Arable farming is at a crossroads, with the pressures of weed and disease resistance forcing many to rethink rotations and cultivations rather than reaching for the chemical can.
Years of continuous autumn cropping has seen Britain’s most damaging weed, blackgrass, spread like wildfire, while the overuse of some fungicides is making diseases tougher to control.
This has led to a clarion call for a change away from monoculture and to bring more variation into rotations so as to support long-term, sustainable farming and reverse damage to soils.
“We have got to change what we are doing. We have got to think more about cultural controls and rotations to solve our problems,” says Colin Lloyd, head of agronomy at distribution group Agrii.
In a vicious circle, autumn drilling encourages blackgrass and the heavy machinery needed for timely sowings damages soils, and so the troublesome grassweed thrives even more on the resultant wet soils.
Miraculous grassweed herbicides were a godsend until they started to fail, forcing growers to pile on ever-more expensive pesticide cocktails, sending costs spiralling skywards.
“There is no new chemical on the horizon and I guess you won’t see one for at least 10 years,” Mr Lloyd says.
Rothamsted Research’s blackgrass weed guru, Stephen Moss, has spent 40 years studying the ubiquitous weed and concludes control must include cultural methods rather than waiting for a new wonderful weedkiller.
“The herbicide option allowed us to ignore biology; now we need to go back to biology, so we need cultural techniques such as delayed drilling and spring cropping,” he says.
Top tips towards a sustainable arable future
- Take a look at rotations. Long rotations can help control herbicide-resistant weeds and improve yields of crops such as oilseed rape.
- Try delayed drilling in the autumn and spring cropping to control weeds like blackgrass and help spread workload on the farm.
- Use fungicides wisely. A mixture of products with different modes of actions can help slow down the build-up of disease resistance.
- Protect the dwindling number of available pesticides by following voluntary guidelines when applying product like slug pellets.
- Consider alternative crops to wheat such as other cereals like barley and oats, and alternatives to oilseed rape like peas and beans.
Dr Moss advises that growers need to think long-term and in bad blackgrass situations, where yields can be cut by up to 70%, it will take two to three years to make a dramatic difference.
“Wheat-rape-wheat rotations are simply not sustainable from a blackgrass and yield point of view,” he says.
In addition, disease resistance to pesticides is building up, with wheat’s most damaging fungal foe, septoria, now very difficult if not impossible to eradicate with a dwindling pool of fungicides.
A wonder group of fungicides, the strobilurins, broke down to septoria in the 1990s and are now ineffective against the disease, and more worrying is the rapid decline in the backbone of any cereal fungicide strategy, the azoles.
“Once we see septoria now, we can not eradicate the disease. We can not do anything to a leaf that shows infection,” says Bill Clark, technical director at crop consultants Niab Tag.
Septoria can cause yield losses of up to 50% and with only two groups of systemic fungicides active against the disease – or those that travel through green leaves – namely the azoles and the SDHIs, the situation is worrying.
With feed wheat prices down 30% over the past year to just below £120/t (see Return graph below) costs are clearly under scrutiny, with yield improvements from the plant breeders only making sluggish progress.
Graham Redman, research economist at consultant Andersons, says after the sharp fall in commodity prices it makes sense for growers to look at longer rotations involving a wider range of crops.
The big fall in wheat and oilseed rape prices make alternative crops, which have seen a smaller fall in price, more attractive to growers.
He argues that as the price gap between rapeseed and other break crops, such as peas and beans, narrows then this makes these alternatives more interesting to grow.
Similarity, as the price difference between wheat and other cereals such as barley and oats shrinks then these less popular cereals become more attractive.
He argues when oilseed rape and wheat prices were high there was every incentive for tight wheat-rape-wheat rotations, but now things have clearly changed.
“When wheat and oilseed rape stood out in terms of gross margins it made sense for growers to forgo yield with tight rotations, but now with the sharp fall in commodity prices it makes sense for long rotations,” he says.
The advantage will be to achieve higher yields by growing oilseed rape in longer rotations, while a switch to more spring cropping will spread farm workload and help trim overheads.
Changes have been seen with the area down to oilseed rape sliding from a record high of 756,000ha for harvest 2012 to a little over 600,000ha currently in the ground.
The escalating cost of growing rapeseed and other autumn-sown crops is also weighing on growers compared with the cheaper costs of alternative spring crops.
Mr Lloyd says with some growers spending £160/ha on blackgrass herbicides and still not getting really good control, the current system is totally unsustainable.
The first reaction must be a move away from early-drilled winter wheat in very bad blackgrass situations towards later drilling to allow control of the grassweed and lessen the risk of septoria.
His trials show winter wheat gross margins slipping to £389/ha when drilling early on 27 September, compared with £903/ha when drilling is delayed to 1 November or £729/ha with spring cropping.
“We have to break the cycle of early-drilling winter crops and do something different, such as spring beans, peas or spring cereals,” he says.
Mr Lloyd cautions that late drilling with the wrong system can lead to soil damage so a flexible combination of late drilling and spring drilling is advisable.
Dr Moss points out that growers worried about being caught out in a wet autumn should plan for delayed drilling in the autumn with the option of spring drilling.
“Growers should not put all their eggs in one basket and they should look for a balance between delayed autumn drilling and spring cropping,” he says.
Spring crops may lead to lower yields, but they can cut fungicide bills as those sticking with long runs of winter wheat will struggle to keep spray cost below £100/ha.
Mr Clark says the loss of efficacy of the major azole group of fungicides over the past 15 years (see Resistance graph below) means growers will have to keep rates high and use azoles with SDHIs and a protectant fungicide such as chlorothalonil as part of a resistance strategy.
The focus should be on protecting leaves from disease, and it is a difficult area to cut fungicide costs in high-disease years and with failing pesticides.
“We need a high dose of azole for disease control and to protect the SDHI, but timing is more important than product or dose,” he says.
Some of the agrochemical giants have products in the pipeline, with Syngenta planning a new SDHI launch in 2017 and Dow AgroSciences promising a fungicide with a different mode of action within five years.
However, the outlook for new herbicides is bleaker. Regulator pressures are building on the use of some current residual herbicides, and the pipeline (see Regulation graph, below) of new weedkillers is slowing to a trickle, so the answer to current problems is likely to come mainly from growers’ existing toolbox of products.