The document discusses the apple scab fungus, its life cycle and symptoms, which include olive-green lesions on leaves and fruit that can lead to defoliation and loss of crop yield. It notes the fungus was first reported in Sweden in 1819 and spreads via ascospores in spring and conidia throughout the growing season, infecting leaves, fruit, and other plant parts. Control recommendations include using resistant varieties, clean cultivation, and a fungicide spray schedule from silver tip through fruit set.

2. Department of Plant Pathology
College of Agriculture,
Junagadh Agricultural University,
Mota-bhandariya (Amreli)
Submitted by- Tushar Kumbhani
Roll no.- 44
Reg. no.- 5010518005
Submitted to- Dr V C Gadhiya
(Assistant Professor)

3. Apple Scab

4. Introduction
 Apple 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.
 First reported from Sweden (1819)
 First reported on Ambri variety in Kashmir valley (1935)
 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.

5.  Disease losses attributable to apple scab if scab control measures are not
taken
 Reduction in amount and quality of marketable apple harvest.
 Poor fruit bud development for next year.

6.  Reduction in crabapples aesthetic appeal and wildlife value
caused by premature defoliation and fruit drop.

7.  .

8.  Susceptible Plant Parts
 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
 young twigs/shoots

9.  Lower Leaf surface
 In spring, first spots (lesions) usually located on lower
surface of expanding leaves

10.  Upper Leaf surface
 Lesions progress to olive-green to brown coloration and
velvety texture. As fungal growth stops the lesion margins
change from feathery, indistinct to distinct

11.  Fruit
 circular, necrotic olive
green or brown coloured
warty lesions with distinct
margins on fruit infected
early in development
 fruit infected late in season
Ä small black spots of
“pinpoint” scab noticeable
after harvest apples in
storage

12.  Pedicel just after Petal Fall
 Small, dark green lesions on pedicel before, during,
or after bloom

13. Disease Cycle

14.  Pathogen
V. inaequalisis an Ascomycetes sac fungus producing both sexual and
asexual spores
ascosporesare sexual spores that initiate
one primary cycle of apple scab disease
annually
Inaequalis named for unequal sized
brown “foot print” shaped two-celled
spores
 conidia are asexual spores that initiate
one or more secondary cycle(s) of
apple scab disease annually
 cycle name Spilocaea pomi

15.  V. inaequalisbelongs to the group of pathogenic fungi known
as hemitrophes
 Äparasitic phase is spent as mycelium and spores on living
tissue penetrating only the cuticle and staying between cuticle
and epidermal cells.

16.  Saprophytic phase overwinters as pseudo theciainitial
penetrating dead leaf tissue of fallen debris.

17.  Dissemination
 Movement of fungal pathogen V. inaequalis is passive
 Moisture 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

18.  Inoculation
 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

20. Management
.

21.  Clean cultivation
 Resistant varieties: Emira, red free, Ambstraking,
Ambroyal, Ambrich and Ambred
 Spray captan@0.2% or dodine@0.25% at short
intervals after petal fall
 Single application of difolaton@0.3% at green bud
stage followed by captan@0.2% at petal fall

22.  Spray schedule
 1st spray - Silver tip stage - 0.2% captofol (or)
0.3% captan
 IInd spray pink bud - 0.2% captan (or) 0.3%
mancozeb
 IIIrd spray at petal fall - 0.5% carbendazim
 IVth spray - after 10 days - 0.2% captan
 Vth spray - 15 days after - mancozeb 0.3%
 • Fruit set - 0.15% captafol