Diseases and Insect-pests of cole crops

DiseasesBlack leg (Phoma lingam) Occurs in areas with rainfall during the

growing period Seed borne and hence occurs from the early

stage Stem of affected plant when split vertically

shows severe black discolouration of sap stream.

Whole root system decays from bottom upwards. Often, the affected plants fall over in the field

Hot water treatment Seed infection can be prevented by spraying the

seed crop with copper oxychloride or with an organomercuric compound

Pusa drum head- tolerant under field condition.

Control

Downy mildew (Pernospora parasitica) Causes serious damage at all stages of

plant growth Discolouration occurs in the young

seedlings and in severe cases whole plant perishes.

In adult plants, purplish leaf spots or yellow brown spots on the upper surface of the leaf appear, while fluffy downy fungus growth is found on the lower surface.

During bolting stage the seed stalk show blackish patches and in severe cases whole curd is spoiled.

Spray of redomil MZ 72 @ 0.5 g/lt of water at 10-15 days interval or with Dithane M 45 @ 1.5-2.0 g/lt of water.

Chinese cabbage and kale are resistant to downy mildew while others are susceptible.

Control

Rhizocotonia (R. solani)

Causes damping off, wire stem, bottom rot, head rot or crown rot

Use of resistant variety and application of Brassicol @ 20-30 kg/ha

2-4 foliar sprays of Dithane-M-45, Difolatan 80 or Daconil (Kavach) @ 1.5 – 2.0 g / lt at an interval of 15 days.

Control

Black spot (Alternaria brassicicola & Alternaria brassicae)

The seed crop is affected mostly. Young plants show soft , water soaked

spots on the skin just above the ground, the cotyledons wither and plants eventually fall over and perishes (resembles Rhizoctonia solani)

In older plants, small, brown to black, circular to slightly elongated spots appear on leaves, petioles and stems. Sometimes, the spots join together.

It causes damage to cabbage heads and cauliflower curds after maturity and during seed production.

Mainly caused by A. brassicicola and known as curd and inflorescence blight or brown rot.

Resistance was initially found in MGS-2-3, Puakea 246-4 etc.

Yellows (Fusarium oxysporum f. conglutinans) Foliage of affected plants turn yellow,

dies and eventually drops off, the lowest being the first to show the symptoms.

Vascular tissues become yellow to dark brown.

Young seedlings may occasionally show signs of damping off.

Use of resistant cultivar which are of two types1. Type A: resistance control by single

dominant gene. All Head Early, Copenhagen Market, Glory of Enkhuizen.

2. Type B: inherited as a quantitative character and is controlled by a number of genes. Cabbage cv. Wisconson Hollander.

3. Both A & B are found in Wisconson All Season.

Club root (Plasmodiophora brassicae)

A typical root parasite. Irregular galls on the roots

and lateral roots take the shape of spindle.

Leaves become yellowish and wilt on hot days

Prevalent in soils with a pH below 7

DD (1, 2 Dichloropropane with 1,3-dichloropropene) @ 5 l/ha followed by soil covering with plastic film or 10 l/ha with or without covering.

Liming of soil at the earliest.

Watery soft rot (Sclerotinia sclerotiorum) Causes considerable damage in the seed

crops of snowball in Himachal Pradesh. It is not yet a problem in plains. In seedling crop, the infection starts on

leaves, particularly on the base of petioles and passes into the adjoining part of the stem.

Large grayish white, elliptical spots arise sometimes involving the whole surface of stem.

At the point of attack, the seed stalks can break, wither and eventually die.

In seed crop, most commonly known as Sclerotinia stalk rot.

Damp weather favour the occurrence of this disease.

Control

Spray of bavistin

Powdery mildew (Erysiphe polygoni)

Occurs occasionally and known to cause limited damage.

Karathane spray

Control

Damping off (Pythium debaryanum)

Causes damping off of young seedlings

Fungus hibernates in the soil Affected seedling fall over and perish. The disease is promoted by high

humidity and high temperature

Soil sterilization and seed treatment are effective in reducing the attack.

Control

Control

BACTERIAL DISEASES:Black rot (Xanthomonas campestris)

Destructive in warm and wet climate. Infection of foliage results in yellow V- shaped spots

arising along the margin which extend in the direction of mid rib.

These spots are associated with the typical black discolouration of the veins.

Infection extends through the xylem to the stalk and the vascular bundles turn black.

In severe infection, the whole leaf show discolouration and eventually falls off.

Plants raised from infected seed may die prematurely.

Hot water treatment of seeds at 50 ± 2 0C for 30 minutes followed by 20 minute dip in 100 ppm streptocycline.

Antibiotics like Agrimycin 100 (0.01%), streptocycline (0.01%) and Aureomycin etc are also found to be effective.

Bacterial soft rot (Erwinia carotovora) A weak parasite which penetrates the plants

through damaged tissue e.g. lesions caused by other pathogen.

In the field, it occurs only following black rot or after mechanical injury of nearly mature cabbage head.

Infection favours by high humidity Affected plants show a soft, slimy, bad

smelling rot which under favourable conditions rapidly spreads throughout the plant.

The disease can be kept down by controlling other diseases and preventing damages

Spraying 100-200 ppm streptocycline or plantomycin combined with copperoxychloride (0.3%) at 15 days interval.

Control

Insect-pests of cole crops

Stems are chewed near the soil level during night. Some cutworms climb the host and feed on unopened buds. Many cutworms prefer wilted plant material and sever the plants sometime prior to feeding.

Damages seedlings in the newly planted crop

CUTWORMS

• Use of well decomposed manure helps in reducing the incidence.

• Collection and destruction of larvae after flooding of fields/ beds.

• Soil drenching with chlorpyriphos (0.04%) or spraying of cypermethrin (0.0075%) on foliage and soil surface reduces the incidence.

Control

CABBAGE APHIDInitially, damaged leaves show yellowing. Aphids attack plants during the cool dry season.

• Encourage the biological control agents like parasitoid Diaeretiella rapae, coccinellid and syrphid predators.

• Selective use of insecticides on head and seed crops.

Head Crop: Foliar application of malathion (0.05%) with

the appearance of the pest and repeating every 15 days. But stop spraying atleast 7 days before harvesting.

Seed Crop: Apply phorate granules @ 1.5 kg a.i./ha as

side dressing during mid February to early March or spray methyl demeton (0.025%) or dimethoate (0.03%) as soon as aphid population is above 50 aphids per plant.

Control

CABBAGE BUTTERFLY (Pieris brassicae) Damage is caused by caterpillars which when

young are pale-yellow but later change to greenish-yellow and measures 30 mm in length.

The white winged butterflies deposits yellow coloured eggs in clusters on the undersurface of leaves.

The caterpillars in the early stages scrap the leaf surface and feed gregariously whereas later instars eat up leaves from the margin inward leaving the main vein intact.

Mechanical control: Collection and destruction of yellow egg masses and early stage larvae of cabbage butterfly.

Biological Control:Cotesia glomeratus parasitizes the larvae.

Malathion (0.05%)/ deltamethrin (0.0028%)/ cypermethrin (0.0075%) and fenvalerate (0.01%) can be used for effective suppression of caterpillar complex of cabbage and cauliflower.

Since, these crops may be infested at or near harvesting; it will be wise to spray malathion (0.05%) to minimize the danger of toxic residues in marketable produce.

DIAMONDBACK MOTHIt infests all types of Brassica crops.

Spindle shaped pale yellowish green caterpillars (8 mm when full-fed) in the earlier instars feed on the lower side of leaves but later feed on the exposed leaves and enter the head/ curd affecting the produce as well as quality.

Trap crop: Indian mustard is effective in suppressing the incidence of diamondback moth and cabbage aphid. Growing paired rows of mustard after every 25 rows of cabbage and cauliflower each at 15 days prior and 25 days after cabbage transplanting. This will ensure adequate mustard foliage throughout the cropping period.

Release of Trichogrammatoidea bectrae @ 0.5-0.75 lakh eggs per ha at weekly intervals.

Pheromone traps installation @5-6 traps/ha for monitoring of population of DBM.

Use of 2 to 5 % NSKE at head initiation stage. Malathion (0.05%), deltamethrin (0.028%), cypermethrin

(0.0075%) and fenvalerate (0.01%) can be used for effective suppression of caterpillar complex.

Control

Damage the growing tips of plant and also the surface of curd in cauliflower.

They are problematic when crop is irrigated with sewerage water.

Snails and slugs

Baiting with metaldehyde and bran (1: 25 in 12 l of water)

As a repellant, alum may be sprayed @ 2% solution.

Control

DISORDERS

Disorder Symptoms Management

Riceyness A premature initiation of floral buds is characterised by riceyness in cauliflower and is considered to be of poor quality for marketing.

It can be controlled by cultivation of genetically pure seed and appropriate varietieswith recommended cultural practices. Harvest while the curd is still firm, compact

Fuzziness It appears as the flower pedicels of velvety curds elongate. The anomaly is both hereditary and non-hereditary.

Sowing good quality seed in right season under proper cultural practices minimizes fuzziness

Leafiness formation of small thin leaves from the curds which reduce quality of curd. Prevalence of high temperature during curding phase aggravates leafiness.

Controlled by selection of varieties according to their adaptability and seasons

Disorder SymptomsManagement

Browning Water soaked areas in the stem and centre

of the branches of the curds. Hollow stem

is a typical features.

Due to Boron deficiency

Spray of 20kg/ha of

common Borax

Buttoning Development of small button shape curds. Optimum use of N

fertilizer

Blindness Plants without terminal bud and large, dark

green, thick leathery foliage

Avoid over wintering

Whip tail Severe reduction of lamina and leaf blade

leaving the large bare mid rib in acute

condition.

Spray 1Kg of MO as a

Sodium or Ammonium

Molybdate

Name of Disorder

Symptoms Management

Chlorosis Chlorosis shows on intervenial and yellow

mottling of lower leaves. The affected

leaves turn bronze in colour and become

stiff.

Use of fertilizers

containing soluble

magnesium, keeps the

disorder under control.

 

Premature Seeding/Bolting

Before the formation of heads or failure of

leaves to form a solid head. The possible

causes of bolting include- Early sowing of

seeds, warm winter, extreme change in

temperature, poor growth of seedlings and

varietal characters.

Use resistant cultivars,

avoid setting plants two

early into field and prevent

the stimulation of early

plant growth are some of

the control measures.

 

Thanks…