Pre-Emergent Herbicide and Disc Seeder Demonstration
Aim: To identify the crop safety issues associated with pre-em herbicides and the minimal soil throw that comes from using a single disc seeder.
Equipment: Commercial gear – 36m boom spray, 12m John Deere single disc seeder
Sowing: Vixen Wheat sown 19-May aim to sow 30mm deep.
Treatments:
| Trt. No. | Treatment | Density, men/km2 |
|---|---|---|
| 1 | Sakura + Callisto* | 118g + 200mL/ha |
| 2 | Overwatch* | 1.25L/ha |
| 3 | Overwatch* + Callisto* | 1.25L/ha + 200mL/ha |
| 4 | Boxer Gold | 2.5L/ha |
| 5 | Boxer Gold + Callisto* | 2.5L/ha + 200mL/ha |
| 6 | Mateno Complete (IBS) | 1L/ha |
| 7 | Mateno Complete (EPE) | 1L/ha |
| 8 | Sakura + Avadex | 118g + 1.6L/ha |
| 9 | Arcade | 3L/ha |
| 10 | Nil Control | 0 |
*Not registered for single disc seeders.
Figure 1 – NDVI Imagery of the pre-emergent demonstration taken on the 12th July
Figure 2 – 3 NDVI imagery dates as well as the final grain yield for each treatment in the pre-emergent herbicide demonstration.
In recent years we have been spoilt for choice with many new pre-emergent herbicides coming to market to complement the older chemistry. This is providing more options in controlling hard-to-kill weeds, allowing more rotation between chemistry groups and being less reliant on older herbicides to which weeds might be building resistance. However, it is very important to always remember the number 1 rule when using herbicides: Follow the label. Each company has extensive research and development programs to test their chemistry in many different conditions to know what the product can and can’t do. This becomes very important for pre-emergent herbicides as their suitability depends on soil type and what type of sowing implements are used.
FarmLink have been using a single disc seeder at TAIC for a number of seasons. While there are a range of benefits in using a disc seeder, including narrow row spacing and increased crop competition and maintaining high stubble loads, there are limitations with the suitability of pre-emergent herbicides. This is because there is not enough soil throw from the disc seeder units, meaning seedlings have to grow through treated soil. To demonstrate these crop safety issues, during 2021 we ran a full paddock scale demonstration using various herbicides. Some products are registered for the use in wheat while others are not “on label” and should not be used with a single disc seeder.
The paddock shown in figure 1 had the treatments applied with one pass of a 36m boom spray across the paddock. A nil control strip ran across the paddock in the opposite direction to show a comparison between the treatments. Using the unregistered products may result in stunted growth and this was investigated through the season using drone NDVI imagery. Using this tool made it very evident the effect the herbicide was having on the crop, especially when two unregistered products were combined. The impact that may have had an effect on only the seedling plant can be seen through multiple NDVI imagery dates and even right through to harvest.
The important message is that we may not realise how much impact some pre-emergent herbicides are having on crop safety when the whole paddock has the product applied. Some products are very visual and plants become bleached, but sometimes it may not be so obvious with stunted growth. The effect on grain yield may be the same. The simple solution is to make sure we follow the label of the product. Pre-emergent herbicides are just one tool to use for weed control. By combining pre-emergents used at the right time and in the right place with other tools, such as crop competition and harvest weed seed control, troublesome weeds can be controlled effectively, without compromising on grain yield.
