Cruciferous Vegetables (Cabbage, Cauliflower, Radish, Beetroot and Knolkhol)
1. Diamond back moth (Plutella xylostella (L.) (Plutellidae: Lepidoptera)
Distribution: It is a well known pest of cruciferous crops throughout the world.
Nature of damage: The larvae bite holes in leaves and cause serious damage. The larvae cause blisters on the leaves which dry away in course of time. It attacks cabbage, cauliflower, radish and knolkhol.
Life history: The moth is grayish brown with narrow wings having pale white markings anteriorly which from diamond-like white patches dorsally when wings are folded over back at rest. It lays up to 57 eggs singly on the under surface of leaves along the veins. Egg period is 4 – 5 days. The larva is greenish with short thin hairs on the body. The larval period is 13 – 21 days. It pupates in a thin loose mesh of silken cocoon and the pupal period is 7 – 9 days. The period from egg to adult occupies 24 – 35 days.
(i) Mustard sown as trap crop twice i.e. 12 days preceding planting cabbage and again 40 days later controls DBM.
(ii). Spraying cypermethrin @ 30 g a.i. or fenvalerate @ 50 g a.i. or deltamethrin @ 10 g a.i. or cartap hydrochloride @ 175 g a.i./ha once at primordial initiation (22 days after planting) and repeated either thrice at 7 days interval or twice at 10 days interval.
(iii). Spray application of Bacillus thuringiensis var. kurstaki @ 1 kg/ha.
2. Leaf webber (Crocidolomia binotalis Z.)(Pyraustidae: Lepidoptera)
Distribution: Present in all localities where cabbage and cauliflower are grown.
Nature of damage: The leaves are skeletonized by the larvae which remain on the under surface of leaves in webs and feed on them. They also attack flower buds and pods. Often it assumes serious proportions. It attacks cabbage, cauliflower, radish, mustard and other crucifers and the weed Gynandropsis pentaphylla.
Life history: The small moth with light brownish fore wings lays the eggs in masses, each mass containing 40 – 100 overlapping flat eggs. The incubation period ranges from 5 – 15 days depending on weather. The larva with red head has brown longitudinal stripes and rows of tubercles with short hairs on its pale violaceous body. It becomes full grown in 24 – 27 days during summer and in 51 days during winter. It pupates in an earthen cocoon and emerges as adult in 14 – 20 days.
(i). Mustard sown as trap crop twice i.e. 12 days preceding planting cabbage and again 40 days later controls DBM.
(ii). Spraying cypermethrin @ 30 g a.i./ha or fenvalerate @ 50 g a.i. /ha or deltamethrin @ 10 g a.i. /ha or cartap hydrochloride @ 175 g a.i./ha once at primordial initiation (22 days after planting) and repeated either thrice at 7 days interval or twice at 10 days interval.
3. Cabbage butterfly (Pieris brassicae (Linnaeus) (Pieriidae: Lepidoptera)
Distribution: In India, it is widely distributed along the entire Himalayan region. P. brassicae is comparatively more common and destructive. It causes severe damage to cabbage, cauliflower, radish, turnip as also mustard and rape. The pest passes winter in the plains and migrates to hilly regions during summer. During September to April, it breeds on rape and mustard.
Nature of damage: On hatching, the young caterpillars feed gregariously on leaves for a couple of days, then disperse, spreading infestation to the adjacent plants and fields. As a result of their feeding the leaves are skeletonized, sometimes the caterpillars bore into the heads of cabbage and cauliflower.
Life history: Eggs are laid in clusters under surface of the leaf.
A single female lays only 2 – 3 egg-masses of 50 – 80 eggs each. Eggs are flask-shaped, about one mm long and yellowish in colour. Full grown caterpillars are 38 – 44 mm long, velvety bluish-green in colour with black dots and yellow dorsal and lateral stripes covered with white hair. Pupae are yellowish-green with black spots and dots. Adult butterflies have snow-white forewings with black distal margins more developed in females than in males; hind wings are also pure white with black apical spots.
Wing expanse is 60 – 70 mm. Moths emerging in summer are larger in size than those of winter. Incubation, larval and pupal periods are on an average 3.2, 5.6 and 7.3 days during May extending upto 17.6, 40.7 and 28.8 days respectively in January. Generally there are two generations during winter (plains) and 4 – 5 in summer (hilly region).
(i) Pest can be checked by handpicking and mechanical destruction of caterpillars during early stage of attack when the caterpillars feed gregariously.
(ii) In case of widespread infestation spray with 0.05% dichlorvos or 0.1% Malathion.
4. Cabbage aphid (Brevicoryne brassicae) (Aphididae: Homoptera)
Distribution: Cabbage aphid Brevicoryne brassicae was originally confined to Palaearctic or Holarctic regions but at present it has a very wide range of distribution.
Nature of damage : Colonies of these insects are often found on tender shoots and as a result of sucking of vital sap from the tissues, the plant remain stunted in growth resulting in poor head formation. In the case of severe infestation plants may completely dry up and die away. When infestation occurs on seedlings, they loose their vigour, get distorted and become unfit for transplanting. The aphids also produce copious quantity of honeydew which makes the plants sticky and favour the growth of sooty mould, as a result a black coating is formed on affected plant parts hindering the photosynthesis and adversely affecting the plant growth.
Life history: Reproduction is mostly viviparous parthenogenetic during summer and mild winter. However, during severe winter sexual reproduction may also occur. Eggs when present are pale yellow with greenish tinge. Nymphs are 1.0 – 1.5 mm long and yellowish-green in colour while adults are 1.8 – 2.0 mm long and darker in colour than nymphs. Eggs are laid during November – December. These hatch in 20 – 22 weeks.The nymphs mature in about 2 weeks and immediately start producing young ones, without mating. A single female may produce 40 – 45 young ones during her life time. The life cycle is completed in 11 – 45 days and as many as 21 generations have been recorded during a year when provided with favourable conditions.
(i) As soon as aphid infestation appears, cut and destroy the infested shoots mechanically.
(ii) When more than 5% plants are infested, spray with 0.025% phosphamidon or methyl demeton or 0.01% imidacloprid. Repeat the spraying after a fortnight if still 5% infestation is there.
5. Mustard Sawfly, (Athalia lugens proxima Kulg) (Tenthredinidae: Hymenoptera)
Distribution: Mustard sawfly is one of the very few hymenopterous insects reported as crop pests, and that too with chewing and biting habits. It is a cold weather pest found all over the Indian sub-continent. It is a major pest of not only cole crops but of almost all cruciferous plants, including rape and mustard. The peak period of activity is during September to December after which the activity declines; the pest is hardly noticed from March to July and appears on radish by the end of July.
Nature of damage: Eggs are laid singly, mostly during day time and inserted into leaf tissues near the periphery of leaves. On hatching the grubs nibble the margins of tender leaves but later on bite holes in the leaves. Grubs are diurnal in habit and feed generally during early morning and evening hours. With slight disturbance they fall on the soil and feign death.
Life history: A female lays on an average 35 eggs (20 – 150). Egg period is 6 – 8 days. Newly hatched grubs are 2 – 3 mm long, smooth, cylindrical and greenish-grey in colour; full grown ones are cylindrical in shape, 16 – 20 mm long and greenish-black in colour. They look and behave like caterpillars but have 8 pairs of prolegs. Grub development takes 21 – 31 days.
Adults are 8 – 12 mm long, having dark head and thorax, orange coloured abdomen and translucent smoky wings with black veins. Females have a strong saw-like ovipositor – hence it has been given the popular name sawfly. They generally do not fly long distances but hop from leaf to leaf or fly from one plant to another plant. Their activity is pronounced during days while the insects remain practically motionless at night. Pre-pupal and pupal periods last for 3 – 4 and 7 – 10 days respectively. Severe winter is passed in pupal stage and lasts for about 14 weeks. In Northern India there are three generations during cold season. In South India where there is no severe winter, the pest undergoes as many as 10 overlapping generations in a year.
(i) Hand-picking of grubs which are not active during dawn and dusk if the area under crop is limited.
(ii) Spraying with 0.05% endosulfan or 0.05% monocrotophos or 0.2% carbaryl.
(iii) Dusting with 5% Malathion or 10 % carbaryl is also effective.
6. Painted Bug (Bagrada cruciferarum Kirkaldy) (Pentatomidae: Hemiptera)
Distribution: Painted bug Bagrada cruciferarum and B. hilaris (Burmester) have been recorded as major pests of various Brassica spp. as also other cruciferous crops and weeds. B. cruciferarum has been reported from East Africa, Afghanistan, Pakistan, Sri Lanka, India and South-east Asia while B. hilaris is found in East, West and South Africa, Italy, Iran, Iraq, Pakistan, India, Sri Lanka and USSR. The adults appear in field around October and their activity decreases with the onset of summer but is again accelerated in autumn.
Nature of damage : Both nymphs and adults suck cell sap from tender plant parts causing yellowing of leaves which gradually dry up and ultimately fall down exposing the plants to secondary invasion of bacteria and fungi. The plants wilt and wither affecting adversely the yield both quantitatively and qualitatively.
Life history: Eggs are laid singly or in batches of 2 – 12 on leaves, stems and flower buds. These are oval in shape about one mm long, pale yellow when freshly laid gradually becoming pinkish-orange. Nymphs are beautifully patterned with a mixture of black, white and orange colour, 1.5 – 4.5 mm long depending on their age. Adults are also black and orange colour bugs similar in colour pattern as nymphs – that’s why they have earned the common name of painted bugs. Males are 6 – 7 mm long and females 7 – 8 mm. The mating takes place 2 – 6 days after the final nymphal moult and the oviposition commences a week after first mating and may continue intermittently throughout the life span of the female. A single female may lay as many as 230 eggs @ 15 – 20 eggs per day. Eggs and nymphal duration is recorded as 2 – 5 and 18 – 20 days respectively. A single life-cycle is completed in 3 – 4 weeks and adults live for 16 -18 days with 6 – 8 generations in a year.
(i) Clean cultivation by removing weeds harbouring this pest is imperative for avoiding infestation of these bugs.
(ii) In case of heavy infestation, spray with 0.05% dichlorvos or 0.05% endosulfan or 0.05% phosalone. Atleast 7 – 10 days waiting period should be there between treatment and harvest.