Is inter-row spraying the weed control answer?

Article taken from the Agronomist & Arable Farmer

In the face of growing regulatory pressure on herbicide use, one thing you can do is to look at spraying between the rows of the crop, which is particularly suited to oilseed rape and potentially maize, which are grown on what can be quite wide row spacings.

Oilseed rape is coming increasingly under pressure with key herbicides such as metazachlor and propyzamide being found in water, therefore we must ensure these products are looked after and used wisely.

In our trial sites we have been looking at technology that is essentially able to spray a non-selective herbicide such as diquat between the rows of crop. This involves using GPS steering to make sure that you are driving straight and in the right place.

Shrouded nozzles

With the three years of trial work that we have conducted so far we have been using specialist band sprayers by Garford and Micron.  There sprayers are the type that are more commonly used in specialist veg crops and are essentially ground-based sprayers with the nozzles contained within plastic shrouds.

Once all set up, it is just a case of driving through the crop and applying the non-selective herbicide.  One extra advantage of the shrouded nozzles is that there is negligible drift, which allows more application windows.  Depending on the size of the crop you may inevitably get some spray on a couple of the leaves, which makes diquat a suitable option, as it will kill only the leaf it touches, not the whole plant as glyphosate potentially would.

The interesting thing this season will be to see how the system works in forward crops as all the sites are looking very well compared with the last two years.

For the GPS steering the best results come from using an accurate RTK signal which should be giving accuracy in the region of 2-5cm.  The first step with this is to set up the initial A to B line across the field when drilling the crop.  When coming back to apply the herbicide the same guidance line is used, only this time it should be offset by a number of centimetres to make sure that you are going between the crop.  The crop row spacing has to be at least 40cm to allow room for the machinery to pass through – in trials we found that 50cm rows were about ideal.

The work we have done has also shown that there is no yield penalty for going to wide spacings, however you need to get the seed rate correct so as not to have too many plants along each row.

There are two routes for RTK steering signals, you have either got a fixed base station or you can get subscription services that work through the mobile phone network.  Mobile RTK has the advantage that you don’t have to carry around a base station and it is not so limited, but it does require the correct hardware to pick up the signal.  It was very clear from the early trial work that GPS is an absolute must to do this operation on a commercial scale; no matter how good the operator, the room for error is tiny.

One great advantage is that this allows you another way to tackle problem weeds.  Even though we throw a lot of money at herbicide, there are always a couple of problem weeds that slip through the throw a lot of money at herbicide, there are always a couple of problem weeds that slip through the net.  Charlock, for example, is a challenge because it is very similar to the oilseed rape plant.  Another benefit of this type of system is that you are tackling weeds other herbicides might struggle to deal with, such as black-grass.

Maize trials

Our oilseed rape trial sites have been using this technique highly successfully.  We have been trialling the system over six of our Growcrop Gold sites throughout the country.  This year we also looked at the system in maize and initial results have been very good.  The next step is to start applying selective herbicides such as Propyzamide on top of the crop and the non-selective between.  This also gives the opportunity to target trace elements and fertiliser to the crop band.

This system looks to have great potential, it ticks many boxes in terms of herbicide stewardship and weed control in the rotation.  There is no doubt that legislation pressure will not go away so the aim of these trials is to provide practical solutions to growers for the future.


14 October 2013

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