A survey of the arable weeds of Botswana

Abstract

A survey of weeds of the main arable areas of Botswana was made over three seasons from 1987 to 1990. A total of 326 species representing 49 families was recorded from 186 fields and one‐third of the commerical farms of Pandamatenga. The majority of crops were sorghum or sorghum and cowpeas inter‐cropped. Maize, millet and sole cowpeas were also represented. The majority of weeds were dicotyledonous (80%), 16% were grasses and 4% sedges. Most species were rare and only 10% were found in more than one‐fifth of fields. Fields generally had many species (average 20.5) at trace to frequent levels of infestation. Soil differences accounted for much of the variation in distribution. The clay soil at Pandamatenga had a different flora from that found on the sandy soils that prevail in most of the country. Fields in the Okavango Delta likely to flood during the dry season, supported species not found on the sands. Two parasitic weeds were recorded; Alectra vogelii Benth. was common on cowpeas and Striga asiatica (L.) Kuntze was recorded at low levels, mainly on sorghum.

Keywords:

• Botswana
• weed species
• abundance
• significance
• distribution