Article taken from Agronomist & Arable Farmer
A simple and cheap modification to boost the number of spray droplets can have a dramatic effect on the performance of pre-emergence black-grass herbicides, according to Agrovista trials
A freshly drilled seed-bed looks an easy enough target to cover effectively with pre-emergence herbicides. However, development work carried out by Agrovista on a heavily infested black-grass site near Lamport in Northamptonshire shows tweaking application technique can make the difference between indifferent and excellent weed control. ""To get the best results from preems you want good soil coverage. In practice black-grass control can fall to 60% and much lower. But 95+% is achievable by paying attention to application," says Agrovista technical manager Mark Hemmant. Best control in previous years has come from applying preem herbicide (Liberator at 0.6 litres/ha) in Agrovista trials through a twin-line sprayer. Each line applied 100L/ha through blue 80-03 flat fan nozzles at 3 bar. The nozzles were facing forwards on the front line and straight down on the back line to minimise shadowing caused by the spray clods.
""The most important concept to grasp is that this produces a lot more droplets than using a single line standard set up. This was fitted with half the number of nozzles, using 80-04 flat fans, alternating forwards and backwards, to apply 200L/ha at 3 bar, the default set-up on many farms."" In previous years this has produced about 80% control compared with 90+% for the twin-line set up. Increasing the overall spray volume on the latter to 300L/ha by reducing the speed to around lOkph achieves even better control, upwards of 95%, he adds. However, many spray operators don't have twin line sprayers. With this in mind, Mr Hemmant included a new set-up in this year's trials using a Hypro Twincap that provides two back-to-back nozzle apertures fitted to a single line, adapted to apply spray forwards and straight down to mimic the twin-line approach. ""We used a Defy nozzle in the rear-facing aperture to convert this to a more-or-less vertical plane," says Mr Hemmant.
""The result is a combination that has the same number of nozzles as the twin-line arrangement and delivers the same volume and droplet number. It pretty much matches the twin-line in terms of black-grass control for very little additional cost."" This arrangement also allows forward speed to be increased from about 9.5kph to 14.4kph, matching the twin-line set-up for output, he adds.
All trials were applied at a boom height of 50cm above the soil surface, to minimise drift. Mr Hemmant recommends adding Remix, a parafinnic oil made up of long-chain molecules that was used in all the top-performing plots above. It greatly reduces spray drift and keeps the chemical in the top few centimetres of soil. ""Remix improves the spray pattern, giving a more even distribution of herbicide onto the soil. Its long-chain molecules also wrap around the herbicide molecules and give them a positive charge, helping them to bind to clay and organic matter, keeping herbicide in the surface layer for longer!' On average, across all trials, adding Remix has boosted black-grass control by 9%, says Mr Hemmant. ""It has consistently given better control than any other adjuvant we've tried that claims to have a similar effect.""