intheir susceptibility to apple scab disease:

Very susceptible Moderately susceptible

♦ Red Delicious ♦ Golden Delicious

♦ Rome Beauty ♦ Jonathan♦ McIntosh

while some are highly resistant and immune to scab and well suited to organic commercial & backyard growers:

♦ Enterprise ♦ Liberty ♦Priscilla

♦ Freedom ♦ Macfree ♦ Redfree

♦ Gold Rush ♦ Nova Easy ♦ Sir Prize♦ Jonafree ♦ Prima ♦ William’s Pride

1www.ipmcenters.org/cropprofiles/docs/ohapples.html


All require fungicide

usage

ohioline.osu.edu/hyg-fact/3000/3003.html

crabapple cultivars with excellent scab resistance and

superior horticultural characteristics for Ohio, including

being small-fruited for wildlife:

♦ Malus baccara ‘Jackii’ ♦ Red Jewel ♦ Silver Moon

♦ Bob White ♦ Royal Splendor ♦ Strawberry Parfait♦ Ormiston Roy ♦ Malus sargentii ♦ Sugar Tyme

♦ Prairifire ♦ Sentinel ♦ Malus x zumi‘Calocarpa’

crabapples initiate buds for next season mid-June to early July


Create unfavorable environment for pathogenreduce occurrence of primary innoculum♦ collect & destroy all fallen leaves♦ dolomitic lime or 5% urea applied to ground of fallen

leaves hastens leaf decomposition♦ flail mowing to chop leaf litter in autumn decrease drying time of plant tissues during growth♦ prune to increase sunlight penetration into and

improve air movement through tree canopy♦ avoid overhead irrigation

◊ irrigate soil around treesplant right tree in right location♦ plant new trees in well-drained, sunny locations♦ pathogens can attack healthy plants

Apple Scab: Disease ControlCultural

no chemical treatments were employed until the

late 1800’s

♦ at that time, cooper- and sulphur- based fungicides

were used as pre-infection protection.

◊ these treatments caused substantial foliar damage

cultural practices influence fungicide usage

♦ fungicides are not an alternative to the use of sound cultural practices

standard Malus sp. cultivars vary widely in their susceptibility to scab

♦ influences intensity of control program

Apple Scab: Disease ControlChemical

Apple Scab: Disease ControlChemical -- Fungicides

Protectant -- 5-7 day spraying schedule in early season

♦ prevent spores from germinating or penetrating leaf tissue

♦ must apply to susceptible tissue before infection occurs

◊ green tip & 1 week past petal fall critical time

Post-infection – every 7-10 days later in season

♦ penetrates tissue to eliminate/inhibit lesion development

♦ effectiveness limited to few hours/days depending on

fungicide

monitor rainfall in orchard

♦ 1/2”-1” rain needed to deplete half fungicide residue on

fruit and foliage


www.ipmcenters.org/cropprofiles/docs/ohapples.html

green tip x x xtight cluster x x x xpink x x xbloom x x x xpetal fall x x

3d cover x xremaining x x

1st & 2d cover x x x x

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Fungicide selection should be based on:♦ other diseases that must be managed♦ scab fungus resistance♦ history of disease in orchard or property landscape♦ final market for fruit♦ other social and economic factors

Multi-purpose sprays containing insecticides andfungicides are convenient , but have disadvantages

♦ none controls all insects and diseases ♦ lack flexibility◊ only use after bloom period to prevent lethal harm

to bees; fungicides alone are not harmful to bees♦ more expensive than chemicals you prepare


Integration of all available control methodsEffective disease management program should emphasize integrated use of:

♦ knowledge of pathogen and disease;

♦ disease resistant plants;

♦ specific cultural practices; and

♦ timely application of chemicals when needed.

◊ weather monitoring equipment and disease forecasting computer programs can predict scab infection periods

▪ Envirocaster ; Metros

Apple Scab: Disease ControlIntegrated Pest Management (IPM)

Agrios, G.N. (2005). Plant Pathology (5th ed.) Burlington, MA:Elsevier Academic Press.

Cloyd, R.A., Nixon, P.L., & Pataky, N.R. (2004). IPM for Gardeners:A Guide to Integrated Pest Management. Portland, OR: Timber

Press.

Dirr, M.A. (1998). Manual of Woody Landscape Plants (5th ed.)(pp. 630-660). Champaign, IL: Stipes Publishing.

Sinclair, W.A., & Lyon, H.H. (2005). Diseases of Trees and Shrubs (2nd

ed.)(pp. 86-87). Ithaca, NY: Cornell University Press.

Apple Scab: ReferencesBooks

Apple Scab (April 2006). Retrieved 2 Nov. 2006, from Cornell University, Plant Disease Diagnostic Clinic Web site:http://plantclinic.cornell.edu/FactSheets/apple_scab_factsheets/apple_scab.htm

Apple Scab. Retrieved 17 Nov. 2006, from New York State IPM Program, from Cornell Cooperative Extension Web site:www.nysipm.cornell.edu/factsheets/treefruit/diseases/as/as.asp

Apple Scab of Flowering Crabapples (March 2002). Retrieved 20 Nov. 2006,Bull.BP-39-W,from Purdue University Cooperative Extension Service Web site.

Biggs A.R. & Hickey K.D. Apple Scab. Retreived 20 Nov. 2006, from NYS IPM TreeFruit Factsheet, New York State Agricultural Experiment Station Web site:http://www.nysaes.cornell.edu/pp/extension/tfabp/apscpm.shtml

Chatfield J.A., Draper E.A., Cochran K.C., Bristol P.W., & Tubesing C.F. (1999).Ornamental Plants – Annual Reports and Research Reviews 1999. Retrieved 7 Nov. 2006,from Ohio State University, Ohioline Web site:http://ohioline.osu.edu/sc173/sc173_16.html

Chatfield J.A., Rose M.A., Ellett C.W.,et al.(1996). Disease Control in the Landscape.Retrieved 10 Nov. 2006,Bull.614, from Ohio State University Ohioline Web site:http://ohioline.osu.edu/b614/b614.html

Apple Scab: ReferencesElectronic

Ellis M.A., Chatfield J., & Draper E. (1994). Scab of Apple and Crabapple. Retrieved 7 Nov. 2006, from Ohio State University, Ohioline Web site:http://ohioline.osu.edu/hyg-fact/3000/3003.html

EU researches promise disease-free apples (July 2006). Retrieved 21 Nov. 2006, fromFood navigator Web site:http://www.foodnavigator.com/news/printNewsBis.asp?id=69114

Grove G., & Xiao, C-L (2005). Apple Scab. Retrieved 2 Nov. 2006, from WashingtonState University Extension Web site:http://cru.cahe.wsu.edu/CEPublications/pnw0582/pnw0582.pdf

Hartman J.R.(June 1996). Apple Scab. Retrieved 2 Nov. 2006, from University of Kentucky, Cooperative Extension Service Web site:http://www.ca.uky.edu/agc/pubs/ppa/ppa24/ppa24.pdf

Schroeder D.B. Marrotte E.L. (Ed.), Apple Scab (February 2003). Retrieved 7 Nov. 2006, from University of Connecticut, Integrated Pest Management Web site:http://www.hort.uconn.edu/ipm/homegrnd/htms/19apscab.htm

Turechek J. & Carroll J., The Mill’s Table. Retrieved 27 Nov. 2006, from New York State Agricultural Experiment Station Web site:http://www.nysaes.cornell.edu/pp/extension/tfabp/mills.shtml


Volk, T. (2002). Tom Volk’s Fungus of the Month for September 2002. Retrieved 7 Nov. 2006, from University of Wisconsin-La Crosse, Tom Volk Fungi Web site:http://botit.botany.wisc.edu/toms_fungi/sep2002.html

Wilcox W.F. Apple Scab. Retrieved 17 Nov. 2006, from New York State Integrated Pest Management Web site:

www.nysipm.cornell.edu/factsheets/treefruit/diseases/as/as.asp

Wilcox W.(2001). Apple Scab. Retrieved 20 Nov. 2006, from NYS IPM Tree Fruit Factsheet, New York State Agricultural Experiment Station Web site:

http://www.nysaes.cornell.edu/pp/extension/tfabp/apscpm.shtml

The American Phytopathological Society web site presents information on many plant diseases and their control. Retrieved 31 October 2006.

www.apsnet.org


Documents

Apple Scab Presentation