31 May 1996


Sprayer manufacturers are more cautious about claiming cut rates from air-assisted spraying. But after four years experience, one user is convinced that rates can be slashed without hitting pesticide performance.

Peter Hill reports

ONE look at Richard Wakehams spraying records shows the extent to which he is throwing pesticide manufacturers rate recommendations out of the window.

On his farm Meteor plant-growth regulator has gone on at 0.75 litre/ha, Genie fungicide at 0.1 litre/ha, Pointer fungicide at 0.2 litre/ha, Starane cleavers killer at 0.25 litre/ha and Folicur fungicide at 0.25 to 0.3 litre/ha.

Mr Wakeham has difficulty convincing his agronomy adviser of the wisdom of such rates sometimes. But with winter wheat yields climbing from a farm average of 6.8t/ha (2.75t/acre) six years ago to 9t/ha (3.66t/acre) last year, it would appear that weed, pest and disease control is no barrier to crop performance.

"I cant put it all down to the spraying technique, of course," he notes. "But I am convinced air-assisted spraying is helping us do a better job of protecting yield potential. And it is certainly driving down spray costs."

Mr Wakeham looks after all spraying operations at Whitfield Farm, Ettington, Warwicks, a 125ha (310-acre) all-arable unit where he and his father grow winter wheat, winter oilseed rape and winter beans. The wheats are targeted at high-grade feed/export markets with Estica, Rialto and Soissons in the portfolio this year, plus a seed crop of Reaper.

"Were out to get the best yields we can from land that is not brilliant wheat ground and earn a bit of a premium as well," he explains.

The move to air-assisted spraying came four years ago when Mr Wakeham took on responsibility for crop management and spraying operations.

The 12m (40ft) Degania used originally was changed last autumn for a 20m (66ft)/1000 litre (220gal) Knight sleeve boom-mounted sprayer with RDS Delta 3 electronic control system.

High air volume

The Knight sprayer employs the Degania principle which boils down to the use of hollow cone nozzles to give a very fine spray, propelled into the crop by a high volume of air from the inflatable sleeve. Mr Wakehams twin-line sprayer also has flat-fan nozzles carried in triple-jet bodies for use earlier in the spray season.

With a 750 litre (165gal) front tank carried on the spraying tractor, the outfit has sufficient liquid capacity to cover 20ha (50 acres) a fill at typical 100 to 150 litre/ha (9 to 13 gal/acre) water volumes.

"Im not keen on pushing the water volume any lower because I think crop coverage will start to suffer," says Mr Wakeham.

The key requirements for successful air-assisted spraying, he maintains, amount to a sprayer which can deliver a high volume of air with sufficient speed adjustment to suit different crops and situations, and an operator with a fundamental understanding of how the system works and how the sprayer can best be used in different circumstances.

"For drift control, the sprayer has to deliver a lot of air at high speed to counteract the large mass of air moving across a crop on anything but a completely calm spraying day. You then need to be able to adjust the air speed sufficiently to cope with contrasting situations such as putting autumn herbicide on to virtually bare ground and fungicides into dense foliage.

"Fine adjustments can make all the difference so it always pays to go a few yards, stop, see where the spray droplets are being deposited, make an adjustment if necessary, and try again," says Mr Wakeham.

Conventional flat-fan nozzles delivering a "medium" quality spray are used for autumn herbicide applications with just enough air to propel the spray to the ground without lifting it off again. Smaller nozzles giving a "fine" spray take over for plant-growth regulators and spring blackgrass or cleavers sprays, and are used in conjunction with a faster air setting to agitate the crop for better spray penetration.

The hollow cone nozzles, delivering an ultra-fine spray, go on for the fungicide season, along with a further increase in air speed rate – partly to get the spray into the crop, but more importantly to increase crop agitation for maximum crop leaf coverage.

Ear sprays also go on with a decent amount of air to get the crop moving for good ear coverage, but also to get the spray down into the top half of the canopy.

"Were looking to protect the top three leaves for as long as possible for yield and protein," notes Mr Wakeham. "Modern chemicals can move up through the plant but they cant move from the top down so we need to spray the top half of the plant."

Eradication of mildew using quarter-rate morpholine sprays, highly effective control of other foliar diseases, and planned follow-up treatments that have been dropped because earlier sprays proved more effective than expected, are offered as evidence of the performance of the system.

"Earlier this year, for example, we used a low-rate spray of Stomp (pendimethalin) + IPU to soften up some well-tillered blackgrass, intending to finish it off with an application of Cheetah," Mr Wakeham recalls. "But the first treatment was so effective we didnt need to.

"We have to be very careful with Pointer (flutriafol), even at quarter-rate, and Avenge (difenzoquat) at one-eighth rate has caused some crop yellowing; weve stopped using Spitfire (cyanazine + fluroxypyr) altogether because it tended to scorch the crop," he adds.


The incentives for driving down pesticide rates are three-fold as far as Mr Wakeham is concerned – to save costs, to reduce any environmental burden that results from the use of pesticides, and to minimise any toxic effects on the crop from concentrated applications.

"I didnt dare reduce rates when we used a conventional sprayer; Im sure its possible but there is more risk of poor results," he maintains. "Im still learning and still pushing the rates, but spray bills have already come down by about a third and as the yields show, that has not been at the expense of either production or quality." &#42

&#8226 Yields up from average 6.8t/ha 6 years ago to 9t/ha last year.

&#8226 Sleeve boom sprayer helps.

&#8226 Allows rate reductions.

&#8226 Control not compromised.

&#8226 Offers more spray days.

&#8226 Cuts spray costs.

&#8226 Careful operation vital.

Richard Wakeham – convinced that air-assisted spraying is helping pesticides do a better job of protecting yield potential at lower rates.