Learn about the pests that damage sorghum and its control.
1. Sorghum Earhead Bug, Calocoris Angustatus Lethiery (Hemiptera: Miridae):
It is one of the most destructive pests of sorghum in southern India. Both the nymphs and the adults feed in the green ear heads. The adult is a small, slender, greenish yellow bug, measuring 5-8 mm in length and over 1 mm in width. This bug has been recorded feeding on a number of cereals, millets and grasses, but its breeding is mainly restricted to sorghum, on which it assumes the status of a pest.
Life-Cycle:
The adults appear on sorghum crop as soon as the ears emerge from the leaf sheaths. The bug lays eggs under the glumes or in between anthers of florets, by inserting its ovipositor. The female lays 150-200 eggs which are cigar- shaped and measure about 1.5 mm.
The eggs hatch in 5-7 days and the nymphs start feeding on developing grains in the milk stage. The nymphs pass through 5 instars and develop into adults in about 3 weeks. The adults of the second generation are again ready to oviposit in the ears having developing grains which might be available on the same crop. As soon as the grains are ripe, the bugs stop multiplying on that crop. The insect completes its life-cycle in about one month and produces a number of generations in a year.
Damage:
As a result of feeding by the bugs, the grains remain chaffy or shrivelled. When a large army of tiny nymphs feeds, the whole ear may become blackened at first and May eventually dry up, producing no grains.
Control:
Spray 625 ml of malathion 50 EC or 3 kg of carbaryl 50 WP or 200 ml of phosphamidon 85 WSC in 500 litres of water per ha.
2. Sorghum Shoot Bug, Peregrinus Maidis (Ashmead) Hemiptera: Delphacidae):
The nymphs and adults of this insect are serious pests of millets, sorghum and maize in south India. The insect has also been reported feeding on sugarcane, oats and various species of grasses. It is pan-tropical in distribution and has been recorded in Barmuda, West Indies, Hawaii, Cuba, East Africa and the Philippines.
The adult hopper is yellowish brown, with translucent wings and measures 3.2-3.8 mm in length. The full-grown nymphs are light brown with prominent eyes and wing pads.
Life-Cycle:
This pest is active from September to January and is rather scarce from March to June. The adults, on emergence, mate and the females take 1-3 days before they start depositing eggs. The female bugs make slits in the midrib of the leaves with the help of their ovipositors and lay white, elongated and cylindrical eggs in groups of 1-4. Within the oviposition period of about 7 days, she can lay, on an average, 97 eggs.
The eggs hatch in 7-10 days and the young nymphs feed at first within the leaf sheaths and the leaf whorls. As they grow, they spread out to wider areas. After undergoing 5 moultings, they become adults in 16-18 days. The total life-cycle is completed in 3-4 weeks.
The young nymphs are attacked by its natural enemies, the lady birds, Coccinella septempunctata Linnaeus and Menochilus sexmaculatus (Fabricius) (Coccinellidae). The eggs are also parasitized by Anagrus optabilis (Perkins) (Mymaridae) and Ootetrastichus indicus Gir. (Eulophidae). These natural enemies play a significant role in reducing population of the insect.
Damage:
The adults and nymphs feed gregariously within the leaf whorls, the leaf sheaths and also on the leaves. As a result of their sucking the cell sap, the leaves become yellow and the growth of the plants is retarded. When the attack is severe, the ears fail to emerge.
The adults also transmit the virus diseases, ‘corn moasic’ and ‘freckled yellow’ of sorghum and other virus diseases of sugarcane and pearl millet.
3. Sorghum Shoot Fly, Atherigona Soccata Rondani (Diptera: Muscidae):
The sorghum shootfly, also known as the sorghum stemfly, is a widely distributed pest in Europe, Africa and Asia. In India, it is more serious in southern parts. Besides sorghum, it infests maize, wheat, broom corn, small millets (Panicum spp.) and grasses. It causes damage to the seedlings as well as to the early stages of the crop. The maggots bore into the stem and cut the main shoot. The high-yielding hybrids are more susceptible to the attack of this fly.
Life-Cycle:
The female fly lays approximately 40 eggs singly on the underside of the leaves during its life span of about one month. The eggs are elongate, flattened and somewhat boat- shaped and is provided with two wings like lateral projections. The eggs hatch in 1-2 days and the tiny maggots creep out and reach in between the sheath and the axis, and bore into the stem.
They feed inside the main shoot for 6-10 days and, when full grown, they may pupate either inside the stem or come out and pupate in the soil. The pupal period in the summer lasts about a week. Several generations are completed in a year. In northern India, the pest over-winters in the pupal stage.
Damage:
The insect attacks the young crop when it is in the six leaf stage. Six weeks after planting, the crop is seldom attacked. As the maggots feed on the main shoot, the growing point is destroyed and by the time they pupate, the plant is almost dead. The young plants show typical dead-heart symptoms.
When the attacked plants are somewhat older, tillers are produced, which mature later than the main crop. The total loss in yield is sometimes as high as 60 per cent. Cloudy weather favours the multiplication of this insect and it is believed that infestation is also higher in irrigated fields.
Control:
(i) The crop sown from early June to the second week of July normally escapes the attack of shoot fly.
(ii) Grow resistant varieties like CHS-7, CHS-8, Indian sorghum types IS-5566, 5285 and 5613.
(iii) Seed coating with imidacloprid 600FS @15 ml/kg seed or isofenphos 5G @ 300 g/kg seed provides protection against shootfly up to 2 weeks.
(iv) In case seed treatment has not been done, apply 12.5 kg of carbofuran 3G or 10 kg of phorate 10G per ha in furrows before sowing,
(v) Alternatively, spray 1.25 litres of malathion 50EC or 2.0 kg of carbaryl 50WP in 500 litres of water/ha.
4. Sorghum Midge, Stenodiplosis Sorghicola (Coquillett) (Diptera: Cecidomyidae):
This insect is distributed in all the sorghum growing tracts of the country and causes considerable losses. The adult fly is a very small (2 mm) fragile mosquito-like insect with a bright orange abdomen and a pair of transparent wings.
Life-Cycle:
The female inserts the eggs singly into developing florets at the time pollen is being shed and lays about 30-100.eggs. The eggs hatch in 2-3 days and the maggot feeds inside the developing grain and pupates there itself. The larva has four instars with a total duration of 10-11 days. It emerges between the tips of the glumes leaving the white pupal case attached to the tip of the floret which is very characteristic. The pupal stage lasts about a week and the total life- cycle is completed in 14-22 days.
Damage:
The damage is caused by the maggots which feed on the ovaries and thus preventing the formation of grains. The infestation is dependent on humidity (more severe in low lying humid areas), initial infestation and duration of flowering of sorghum. The loss in yield varies from 20 to 50 per cent.
Control:
(i) Both early and late maturing varieties of sorghum should not be grown in the same area as it would provide the pest a continuous supply of flowers. The varieties having the same flowering and maturity time would reduce midge damage considerably,
(ii) Since the damaged and aborted seeds are the main source of carry-over of the pest from one season to another, collect and burn the panicle and post-harvest trash,
(iii) Spray 1 litre of malathion 50EC or 1.25 litres of lindane 20EC or 2.0 kg of carbaryl 50WP in 500 litres of water/ha. Only the earheads should be treated at 90 per cent panicle emergence followed by second spray after 4-5 days,
(iv) Dusting the earheads with endosulfan 4% or carbaryl 5% or lindane 2% @ 12 kg/ha has also proved effective.