| dc.description.abstract | Cotton (Gossypium hirstum L.) is an important cash crop in Kenya but its yields are low
due to various constraints including weeds, pests and diseases. Cotton is especially sensitive
to weed competition because it grows relatively slowly in the early stages, and does not reach
full ground cover until eight or more weeks after germination. The effects of weeds on the cotton
crop can be caused by competition for light, water and nutrients, and will depend on the type and
density of weed growth. Weeds also act as alternative host for insect pests that attract the cotton
plants. The African bollworm, if not properly controlled, is an important pest responsible
for close to 100% yield loss. Although Bt cotton is known to affect insect pests, not much is
known about its competition with weeds. It is however postulated that unlike conventional
cotton, Bt cotton may out compete weeds as it is believed that it has a competitive advantage
than conventional cotton over weeds because of the fact that it would not be attacked by pests
and would have a head start in the early growth stages.
The main objective of this study was to establish the effect of weeds on cotton growth and to
evaluate the competitive ability of Bt cotton against common weeds in Kenya. This study
therefore sought to find whether and when this competitive advantage was achieved under field
conditions, and the role of weeds in harbouring pests of cotton. The experiment used a
completely randomized block sampling regime using weeded and non-weeded plots. Growth
parameters ( namely plant heights, number of bolls, number of leaves and number of attacked
leaves) of Bt and conventional cotton plants were assessed under both weedy and weed free
conditions during the growing season.
There was no significant (p>O.OS) difference in number of leaves, bolls and pest damage between
Bt and non-Bt cotton (HART89M) varieties. HART89M had higher (P<O.OS) final height
compared to Bt cotton variety. The difference in plant growth parameters between weeded and
non-weeded plots was found to be significant (P<O.OS). The common weeds found were
Commelina benghalensis (mean density = SO.041±1.79), Waltheria indica (mean density =
49.416±1.34) and Cleome monophylla (mean density = 49.2S±0.8S). Generally it was concluded
that Bt cotton had no competitive advantage over weeds compared to conventional cotton. This
conclusion has implications in cotton stewardship programmes in that farmers need to
understand that Bt cotton, thuogh is not attacked by bollworms, requires the necessary number of
weedings in order to avoid losses caused by weeds | en |
