Time is money.

Worried about cutting spray application volumes for fear of losing efficacy against diseases and weeds? There's no need to be.

You can go as low as 50 litres/ha with many products without control and drift becoming a problem, suggests Paul Miller of Silsoe Spray Applications Unit (SSAU), formerly SRI and now owned by TAG.

"Many growers have already reduced volumes below the long-time industry standard of 200 litres/ha. But we now have strong evidence that 100 litres/ha is just as effective, and half that again is probably enough when targeting diseases and small grass weeds."

Cutting the volume from 200 to 50 litres/ha increases the work rate by 85% in wheat with a 24m boom at typical operating speeds, according to computer simulation models. In field trials, using the lower volume didn't result in nozzle blockage or poorer control, even when air-induction nozzles producing larger droplets were used to minimise spray drift.

The advantages of reduced water volumes are numerous: Less time loading and applying pesticides; faster work rates improving the timeliness and efficiency of pesticide use, leading to higher yields and profit.

Obviously there's a cut-off. Earlier in the project there were suggestions that 25 litres/ha was adequate, but Prof Miller believes the final results will confirm that 50 litres/ha is the practical minimum.

"We've studied spray characteristics in the laboratory, measured deposit in field trials, and are confident that both conventional and some designs of air-induction nozzles allow sufficient coverage of diseases and small grass weeds at 50 litres/ha."

However, he also knows that some products are sensitive to droplet size and that the use of air-induction nozzles is not appropriate when treating small grass weeds with such products. Check the label, he recommends.

Nozzle choice should take into account the risk of drift. Air-induction types are preferable in high risk situations, though a related project found that a 03 designed by one manufacturer can produce a significantly different result in the field from another 03 brand because of differences in droplet size.

In recent field trials, a large droplet air-included spray performed poorly, whereas a smaller droplet air-included spray gave performance equivalent to conventional flat fan nozzles using fungicide mixtures, Opus (epoxiconazole) plus Comet (pyraclostrobin), and Opus plus Amistar (azoxystrobin). Product efficacy was influenced by application volume only when disease pressure on winter wheat was very high, and then volumes between 50-100 litres/ha gave the best results.

The herbicide tralkoxydim (Grasp) performed equally well on ryegrass in wheat at all volumes (37,73and 164 litres/ha) and with both conventional flat fan nozzles and medium-sized droplets from air induction nozzles, except in one trial. This is currently being repeated as the inconsistency in results could be related to experimental conditions.

Prof Miller expects the final outcome to remain the same. Future spray guidelines will quote an optimum range of spray volumes of between 50 and 100 litres/ha, with a recommendation to choose an appropriate nozzle to control drift.

The optimum application volume hasn't yet been established for other targets, such as larger weeds. But unless spray penetration is hindered by an exceptionally dense canopy, a similar figure should apply, he believes.

"It would be great to investigate deposition with all types of products on a range of targets, but funds are limited. The HGCA has already generously provided £112,000 towards the two projects. Perhaps our findings will spur on agrochemical and sprayer manufacturers to review their recommendations."

crops@rbi.co.uk