Efficacy of Herbicides for weed control in Soyabean cropping systems of Zambia

A trial was conducted at two sites, Lilayi Farm using no-tillage
system and Ellensdale Farm using conventional tillage. The objective
was to assess the efficacy of new herbicides under Zambian conditions
so as to' provide recommendations for effective herbicides. Ten
treatments were used at both sites: three pre-emergence treatments
(metribuzin plus metolachlor, oxadiazon and oxadiazon plus metolachlor)
and five post-emergence treatments (fomesafen plus fluazifop-butyl,
bentazone plus fluazif op-butyl, bentazone plus acif luorfen, acif luorfen
plus fluazifop-butyl and bentazone plus fenoxaprop-ethyl). Other
treatments were no weeding and hand hoe weeding at 2 and 4 weeks after
planting. Pre-emergence herbicides were applied soon after planting,
while post-emergence herbicides were applied 22 days after planting.
At Lilayi, pre-emergence herbicides gave excellent control of
weeds for the first three weeks after planting, thereafter new weeds
particularly broadleaf weeds emerged and competed with the crop.
Fomesafen and acifluorfen gave good control of all broadleaf weeds but
the effect lasted only the two weeks following application after which
new weeds emerged. Inadequate crop cover formation during the first six
weeks of crop growth also encouraged the growth of new weeds which
competed with the crop, resulting into low yields.
At Ellensdale Farm, metribuzin plus metolachlor gave a seasonlong
complete control of both broadleaf and grass weeds; while the
other pre-emergence and the post-emergence herbicides gave excellent
control of most weeds found in the experimental plots. Oxadiazon and
bentazone gave poor control of Bidens pilosa L. and Amaranthus hybridus
L. respectively.