NOZZLE choice may make a large contribution to spray efficacy, but product labels are often unhelpful in pointing growers to the right tip to use.
"A guide is given to spray quality, but this can be affected by new nozzle types, adjuvant or tank mix used, water quality and other variables," says Tom Robinson, application manager for Novartis Crop Protection.
For best guidance on nozzle choice consult a distributor or adviser, he says. But generalisations can be made. Soil acting chemicals and fungicides, except those with a protectant action, are best applied with a drift-reducing bubble jet or air-inclusion nozzle rather than a low drift type.
For protectant fungicides, which need to achieve penetration and cover, a reasonably coarse droplet from a low drift nozzle is favourite, he adds.
Contact herbicides need a balancing act between a spray that is fine enough to penetrate and cover, but at the same time has few of the large droplets that tend to bounce through the crop without sticking. "The traditional 110í flat fan nozzle at 3 bar pressure and applied at 100 to 200 litres/ha gives good results," Mr Robinson comments.
To hit the flatter broad-leaved weeds in a cereal crop with a translocated hormone spray needs good penetration and this is best achieved with a coarser spray – low drift and air inclusion nozzles work well in these circumstances.
"Ear wash sprays for cereals need to be fine and the spray from hollow cone or twin outlet fan nozzles is ideal," he continues.
Boom height must also be right. Work at IACR Long Ashton shows that when using Lurmark or Tee Jet 110í fan nozzles, tips need to be 40cm (15.7in) above the tallest part of the crop or target to achieve even distribution.
If the boom is 40cm (15.7in) above weeds sheltering in the bottom of a taller crop the distribution at target level can be uneven. *