Could a combination of camera-guided inter-row hoeing and banded in-row applications of selective herbicides be the future for grassweed control on-farm? That is what NIAB duo Will Smith and John Cussans are investigating as part of the EU-funded IWM Praise project (see p21-22), although it has a tough road ahead to take over from conventionally sprayed herbicides.

Mr Cussans, weed biology specialist for NIAB, says: “There are not many things you can do in crop management that are so cost-effective as the first lump of expenditure you make on your herbicide.

“The problem is to go from the 75% control that £100/ hectare gets you, to 96% with herbicide resistance is becoming disproportionately expensive.”

While in isolation non-chemical control is both more expensive and less effective than herbicides, thinking of these alternative techniques as a way to reach those higher levels of control after using herbicides changes the com parison to one where continuing to use herbicides is much less cost-effective, he adds.

“That could change the way we value these alternative technologies.”

TRIALLING One possible option that could displace the least effective herbicide use is inter-row hoeing.

NIAB is trialling a six-metre Garford Robocrop, although there are several other hoes available (see panel).

The Robocrop’s camera-guidance system views the crop ahead of the tractor and uses vision analysis to determine the exact centre of the crop row to millimetres, to guide the hoe and avoid crop damage.

Camera guidance has made using inter-row hoes more suitable for narrow row crops such as cereals.

Mr Smith, NIAB trials manager, says: “We’ve got systems that can guide hoe blades through narrow rows quite late in the season.”

In the trials at NIAB’s Black grass Centre at Hardwick, near Cambridge, overall black grass heads/sq.m left in crops with row spacings of 166mm and 332mm have been similar, he adds.

“The number of plants left in wider row spacings tends to be a bit lower because of the greater area hoed, but the black-grass compensates to produce more tillers and heads because of less crop competition.”

Black-grass control in the tri al was around 30% – less than the 60% achieved by broadacre herbicides of the near 300 black-grass heads/sq.m.

The combination of the two boosted control to 80%, and slightly higher yields, highlighting as a system that approach could work, he says.

In the second year, herbicide control was better and yields were similar between the combined approach and conventional herbicides.

The success of the concept has led to further trials investigating whether inter-row hoeing could be combined with band-spraying with selective herbicide of the crop rows to potentially reduce herbicide use while maintaining or increasing overall control.

“It’s important to note for the area sprayed we are still applying the label rate of the herbicide – we’re not concentrating the herbicide into the crop row.

I can’t see legislation changing so we can put more herbicide on in a smaller area,” Mr Smith says.

“It also doesn’t meet the idea of reducing herbicide use if you concentrate the herbicide – the benefit of only spraying on row is that you’re cutting herbicides by 40-60% depending on system.”

He has used standard flat fan or air induction nozzles mounted on the Robocrop’s side shift toolbar platform around 6cm above the crop to guide applications to the crop rows.

Potentially this set up could allow band spraying and hoeing in one operation, although optimum timing for both in winter cereals is different.

RTK-TYPE TECH Pre-emergence applications are possible using RTK-type technology, Mr Smith adds.

“We’re looking at the possibility of having the sprayer set up on the drill to make it a one-pass system.”

Initial results from this season’s trials suggest the control of black-grass in the row is higher than with a conven tional broadacre application, he says.

Results from the combined band spraying plus inter-row hoeing will be available after the black-grass heads.

Despite the saving in herbicides, the cost of in-row herbicides is only slightly cheaper than an overall spray, according to Mr Smith’s calculations.

Inter-row cultivation is significantly cheaper at around £45/ha, including fixed and variable costs compared with £140/ha for herbicides.

“Labour is a factor that could limit its use – you’ve got an inter-row cultivator that moves at 8km/hour and perhaps a half or even a quarter of your sprayer width.”

Inter-row cultivators can cost anything upwards of £50,000 for a 6m machine to well over £150,000 depending on make, width and specification.

“The on-row herbicide machine is even more money and goes even slower, so in financial cost it’s about on a par, although that doesn’t take into account the cost of lowering your risk of resistance or any other type of benefit.”

Typical work rates for inter-row cultivations are 4ha/ hour with a 6m machine, and just 2-2.5ha/hour for in-row spraying compared with 23ha/ hour for a 24m sprayer, he points out.

While inter-row hoeing is gaining some traction, those extra labour requirements mean that take up is likely to be limited and even more so of on-row herbicide applications, unless something radical changes, Mr Cussans says.

“On-row herbicides is a way of dealing with some sort of public policy change.

Currently it’s not cost-effective.

You might be reducing your use of herbicides by 50%, but you’re also reducing your work rate, requires investment and increasing labour requirements.

“But it’s not beyond the realms of possibility in a future Environmental Land Management scheme 2.0 that alongside support for environmental areas, agroforestry, etc., that if you can reduce your pesticide use by 50% we’ll give you a payment, and this would be one way of doing that,” he adds.