11 April 1997

Fast spray, lower volumes?

By Andy Collings

HIGH speed spraying with a purpose built, self-propelled sprayer could mean lower volumes and increased chemical deposition.

That is the conclusion of trial work carried out at the Morley Research Centre, Norfolk, last year to investigate the influence of forward speed and water volumes on spray deposition.

Agronomist Mike May, now working at IACR-Brooms Barn, compared the results from a range of spray volumes – from 55 to 210 litres/ha using a Spra Coupe self-propelled sprayer working at different speeds.

Deposits from treatments applied with XR 04 nozzles operating at 2.5 bar pressure, delivering 55, 70, 105 and 210 litres/ha at 32, 24, 16 and 8 kph, respectively were compared with deposits of a dye containing 0.1% Agral wetter solution on the ground, on vertical and horizontal targets within the crop.

According to Mr May, high speed, low volume treatments – 55 litres/ha at 32kph – gave the highest levels of deposits on horizontal pipe-cleaner targets placed within the crop. A 70 litres/ha rate matched the deposition of the 55 litres/ha rate on vertical triangles and were greater than those achieved when higher volumes were applied.

"With a conventional sprayer working at 8kph applying 210 litres/ha as a fine spray there is often a trade-off between deposition on the leaves and what goes on the stems," explains Mr May. "In our trials that trade off did not exist, we actually got more chemical on both target areas."

But the high speed/low volume technique does not necessarily work for all field conditions, points out Mr May. "Spraying contact pesticides at high speeds using the Spra Coupe appeared to work well because the crop helped to catch the spray and minimise drift. Applying a pre-emergence herbicide to bare earth would present a very different set of circumstances.

"In that case it could be prudent to reduce forward speed and use larger droplets."

Mr May also points out that there is a lot more work to perform to determine the exact correlation between chemical deposition and biological efficacy.

"Although the initial work looks promising, farmers should exercise caution before drawing too many conclusions," he warns. "Different wheat varieties might respond differently, and the closer one moves towards the boundary of dose response, the more careful one has to be."

"The results pose the question as to whether the improvements in deposition were caused by the angle of droplet penetration into the crop, changes in droplet size and/or turbulence within the crop – all of which require further investigation," he concludes. &#42

Mike May:"With a fine spray, there is often a trade-off between deposition on the leaves and what goes on the stems."

Does high speed/low volume spraying with the Chavtrac Spra Coupe self-propelled sprayer offer advantages over conventional spraying procedures? Initial trials at Morley Research Centre would suggest it does – but a lot more research is still required.

Treatments tried

Volumes appliedForward speed

litres/ha (gal/acre)kph (mph)

55 (5)32 (20)

70 (6)24 (15)

105 (9)16 (10)

210 (19)8 (5)

Deposits measured from XR 04 nozzles operating at 2.5bar pressure.