Learn about the pests that damage sunnhemp and its control.
1. Sunnhemp Capsid, Ragmus Importunitas Distant (Hemiptera: Miridae):
This is a small, active, green bug which sucks plant sap and when present in large swarms, causes appreciable damage. The pest is widely distributed in southern India.
Life-Cycle:
The bugs lay white cylindrical eggs in the plant tissue, generally under the surface layer of leaves. The nymphs hatch out from the eggs in 7-8 days. The young nymphs, on emergence, begin to feed on the plants. The nymphs become adults in 10-12 days. The total life-cycle is completed in 35-62 days. All stages of the insect may be found simultaneously.
Damage:
The nymphs and adults suck the sap from tender leaves and shoots, and cause yellowing of leaves. In case of severe attack, there is death of the plants.
Prevention and Control:
(i) The population of the pest can be suppressed by collecting the bugs with nets or sticky boards,
(ii) Spray 2.5 kg of carbaryl 50WP or 625 ml of malathion 50WP in 625 litres of water per ha.
2. Sunnhemp Hairy Caterpillar, Utetheisa Pulchella (Linnaeus) (Lepidoptera: Arctiidae):
This insect is the most important pest of sunnhemp in Tamil Nadu. The caterpillars feed on leaves and bore into the capsules. The adult moth is pale, whitish with red black spots on the upper wings and black marginal blotches on the lower wings. The full-grown caterpillar is about 3.8 mm in length and has red, dark and white markings on its body and a brownish head.
Life-Cycle:
The moths lay small whitish eggs on the tender leaves and shoots. On emergence from the eggs, the larvae feed on leaves. As the crop matures and pods appear, the caterpillars feed by thrusting the head in and leaving the rest of the body exposed. Pupation takes place either in the leaf folds or in the soil. The life-cycle is completed in about 5 weeks and a number of generations are completed in a year.
Damage:
The caterpillars feed on leaves and also cause severe damage by feeding on the contents of developing pods. They defoliate the crop and cause a decrease in seed production. When the population is high and the attack severe, the plants become pale and appear unhealthy.
Prevention and Control:
(i) The pest can be suppressed by hand picking and killing the caterpillars as well as by collecting the moths with nets during the day time,
(ii) Spray 2.5 kg of carbaryl 50WP in 625 litres of water per ha.
3. Flea Beetle, Longitarsus Belegaumensis Fabricius (Coleoptera: Chrysomelidae):
The yellowish brown beetle has enlarged hind femur.
Life-Cycle:
The eggs are laid in the soil. The grubs feed by mining into tender roots of sunnhemp plants and when full-grown, pupate in the earthen cells in the soil. The life-cycle is completed in 23-28 days.
Damage:
Both adults and larvae cause damage. The adult beetles bite holes in the leaves and cause severe damage. The larvae feed on the roots and reduce the vitality of the plants.
Prevention and Control:
Apply carbofuran 3G @ 12.5 kg/ha in soil followed by spray of carbarcyl 50WP @ 2.5 kg/ha.