Air nozzles given a thumbs up in beet

1 May 1998

Air nozzles given a thumbs up in beet

SUGAR beet growers planning their herbicide spraying programmes can use "air entrainment" nozzles with confidence, according to trials at Morley Research Centre, Norfolk.

Representing the latest technology in conventional spray nozzle design, "air entrainment" or "air induction" nozzles have small air inlets in the nozzle body. These cause a significant pressure drop at the outlet orifice. As a result, the spray produced has fewer very small droplets than sprays from conventional or low-drift nozzles operating at the same system pressure.

Tightening the droplet size spectrum in this way reduces drift, an effect proven in experiments at Silsoe Research Institute in Bedfordshire. Morley researchers wanted to find out whether the relatively coarser spray composition would have a detrimental effect on the efficacy of broad-leaved weed control.

Trial results

In last years trials, examples of the Billericay Farm Services Bubble-Jet, the Spraying Systems Turbo TeeJet and Agrotops Turbodrop air inlet nozzle from Lurmark were used to apply a conventional three-spray post-emergence herbicide programme alongside a standard 110í (flat fan nozzle and a Lurmark Lo-Drift tip. Sprayers were set-up to apply 100litres/ha in a fine spray at pressures and speeds recommended by the nozzle manufacturers.

"Although there were some differences in weed control, with the Turbodrop coming closest to the performance of the standard flat fan nozzle, there was no significant difference in overall weed control between these designs and the standard flat fan," says Morleys Libby Powell.

Fine sprays and even coverage are essential to achieve good control of emerged weed seedlings while they are very small and most vulnerable to herbicides. Earlier trials with air-assisted sprayers at Morley have produced good results, partly, it is thought, because agitation of weeds using a finely judged blast of air helps get herbicide on to the undersides of leaves.

However, good results can still be achieved with conventional spraying systems, Miss Powell emphasises, although fine spray compositions do raise the risk of drift.

"We didnt measure drift or spray deposition in last years trials but visually the Billericay Bubble-Jet appeared the most effective as far as drift control is concerned," she says.

The Turbodrops drawback is the 5-7 bar (72-100psi) operating pressure needed to achieve 100 litres/ha – rather higher than the 2-3 bar (29-44psi) used by the others to achieve the same application rate. Lurmarks new release, the DriftBeta nozzle, operates at the lower, more practical level. &#42

Coarser sprays from alternatives to flat fan nozzles can give just as good weed control, says Libby Powell.

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