Integrated Pest Management on Cotton in South Africa
Mar 6, 2019
A wide variety of insects attack cotton in South Africa. Some are such serious pests that chemical control is necessary to ensure a viable yield. Chemical control of one species can influence the occurrence and population density of other species. The bollworm complex can cause severe crop losses and holds the key to overall efficiency of insect and mite control. The American bollworm, Helicoverpa armigera (Hübner), is responsible for most of the losses in seed cotton. The use of American bollworm pheromone traps shows potential as a substitute for time-consuming scouting, and may enhance an IPM approach. Where producers ratoon cotton, red bollworm, Diparopsis castanea (Hampson), can decrease the yield drastically. The spiny bollworm species, Earias insulana (Boisduval) and E. biplaga (Walker), occur in low numbers. The control of bollworms with insecticides such as pyrethroids and organophosphates can cause a severe build-up of these pests because these insecticides are harmful to predators and parasites of the cotton aphid Aphis gossypii (Glover) and the tetranychid mites (Acari) Tetranychus urticae (Kock), T. lombardinii (Baker and Pritchard) and T. ludeni (Zacker). Mites and aphids have the ability to develop resistance to pesticides. Under favourable conditions, cotton leafhoppers, Jacobiella fascialis (Jacobi), can cause the leaves of certain cultivars to turn purple and curl up, thus retarding growth and development. Leafhoppers cannot feed on hairy cotton and can be controlled in an IPM system by planting cultivars with hairy leaves. Thrips tabaci (Lindeman), Frankiniella schultzei (Trybom), and cutworms, Agrotis spp., appear in the early growing season, while stainers, Dysdercus fasciatus (Signoret), D. nigrofasciatus (Stål), D. intermedius (Distant) and Oxycarenus hyalinipennis (Costa) do more damage towards the end of the season. Spodoptera littoralis (Boisdeval) and grasshoppers, Zonocerus spp. sometimes appear, but are normally kept in check by bollworm control programmes. In ratoon cotton, D. castanea and the black cotton beetle, Syagrus rugifrons (Baly), can cause serious problems. The juvenile stages of the cotton stem weevil, Apion soleatum (Wagner), a serious pest in the eastern subtropical areas of South Africa, are difficult to control because they complete their life cycle in the cotton stem. Chemical control should be practised with circumspection, using all possible systems to monitor insect damage and population densities. The injudicious use of insecticides early in the season can lead to the build-up of mites and aphids. Chemical control should only be considered when the number of pests exceeds the economic threshold.