Weed survey in cotton (Gossypium hirsutum L.) and sunflower (Helianthus annuus L.) fields in the Pandamatenga plains of northeastern Botswana

Abstract

Sunflower and cotton fields in the Pandamatenga plains of northeastern Botswana were surveyed in 1998 and 1999 for weed infestations. Twenty-seven and 24 species were identified from the fields in 1998 and 1999, respectively. Nineteen and 17 species were found to be annuals in 1998 and 1999, respectively, with Amaranthus hybridus L. as the most abundant species. In 1998, Ipomoea coscinosperma Hochst., Phyllanthus maderaspatensis L., Trichodesma zylanicum (Burm. f.) R. Br. and Acalypha crenata L., all broadleaved species, were the most abundant after A. hybridus in that order; whereas in 1999 the most abundant species after A. hybridus were A. crenata, P. maderaspatensis, Euphorbia hirta L., and T. zylanicum. Setaria verticillata (L.)P. Beauv., which was the most abundant grass weed in 1998, declined in abundance in the following year and in 1999 Brachiaria eruciformis (Sm.) Griseb appeared in larger numbers than S. verticillata. Two grass weeds, Sorghum verticilliflorum (Steud)Stapf and Rottboellia exaitata L., which were present in small numbers in both crops during this survey, can pose a serious challenge to crop production in the area if not adequately controlled.