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Spraying in Stubbles

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The sharp increase in minimum tillage and no till farming has left many paddocks with a heavy stubble load.

The sharp increase in minimum tillage and no till farming has left many paddocks with a heavy stubble load. In those situations it is difficult to penetrate the stubble cover and achieve satisfactory coverage on the ground. Getting trapped on stubbles generally inactivates most herbicides. Many trials have shown that anticipating losses and choosing a robust product rate is most beneficial for efficacy. So is an increase in water volume and spray quality. COARSE or VERY COARSE droplets have more potential to bounce of the stubbles and land on the ground or target underneath. In erected stubbles the vertical structure of the stubble row interferes with the side movement of the spray fan and can filter out spray droplets. This is especially evident with FINE droplets even in low level wind situations. Penetrating into stubbles faces in many respects the same issues as penetrating into a canopy, so decreasing speed is an option. Another theoretical option to get more droplets passed the stubbles is to decrease the spray angle by using less than a 110° nozzle and to raise the boom height (only when using COARSE to VERY COARSE spray quality – be aware of drift!) to allow droplets a more vertical fall. Limited trial work has confirmed those assumptions when using lower label rates but the verdict with higher label rates is still to come.
The agrotop TurboDrop (link) could be an ideal nozzle for stubble application. It produces a COARSE to VERY COARSE spray quality. On the paper the nozzles should produce a 110° fan angle but in reality it is more a 95°–100° angle.
A good idea to check how much of your product is caught in the stubbles is to put some water sensitive paper (link) on the ground. Clear approximately 2 x 2 m from stubbles and place at least 5 water sensitive papers on the ground. Do the same in an area where stubbles remain. Place them underneath stubbles if they are flat on the ground. Try some different application parameters, e.g. higher waterrate.
Top Tips
• Increase product rate !
• Increase water volume !
• Increase Spray quality to COARSE – VERY COARSE !
Decrease Speed !
• Possibly decrease fan angle in erected stubble
• Increase spray height in erected stubble (only with minimum COARSE spray quality)
• Consider using the TurboDrop nozzle.