The document provides an overview of apple scab, a significant fungal disease affecting apple trees, detailing its biology, epidemiology, and management strategies in India. It discusses the history of the disease, symptoms, and various strains, as well as the economic impact on apple production. Management practices include cultural and chemical controls, alongside forecasting models to predict disease outbreaks.

2. Apple scab- Biology,Epidemiology
and Management
Nazia Manzar
PhD(ID-47067)
plant pathology

3. Overview

4.  Apple (Malus domestica) is one of the most widely cultivated tree
fruits.
 In India apple is the most important temperate fruit of the north
western Himalayan region.
 The antioxidants in apple have much health promoting and disease
prevention properties; thus truly justifying the adage, “an apple a
day keeps the doctor away”.
1

5. Botanical Classification
Kingdom : Plantae
Division : Magnoliopsida
Order : Rosales
Family : Rosaceae
Sub-family : Maloideae
Genus : Malus
Species : domestica ( X = 17)
Botanical Classification
Kingdom : Plantae
Division : Magnoliopsida
Order : Rosales
Family : Rosaceae
Sub-family : Maloideae
Genus : Malus
Species : domestica ( X = 17)
Origin –
Asia Minor and Soviet Central Asia.
2

6. IndiaStat.Com(2014-15)IndiaStat.Com(2014-15) 3

7. Leading Apple Producing States
4

8. Common name Binomial
List of fungal diseases
a)Spring season
Apple scab Venturia inaequalis
Powdery mildew Podosphaera leucotricha
b)Summer season
Apple scab Venturia inaequalis
Pre-mature leaf blotch Marssonina coronaria, Alternaria
mali, Zygophiala jamaicensis
Brooks fruit spot Mycosphaerella pomi
Leaf spots Alternaria mali,
c)Dormant season
Canker Corticium salmonicolor,
Botryosphaeria dothidea
Root rot Dematophora necatrix
Phytophthora cactorum
List of Apple diseasesList of Apple diseases
5

9. Bacterial Disease
Crown gall Agrobacterium tumefaciens
Hairy root Agrobacterium rhizogenes
Viral/ Viroid Disease
Apple mosaic Apple mosaic virus (ApMV)
Apple chlorotic leaf spot Apple chlorotic leaf spot virus
(ACLSV)
Dapple apple viroid
Apple scar skin viroid
(ASSVd)
6

10. Powdery Mildew
Crown gall
Apple scab
Sooty blotchApple mosaic
Pre-mature leaf
blotch
Canker
7

11. Apple scab
Venturia inaequalis
8

12. Apple scab in India
 In India-First detected in 1930 on the native cultivar Ambri in
Kashmir Valley.
 1973- Apple scab appeared in epidemic. 70,000 acres orchard area
got infected. Yield losses up to 70 per cent .
 1996 and 2008- Epidemic in the Gangotri valley (Uttarakashi) of
Uttarakhand. Loss up to Rs. 1.25 crores .
9

13. Research station and Universities exclusively work on
Apple scab in India
Central Institute for
Temperate
Horticulture(CITH)
Headquarter
Srinagar
(J&K)
Regional
Station
Mukteshwar
(Uttarakhand)Other stations
Shalimar-
Bagh J&K
Mashboora
( H.P)
Chaubatia
(U.P hills)
10

14. Contd..
Universities
Sher-e-Kashmir
University for Agriculture
Science &
Technology,J&K
Y.S.Parmar University
for Horticulture and
Forestry,
H.P
G.B.Pant University for
Agriculture&Technology
Uttarakhand
11

15.  Young lesions on the leaves -velvety brown to olive green .
Later appear metallic black in color
Scab lesions on apple leavesScab lesions on apple leaves
Symptom on Leaves
12

16.  Fruits-Lesions on the fruits are similar to those on the leaves.
After age they form cracks and the fruit become distorted
Scab symptom on apple fruit
13

17. Systematic Classification
14

18. Characteristic of Venturia inaequalis
 Perfect stage - Venturia inaequalis
 Imperfect stage - Spilocaea pomi
 Pseudothecia - dark brown to black in color, spherical(90-
150 µm in diameter), contains50 to 100 asci.
Pseudothecium
15

19.  Ascospore -11-15×5-7µm, yellowish green to tan ,unequally
two celled, upper cell shorter and wider than the lower cell.
 Conidia- ( 12-22× 6-9µm) yellowish olive, one or two celled
Ascospores are brown two celled and have
a characteristic of footprint shape
Conidia are single to two celled
16

20. Apple Scab Races
Race Source
1 Worldwide
2 South Dakota, USA
3 Nova Scotia,Canada
4 Lafayette Indiana, USA
5 Norwich, England
6 Ahrensburg, Germany
7 Great Britain
17

21. Disease Cycle
Hartman and Vaillancourt,2005
18

22. Apple scab epidemics
 First phase - inactive phase.
 Second phase- Monocyclic
phase (primary infections
period).
 Third phase- Polycyclic
phase (secondary infections
period). Progress of the disease when infection is uncontrolled
19

23. Prediction for apple scab disease
Prediction of primary inoculum Phenological stage Infection periods
Ascospore
dose
Ascospore
discharge
Primary infection period
Secondary infection period
Fruit infection
20

24. Ascospore dose
 Ascospore dose=number of spore / volume air.
 The rate at which ascospore mature in the pseudothecial
population in an orchard is determined mainly by temperature.
 Temperature is determined by degree days(DD).
DD=[(maxT+minT)/2]-32
21

25. Degree-day for primary infection of scab in different places
of Uttarakhand
Apple fruit belts Required degree-day for
cumulative
ascospores maturation (%)
50 per cent 75 per cent
Harsil, Uttarakhasi 899.5 1080
Sukhi, Uttarakhasi 557.2 842
Syouri, Uttarakhasi 286.7 456.35
Koti-Kanasar, Dehradun 278.45 412.25
Tal-Talwari, Chamoli 480.15 587.75
Auli, Chamoli 983 983
Joshimath, Chamoli 338.6 493.7
22

26. Ascospore maturation
Phase Tree phenological
stage
Degree days
Lag phase Green tip stage to tight
cluster
1 DD to 300 DD
Accelerated phase Tight cluster to petal
fall
300 DD to 700 DD
Final phase Two weeks after fruit-
set
700 DD to 800 DD.
23

27. Discharge of ascospores
 Ascospore discharge= number of mature spores/
cm² overwintered leaf area
Type of Rain Event Percentage of Available Ascospores
discharged under various
environmental conditions
Night rain only 5%
Day rain <0.25 cm, temperature
<10°C
25%
Day rain >0.25 cm, temperature
<10°C
50%
Day rain <0.25 cm, temperature
>10°C
50%
Day rain >0.25 cm, temperature
>10°C
90%
24

28. 25

29. Compression of different component variable of
PAD
26

30. Scab incidence at harvesting stage in Gangotri valley of
Uttarakhand
27

31. 28

32. Sequence of Successive Ascospore Catches from Wetted Leaves
Held at First in Darkness and then in Light in the Wind Tunnel
Period No. Leaf
Temperature
°c
Air
Temperature
In Wind
Tunnel °c
Leaves
in
Duration
of Period
(min)
No
Ascospores
1 24-25 23 Dark 60 207
2 24-25 26 Dark 60 47
3 24-25 25 Light 30 2,110
4 24-25 26 Light 60 1,328
29

33. Sequence of Successive Ascospore Catches from Leaves Subjected
Progressively to Temperature and Light.
Perio
d
Leaf
Temp. °C
Air
Temp.in
WindTunnel
°C
Leaf
Surface
Lamp No.
Ascospo
res
Test
Conditions
1 19-19.5 20.5 Dry off Nil No leaf
Wetting
2 5-6 21 Wet off 80 Leaves wet at
low
Temp.
Low Light
3 25 23 Wet off 75 Leaves wet
at day temp.
low light
4 25 24 Wet on 5,407 Leaves wet
at day temp.
high light
30

34. Infection Periods
31

35. Primary infection periods-
Once the tree breaks dormancy and green tissue is present, a
primary infection occurs if the following conditions are met:
 Mature ascospores.
 Weather conditions.
 Fungicides protection is inadequate.
Primary infection through ascospore
32

36. Primary infection of ascospore on apple leaves at
different place of Uttarakhand hills
Primary infection of ascospore on apple leaves at
different place of Uttarakhand hills
Apple fruit belt Phenological stage of tree and time
for primary infection
Tree stage Primary
infection
Gangotri Valley,
Uttarakashi (>2500 m asl)
Harsil, Dharali, Jhalla,
Sukhi etc.
Bloom stage
to fruit stage
(Pea size)
Last week of May
to 2nd
week of
June
Auli-Joshimath, Chamoli
(2200 to 2500 m asl)
Pink bud stage
to bloom and
petal fall stage
Last week of May
to 1st
week of
June
Syori-Naugao, Uttarakashi
(1950-2200 m asl)
Pink bud stage
to Petal fall
stage
3rd week of
April to 2nd
week of May
Tal-Talwari, Gwaldam,
Chamoli (1750 to 1950 m
asl)
Tight cluster
to Petal fall
stage
3rd week of
April to 2nd
week of May
33

37. b)Secondary infection periods
 Secondary scab infections occur when splashing rain spreads
conidia, developed from scab lesions on leaves.
c)Fruit infection
 As fruit matures, it takes a longer wetting period for infection by
apple scab to occur
Contd..
33

38. Determination of Infection Periods- The Mills table relating
leaf wetness duration and temperature to predict infection time
Determination of Infection Periods- The Mills table relating
leaf wetness duration and temperature to predict infection time
Wetting hours
Average
Temp. (C)
Light
Infectio
n
Moderate
Infection
Heavy Infection
25.0 11 14 21
17.2-23.9
9 12 18
16.1 9 13 20
15.0 10 13 21
13.9 10 14 22
12.8 11 16 24
11.7 12 17 25
10.0 14 19 29
8.9 15 20 30
6.0 22 28 45
34

39. Mills table using the data generated in Garhwal hills to
arrive at incubation period based on temperature and leaf
wetness
Average
daily
Temperature
(°C)
Minimum wetting hours of
leaves for infection (approx.
hours)
Days required
after infection for
symptom
appearanceAs per Mills
table
As per Garhwal
hills data
25 11 9
16 24 6 9
15 10 8 12
14 10 8 13
13 11 9 13
12 11-5 9 14
11 12 10 15
10 14 13 16
35

40. Warning system models
 EPIVEN- Kranz et al., 1973
 Ventem - Aalbers, 1989
 WELTE- Butt, 1992
 RIMPro-Trapman, 1994
 Spraychek- Stewart et al., 1998
 A-SCAB
 µMETOS-Electronic Disease
Predictor for Apple Scab
36

41. Infection risk data of Mills infection periods,RIMPro and
Welte model
37

42. RIMpro Scab forecast model
38

43. RIMpro Scab forecast model for
the primary ascospores season
1 Leaf wetness periods
2 Periods of rainfall
3 Ascospore potential
4 Ripe ascospores
5 Discharged ascospores
6 Infecting spores = RIM Wert
7 Amount of living spores on the
leaf
Secondary infections on leafs
and fruits in RIMpro
39

44. Broadcasting
of disease
forewarning
and
management
Direct contact
of control lab
with AIR
Installation of
disease
diagnosis lab in
every affected
fruit belt
Forewarning
through scab
predictor
Compilation of
disease forewarning by
control lab
Scab management strategy through
warning services
40

45. Management of apple scab
41

46. 42

47. Cultural control-
Reducing primary inoculum-Fall
treatments-Mechanical sanitation
process and application of urea.
Burning Apple scab-infected leaf litter Shredding overwintering leaves in the
spring with a flail mower
43

48. 44

49. Total ascospore production during spring 1996, 1997 1998 and 1999 from
scabbed leaves
45

50. Chemical control-
 Use of sterol biosynthesis inhibiting fungicide
 Use of strobilurin fungicides
 Other approaches to chemical control
45

51. Protective spray schedule
Tree stage Chemicals
Silver tip to Green tip stage Mancozeb(0.3%) or Dodine(0.1%)
or Captan (0.3%)
Pink bud stage Mancozeb (0.3%)+ Sulphur(0.2%)
Petal fall stage Carbendazim or Thiophenate
methyl (0.05%)
Pea sized fruit stage Dodine (0.075%) or Mancozeb
(0.3%)
Walnut sized fruit stage Carbendazim (0.025%)+
Mancozeb (0.25%)
Fruit development stage Captan(0.3%) or Mancozeb(0.3%)
20-25 days before harvesting Captan(0.3%) or Mancozeb(0.3%).
Handbook of Horticulture(2010)
46

52. 47

53. Spray schedule for the control of apple scab at Harsil fruit belt of
Garhwal hills
Tree stage I II III IV V
Petal fall Carbendazim
(0.05%)
Thiophanate
methyl (0.1%)
Mancozeb(0
.30%)
Bitertanol
(0.075%)
Chlorothalonil
(0.20%)
Fruit set
(pea size)
Fenarimol
(0.04%)
Dodine (0.1%) Captan
(0.20%)
Carbendazim(0.
05%)
Fenarimol
(0.04%)
Fruit
development(
walnut size)
Dodine
(0.1%)
Bitertanol
(0.075%)
Thiophanate
methyl
(O.1%)
Fenarimol
(0.04%)
Dodine
(0.1%)
Fruit
development
Thiophanate
methyl
(O.1%)
Fenarimol
(0.04%)
Dithianon
(0.075%)
Mancozeb
(0.30%)
Dithianon
(0.075%)
20-25 days
before
harvest
Mancozeb
(0.30%)
Mancozeb
(0.30%)
Bitertanol
(0.075%)
Captan(0.20%) Mancozeb
(0.30%)
Pre-leaf fall Urea
(5%)
Urea (5%) Urea(5%) Urea(5%) Urea(5%)
48

54. Effectiveness of different fungicidal spray schedules against apple
scab
Spray
Schedule
Reduction over
check
1993 1994 1995 Mean
L* F** L F L F L F
I 82.39 97.46 83.92 90.99 69.85 86.13 78.06 89.49
II 87.26 100.00 85.49 92.37 72.45 87.19 81.22 90.91
III 70.69 84.64 71.82 87.43 62.36 77.96 67.82 82.47
IV 79.28 87.99 77.87 90.10 67.64 85.04 74.44 87.35
V 75.87 83.37 74.24 89.21 64.48 83.66 71.08 85.73
* L( Per cent leaves); ** F( Per cent fruit)
49

55. Effect of different spray schedules on scab incidence and area under
scab progress curve (AUSPC) at different phenological stage of Red
Delecious apple trees*.
Spray
schedul
e
FS FD(pea
size)
FD(waln
ut size)
FD(3.6c
m)
BH AUSPC
I T 13.33 28.67 35.56 52.22 58.89 203.53
L 1.23 2.69 3.25 4.47 5.45 210.08
F 1.48 2.59 3.94 8.89 9.93 138.42
T 12.34 27.9 34.54 44.44 51.11 186.90
II L 1.16 1.24 3.30 4.52 4.91 207.38
F 1.08 2.46 2.02 7.68 8.37 134.03
T 14.34 56.67 61.10 70.00 78.89 219.89
III L 2.45 5.15 6.48 7.79 8.97 226.36
F 2.29 8.14 12.21 13.32' 15.44 202.58
Scab incidence
50

56. Table cont..
T 16.67 41.11 43.33 55.56 66.74 219.44
IV L 1.76 3.68 4.29 5.09 7.36 220.27
F 2.74 3.70 5.10 10.47 11.34 179.35
T 21.11 43.33 53.22 63.34 72.22 225.48
V L 1.93 3.97 4.6 1 6.71 8.81 211.52
F 2.82 4.73 8.22 11.47 12.07 185.38
T 44.22 76.67 91.11 96.67 100.00 253.84
Cont
rol
L 7.97 12.34 21.90 29.92 30.38 231.89
F 13.34 28.33 40.81 53.38 65.96 204.18
Spray
schedule
FS FD(pea
size)
FD(walnu
t size)
FD(3.6cm
)
BH AUSPC
51

57. Spray
schedul
e
Reduction in conidia
number
No. of viable
conidia
produced
lesion
Production
(%)
Germination
I 84.81 53.47 2598
II 89.67 58.53 0945
III 74.82 42.74 1876
IV 82.19 52.26 3688
V 81.56 50.38 5864
Antisporulant activity of fungicides used in spray schedules against
Venturia inaequalis on naturally infected Red Delicious apple trees
Antisporulant activity of fungicides used in spray schedules against
Venturia inaequalis on naturally infected Red Delicious apple trees
52

58. Effect of pre leaf fall spray of various fungicides and urea on the production of
pseudothecia and discharge of ascospores of Venturia inaequalis
Treatment Concentration Pseudothecia/
cm2
ROC Ascospore
discharged/c
m2
ROC
(Reduction
over chek)
Carbendazim 0.05 5.39 90.37 715 94.28
Fenarimol 0.04 23.79 59.10 4182 66.56
Dodine 0.10 28.17 51.57 6194 50.47
Thiophanate
methyl
0.10 11.53 80.18 2974 76.22
Mancozeb 0.30 18.18 68.75 4290 65.70
Bitertanol 0.075 21.42 63.18 4140 66.89
Dithianon 0.075 31.49 45.86 9220 26.28
Chlorothalonil 0.20 28.75 50.57 6528 47.80
Captan 0.20 18.42 68.33 4558 63.55
Urea 2.00 14.73 74.68 3278 73.79
Urea 5.00 3.15 94.58 563 95.50
Control - 58.17 - 12507 -
53

59. Other approaches to chemical control
 Use of the natural substances -selected organic and inorganic
salts, sodium bicarbonate(SBC ) and potassium bicarbonate
that have no adverse effect on environment and health.
 Application of 1% sodium bicarbonate to trees at 10 days
interval significantly reduced disease incidence and severity
on leaves and fruits.
54

60. Biological control
 Microsphaeropsis ochracea
 Athalia bombacina
 Chaetomium globosum
55

61. 56

62. Proportion of leaves with scab in subplots sprayed in the fall with
Microsphaeropsis ochracea
57

63. Proportion of fruit with apple scab in subplots sprayed in the fall with
Microsphaeropsis ochracea
58

64. Production of ascospores by Venturia inaequalis over time from
detached scabbed leaves sprayed with Microsphaeropsis ochracea on
different dates
59

65. Sources of Resistance
R gene Sources
Vf Malus floribunda 821
Vm M.micromalus
Vb M. baccata Hansen’s
Vbj M. baccata var jackii
Vr M. pumilaR12740–7A
Va Antonovka Selection
60

66. Introduced Scab resistant cultivars in India-
 Prima
 Priscilla
 Sir Prize
 Jonafree
 Florina,
 Macfree
 Nova easy grow 12
 Liberty
 Freedom.
61

67. 62

68. Evolution of scab incidence on fruits and scab incidence on leaves for each
apple cultivar, and level of the Mills infection periods
63

69. Mean AUDPC of scab incidence on fruit, scab fruit incidence at harvest and
scab fruit severity at harvest for the six apple cultivars in Bois l’Abbe´ in 2000
and 2001
Cultivar 2000 2001
AUDPC Fruit
incidence
at harvest
Fruit
severity at
harvest
AUDPC Fruit
incidence
at harvest
Fruit
severity at
harvest
Gala 130 1.00 79.4 66.2 0.979 71.3
Golden
Delicious
123 1.00 90.1 44.9 0.952 46.7
Reinette
Clochard
31.8 0.326 47.3 24.8 0.437 64.5
Firiki 11.4 0.239 6.83 15.9 0.220 58.1
Colapuis 4.20 0.031 13.0 18.4 0.220 0.220
64

70. 65

71. Progress of Scab Infection in Commercial Cultivars of Apple
in Gangotri Fruit Belt Area, Uttarakhand, India
66

72. Variability of Phenolic Acids in Leaves and Fruits of Apple Cultivars
Infected by Apple Scab [Venturia inaequalis (Cheq) Wint.]
67

73. 68

74. Challenges
Full understanding about omics ofpathogenicity in V. inaequalis.
Need of whole genome sequence of Venturia inaequalis for the
comparative analysis of different races.
More information is needed on factors that affect the relationship
between ascospore discharge, deposition and infection.
Develop Microsphaeropsis ochracea as a commercial biocontrol
agent.
69