Learn about the pests that damage groundnut and its control.
1. Groundunt Aphid, Aphis Craccivora Koch (Hemiptera: Aphididae):
This is one of the most serious pests of groundnut. It also attacks peas, beans, pulses, safflower and some weeds. Its distribution is throughout India. It has also been recorded in Africa, Argentina and Chile. This species is also present in non-groundnut areas of the USA, Europe and Australia.
Colonies of aphids suck the sap from the underside of the leaves, top shoots and stem. In severe cases of infestation, the crop gets withered and blighted. The aphid is also a vector of a virus disease known as the rosette of groundnut. The winged adults have black wings and they reach the freshly germinated groundnut plants after overwintering on collateral host plants.
Life-Cycle:
The offspring of the winged form may be wingless. Even without fertilization the females may produce 8-20 young ones in a life span of 10-12 days. The young nymphs are brownish and they pass through four moults to become adults in 5-8 days. The apterous females start producing brood within 24 hours of attaining that stage. Breeding occurs almost throughout the year and both alatae and apterae are present.
The coccinellid beetle, Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae) and Ischiodon javana (Wiedemann) (Diptera: Syrphidae) are the main predators of this aphid pest.
Damage:
The nymphs and adults suck the sap, usually from the underside of leaves. Infestation in the early stages causes stunting of the plants as well as reducing their vigour. When the attack occurs at the time of flowering and pod formation, the yield is reduced considerably. Infestation on the groundnut crop usually occurs 4-6 weeks after sowing.
Control:
As soon as the pest appears on growing points, spray 625 ml of malathion 50 EC or 425 ml of dimethoate 30EC or 425 ml of oxydemeton methyl 25EC in 200 litres of water per ha.
2. Groundnut Leafminer, Aproaerma Modicella (Deventar) (Lepidoptera: Gelechiidae):
This pest is distributed all over India, Pakistan, Sri Lanka, Myanmar and South Africa. In India, it is most serious in Tamil Nadu. Although it has been reported feeding on other plants, it is considered a serious pest of groundnut only.
Damage is caused by tiny caterpillars which mine into the leaves, skeletonize them and web them together. The larva is small and green, and has a conspicuous dark head. The adult is a small bronze moth with a wing expanse of about 1 cm.
Life-Cycle:
During the day the moths remain concealed under clods of soil or in the crevices. They become active at night when they are also strongly attracted to light. The female moth lays up to several hundred eggs singly on leaves and on shoots. The eggs hatch after about 3 days. The newly hatched larva measures about 1.5 mm in length.
After wandering about for some time, it mines into the leaves and, later on, bites its way out. It then webs together a number of leaflets and feeds inside the chamber, thus formed. The larvae are full-grown in 9-17 weeks, when they measure 6-8 mm in length and turn dirty green. They prepare silken cocoons to pupate in. The pupal period lasts about 4 days. There, are several generations during a year.
The eggs of this pest are parasitized by Trichogramma sp. (Trichogrammatidae). The braconids, Bracon hebetor Say and Apanteles javensis Rohwer (Braconidae) and eulophids, Asympiesiella indica Girault, Stenomesioideus ashmeadi Subha Rao & Sharma and Euplectrus sp. (Eulophidae), parasitize its larvae.
Damage:
As a result of the mining, skeletonizing and webbing together of the leaves, the crop suffers serious losses. In badly infested fields the plants present a look as if the crop has been scorched. The insect also attacks soybean and arhar (Cajanus cajan L.)
Control:
Spray 2.0 kg of carbaryl 50WP or 350 ml of oxydemeton methyl 25EC in 250 litres of water per ha.
3. Groundnut Stem Borer, Sphenoptera Perotetti Guenee (Coleoptera: Buprestidae):
This pest infests the groundnut crop in Andhra Pradesh, Bihar, Delhi, Gujarat, Kerala, Tamil Nadu, Madhya Pradesh, Maharashtra and Karnataka. It has not been recorded anywhere outside India. Besides groundnut, it attacks sesamum, gram and other pulses.
The grub of this beetle bores into the stem and root. The adult is a small jewel-like beetle, 10- 12 mm in length with a striking metallic shine over a dark brown background. The full-grown grub is whitish in appearance.
Life-Cycle:
The beetles lay scale like eggs and glue them on to the branches. The slender, creamy white grubs bore into the branches and travel down the main stem and ultimately reach the tap-root. When full-grown, the larvae pupate inside the tunnels. The pupal period lasts 7-10 days. The beetles emerge from the tunnels by cutting their way out and they start the next generation. The infested plants receive a set-back and are killed when the borer reaches the tap-root.
The grubs are parasitized by a braconid, Glyptomorphci smenus (Cameron) (Braconidae).
Damage:
As a result of the larvae boring into the stems and because of the feeding injury to the roots some plants are killed. The damage appears in patches.
Control:
The pest can be suppressed by cutting and destroying the infested branches thus preventing the grubs from entering the tap-root. No Chemical control is possible.
4. White Grub, Holotrichia Consanguinea Blanchard (Coleoptera: Scarabaeidae):
In some parts of India, this insect is known to infest sugarcane, sorghum, maize, chilli, okra, brinjal, etc. The insect appeared as a pest of groundnut in 1957 in the Gujarat State and later on also in Haryana, Himachal Pradesh, Rajasthan and Punjab. At present, the attack of this pest is localised but is spreading to larger areas.
The damage becomes evident only when the entire plant dries up due to the grubs feeding on fibrous roots. The grubs are mostly found in the upper 5-10 cm layer of soil. When full-grown, they are about 35 mm long and are white, having a brown head and prominent thoracic legs. The adult beetles are dull brown and measure about 18 mm in length and 7 mm in width.
Life-Cycle:
The presence of a large number of newly hatched larvae in June shows that this insect becomes active with the onset of the monsoon. The adult beetles lay eggs singly up to a depth of 10 cm. The eggs hatch in 7-10 days. The newly hatched grubs measure about 12 mm in length and their development is completed in 8-10 weeks.
After the monsoon, the full-grown larvae migrate to a considerable depth in the soil for pupation. The pupa is semicircular and creamy white and the pupal stage lasts about a fortnight. The beetles remain in the soil at a depth of 10-20 cm and come out for feeding at night. Adults formed in November remain in soil till next June. Their population is maximum in the rainy season and there seems to be only one generation in a year.
The grub is parasitized by Scolia aureipennis (Scoliidae). A fungus, Metarrhizium anisopliae (Metchnikoff) (Moniliaceae) parasitizes the adults and the common Indian toad, Bufo melanostictus, and the wall lizard, Gecko gecko feed on the beetles.
Damage:
The grubs eat away the nodules, the fine rootlets and may also girdle the main root, ultimately killing the plants. At night, the beetles feed on foliage and may completely defoliate even trees like neem (Azadirachta indica) and banyan (Ficus bengalensis).
Control:
(i) Plough the fields twice during May-June. It would help in exposing the beetles resting in the soil.
(ii) Wherever possible, sow the crop early, i.e., between June 10 and 20.
(iii) Treat the seed before sowing with 12.5 ml of chlorpyriphos 20EC per kg of kernels,
(iv) Kill the beetles by spraying 500 g of carbaryl 50WP in 250 litres of water per ha on the preferred host plants like ber, guava, rukmanjani, grapevines, almond, etc. The spray should be carried out in the afternoon and repeated after every rainfall till the middle of July,
(v) Apply 10 kg of phorate 10G or 30 kg of carbofuran 3G per ha in the soil at or before sowing.