Weed killers entomology IPM AET 201.pptx

Weed killer insects

1. WEED KILLERS: Many insects feed upon unwanted weeds, just the same manner they do with cultivated plants. They damage the noxious and menacing weeds, these insects are considered helpful or friendly to man. In many cases the occurrence of these insects have contributed much towards eradication of the weed or at least keeping it in check.

2. QUALITIES OF SUCCESSFUL WEED KILLER Should not itself be a pest of cultivated plants and should not even at a later date turn to attack the useful crops. Should be effective in damaging and controlling the weed. Should preferably be a borer or internal feeder of the weed. Should be able to multiply in good numbers without being affected by parasitoids and predators.

3. 1)Opuntia spp.(prickly pear) Various species of Opuntia, which has its origin in the western hemisphere, have been transported for the purpose of human food (fruits), cattle food (pads) and food for the dye producing insects In Australia, it became an extremely aggressive weed, infestating some 25 million ha of cultivable land.

4. A pyralid moth, Cactoblastis cactorum obtained from Argentina and introduced in Australia in 1925, was able to salvage huge areas of land from cactus by 1930. They brought only 2750 Cactoblastis larva to Australia, of which only 1070 became adults. From these, however, more than 1,00,000 eggs were produced, and in February – March of 1926 more than 2.2 million eggs were released in the field .

5. The control was so drastic that the entomologist got concerned about the very survival of these insects themselves due to the shortage of food i.e. Opentia.

6. b) The cochineal (scarlet dye-pruducing) insect, Dactylopius ceylonicus, a coccid or scale insect (homoptera), has been successful in the prickly pear control in Kenya and D. opentiae in the USA (California).

7. c ) In India, O. dillenii was a noxious weed and it has been practically eradicated by the cochineal insects, D. tomentosus. The insect is a native of Mexico and was introduced into India via Sri Lanka in about 1925. within the next five or six years, the weed was almost exterminated.

8. 2) Lantana camara Lantana, a native of Central America, is extensively used throughout the world as an ornamental shrub. But in many countries, it has escaped civilisation and encroached upon vast areas of cultivable land. India shares this weed problem along with Hawaii, Fiji, and Australia .

9. In India two insects have been tried : A lace bug,(Teleonemia scrupulosa) A seed fly, (Ophiomyia lantanae ) (both Central American in origin) In Uganda, Lantana has been controlled by T. scrupulosa lace bug Seedfly

10. 3) Hypericum perforatum This weed poses serious problem in the USA , Australia, Canada, New Zealand and Chile destroying thousands of hectares of land. Various species of the leaf-feeding beetle, Chrysolina have controlled this weed successfully.

11. 4) Senecio jacobaeae (Tansy Ragwort) This is the another weed that has been causing a great damage to pastures in New Zealand , Australia, USA, Canada. The weed has been controlled to a great extent by the moth, Tyria jacobaeae and seed fly, Pegohylemyia seneciella .

12. 5)Water-hyacinth( Eichhornia crassipes ) It is a free floating freshwater plant, it impedes flow of irrigation water, pre-vents free movement of boats. In 1982 tree exotic natural enemies viz. Neochetina bruchi Hustache , N. eichhorniae Warner and the mite Orthogal-umna terebrantis Wallwork were introduced and the former two have proved successful. Adults of both the weevils feed on the leaves of hyacinth and deposit their eggs below the epidermis of petioles and laminae .

13. The adults of N. bruchi and N. eichhorniae lays 681 and 981 eggs respectively. Whitish eggs of these species hatch in about a week. The grubs are white or cream coloured with yellow or orange head, The larval and pupal perioda are completed in two months. N. bruchi and N. eichhorniae live for 134 and 142 days respectively. And they migrets up to 30 km.

14. They can be reared in laboratories in large numbers under controlled condition on the weed artificially inoculated on the weeds in natural conditions. Other management practices such as mechanical removal of the weed can also be followed simultaneously.

15. 6) Aquatic weed Salvinia molesta This weed introduced in indian in1950s. It became a serious weed since 1964. The weevil Cyrtobagous salaviniae Calder and sands, of brazilian origin, was introduced from australia in 1982 for the control of the aqatic fern Salvinia molesta . Adults of the weevil feed on freshly emerged leaves and buds of Salvinia .

16. Adult males and females survive for up to 284 and 271 days respectively. Female lays 148 to 383 eggs. Adults damage the leaf buds and the young terminal leaves; and feeding by larvae causes browning and decay of leaves.

17. 7) Parthenium hysterophorus (Congress weed) The exotic beetle Zygogramma bicolorata Pallinter introduced from Mexicon in 1983 for the control of the congress weed has been established in India. Adults and Grubs feed on leaves and flowers. 2 beetles controls and destroys one plant in 45 days.