Staying in control and one step ahead of resistance to crop sprays

Resistance to crop protection products and reduced availability of sprays due to changes in legislation are impacting on weed control, it has been warned.

The head of the Teagasc Crops Research Programme, John Spink, said high yields and effective control of weeds, pests and diseases were critical to aid profitable tillage production.

A key message from the Teagasc Oakpark Tillage open day was the use of an integrated approach to pest management, from sowing dates to spraying to help save costs and reduce resistance.

Wicklow adviser Martin Bourke says that many farmers may have sprayed unnecessarily for aphids this year, as they did not examine crops.

"We have to change our mindset and be more aware of integrated pest management," he says. There are a lot of natural enemies around at the moment that would help kill off aphids such as hoverflies and ladybirds.

"We need to be wary that we could be upsetting the balance."

Pyrethroid comes in at around €4/ha, while the seed treatment costs around €450/tonne, which adds around €25/ha onto winter barley costs.

"The seed treatment is probably the safer way to go as it is going into the soil, whereas the sprays are being sprayed above ground and it is more likely they could be damaging natural predators.

"We are just at the very early stages of trying to figure out what is going on in the whole area of resistance. We need a lot of joined-up thinking to cross the dots and come up with solutions," said Mr Bourke.

The first year of trials into the control of Barley Yellow Dwarf Virus (BYDV) showed a high level of pressure in some areas. Teagasc's Louise McNamara said the untreated crops had quite high levels in their winter barley sown in the coastal area of Cork.

She warned that the mild winters have been a risk factor for aphids as they are "frost hardy" and without a sustained drop in temperature, they are more likely to overwinter. Ms McNamara says early-sown autumn crops and late-sown spring crops are more at risk of BYDV.

Studies are under way into 'knock-down resistance', or KDR, which was first identified in the UK in 2012 and here in 2013. Ms McNamara said that research has indicated that aphids carrying the KDR gene, which makes them less susceptible to pyrethroids, occur in all the major grain- growing regions.

"But it is only the grain aphid and only one clone of the grain aphid. So it is not all the aphids in your crop," she emphasised. "What we are trying to work on is understanding whether aphids carrying this gene translates to resistance in the field. Do the treatments still work?"

Teagasc's Ciaran Collins warned farmers to be aware that machinery is the number one way of spreading weeds such as sterile brome throughout the farm.