To maximise efficacy, spray at the right dose rate, at the right growth stage and in the right conditions, says Mrs Tatnell.
Dose rate “Get the dose rate right for the weed and growth stage.
“Annual grasses typically require a minimum of 540g active ingredient per hectare for seedlings up to two to three leaves, 720g ai/ha when tillering and 1,080g ai/ha when flowering.”
Growth stage “Ideally, spray when plants are at least 5cm but before the start of rapid stem extension.
Apply prior to ‘shading’ from other plants.”
Conditions “Apply to actively growing plants, in warm conditions (15- 25degC), with at least six hours before any rainfall.
Choice of nozzles, water volume and the addition of water conditioner can also be influential.”
Water volume Use 80-250 litres/ha, says Mrs Tatnell.
“Lower volumes give best results provided correct nozzles are used.
Low dose rates and higher water volumes lead to a low concentration of glyphosate and surfactant.
This can lead to poorer results, especially in conjunction with hard water or other sub-optimal conditions.
Spray quality Medium-coarse BCPC (200-400 microns) are advised.
“Use droplets on the finer side of medium for optimum wetting of spike and seedling stage black-grass.
Conventional flat fan nozzles [such as F110-03 or F110-04] are most suitable for seedlings.
Low drift nozzles can be used on welltillered plants.”
Hard water “Hard water containing high levels of calcium, magnesium and other polyvalent metal cations, such as iron and aluminium, can lock-up glyphosate by a process known as chelation,” explains Mrs Tatnell.
“This effectively reduces the applied dose rate of glyphosate and is most noticeable at low application rates and high water volumes.
“Addition of a proprietary water conditioner, choosing a low water volume and maintaining the correct dose rate will mitigate the effect.”