Summary:A survey of weeds and weeding practices was carried out by a team of agricultural economists and agronomists on 283 farms in five Cassava growing regions of Colombia at three times during a cropping season.Seventy‐one to 78% of all weed species present were broadleaved species. As cassava grew older, grass species were present to a greater and sedge species to a lesser relative frequency. SurprisinglyPteridiumaquilinum(L.) Kuhn was the most frequently listed species andBidens pilosaL. andCyperus rotundusL. were other frequent problems. Regional variations in the most frequently encountered species were found but several of the weeds were common to many zones. The most frequently encountered species did not usually have the highest plant populations. Most of the annual grasses, sedges and broadleaf weeds found can be controlled by currently recommended herbicides for cassava but further research is needed onImperata cylindrica(L) Beauv.,Melinis minutlftoraBeauv., P.aquilinumandSidaspp.The average number of manual weedings was 3.3 per crop, occupying 48 man‐days/ha which is 50% of the total labor requirements for cassava production, and more than one‐third of the total costs. Reasons for not using herbicides were (1) relative costs of herbicides and labor. (2) lack of information, (3) lack of capital, (4) right herbicides were not available, and (5) herbicides were not available in small packages.This survey has usefully identified new field problems and has suggested further research programs to solve
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