ONION DISEASES

1. WEL-COME

2. Assignment on
DISEASES OF ONION
AND GARLIC AND
THEIR MANAGEMENT
Submitted By: -
Vakaliya Mustufa
M. Sc. (Agri.)
Agril. Entomology,
BACA, AAU, ANAND
Sub. PL. Path.- 509 (Diseases of Vegetables and
Spices Crops)

3. DISEASES OF ONION AND GARLIC
AND THEIR MANAGEMENT
Introduction
Onion (Allium cepa L.) and garlic (Allium sativum L.) are two most
important bulbous vegetables crops cultivated in many countries of the
world. In India, it is grown in an area of 0.29 Mha With annual
production of 3.14 million tones production of bulbs for local
consumption as well as for export. The main onion growing states are
Maharashtra, Uttar Pradesh, Haryana, Punjab, Gujarat, TamilNadu,
Andhra Pradesh. Among these Maharashtra is leading with about 26
percent of country production (Pathak, 1994).The onion and garlic
crops are susceptible to several diseases of fungal, bacterial and viral
diseases which cause substantial production losses. A detailed review
of various diseases affecting these crops along with management
strategies is given below.

4. FUNGAL DISEASES
1. DOWNEY MILDEW
C.O. Peronospora destructor (Berk)
Geographical distribution
The diseases was first time reported from England in 1841
by Berkeley (Yarwood, 1943) subsequently , it was reported
from Bermuda , USA, Canada, brazil , Iraq, Holland,
Australia etc. in India, these diseases was first time
reported from Kashmir valley during 1974-75
seasons(Mirakhur et. al.,1978).
Losses
In India, the losses from these diseases ranges from 12-75
per cent in crop yield depending on the time of diseases
outbreak and disease severity (Sugha and Singh, 1991).

5. Symptoms
• Symptoms differ with the type of infection. Infection develops from
three different sources like systemically infected perennating
leaves, plants grown from infected onion bulbs or from local lesion
resulting from air borne inoculum.
• Systematic infection occurs when the plants are raised from
diseased bulbs or infected seedlings used for planting.
• Plants raised from such bulbs remain stunted, become distorted
and light green in colour.
• In humid weather condition, sporulation develop on the leaves and
cover them with felty whitish to grayish fungal growth.
• In secondary and local infections, spots with greenish and chlorotic
zones appear and at times at the points of infection , the plants fall
off.
• In humid weather the fungus develops as white to purplish downy
growth on these spots. In such cases undersized bulbs are
produced.

7. Favorable condition
• Cool, moist nights and moderate warm days
for development of disease
• Heavy dews atmosphere
• Cloudy days
• Humid atmosphere with 4 to 250C temp. with
optimum 130C
• Germination of pathogen occur at temp. 7 to
160C and the optimum lies between 10 to
130C

8. Disease cycle
The carry-over of the fungus from the one season
to another may occur as mycelium in the bulbs,
sees or soil , as oospore on or in the seeds or in
plant debris (yarwood, 1943) and systemically
infected onion bulbs are another important
source of primary infection ,. Bur role of oospores
has not been established in induction of disease
even under controlled conditions(Virayni, 1981).
The onion seedlings from disease prone play
important role in introduction of disease in new
localities. Secondary infection is caused by wind
borne sporangia disseminated from the plants
with primary infection.

9. Management
• cultural practices like use of healthy bulbs for planting.
• collection and destruction of infected crop debris
• crop rotation with non-host crops
• Application of balanced doses of fertilizers along with
potassium as the increases in level of potassium
decreases diseases severity (Devlash and Sugha, 1997).
• use of resistant varieties like as IC-48045, IC-32149,
DOP-11(sharma, 1997)
• Spray crop with various systematic and non-systematic
fungicides like as Mancozeb or Zineb , Copper
oxychloride, propineb, metalaxyl+ Mancozeb etc. have
been reported to check downy mildew effectively (Mir
et.al.,1987, Khalid et. al.,2002)

10. 2. PURPLE BLOTCH
C.O.: Alternaria porri(Ellis) Cif.
Geographical distribution
The disease was first time reported from
Bombay (Ajrekar, 1921). Since then has been
reported from many states of the country like
Maharashtra, Gujarat,Tamilnadu, Rajasthan,
Haryana and Punjab (Pandotra, 1964).
Losses
The disease causes 20-25 per cent losses to
the onion seed crop (Pandotra, 1981)

11. Symptoms
• The characteristic symptoms of the
diseaseappear as a small, light coloured, sunken
lesions, which become zonated with purplish
center.
• These lesions rapidly enlarge and eventually
girdle the leaf or inflorescence stalk.
• In moist weather the surface of the spot is
covered with the brown or almost black
sporulation of the fungus.
• Usually the affected leaf or stem falls down and
dies within 3 or 4 weeks under favorable
environmental conditions.
• In garlic these disease appears on leaves with the
similar symptoms.

13. Disease cycle
The fungus survives from one season to other in
infected plants debris as dormant mycelium. the
fungus can also survive in diseased onion leaves
and seed stalk debris for 12 month buried at 5
to7.5 cm depth (Gupta and Pathak,
1988).wherever the chlamydospores of the
fungus are formed they can also serve as source
of perrenation, invasion takes place either
through stomata or directly through the cuticle ,
to form an intercellular mycelium, which in turn
forms conidiospores and conidia. Conidia
produced on the primary infection lesions serve
as the source of secondary inoculum.

14. Favorable condition:
• The fungus requires rain or persistent dews for reproduction and
penetration.
• The optimum temperature for disease development is 21 – 300C and
relative humidity above 90%.
Management
• various cultural practices like use of healthy seed/planting materials ,
crop rotation with non-related crops, collection and destruction of
infected debris , good drainage , summer ploughing (Srivashtva et. al.
1996)
• use of recommended doses of fertilizers
• Hot water (500C for 20 min. )soak was found to be highly effective in
reducing seed borne inoculum (Aveling et. al.,1993)
• Use of disease resistance varieties viz. Pusa red, IIHR-56-1, hybrid
PVM-7 etc.
• Spraying crop with Copper oxychloride , mancozeb, Metalaxyl+
mancozeb , Fosetyl-as, Difenconazole etc with recommended
doses.(Sastrahidayat, 1994).

15. 3. STEMPHYLIUM BLIGHT
C.O :Stemphylium vesicarium (Wallr.)
Geographical distribution
The disease has been reported from united
states , south Africa , Venezuela(Millar et. al.
1978) in India the occurrence of this disease
on onion was first reported from Uttar
Pradesh during 1973 while on garlic it was
reported on Kullu ,Himachal Pradesh during
1973 (Singh and Sharma, 1977).

16. Symptoms
• The main symptoms of the disease appear in the
middle of the leaf as small, yellow to pale orange
flecks or streaks which later develop into
elongated spindle shaped diffused spots
surrounded by characteristic pinkish margin.
• The spots turn grey at the center and later
become brown to dark brown with the
appearance of conidiospores and conidia of the
fungus.
• Gradually the entire foliage is blighted. Similar
symptoms also develops on inflorescence stalks.

18. Disease cycle
• The pathogen survives in infected plant debris. In
favorable weather spores from the debris are splashed
to the lower leaves and cause infection. Spores
produced on the primary infections cause secondary
infections.
Management
• use of healthy planting materials
• two to three years crop rotation with non host crops
• Collection and destruction of infected plant debris to
reduce inoculum load.
• Spraying crop with Carbendezim 0.2 % or Propineb
,chlorothalonil, difenconazole etc. for effective
management of this diseases.

19. 4. BASAL ROT/BULB ROT
C.O.: Fusarium oxysporum f.sp.cepae
Geographical distribution
• This disease is prevalent in almost all parts of
the world where onion are grown ( Evertset
al.,1985). In India the occurrences of this
disease was first reported from Rajasthan
(Mathur and Sankhala, 1963).

20. Symptoms
• The main symptoms appear as wilting and rapid
dying back of leaves from the tips of the plant
near maturity.
• Watery decay on open the soft bulbs are evident.
• Infected garlic show reddish or reddish purple
discoloration on stem and bulbs early in the
season with some discoloration on bulb sheath at
harvest.
• Infected stem plates may show of brown
discoloration.
• Infected bulbs may rot during storage.

22. Disease cycle
• The fungus over winter in the infected onion sets, garlic
cloves and in soil, in soil the fungus perennates as
chlamydospores. The pathogen may be disseminated
widely through infected onion sets and garlic cloves.
Management
• The diseases can be kept under check by following cultural
practices like long crop Rotation, mixed cropping with
tobacco and jowar , green manuring to increases
antagonistic microbial population in soil.
• Resistance varieties. Viz. hf-555, IIHR Yellow, Hybrid-1.
• Spraying crop with Mancozeb, carbendazim have been
found good efficacy against basal rot (Naik and Burden ,
1981, Gupta et. al.,2000).
• Pre-harvest sprays of Carbendezim(0.1%) reduced decay of
stored onion even after 5 month of storage (Shrivastva and
Tiwari , 1997).

23. 5. RUST
C.O. Puccinia porri (Sow.)
Geographical distribution
The diseases is widely distributed in
temperate regions of the world. The
occurrences of the diseases has been reported
from different parts of Europe, USA, and Asia
(Walker, 1951). In India, the prevalence of this
disease on garlic has been reported from
Ludhiana in 1987 (Sadhu and Kang, 1988).

24. Symptoms
• Early symptoms appear as of small yellow to white flecks,
streaks and spots on leaves.
• As these small areas expand, the leaf tissue covering them
breaks and the orange spores (urediniospores) of the
fungus become visible as pustules.
• Resulting in complete yellowing,wilting and drying of the
leaves.
• As the disease progresses, teliospores may occur on the
same leaves, resulting in black pustules on infected onions
and chives, symptoms consist of small, white to tan spots.
• The orange pustules often from concentric group on the
spot periphery.
• Disease severity on onion and chives is significantly less
severe than on garlic.

26. Disease cycle
• The fungus probably overwinters in plant debris and
also in the soil as teliospores. Urediniospores are
repeative spores and spread and cause secondary
infection.
Favorable condition
• Cool temperature, high humidity, no heavy rainfall,
frequently dews formation and moderate day
temperature
Management
• Crop rotation and sanitation help in reducing the initial
inoculum level in the soil.
• Eradication of alternative hosts from nearby area to
avoid contamination is useful.
• Spraying crop with Copper oxychloride, or Triadimefon
,Propiconazole etc. at recommended doses.

27. 6. ONION SMUDGE
C.O.: Colletotrichum circinans (Berk)
Geographical distribution
The disease is wide spread in temperate
regions of the world and was first described in
England. Since than it has been reported from
many countries of the world like USA, japan ,
Argentina and European countries. The
disease is of common occurrence in India also.

28. Symptoms
• The disease is characterized as small dark green to
black dots that appear on the outer scales.
• These small dotes are scattered over the surface of the
bulbs or grouped together in concentric rings giving a
smudge appearance to the white onions.
• During moist conditions, acervuli of the fungus develop
on the infected areas and spore masses and the setae
can be easily recognized fleshy scales resulting in
yellow depressions on the bulb.
Favorable condition
• Temperature ranges from 10 to 320 C
• Excessive rainfall.
• Moist condition are essential for production of conidia.

30. Management
• Cultural practices like as crop rotation , good
drainage, use of healthy seed materials,
(Walker, 1952)
• Protection of the harvested crop from rains,
rapid and through curing and provision of
well- ventilated storage also reduce the
incidence of the disease.
• Pre-harvest sprays either of Carbendezim or
Mancozeb reduce the infection of this disease
under storage conditions.

31. VIRAL DISEASES
7. GARLIC MOSAIC
C.O.: Garlic Mosaic Virus (GMV)
Geographical distribution
This viral disease prevalent in different garlic growing areas.
(Ahlawat, 1997). Reported the disease from Laimpong town of
Darjeeling (West Bengal) India for the first time.
Symptoms
• The infected plants show typical mosaic symptoms and yield is
also recorded comparatively less than in healthy plants.
• Foliar symptoms can vary greatly, but most consists of mild to
severe mosaic, streaking , striping and chlorotic mottling.
• Symptoms are often most evident in the youngest leaves.
• The overall effect is generally bulb size and yield reductions of
up to 50%.

33. Transmission
• The virus is easily transmissible by two species
of aphids viz. Myzus persicae Suzl. And Aphis
gosypii Grover to garlic only and not to any
other crop.
Management
• Crop rotation and field sanitation help in
reducing the diseases.
• spraying crop with Dimethoate (roger) or
Monocrotophos 36 SL for control of vector.

34. STORAGE DISEASES
Neck rot
C.O.: Botrytis allii
Symptoms:
• This is a wide spread and most destructive storage
disease of onion
• Mildly pungent varieties are more affected
• It has latent infection, thus infection takes place in the
field
• Pathogen causes softening of scales giving a water
soaked appearance
• Under moist condition a greyish sporulatingmycelial
mat develops on the surface of the scales, causing
secondary spread of the diseases.

36. Disease cycle:
• The fungus persists saprophytically on dead onion
tissue, on humus in soil and as sclerotia near the
surface of previous onion crop soils. Sclerotia
germinate in moist weather and produced conidia that
are disseminated by air currents.
Management:
• Dusting the seed with benomyl 1g/kg as soon as after
harvest
• Rapid and thorough drying of bulbs after harvest
• Apply recommended doses of nitrogenous fertilizers
• Presence of downy mildew, weeds and wind barriers
should be avoided
• Onions should be stored in slatted crates or wooden
tubs so that air can circulate thorough and around
them.