Key Points:
- In some soils pre-emergent herbicides are quickly degraded by microbial activity and their ability to control weeds is reduced from weeks to days. In these situations successful weed control is dependent on a combination of cultivation and post-emergence herbicide programmes.
- In these trials, Latro and its combinations provided better weed control than other herbicides. Similar levels of weed control were achieved with applications made at 3 or 4 leaf stage of the crop.
- Weed control is influenced by the weed spectrum and the size of the weeds. Some weeds are tolerant to some herbicides and smaller weeds are easier to control, with efficacy decreasing as height increases. Matching the herbicide to the weed and getting in early will improve the control.
- Timing of the post-emergence applications had a significant impact on the level of weed control attained. Latro and Callisto applied at five weeks post emergence (WPE) gave much lower weed control scores than the earlier applications.
- Latro is an option that can be used in the maize crop where weed control from the pre-emergent or early post‑emergence herbicide applications is poor.
- Crop yield data suggest that the weed coverage, as % cover, at 8 weeks post emergence has a greater negative influence on final maize grain yields than at other times during the life of the crop.
- The cost benefit of the second herbicide application in the Latro and Callisto treatments is approximately $265/ha, with an average yield increase of 0.9t/ha and the cost of the second herbicide application being approximately $106/ha.