• ‘Eliminating pre-em herbicides saved us about £50-60/ha’

There is no need to adopt a blanket approach with pre-emergence and early post-emergence herbicide use in oilseed rape, allowing some savings, agronomists suggest.

While crop prices remain low, it is a good time to reconsider weed control strategies, especially on fields which have a consistent establishment history or a lower broadleaved weed burden, they say.

But compromising on blackgrass control is not advised, especially where a rotational plan is in place to bring weed numbers down.

See also: Better yields from herbicide-tolerant OSR

With a bit more thought, it is possible to delay spending on herbicides until you know the crop has established well and escaped both the slug and the flea beetle threat, confirms Lincolnshire-based independent agronomist Sean Sparling.

“In the right fields, we’re going to have to start experimenting,” he believes. “There isn’t the herbicide armoury or the money for growers to carry on as they were.”

Seed rates

He urges farmers to start by making better use of crop competition.

“It is the key to controlling weeds, so seed rates must be maintained.

“We know that we’re getting losses in the field from pests, so it must be time to reconsider seed rates of 30-50/sq m.”

At 30 seeds/sq m, there isn’t enough crop competition, especially if flea beetle takes half of them and leaves just 15 plants/sq m, he stresses

“There’s no denying that the best weed control results from this year have come from higher seed rates, in the region of 80-100 seeds/sq m, where the crop canopy is still thick.

“Where we went down to 50 seeds/sq m, there’s far more blackgrass.”

Mr Sparling adds that growers don’t have the luxury of stale seed-beds with oilseed rape, so can’t rely on additional help.

“The crop has to be up and away while the soil is still warm, which is a month before the blackgrass gets going. So make the most of this head start by using more seed.”

He acknowledges that using higher seed rates with hybrid varieties does become expensive.

“But that isn’t a good enough reason to just dismiss them. If it’s too much money, drill conventional varieties.

“They are holding their own in terms of yield and, contrary to what you might be told, are no slower to get going in the spring.”

While there are some broadleaved weeds which can’t be left to grow unchecked in the autumn, there are situations where pre-emergence herbicides aren’t called for, agrees Bedfordshire-based AICC member and agronomist, Bill Barr of Prime Agriculture.

“With species such as hedge mustard, crane’s bill and shepherd’s purse, you are tied into an early metazachlor-based treatment, at around £25-£50/ha, depending on what else you have to put in the tank,” he advises.

“The post-emergence options don’t work and these weeds can become very troublesome.”

However, others such as chickweed, thistles and poppies can all be dealt with from later timings, using products such as AstroKerb, he notes. “And that’s useful, especially if you aren’t certain that establishment will be successful.”

The traditional propyzamide timing offers a chance to control these weeds, with AstroKerb fitting into this slot very well, he recalls. “It was used on the majority of our rape last year.”

Cultivation system

The cultivation system also has a bearing, he points out. “The more soil movement, the greater the number of weeds. If you don’t move the soil, you don’t get the weeds.”

Autocasting was used on charlock-infested farms for this reason, he says. “On heavy land, the subcasting method reduces the levels of broadleaved weeds that emerge. So make best use of cultivations for your situation.”

Mr Barr also advocates higher seed rates. “A good oilseed rape crop is very competitive. So establishment is very important and can’t be left to chance.”

Lower seed rates may still be possible on lighter ground, where slugs are less of a problem and the establishment record is consistent, he suggests. “But don’t go too low on heavier soils.”

For conventional varieties, that means 80-100 seeds/sq m, while hybrids shouldn’t be drilled at less than 50 seeds/sq m.

Blackgrass control can’t be compromised and will be the biggest cost, he warns. “It’s a necessary evil. We have choices with clethodim, carbetamide and propyzamide, so it’s a case of seeing what other weeds need controlling as well.”

Both carbetamide and propyzamide will do chickweed and speedwells, he says, while AstroKerb will bring in thistles and poppies. “And AstroKerb is a bit cheaper than using Galera in the spring.”

Otherwise, he points out that crop nutrition is important in the early crop stages. “Use some nitrogen to get the crop up and away quickly. And think about volunteer control, especially where you’ve grown barley.”

Mr Barr sums up by reminding growers to look at fields separately, calculate the risk of broadleaved weeds before deciding whether a pre-emergence treatment is needed and include the influence of the planned cultivation system.

“It’s not a case of dropping out metazachlor as routine, but it may be possible in the right situations.”

Julian Gold, Oxfordshire

Julian Gold

An Oxfordshire farm manager is taking a radical approach to reducing weed control costs in oilseed rape.

Having seen growing costs continue to rise on the 800ha farm that he manages near Wantage, Julian Gold has been experimenting with a low-cost establishment system, which he hopes will allow him to eliminate the front end herbicide costs of growing oilseed rape.

The fact that both flea beetle and slug control can cause crop damage and incur additional costs has also influenced his thinking.

“Oilseed rape costs have run away with us,” he says. “And it’s not just with weed control. We’re being encouraged to spend far more on seed and spray fungicides – more often, as well.”

A trial in part of a field that had to be redrilled has seen him use “bucket loads” of home-saved seed, so that a very thick plant stand developed. That helped to suppress any germinating weeds and allowed for pest attack, but still gave him a high enough plant population going into the winter.

“Not using a metazachlor mix, or any pre-emergence herbicides, saved us £50-£60/ha,” he explains.

“The fact that we put on so much seed means that we could lose some to slugs and flea beetle, without sacrificing the whole crop.”

Last spring, in early March, Mr Gold went through the trial area of oilseed rape with glyphosate in order to thin the crop, with only every third nozzle on the sprayer operating and the boom touching the top of the crop.

“We blocked off the other nozzles,” he explains.

“The idea behind it was to alter the crop architecture to one that had been established in wide rows, so that we got the right canopy for maximum yields.”

It’s too early to say whether the system has been a success, or has potential to be rolled out across all of his oilseed rape, he acknowledges.

“However, I do know that it has almost halved my growing costs, bringing them down to £212/ha, when they are close to £400/ha with a more conventional system.”

He plans to extend the trial to a whole field this autumn. “I’m going to change a couple of things, based on my experience in 2015. I will be spraying the glyphosate a bit earlier, in December, and I will be switching from 110 flat-fan nozzles to 80 nozzles.”

Apart from a £60/ha saving in herbicide costs, his experimental approach also reduced his seed costs by £80/ha.

“It may not be the answer that I’m looking for in the long-term, but we have got to do something to bring costs down. Without any changes, oilseed rape will cost us more to grow than we can sell it for,” says Mr Gold.