We are testing if we can create a variable rate herbicide application map to reduce the amount of pre-emergent herbicide used on the farm, without compromising weed control
Guinea grass we would consider to be the major weed on our farm, and our herbicide rates used on a block is quite often determined by our impression of the weed status of the block e.g. dirty or clean. This leads us to two scenarios. The first is if we consider the block to be dirty, ie has a reasonable quantity of guinea grass, we would traditionally use the top rate or a high rate of pre-emergent herbicide across the entire block. In the second scenario we would consider the block to be reasonably clean, we would then use a lower rate of pre-emergent herbicide. Both of these scenarios have flaws. The first scenario, we will use much more herbicide than is necessary on the majority of the field, the second scenario means that the small areas with guinea grass, may continue to expand so in later ratoons the block is then considered dirty.
In this project, we are recording where we are spot spraying our stools of guinea grass. From this we are buffering each point for a radius of 20 m and then developing a variable rate prescription for herbicide application. This will then allow us to use a higher rate of pre-emergent just in the areas where guinea grass is present, allowing us to maintain good weed control within the crop.