healthy and vigorous crop is the ultimate aim of all farmers because
a poor and diseased crop simply deprives funds available with one
without any output. Onion crop is victim of several enemies each
of which requires specific management practices. Major diseases
and insect pests and their control measures are given below :
Caused mainly by Fusarium oxysporum fungus, this is
very common in almost all onion-growing pockets. Pythium
sp. has also been reported to cause damping off disease in some
pockets. The disease is more prevalent in Northern and Eastern parts
of the country during kharif season, causing 60-75% damage.
Two types of symptoms are observed.
damping off : The fungus kills the radicle and plumule of seed
before emergence from soil.
Post-emergence damping off : The pathogen attacks the collar
region of seedlings on the surface of soil. The collar portion rots
and ultimately the seedlings collapse and die.
managing the disease, healthy seeds should be selected for sowing. The
seed should be treated with thiram @ 2g/kg before sowing. Continuous raising
of nursery in a particular plot should be avoided. Top soil of nursery
should be treated with thiram @ 5 g/m² area and nursery should be drenched
with the same chemical @ 2 g/litre of water at fortnightly interval. Soil
solarization using 250-gauge polythene for 10 days before sowing and application
of Trichoderma viride in soil @ 1,250 g/ha is also effective to
control damping off to a considerable extent.
blotch is caused by Alternaria porri . The disease occurs
under favourable conditions of temperature 28-30ºC and 80-90% relative
humidity. It is more common in kharif season in Maharashtra.
Small, sunken, whitish flecks with purple coloured centres are common
symptoms occurring on leaves and flower stalks. Further, large purple
area develops forming dead patches. The intensity of disease varies
from season-to-season. It causes losses of 25% in rabi, 50%
in kharif in Maharashtra, while in Northern and Eastern parts
25-90% damage in bulbs and seed crop occurs when the disease appears
along with stemphylium blight.
managing the disease effectively, healthy seed should be used. Crop
rotation of 2-3 years with non related crops should be followed.
Further, mancozeb @ 0.25% or chlorothalonil @ 0.2% or rovral @ 0.25%
should be sprayed at fortnightly interval commencing from one month
after transplanting. The sticker triton/sandovit should be mixed
in spray solution.
This disease is very common in Northern and Eastern
India on onion leaves as well as flower stalks. Disease intensity
varies from 20 to 90% in seed crop and 5 to 50% in bulb crop. Infections
occur on radial leaves of transplanted seedlings at 3-4 leaf stage
during late-March and early-April. Small yellow to pale-orange spots
or streaks develop on middle of leaves/flower stalks on one side.
The casual organism is Stemphylium vesicarium. Disease
can be managed effectively if mancozeb @ 0.25% along with monocrotophos
@ 0.18% with sticker triton is sprayed at fortnightly interval starting
before appearance of symptoms.
The disease has been reported
from Maharashtra. It is caused by Colletotrichum gloeosporides.
Its symptoms initiate as pale-yellow water-soaked spots which increase
in length covering whole leaf producing numerous black coloured
slightly raised structures in central portions. These structures
appear in concentric rings. Affected leaves shrivel, droop down
and finally wither. Spraying of mancozeb @ 0.25% or carbendazim
@ 0.1% gives good control.
Caused by Golmerella cingulata, it has
made its occurrence recently in India during kharif season.
Curling, twisting of leaves, chlorosis and abnormal elongation of
neck portion are major symptoms. Bulbs development is affected.
Crop hygiene, use of quality seeds, seed treatment with thiram @
2 g/kg before sowing and spraying with ziram based fungicides like
cuman L @ 0.3%, dithane Z-78 @ 0.25% or soil treatment with benlate
@ 2 g/m² and spraying @ 0.1% benlate are its control measures.
Caused by Perenospora destructor,it is reported
from Northern hilly track and plains particularly humid locations. On
the surface of leaves or flower stalks violet growth of fungus is noticed
which later becomes pale-green yellow and finally leaves or seed stalks
managing the disease effectively, onion bulbs meant for seed crop should
be exposed to sun for 12 days or heated for 4 hours at 41ºC to destroy
the fungus. Spraying of 0.2% zineb also gives good control.
smut is caused by Urosystis cepulae. In India, it is reported
in Karnataka on small onions. The fungus survives in soil in area
where temperature remains below 30ºC. Since the fungus remains in
soil, disease appears on cotyledons of young plants soon after it
emerges. Smut appears as elongated dark, slightly thickened areas
at the base of seedlings. The black lesions appear near the base
of scales on planting. The affected leaves bend downwards abnormally.
On older plants numerous raised blisters occur near the base of
leaves. The lesions on plant at all stages often expose a black
powdery mass of spores. The fungus becomes inactive at soil temperature
of 26.7ºC and above.
disease can be controlled by treating the seeds with captan or thiram
@ 2.5 g /kg of seed before sowing. Seed-bed soil treatment with
methyl bromide at 1 kg/25 m2 or alternative application
of formaldehyde solution @ 8 ml/litre of water /10m2
is effective in controlling the disease.
Caused by Aspergillus niger, it is characterized
by black powdery mass of spores that are borne on exterior of the
scales and can be rubbed off easily. Black spore masses are also
seen on inner scale. For effective control, bulbs should be thoroughly
cured after harvesting and crop should be saved from rains.
Basal rot caused by Fusarium oxysporum,
is a widespread disease. Yellowing of leaves and stunted growth
are its first symptoms. Later on drying of leaves from tip to downwards
is noticed. In early stage of infection, roots of plants become
pink in colour and rotting takes place later. In advanced stage,
bulbs starts decaying from lower ends and ultimately whole plants
die. Drenching with carbendazim @ 0.1% is good for checking the
growth of fungus. Five-year rotation with other crop is also recommended
as its pathogen survives in soil. Dipping of seedling in 0.1% carbendazim
also reduces basal rot in bulb crop significantly.
by Colletotrichcum circinans, it is not very common in
India. Sometimes it occurs on white bulb varieties, reducing market
value of bulbs due to blemishing dots on outer scales. It is characterized
by small-dark green to black dots which appear on outer scales.
disease can be managed by thorough curing of bulbs after harvesting
and storing them in well-ventilated rooms.
The disease is caused by bacteria , Pseudomonas
aeruginosa. It is very serious disease of stored onions in
tropical countries especially in India. The rot begins at the neck
of bulbs, later it gives off smell through the neck when squeezed.
Proper curing and rapid drying of bulbs after harvesting are essential
for managing the disease. Bulbs showing disease symptoms should
be discarded before storage. Spraying of streptocycline @ 0.02%
before harvesting if rains occur at maturity, is suggested to reduce
This is a viral disease caused by onion yellow dwarf virus. Its diagnostic
symptoms are severe stunting of plants, dwarfing and twisting of flower
stalks. The affected leaves and stems change their normal green colour
to various degrees of yellow and leaves tend to flatten and crinkle and
as a result bend over. The virus is transmitted mechanically as well as
by insect vectors. Diseased plants should be removed and burnt. Spary
malathion (0.1%) or metasytox (0.1%) . Healthy bulbs should be used for
Thrips (Thrips tabaci) is most injurious
insect pests of onion. These are common all over the country where
onion crop is grown. Onions infected with thrips develop spotted
appearance on leaves which turn pale-white blotches due to drainage
of sap. Sometimes 50-60% losses in bulb crop are observed due to
thrips attack. Seed production including viability of seeds are
hampered due to attack of thrips. The insect is very minute and
yellow to dark brown in colour. The life-cycle of insect is 8-10
days. It is found in the axil of green leaves where it sucks juice
of early-emerging leaves. The adults hibernate in soil, on grass
and other plants in onion fields. The thrips also over-winter in
bulbs and act as source of infestation in the following year. They
multiply in a large number during March-April on seed and bulb onions
in Northern parts of India, whereas at Nasik incidence is observed
even in January-February. The infested plants show stunted growth
with twisted leaves. If the infestation comes in early stage of
growth, bulb formation stops completely and plants die slowly. Bulbs
in store are also attacked by thrips. Malathion (0.1%) or metasystox
(0.1%) and cypermethrin (0.01%) or deltamethrin (20 ml/ha) should
be sprayed along with triton or sandovit to control the insect.
Soil application of phorate or carbofuran granules @ 1 kg ai/ha
is also recommended.
Head-borer (Heliothis armigera) is a serious pest of onion seed
crop in Northern India. Its larva cuts the pedicel of flowers and feeds
on stalks. Many flower stalks are damaged by single larva. The bulb crop
is also damaged by larva by cutting and eating aerial portions of plant.
The fully-grown larva is greenish with dark brown gray lines along with
the side of body and measures about 35-45 mm in length. Larva pupates
inside scape. It also pupates in soil. Spraying of endosulfan or zolone
(2-3 ml/litres of water) along with triton/sandovit sticker is recommended
to control it. Soil application of chloropyriphos (5 ml/litre) can also
control this pest.
The adults of onion maggot (Hylemia antiqua) appears like house
fly. The flies lay their eggs on old leaves or on soil and larva enters
into soil and damage disc portion of onion bulb. Infested plants turn
yellowish brown and finally dry up. The affected bulbs rot in storage
as infestation leads to secondary infection by pathogenic organisms. The
crop rotation should be followed and thimet should be applied in the soil
The larvae of cut worms (Agrotis ipslon) are seen in nursery-beds
and newly-transplanted onion fields. The tender plants are damaged at
ground level during the night. The moth of insect has dull brownish forewings
with numerous wavy lines and spots, and brown coloured hind wings. The
larva is dark brown with a red head. Soil application of carbofuran (1
kg ai/ha) at the times of planting is recommended. Cloropyriphos (5 ml/litres
of water) also controls this pest.
Dry weather is conducive to infestation of mites (Rhizoghyphus sp.).
It sucks the sap turning the plants pale with sticky appearance. It also
infects stored onions, inducing sprouting. The mite is reddish-green with
8 legs and measures about 4 mm. Application of sulhpur dust (22 kg/ha)
is recommended. Spraying of kelthane (0.1%) also gives good control to