Onion: Diseases and Symptoms Damping off Purple blotch Stemphylium leaf blight Colletotrichum blight/anthracnose/twister ...
Onion: Diseases and
Symptoms
- Damping off
- Purple blotch
- Stemphylium leaf blight
- Colletotrichum blight/anthracnose/twister
disease
- Fusarium basal rot/basal rot
- White rot (Sclerotial rot)
- Pink root rot
- Black mould
- Bacterial soft rot
- Iris yellow spot disease
- Onion yellow dwarf disease
- Downy mildew
- Green mould
- Bacterial brown rot
- IPM for Onion
Damping off
Disease
symptoms
Two types
of symptoms are observed
Pre-emergence damping-off: This results in seed and seedling rot before they
emerge out of the 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.
Survival and spread
- Pathogen(s) survives on
infected crop debris and soil which are source of primary inoculum.
Favourable conditions
- The disease is more prevalent
during Kharif season/rainy season and causes about 60-75% damage.
- High soil moisture and moderate
temperature along with high humidity leads to the development of the
disease.
Purple blotch
Disease symptoms
The
symptoms occur on leaves and flower stalks as small, sunken, whitish
flecks with purple coloured centres.- The lesions may girdle
leaves/stalk and cause their drooping. The infected plants fail to develop
bulbs
Survival and spread
- The disease is soil borne and
fungus survives in soil, infected bulbs and may persist in plant debris or
on roots of weeds.
Favourable conditions
- Hot and humid climate with
temperature ranging from 21-30°C and high relative humidity (80-90%)
favour the development of the disease.
Stemphylium leaf blight
Disease symptoms
Infection
occurs on radial leaves of transplanted seedlings at 3- 4 leaf stage
during late March and early April.- The symptoms appear as small
yellowish to orange flecks or streaks in the middle of the leaves, which
soon develop into elongated spindle shaped spots surrounded by pinkish
margin.
- The disease on the
inflorescence stalk causes severe damage to the seed crop.
Survival and spread
- The fungus survives in plant
debris or soil.
Favourable conditions
- Warm (18-25°C) humid conditions
and long periods of leaf wetness (16 hours or more) favour disease
development.
Colletotrichum blight/anthracnose/twister
disease
Disease symptoms
The
symptoms appear initially on the leaves as water soaked pale yellow spots,
which spread lengthwise covering entire leaf blade.- The affected leaves shrivel and
droop down.
Survival and spread
- The fungus can survive for many
years as sclerotia in the soil or for shorter periods in infected plant
debris.
Favourable conditions
- Disease is most severe in warm
[25-30°C], moist soils that are high in organic matter.
- Fungal growth rapidly decreases
below 15°C, resulting in little disease development.
Fusarium basal rot/basal rot
Disease symptoms
Initially
yellowing of leaves and stunted growth of plant is observed, which later
on dry from tip to downwards.- In early stage of infection,
the roots of the plants become pink in colour and rotting take place
later. In advanced stage, the bulb starts decaying from lower ends and
ultimately whole plant dies.
Survival and spread
- Pathogen survives in soil and
onion bulb as a primary source of inoculum in the form of Chlamydospore,
resting spore) for many years.
Favourable conditions
- Moist soil and 27°C temperature
favours the development of disease.
White rot (Sclerotial rot)
Disease symptoms
The
initial symptoms are yellowing and dieback of leaf tips. Later, scales
stem plate and roots get destroyed.- The bulbs become soft and water
soaked.
- Later, white fluffy or cottony
growth of mycelium with abundant black sclerotia resembling mustard grain
develops on the infected bulbs.
Survival and spread
- Fungus survives in soil as
sclerotia for many years and it can over-winter in infected onion debris
and in diseased onion sets.
Favourable conditions
- This disease is most severe in
cool and dry soils.
Pink root rot
Disease symptoms
Reduced
bulb size.- Roots turn pink or maroon when
infected.
- In severe cases the roots may
die and the plants become weakened or stunted, especially in drier areas
of the field.
- Crop suffering from heat or
drought stress due to poor soil is more prone to yield losses.
Survival and spread:
- Fungus can survive in the soil,
in diseased roots and the debris of susceptible crops for several years.
- The fungus can be spread
through soil movement and in irrigation water.
Favourable conditions:
- This disease can develop at all
soil moisture levels that allow onion growth. Optimum temperatures for
growth of the pathogen and disease development are 24-28°C.
Black mould
Disease symptoms
Infection
usually is through neck tissues as foliage dies down at maturity.- Infected bulbs are discolored
black around the neck, and affected scales shrivel.
- Masses of powdery black spores
develop as streaks along veins on and between outer dry scales.
- Infection may advance from the
neck into the central fleshy scales.
Survival and spread
- Fungus survives in air, soil
and infected plant debris.
- Spores of this fungus are very
common in the air and soil which are the source of infection.
Favourable conditions
- Black mold is most common when
temperatures are higher than 30°C (86°f ) in the field or 24°C in storage.
- Free moisture for six hours or
longer on the onion surface is necessary for infection to occur.
Bacterial soft rot
Disease symptoms
Bacterial
soft rot is mainly a problem on mature bulbs. Affected scales first appear
water-soaked and pale yellow to light brown.- As the soft rot progresses,
invaded fleshy scales become soft and sticky with the interior of the bulb
breaking-down.
- A watery, foul-smelling thick
liquid can be squeezed from the neck of diseased bulbs.
Survival and spread
- The pathogen is soil borne and
after heavy rains and when leaves are drying the main sources of inoculum
are contaminated soil and crop residues.
- The bacterium is also spread by
splashing rain, irrigation water and insects.
Favourable conditions
- This disease is favored by warm,
humid conditions with an optimum temperature range of 20-30°C.
- However, during storage or
transit soft rot can develop when temperatures are above 3°C.
Iris yellow spot disease
Disease symptoms
Symptoms
of iris yellow spot virus are often seen as a cream, elliptical spots on
the leaves. The spots also appear on onion scapes or flower stalks of
onions.- As both infected leaves and
scapes age, they can collapse at the site of the spots. The spots may be
clear or less obvious. Although the spots may at first be insignificant,
the disease has the potential of devastating the whole crop.
Transmission and favourable conditions:
- Onion thrips (Thrips tabaci)
transmit IYSV in a persistent manner. Disease severity is positively
correlated with thrips populations in the field.
- This virus is not seed
transmitted. over-wintering onions, volunteers from prior productions,
infected transplants and alternate hosts can all serve as sources of both
vector and virus.
Onion yellow dwarf disease
Disease symptoms
The
first symptoms of onion yellow dwarf in young onions are yellow streaks at
the bases of the first true leaves.- All leaves developing after
these initial symptoms show symptoms ranging from yellow streaks to complete
yellowing of leaves.
- Leaves are sometimes crinkled
and flattened and tend to fall over. Bulbs are undersized.
Transmission and favourable conditions
- The virus is carried by
infected seed bulbs, onion sets and volunteer onions. Many aphid species
can transmit this virus from infected to healthy plants.
Downy mildew
Disease symptoms
Leaves
turn to pale green.- On leaves, cottony white
mycelial growth develops and appears white. Gradually the leaves turn pale
yellow to dark brown and dries up.
Survival and spread
- Fungus survive in soil and
infected plant debris.
Favourable condition:
- Warm and humid climate favours
the development of disease.
Green mould
Disease symptoms
Infection
usually is through neck tissues as foliage dies down at maturity.- Infected bulbs are discolored
green around the neck, and affected scales shrivel.
- Masses of powdery green spores
generally are arranged as streaks along veins on and between outer dry
scales.
- Infection may advance from the
neck into the central fleshy scales.
Survival and spread
- Spores of this fungus are very
common in the air and soil which act as the source of infection.
Favourable conditions
- Black mold is most common when
temperatures are higher than 30°C in the field or 24°C in storage.
- Free moisture for six hours or
longer on the onion surface is conducive for infection to occur.
Bacterial brown rot
Disease symptoms
Field
symptoms often appear as one or two wilted leaves in the center of the
leaf cluster. These leaves eventually turn pale yellow and dieback from
the tip while older and younger leaves maintain a healthy green
appearance.- During the early stages of this
disease, the bulbs may appear healthy except for a softening of the neck
tissue. In a longitudinal section, one or more inner scales become watery
or cooked.
- The disease progresses from the
top of the infected scale to the base
- Eventually, all the internal
tissue will rot. Finally, the internal scales dry and the bulb shrivel.
- Squeezing the base of infected
plants causes the rotted inner portion of the bulbs to slide out through
the neck, hence the name slippery skin.
Survival and spread
- This bacterium is soil-borne
and can be readily water-splashed to the foliage and necks where it can
enter through wounds.
Favourable conditions
- This bacterium requires
moisture for infection and grows in the temperature range of 5-41°C.
- Heavy irrigation and persistent
dews are also conducive to this disease.
IPM for Onion
To know
the IPM practices for Onion, click here.
Source: NIPHM,
and Directorate
of Plant
Protection, Quarantine & Storage
147 ratings
Onion: Pests
Pests of National Significance
Insect and mite pests
- Onion thrips: Thrips tabaci Lindeman (Thysanoptera: Thripidae)
- Onion maggot: Delia antiqua Meigen (Diptera: Anthomyiidae)
- Bulb mite: Rhizoglyphus robini Claparédè (Sarcoptiformes:
Acaridae)
- Eriophyid mite: Aceria tulipae (Keifer) (Prostigmata:
Eriophyidae)
- Red spider mite: Tetranychus cinnabarinus (Boisduval)
(Trombidiformes: Tetranychidae)
Diseases
- Damping off: Pythium spp., Rhizoctonia solani ( Kühn), Fusarium
oxysporum (Schlecht), F. oxysporum f. sp. cepae (Schlecht. emend. Snyder
& Hansen); Sclerotium rolfsii (Sacc.) & S. cepivorum (Berk ) and
Colletotrichum sp
- Purple blotch: Alternaria porri (Ellis)
- Stemphylium leaf blight: Stemphylium cesicarium/ vesicarium [(Wallr.) E.G.
Simmons]
- Colletotrichum
blight/Anthracnose/Twister disease: Colletotrichum
gloeosporioides [(Penz.) Penz. and Sacc]
- Onion yellow dwarf: Onion yellow dwarf virus
- Iris yellow spot: Iris yellow spot virus
Weeds
Major kharif
Broad leaf
- Pigweed: Amaranthus viridis Hook. F. (Amaranthaceae)
- Swine cress: Coronopus didymus (L.) Sm. (Brassicaceae)
- Black nightshade: Solanum nigrum L. (Solanaceae)
- Common purselane: Portulaca oleracea L. (Portulacaceae)
- False amaranth: Digera arvensis Forssk. (Amaranthaceae)
Grassy
- Rabbit/crow foot grass: Dactyloctenium aegyptium (L.) Beauv. (Poaceae)
- Crab grass: Digiteria sanguinalis (L.) Willd. (Poaceae)
- Barnyard grass: Echinochloa crusgalli (L.) Scop. (Poaceae)
Sedge
- Purple nutsedge: Cyperus rotundus L. (Cyperaceae)
- Flat sedge: Cyperus iria L. (Cyperaceae)
Major rabi weeds
Broad leaf
- Lamb’s quarter: Chenopodium album L. (Chenopodiaceae)
- Scarlet pimpernel: Anagallis arvensis L. (Primulaceae)
- Sweet clover: Melilotus indica (L.) All. (Fabaceae)
- Fine leaf fumitory: Fumaria parvifl ora Lam. (Fumariaceae)
- Corn spurry: Spergula arvensis L. (Caryophyllaceae)
- Carrot grass: Parthenium hysterophorus L. (Asteraceae)
Grassy
- Blue grass: Poa annua L. (Poaceae)
- Canary grass: Phalaris minor Retz. (Poaceae)
- Chinese love grass: Eragrostis unioloides (Retz.) Nees. Ex Steud.
(Poaceae)
- Goose grass: Eleusine indica (L.) Gaertner (Poaceae)
Sedge
- Purple nut sedge: Cyperus rotundus L. (Cyperaceae)
Pests of Regional Significance
Insect pests
- Gram pod borer: Helicoverpa armigera (Hübner) (Lepidoptera:
Noctuidae) (Punjab)
- Tobacco caterpillar: Spodoptera litura (Fabricius) (Lepidoptera:
Noctuidae)
- Cutworm: Agrotis ipsilon (Hufnagel) (Lepidoptera:
Noctuidae) (Assam)
Diseases
- Downy mildew: Perenospora destructor (Berkeley) Caspary (Himachal Pradesh, Delhi)
- Fusarium basal rot/ Basal
rot: Fusarium oxysporum f. sp. cepae
Schlecht (Rajasthan, Maharashtra, Karnataka)
- White rot: Sclerotium cepivorum Berk.
- Pink root rot: Phoma (Pyrenochaeta) terrestris (Hansen) Gorenz,
Walker & Larson, Fusarium solani (Mart.) Sacc. (Rajasthan, Tamil Nadu)
- Black mold: Aspergillus niger van Tiegham
- Green mold: Aspergillus fumigatus Fresenius, A. alliaceus
Thom & Church
- Bacterial brown rot/ Slippery
skin: Pseudomonas aeruginosa
(Schroter) Migula Pseudomonas allicola Starr and Burk (Haryana,
Delhi, Uttar Pradesh)
- Soft rot: Erwinia carotovora pv. carotovora Jones
IPM for Onion
To know
the IPM practices for Onion, click here.
Source: NIPHM and Directorate
of Plant
Protection, Quarantine & Storage
130 ratings
Onion: Insect and Mite
Pests Management
Onion thrips
Biology
- Egg: White to yellow, kidney-bean shaped, microscopic
in size. Develop within leaf tissue with one end near the leaf surface.
Egg stage is 5-10 days.
- Larva: Instars I and II are active, feeding stages.
White to pale yellow, elongate and slender body. Resemble adult, but
without wings. Antennae are short and eyes are dark in color. Feed on new
leaves in the center of the onion neck. Crawl quickly when disturbed.
Larval stage is 10-14 days.
- Pre-pupa and pupa: Instars III and IV are inactive, non-feeding
stages called pre-pupa and pupa. Pale yellow to brown; body more stout
than younger instars. Antennae are bent to head; wing buds are visible.
Found in the soil, at the base of the onion plant neck, or underneath bulb
scales. Lasts 5-10 days.
- Adult: About 1.5 mm long; elongate, yellow and brown
body with two pairs of fringed (hairy) wings. Mouthparts are beak-like and
antennae are 7-segmented. Spend the winter in protected sites under plants
and debris in onion, alfalfa and small grain fields, and other plant
habitats. In the spring when temperatures warm, adults fly to new onion
fields. Parthenogenic (asexually reproducing) females; males are extremely
rare. Feed on young leaves in center of onion neck and insert eggs
individually into leaves. Fly readily when disturbed. Adult life span is
about 1 month; pre-oviposition period (time before egg-laying begins) is 1
week and females will lay eggs for about 3 Weeks
Damage symptoms
Both
adult and larval thrips feed within the mesophyll layer using a punch-and
suck motion.- The beak and mandible is thrust
forward to puncture the leaf epidermis and sap released from injured plant
cells is sucked up.
- Removal of chlorophyll causes
the feeding area to appear white to silvery in color.
- Areas of leaf injury can occur
as patches and streaks.
- When feeding injury is severe,
leaves take on a silvery cast and can wither.
- Tiny black “tar” spots of
thrips excrement are evident on leaves with heavy feeding injury.
Onion maggot
Biology
- Egg: The onion fly deposits white elongated eggs.
About 1/25 inch (I.25mm) in length on the soil near the stem and
occasionally on the young leaves and neck of the onion plant Eggs hatch
into maggots 2-3 days after being laid.
- Maggot: The legless maggots are tapered, creamy-white in
color, and reach a length of about 1/3 inch (8mm). Maggots develop through
three larval stages in 2 to 4 weeks depending on the temperature. Most
newly hatched larvae crawl below the soil surface and feed upon the roots
or burrow into the basal plate of the bulbs. Some maggot larvae may enter into
the sides of bulbs rather than through the basal plate, after undercutting
has occurred. Any injury site on the bulb facilitates the maggot’s entry.
- Pupa: When full-sized, the maggot leaves the bulb and
enters the soil to pupate at a depth of 1-4 inches (5-10 cm). The pupa is
chestnut brown and 1/3 inch (7mm) long. First and second generation pupae
remain in the soil for 2-4 weeks before adult emergence. Larvae of the
third (fall) generation develop into pupae and pass the winter in that
stage. Flies emerging the following spring constitute the spring flight.
- Adult: Onion flies are slightly smaller than house
flies. They have longer legs, are more slender, and overlap their wings
when at rest.
Damage symptoms
- Only the larva causes damage by
using its hooked mouth parts to enter the base of the plant.
- Damaged seedlings first wilt,
eventually become flaccid, and die.
- Frequently, attacked seedlings
die before the maggots are fully grown, forcing them to move to adjacent
plants.
- Second generation maggot
feeding on developing bulbs usually results in distorted growth
accompanied by rotting tissue.
- Feeding by third generation
maggots on late season onion bulbs results in an unmarketable product
Red spider mite
Biology
The
carmine spider mite normally completes a life cycle from egg to adult in about
a week. All stages of this mite are present throughput the year. Reproduction
is most favorable when the weather is hot and dry.
- Egg: Eggs are spherical, shiny, straw colored, and
hatch in 3 days. They are only about 1/254 inch in diameter. They are laid
singly on the underside of the leaf surface or attached to the silken webs
spun by the adults.
- Larva: Larvae are slightly larger than the egg, pinkish,
and have three pairs of legs. This stage lasts a short time, perhaps a
day.
- Nymph: There are two nymphal stages, the protonymph and
deutonymph. The nymphal stage differs from the larval stage by being
slightly larger, reddish or greenish, and having 4 pairs of legs. This
nymphal stage lasts about 4 days.
- Adult: Adult females are about 1/50 inch long, reddish,
and more or less elliptical. The males are slightly smaller and wedge
shaped. They have a black spot on either side of their relatively
colorless bodies. The adult female may live for up to 24 days and lay 200
eggs.
Damage symptoms
Adults
and nymphs feed primarily on the undersides of the leaves.- The upper surface of the leaves
becomes stippled with little dots that are the feeding punctures.
- The mites tend to feed in
“pockets” often near the midrib and veins.
- Silk webbing produced by these
mites is usually visible.
- The leaves eventually become
bleached and discolored and may fall off.
Bulb mite
Biology
The
developmental stages in the life cycle are egg, larva, protonymph,
heteromorphic deutonymph, tritonymph and adult.
- Egg: Females lay up to 700 eggs each depending on the
host. The eggs mature in 3 to 5 days. The egg is white and translucent,
0.12 mm long, and ellipsoidal.
- Larva: Larval period is 3 to 7 days. The protonymph
period 3 to 5 days. This stage can be distinguished from the tritonymph by
having two genital suckers, whereas the tritonymph has three or four
suckers. Deutonymph or Hypopus- This quiescent stage is oval, convex on
top, flattened below, brown, and 0.2 to 0.3 mm long. The ntritonymph is
about 0.5 mm in length and has not yet developed a distinct genital
aperture. Hypopi form when the population becomes crowded, or the
substrate becomes too polluted by decay. The hypopal stage attaches to
insects visiting the bulbs and may be carried to other bulbs.
- Adult: The longevity male adult is 62 days and female is
31 days. Mature bulb mites vary from 0.5 to 0.9 mm long and have four
pairs of legs. Their bodies are shiny, white, somewhat transparent, and
smooth with reddish brown appendages. The total life cycle from egg to
adult could be as short as 12.2 days (at 25°C)
Damage symptoms
- Bulbs infested with bulb mites
may rot and fail to produce new growth, or new growth may be off color,
stunted, and distorted.
- Although the bulb mite is not
considered a primary pest of bulbs, it is often responsible for serious
losses; the slightest injury to a bulb will allow bulb mites to enter and
become established.
- Once the mites are inside the
bulb, they rapidly turn the bulbs into rotten pulp.
- Infestations of the bulb mite
generally indicate that the bulbs have already been injured.
- This damage could have been
caused by other pests, such as the bulb scale mite or bulb flies,
mechanical injury, or improper storage.
- The root primordia of freesia
and gladiolus may be bruised at planting.
- Apparently bulb mites can
attack healthy new roots and corms, especially in greenhouses. The mites
may penetrate into lily stems which become brittle. Infested lilies are
often dwarfed, distorted, and the stem roots are suppressed.
- Bulb mites may enter
prematurely opened tulip buds (due to high storage temperatures or ethylene
generated by diseased bulbs in storage) and cause bud necrosis.
Eriophyid mite
Biology
The life
cycle is composed of the egg, the larva, two nymphal stages (protonymph and
deutonymph) and the adult.
- Egg: Egg incubation period 2-4 days; the eggs are attached
to fi ne silk webbing and hatch in approximately three days.
- Nymph: Protonymphal and deutonymphal period is 2 to 3
days, each.
- Adult: Adult mites survive about 8 days. Length 200 to
250 μm and width 36 to 52 μm, The adult female is capable of laying
several hundred eggs during her life. Total life cycle 7 to 9 days. The
length of time from egg to adult varies greatly depending on temperature.
Damage symptoms:
- Both adults and immature feed
on the young leaves and between the layers in bulbs of onion
- Their feeding causes stunting,
twisting, curling and discoloration of foliage and scarification and
drying of bulb tissue
- This damage has been attributed
to various viruses thought to be transmitted by the mites
IPM for Onion
To know
the IPM practices for Onion, click here.
Source: NIPHM and Directorate
of Plant Protection, Quarantine & Storage
121 ratings
Onion: Crop Stage-wise
IPM
|
Management |
Activity |
|
Pre-sowing
* |
|
|
Nutrients |
• Before sowing, soil testing should be
done to find out the soil fertility status. Nutrient should be provided as
per soil test recommendations. |
|
Weeds |
• Deep ploughing during summer. |
|
Soil borne pathogens, nematodes, and
resting stages of insects |
Cultural
control: |
|
Damping off |
Cultural
control: |
|
Sowing
/ planting* |
|
|
Nutrients |
• Biofertilizers: Seed/seedling
treatment with Azotobacter and PSB cultures @ 240 g each/acre seed/ seedling. |
|
Weeds |
• In high weed infested fields, apply
approved herbicides as mentioned below; |
|
Vegetative
stage |
|
|
Nutrients |
• Apply 1/3 of N at 21days and
remaining 1/3 at 45 days after transplanting. |
|
Weeds |
• The crop should be maintained weed
free initially for 30-45 days by following timely intercultural and hand weeding
if required. |
|
Onion thrips |
Cultural
control: |
|
Onion maggot |
Cultural
control: |
|
Bulb mite |
Cultural
control: |
|
Eriophyid mite |
Cultural
control: |
|
Red spider mite |
Cultural
control: |
|
Gram pod borer, Tobacco caterpillar** |
Cultural
control: |
|
Damping off |
Cultural
control: |
|
Purple blotch |
Cultural
control: |
|
Stemphylium leaf blight |
Cultural
control: |
|
Colletotrichum blight/
anthracnose/twister disease |
Cultural
control: |
|
Downy mildew** |
Cultural
control: |
|
Fusarium basal rot/basal plate rot** |
Cultural
control: |
|
White rot** |
Cultural
control: |
|
Pink root rot** |
Cultural
control: |
|
Black mold/green mold** |
Cultural
control: |
|
Bacterial rots (brown rot/soft
rot/slippery skin)** |
Cultural
control: |
|
Onion yellow dwarf disease |
Cultural
control: |
|
Iris yellow spot disease |
Cultural
control: |
|
Reproductive
stage |
|
|
Nutrients |
Cultural
control: |
|
Weeds |
Cultural
control: |
|
Insects and diseases |
Cultural
control: |
|
Note: The
pesticide dosages and spray fluid volumes are based on high volume sprayer. |
|
Source: NIPHM and Directorate
of Plant Protection, Quarantine & Storage
120 ratings and 4 comments
Onion:Natural Enemies
- Natural Enemies of Onion Insect Pests
- Flowering plants that attract natural
enemies/repel pests
- IPM for Onion
Natural Enemies of Onion Insect Pests
Parasitoids
Predators
Flowering plants that attract natural
enemies/repel pests
|
Natural enemies |
Attractant/repellent/trap
plants |
|
Thrips: |
|
|
• Parasitoid: Ceranisus menes (nymph) |
• Attractant plants: Carrot family,
sunflower family, buckwheat, alfalfa, corn, shrubs, marigold, spearmint
(ladybug beetle, minute pirate bug & lacewing, syrphid fly, damselfly) |
|
Maggot: |
|
|
• Parasitoid: A braconid wasp
(Aphaereta pallipes). |
• Interplant strips of ryegrass and
cover crops, mulch beds (rove beetle). |
|
Gram
pod borer: |
|
|
• Parasitoids: Trichogramma chilonis
(egg), Tetrastichus spp. (egg), Telenomus spp. (egg), Chelonus blackburni
(egg-larval), Carcelia spp. (larval-pupal), Campoletis chlorideae (larval),
Goniophthalmus halli (larval), Bracon spp. (larval) etc. |
• Repellant plants: Basil |
|
Tobacco
caterpillar: |
|
|
• Parasitoids: Trichogramma chilonis
(egg), Tetrastichus spp. (egg), Telenomus spp. (egg), Chelonus blackburni
(egg-larval), Carcelia spp. (larval-pupal), Campoletis chlorideae (larval),
Eriborus argenteopilosus (larval), Microplitis sp (larval) etc. |
• Repellant plants: Basil |
|
Mites: |
|
|
• Predators: Anthocorid bugs (Orius
spp.), mirid bugs, syrphid/hover flies, green lacewings (Mallada basalis and
Chrysoperla zastrowi sillemi), predatory mites (Amblyseius alstoniae, A.
womersleyi, A. fallacies and Phytoseiulus persimilis), predatory coccinellids
(Stethorus punctillum), staphylinid beetle (Oligota spp.), predatory
cecidomyiid fly (Anthrocnodax occidentalis), predatory gall midge (Feltiella
minuta), spiders etc. |
• Citrus, avocadoes, bananas, papaya,
palms, tea, cassava, maize, strawberries, vegetables, and cotton, as well as
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IPM for Onion
To know
the IPM practices for Onion, click here.
Source: NIPHM and Directorate
of Plant
Protection, Quarantine & Storage
133 ratings
Nutritional
Deficiencies/Disorders of Onion
- Nitrogen
- Phosphorus
- Potassium
- Sulfur
- Manganese
- Zinc
- Iron
- Physiological and nutritional disorders
- IPM for Onion
Nitrogen
Leaves become yellowish green
erect and upright curled, wilted and dwarf. At maturity tissue above bulbs
become soft.
Correction
measure: Foliar spray of Urea 1% or DAP 2% twice at weekly
intervals.
Phosphorus
Slow growth, maturity blazed.
Leaf colour becomes light green and bulbs have few dried outer peals. Tip burn
in older leaves.
Correction
measure: Soil application of recommended dose of phosphorous should
be applied at the time of sowing or planting. Foliar spray of DAP 2% twice at
fortnightly intervals.
Potassium
Since potassium is very mobile
within the plant, symptoms only develop on young leaves in the case of extreme
deficiency. Tip burn symptoms, leaves become dark green and erect. Bolting
promoted. Older leaves become yellow and necrotic.
Correction
measure: Foliar application of K2SO4 @1% twice
at weekly interval.
Sulfur
The leaves show a general overall
chlorosis. The yellowing is much more uniform over the entire plant including
young leaves.
Correction
measure: Foliar spray of K2SO4 or
CaSO4 @ 1% twice at fortnightly interval.
Manganese
Leaves show tip burn, light
coloured and curling. Growth restricted. Bulbing delayed with thick necks.
Correction
measure: Foliar spray of MnSO4 @
0.3% twice at fortnightly interval.
Zinc
Growth restricted. The leaves
show interveinal necrosis. In the early stages of zinc deficiency the younger
leaves become yellow and pitting develops in the interveinal upper surfaces of
the mature leaves. As the deficiency progress these symptoms develop into an
intense interveinal necrosis but the main veins remain green.
Correction
measure: Foliar spray of ZnSO4 @
0.5% twice at for nightly interval.
Iron
Complete yellowing of young
leaves. The most common symptom for iron deficiency starts out as an
interveinal chlorosis of the youngest leaves, evolves into an overall
chlorosis, and ends as a totally bleached leaf. Because iron has a low
mobility, iron deficiency symptoms appear fi rst on the youngest leaves. Iron
deficiency is strongly associated with calcareous soils, anaerobic conditions,
and it is often induced by an excess of heavy metals.
Correction
measure: Foliar spray of FeSO4 @ 0.5%.
Physiological and nutritional disorders
Sprouting
of bulbs in the field is noticed sometimes towards the start of maturity stage
of bulbs particularly when there are winter rains or excessive soil moisture
and nitrogen supply. This disorder is, however, not of permanent nature and
varies from variety-to-variety. Early-planting also causes sprouting. Splitting
is also noticed sometimes in some varieties, which is due to delayed harvesting
or irrigation after long spell of drought. For past few years rubberification
problem is noticed in Rajkot area and also Nilgiri hills of Tamil Nadu. It is
increasing day-by day. The effects of insecticides, fungicides, micronutrients
and growth regulator were studied. It was observed that rubberification was
totally controlled by application of micronutrients i.e. zinc sulphate and
ammonium molybdate. It was also controlled by neem cake insecticides and growth
regulator like gibberellic acid. The aerial bulbil formation is also quite
common in onion where lower temperature prevails for more period or there are
more temperature variation. It, however, does not affect much on yield or
quality of bulbs and varietal variation is noticed. The rubberification and
premature sprouting of bulbs are main physiological disorders in onion. The
reasons for these disorders are summarized below for hill grown onion.
Rubberification
and premature sprouting of bulbs are noticed mostly in fields which are located
in low-lying areas of watershed where there is heavy deposition of nutrients
along with silt during heavy rains. These problems are severe in onion fields
which are more frequently irrigated than the normal requirements of onion
bulbs. With the application of higher levels of nitrogen, there is an increased
level of pre-mature sprouting of bulbs which results in splitting and
rubberification of bulbs. Rubberification incidence also increases when higher
level of nitrogen is applied in the form of urea. Due to increased levels of
nitrogen, in addition to the increased production of rubberized, there is an
increased level of thrips incidence in leaves during the later stage of crop.
The thrips lacerate leaves and cause severe damage to the crop. Through
lacerated wounds by thrips, there is a severe incidence of blast disease,
caused by Boltrytis allii, when crops is 70-90 days old, which further
deteriorates the quality of onion bulbs. Short duration type of onion is more
susceptible than long duration type. Premature sprouting of bulbs is more in
the crop (April-August) when there is high moisture level in soil at maturity
of crop due to heavy rains. Delayed harvest during rainy season has increased
premature sprouting and splitting of bulbs. Wider spacing of cloves at the time
of planting increases uptake of nitrogen and water by the individual plants
which increases premature sprouting and rubberification of onion bulbs
IPM for Onion
To know
the IPM practices for Onion, click here.
Source: NIPHM and Directorate
of Plant Protection, Quarantine & Storage
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