MATERIALS AND METHOD
A herbicide evaluation trial was conducted on maize at Henderson Research Station during the 2018-19 cropping season with the following evaluation objectives:
- To evaluate the effectiveness of S-Metolachlor herbicide in the controlling weeds in maize by comparison with the herbicide Integrity.
- To evaluate any phytotoxic effect of S-Metolachlor.
The trial was conducted in a field plot with heavy red clay soils planted to soya beans in the previous season. Land preparation was done using a tractor drawn disc harrow. Hoes were used to break the clods and leveling the seed bed. The Pioneer Seeds-bred medium maturing (135-145 days to maturity) maize variety PHB30G19, with a yield potential of 7-11 t/ha, was used. It was spaced at 90cm x 25cm and the net plot measured 4m x 3.6m. Planting was done on 26 November 2018. Two maize seeds were planted per station and were later thinned to one plant per station at two weeks after crop emergence. The basal fertilizer Maizefert (7N:14P:7K2O) was applied at 400kg at planting and the top dressing fertilizer Ammonium Nitrate (34.5%N) was split applied at 3 and 6 weeks after crop emergence to give a total rate of 400kg/ha.
S-Metolachlor and the check (herbicide Integrity) were applied as pre-emergence herbicides in moist soil a day after planting the maize. Application was done using a knapsack sprayer calibrated to deliver 192.2 l/ha on 26 November 2018. The trial was laid out in a Randomized Complete Block Design (RCBD) replicated 4 times. Three rates of S-Metolachlor were used. The treatments were as follows:
- Control (no weeding)
- Integrity 1 l/ha
- S-Metolachlor 1.1 l/ha
- S-Metolachlor 1.5 l/ha
- S-Metolachlor 1.9 l/ha
Results showed that S - Metolachlor 1.9 l/ha is effective to control most weeds in a maize crop as a pre – emergent herbicide. However, Rottboellia cochinchinensis and Commelina benghalensis werenot controlled by the herbicide S- Metolachlor.
S- Metolachlor can used effectively as a pre-emergent herbicide in maize for most weeds except Rottboellia cochinchinensis and Commelina benghalensis.
Nyasha Rushwaya (Research)