Pests
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One of the serious constraints in rapeseed-mustard production is the lack of varieties resistant to diseases and insect pests. To protect the crop from diseases and insect pests, it is essential to undertake timely plant-protection measures. The mustard sawfly, painted bug and mustard aphid normally attack the mustard crop. The aphid is the most destructive in late-maturing mustard.
Mustard aphid
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The mustard aphid (Lipaphis erysimi KaIt.) is pale-green, soft bodied and 1-2 mm long. The nymphs and adults suck the cell sap from various parts of the plant and live in colonies. Due to the sucking of the plant sap, plants remain stunted, the leaves show curling and yellowing, the pods shrivel up and the seeds do not develop in the infested pods. The infestation due to mustard aphid is more serious from the end of December to the middle of March. They become innumerable, completely covering the inflorescence and pods. To control this important pest, the following corrective measures are required: (i) wherever the aphid problem is serious and acute, the mustard varieties may be sown instead of rapeseed which is more susceptible to the pest; (ii) early sowings, i.e., in the first fortnight of October, to escape the mustard-aphid infestation; (iii) the removal of early infested, twig-bearing stems by the end of December is very useful; (iv) the crop may be sprayed with 0.025% Methyl oxydemeton or 0.03% Dimethoate or 0.025% Quinalphos or 625, 850 and 1,000 ml of either of these insecticides or Phosphomidon 0.025% i.e., 150, 210 and 250 ml mixed with 625,850 and 1,000 litres water, depending upon the crop-growth stage.
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Spraying should be done thrice at 15- day intervals, starting from the end of December or early January when 9-10 aphids/twig and 30% of the plants are infested. The number of sprays may be reduced, depending upon the severity of the infestation. The above-mentioned quantity of water is for high-volume sprayers such as foot-sprayers. The precautions to be taken are: (I) If the crop is to be used for saag (leafy vegetable)/f odder purposes, it may be sprayed with 0.05% Malathion 50 EC (500 ml Malathion 50 EC mixed in 500 litres water/ ha), 5 times at 10-day intervals. Do not pluck the leaves within 7 days after spraying; (ii) insecticides should be sprayed in the afternoon to avoid any adverse effect on pollination; (iii) the quantity of water will be one-tenth of the normal spray of liquid if a motorised sprayer is used (the quantity of insecticides remain the same).
Mustard sawfly
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The Adult fly (Athalia proxima Klug) is orange yellow with smoky wings and black veins. The young larva is green with a black head, about 4 mm long. The full-grown larva is greenish-grey, having 5 strips of black dots on the lower side of the body and is about 1 cm long. The larva attacks the young crop. All the leaves are damaged under the heavy incidence of the pest. The pest appears in October and The application of 10% Carbaryl dust @ 25 kg/ha or spraying the crop with 0.2% Carbaryl 50 WP (2 kg Carbaryl 50 WP mixed in 500 litres water/ha) controls the pest.
Painted bug
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The nymphs of Bagrada cruciferarum Kirk have a number of pale, brown and red markings on their bodies. The nymphs and adults suck the cell sap from the foliage and pods, making them dry. The sucking of the leaf sap causes white blotchy spots. Its high population becomes a nuisance at the threshing floor also. This pest appears at the seedling stage and again at the pod-formation stage.
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The application of 10% Carbaryl dust @ 25 kg/ha at seedling stage or spraying the crop with Malathion, 50 EC (0.05%), i.e., 500 ml Malathion 50 EC mixed in 500 litres water per hectare at the seedling stage, controls the pest. The second round of spraying with Malathion 50 EC may be given in March (after the pod formation), if necessary.
Cabbage butterfly (Pieris brassicae)
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The pest appears at the flowering and pod-formation stages. The caterpillars feed on the leaves, buds and developing pods. The insect can be controlled by spraying Endosulfan @ 1.2 lit or Dichlorvos @ 300 ml in 600 litres of water, per hectare.
Bihar hairy caterpillar
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The abdomen of the moth (Spilosoma oblique Walker) is bright red with black spots; the thorax, antennae and eyes are black. The fore-wings have a reddish tinge and the hind-wings have dark brown spots. The newly-hatched larvae are brown and feed gregariously (in groups) on the leaves of a few plants. The fully grown caterpillars are 4-5 cm long and have numerous dark brown, long hairs on the body. The mature caterpillars spread to the whole field and cause huge losses. The pest is more serious on toria during periods of droughts.
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To control the pest, the affected leaves should be destroyed in the initial stages of infestation. This would reduce the spread of the damage. The destruction of the larvae in the gregarious phase is quite easy and effective. The young caterpillars can be easily killed by dusting the infested crop with Carbaryl 10% (25 kg/ha). Spraying the crop with 0.07% Endosulfan (Thiodan 35 EC) 1200 ml or 0.05% Dichlorvos (Nuvan 70 EC) 300 ml mixed in 600 litres water/ha controls the pest. The rhizosphere nematode problem has been noticed in B. juncea, which can be managed by different weed control practices. The beet cyst nematode (Heterodera sachactii) has also been reported to cause damage to white mustard.
Diseases
The major fungal diseases affecting rapeseed and mustard crops are Alternaria blight, white rust, downy mildew, powdery mildew and phyllody.
Alternaria blight
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The blight caused by Alternaria brassicae is characterised by brown or greyish spots on the leaves, stems and pods, and is the most destructive and widespread. Compared to mustard, sarson is more prone to this disease; moist and warm weather favours the disease. To control this disease, the following measures should be taken: (i) the debris of the previous crop should be burnt (ii) removal of weeds like Chenopodium album to reduce the disease. (iii) the crop should be sprayed with Mancozeb or Captafol (1.5 kg/ha) at intervals of 15 days, 40-45 days after sowing. This fungicide is cheap and helps in reducing the intensity of another important disease, white rust, which is characterised by the white pustules of Albugo candida on the lower surface of the leaves in the early stage, i.e., when plants are 45-50 days old. Later, the malformation of the floral parts takes place, which is known as the stage of stag-head formation.
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Apron @ 0.2% as seed-dresser along with 3 sprays of Dithane M-45 @ 0.2% or Dithane Z-78 or Captafol or Copper oxychloride is recommended for reducing white rust and the simultaneous occurrence of downy mildew (Peronospora parasitica) incidence at the seedling stage. Sprays of Dithane M-45 or Zineb also help in minimising the severity of all these diseases on the leaves and pods. If Apron is not available, the spray of Dithane M-45 should be continued.
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When there is an attack of powdery mildew (Erysiphe cruciferarum), which is characterised by a white powdery mass on the stems and leaves at the later stages of plant growth, it should be sprayed with Wettable sulphur (0.3%).
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It is necessary to ensure that there is no delay in sowing. This would protect the crop from various diseases. To avoid the spread of club-root (Plasmodiophora sp.), crop rotation with cereals should be adopted and growing yellow sarson should be avoided.
Stem-rot or blight
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The disease caused by Sclerotinia sclerotirum is characterised by elongated, water-soaked lesions on the stem with the cottony mycelial growth of fungus, wilting and drying of plants, stunting and premature ripening of the plant and the shredding of the stem. The disease can be controlled by collecting and burning the disease debris and refuse of the plants. Crop rotation may be followed using non-susceptible hosts to reduce the sclerotial population in the soil.
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