Learn about the pests that damage brassica crops and its control.
1. Mustard Aphid, Lipaphis Erysimi (Kaltenbach) (Hemiptera: Aphididae):
The mustard aphid is worldwide and is a serious pest of cruciferous oilseeds like toria, sarson, raya, taramira and Brassica vegetables like cabbage, cauliflower, knol-khol, etc. The damage is caused by nymphs and adults, which are louse like, pale-greenish insects. They are seen feeding in large numbers, often covering the entire surface of flower-buds, shoots, pods, etc.
Life-Cycle:
This insect is most abundant from December to March when it infests various cruciferous oilseeds and vegetables. During summer, it is believed to migrate to the hills and there is some evidence that aphids also survive on abandoned stray plants of cabbage and on cruciferous weeds in the plains. The pest breeds parthenogenetically and the females give birth to 26-133 nymphs.
They grow very fast and are full-fed in 7-10 days. About 45 generations are completed in a year. Cloudy and cold weather (20°C or below) is very favourable for the multiplication of this pest. The winged forms are produced in autumn and spring, and they spread from field to field and from locality to locality.
Some of the parasitoids of the pest include Ischiodon scutellaris (Fabricius) and Syrphus serarius (Wiedmann) (Syrphidae). Brinckochrysa scelestes (Banks) (Chrysopidae), Coccinella septempunctata Linnaeus and Menochilus sexmaculatus (Fabricius) (Coccinellidae) predate on the mustard aphid. Diaeretiella rapae M’Intosh (Braconidae) and Lipolexis gracilis Forester (Aphididae) parasitize the aphid. Entomophthora coronata and Cephalosporium aphidicola infect L. erysimi.
Damage:
Both the nymphs and adults suck cell-sap from leaves, stems, inflorescence or the developing pods. Due to the very high population of the pest, the vitality of plants is greatly reduced. The leaves acquire a curly appearance, the flowers fail to form pods and the developing pods do not produce healthy seeds. The yield of an infested crop is reduced to one-fourth or one-fifth.
Control:
(i) Sow the crop early wherever possible, preferably upto third week of October.
(ii) Apply recommended dose of fertilizers.
(iii) Apply any one of the following insecticides when the .population of the pest reaches 50-60 aphids per 10 cm terminal portion of the central shoot or when an average of 0.5-1.0 cm terminal portion of central shoot is covered by aphids or when plants infested by aphids reach 40-50 per cent- (a) Foliar sprays- One litre of oxydemeon methyl 25EC, dimethoate 30EC, quinalphos 25EC, malathion 50EC; 1.5 litres of chlorpyriphos 20EC; 100 g of thiamethoxam 25WG in 200-315 litres of water per ha, depending on the stage of the crop, or (b) Granular insecticides- 10 kg of phorate 10G, 33 kg of carbofuran 3G per ha followed by a light irrigation.
2. Painted Bug, Bagrada Hilaris (Burmeister) (Hemiptera: Pentatomidae):
The painted bug is a serious pest of cruciferous crops and is widely distributed in Myanmar, Sri Lanka, India, Iraq, Arabia and East Africa. Besides cruciferous crops, it has also been observed feeding on rice, sugarcane, indigo and coffee.
Damage is caused by nymphs as well as by adults. The full-grown nymphs are about 4 mm long and 2.66 mm broad. They are black with a number of brown markings. The adult bugs are 3.71 mm long and 3.33 mm broad. They are sub-ovate, black and have a number of orange or brownish spots.
Life-Cycle:
The painted bug is active from March to December and during this period all the stages can be seen. It passes the winter months of January and February in the adult stage under heaps of dried oilseed plants lying in the fields. These bugs lay oval, pale-yellow eggs singly or in groups of 3-8 on leaves, stalks, and pods sometimes on the soil. Eggs may be laid during day or night. A female bug may lay 37-102 eggs in its life-span of 3-4 weeks.
The eggs hatch in 3-5 days during summer and 20 days during December. The nymphs develop fully in five stages and transform themselves into adults in 16-22 days during the summer and 25-34 days during the winter. The entire life-cycle is completed in 19- 54 days and it passes through 9 generations in a year.
The eggs are parasitized by Gryon sp. (Scelionidae), while Alophora sp. (Tachinidae) parasitizes the adults.
Damage:
Both nymphs and adults suck cell sap from the leaves and developing pods, which gradually wilt and dry up. The nymphs and adult bugs also excrete a sort of resinous material which spoils the pods.
Control:
(i) Give first irrigation 3-4 weeks after sowing as it reduces the bug population significantly,
(ii) Spray one litre of malathion 50EC or 625 ml of quinalphos 25EC in 150-200 litres of water per ha once in October and again in March-April.
3. Mustard Sawfly, Athalia Lugens (Klug):
(Hymenoptera: Tenthredinidae):
The mustard sawfly is widely distributed in Indonesia, Formosa, Myanmar and the Indian Sub-continent. It feeds on various cruciferous plants like mustard, torici (Brassica campestris), rapeseed, cabbage, cauliflower, knol-khol, turnip, radish, etc.
Damage is done by the larvae which are dark green and have 8 pairs of abdominal prolegs. There are five black stripes on the back, and the body has a wrinkled appearance. A full- grown larva measures 16-18 mm in length. The adults are small orange yellow insects with black markings on the body and have smoky wings with black veins.
Life-Cycle:
The mustard sawfly breeds from October to March and the larvae rest in their pupal cocoons in the ground during summer. The adults emerge from these cocoons early in October. They live for 2-8 days and lay 30-35 eggs singly, in slits made with saw like ovipositors along the underside of the leaf margins.
The eggs hatch in 4-8 days and the larvae feed exposed in groups of 3-6 on the leaves during morning and evening. They remain hidden during the day time and, when disturbed, fall to the ground and feign death. They pass through seven stages and are full-grown in 16-35 days.
The full-fed larvae descend the plant and enter the soil to a depth of 25-30 mm. There, they pupate in water proof oval cocoons made of silk and emerge from them as adults in 11-31 days. Thus, the life-cycle is completed in 31-34 days. The pest completes 2-3 generations from October to March.
Perilissus cingulator Morby (Ichneumonidae) parasitizes the grubs. The bacterium, Serratia marcescens Bizio (Enterobacteriaceae) causes mortality of the grubs.
Damage:
The grubs alone are destructive. They bite holes into leaves preferring the young growth and skeletonize the leaves completely. Sometimes, even the epidermis of the shoot is eaten up. Although the seedlings succumb; the older plants, when attacked, do not bear seed.
4. Green Peach Aphid, Myzus Persicae (Sulzer) (Hemiptera: Aphididae):
This insect is distributed throughout India. Besides mustard and other cruciferous plants, the pest also attacks peaches, beans, potato, tobacco, etc. The aphids are minute (2.0-2.5 mm long), delicate, pear-shaped, yellowish-green winged or wingless insects.
Life-History:
The green peach aphid remains active from December to March with peak activity during February. The nymph undergoes 4-5 instars taking 4-7 days for apterous and 5-8 days for alate forms. Apterous adults produce 5-92 young ones per female while the alate forms produce 8- 49 nymphs. Longevity of adult is 15-27 days for alate and 10-25 days for apterous forms.
Damage:
Both nymphs and adults damage plants by actively sucking their sap. After the appearance of inflorescence, the aphid congregates on terminal buds and feeds there. As a result, there is flower shedding, poor-pod formation and shrivelling of grains. The insect also transmits virus diseases. The honeydew attracts sooty mould.
Control:
(i) Sow the crop in first week of October.
(ii) Spray 500 ml of dimethoate 30EC or 625 ml of oxydemeton methyl 25EC in 250 litres of water/ha when aphids start congregating on top flower buds. Only one spray is needed.
5. Pea Leafminer, Chromatomyia Horticola (Goureau) (Diptera: Agromyzidae):
The larvae feed by making mines into the leaves and cause heavy damage.
Control:
The systemic insecticides (oxydemeton methyl 25EC or dimethoate 30EC or granular insecticides) recommended for the control of mustard aphid should also be used for controlling the leaf-miner.
6. Cabbage Caterpillar, Pieris Brassicae (Linnaeus) (Lepidoptera: Pieridae):
The caterpillars feed on leaves, young shoots and green pods. When young, they feed gregariously but the grown-up caterpillars migrate from one field to another.
Control:
When in the gregarious stage, the caterpillars can be easily controlled by picking and destroying the infested leaves. The grown-up caterpillars should be controlled with malathion 5 per cent @ 37.5 kg per ha or by spraying 500 ml of dichlorvos 85SL in 200-300 litres of water per ha.
7. Linseed Bud Fly, Dasineura Lini Barnes (Diptera: Cecidomyiidae):
The adult of this bud fly is a small orange fly. Its tiny maggots feed and produce galls. They destroy flower-buds and thus prevent pod formation. This insect appears as a serious pest of linseed in some parts of India, including Andhra Pradesh, Madhya Pradesh, Bihar, Uttar Pradesh, Delhi and Punjab.
Life-Cycle:
The female lays 29-103 smooth, transparent eggs in the folds of 8-17 flowers or in tender green buds, either singly or in clusters of 3-5. The eggs hatch in 2-5 days. Just after emergence, the larvae are transparent, with a yellow patch on the abdomen. These larvae feed inside flower buds and eat the contents.
They pass through four instars in 4-10 days and when full-grown become deep pink and measure about 2 mm in length. The full-grown maggots drop to the ground, prepare a cocoon and pupate in the soil. The pupal period lasts 4-9 days. A generation is completed in 10-24 days. There are four overlapping generations during the season.
The maggots are parasitized by Systasis dasyneurae Mani (Miscogasteridae). Other larval parasites include Elasmus sp. (Elasmidae), Eurytoma sp. (Eurytomidae), Torymus sp. (Torymidae) and Tetrastichus sp. (Eulophidae).
Damage:
Damage is the result of feeding by maggots on buds and flowers. Consequently, no pod formation takes place.
Control:
(i) The adult flies can be killed by using light traps. The flies are also attracted in day-time to molasses or gur added to water.
(ii) As the incidence of this pest is more on the late- sown crop as compared with the normal-sown crop, the practice of normal-sown crops should be adopted if possible,
(iii) Dust 5 per cent carbaryl @ 15-20 kg/ha or spray carbaryl 50WP @ 1.125 kg/ ha in 200-250 litres of water/ha.