Insecticide ban leaves search for new ways to save cereal crops from aphids

Insecticide ban leaves search for new ways to save cereal crops from aphids
The grain aphid, Sitobion avenae; farmers must find new ways to control it, without neonicotinoid insecticides, which are too risky for bees. Aphids spread Barley Yellow Dwarf Virus which can reduce barley and wheat crop values by €555 and €192/ha, respectively, according to Irish estimates.

Grain growers will have to put their faith in low-tech methods, as they bid to stay in business without relying on neonicotinoid seed treatments.

This insecticide was found by a European Food Safety Authority risk assessment to pose ‘high acute risks’ to bees.

It was partially banned in the EU in 2013, and could no longer be used on flowering crops.

Neonicotinoids, also known as neonics, may soon be banned for use on all field crops.

Here in Ireland, the IFA had written to Agriculture Minister Michael Creed requesting a derogation for continued use of Redigo Deter, which controls autumn infestations of aphid vectors of Barley Yellow Dwarf Virus (BYDV), and thereby prevents the spread of this disease within the crop.

It also improves crop establishment by reducing damage caused by wireworms and slugs.

IFA Grain Committee Chairman, Mark Browne has said not granting a derogation for Redigo Deter would be yet another severe blow for Irish tillage farmers, because BYDV causes yield losses of up to 3.7 tonnes per hectare in winter barley and 1.2t/ha in winter wheat (Teagasc figures).

IFA says that would reduce barley and wheat crop values by €555 and €192/ha, respectively.

“The failure to grant a derogation for Redigo Deter will further jeopardise the viability of Irish cereal crop production, which is already down over 50,000 hectares since 2012,” Browne said.

Meanwhile, Ireland imports almost 500,000 tonnes of maize from Brazilian farmers, who can grow genetically modified crops and use pesticides banned in the EU, said Browne.

The Agriculture and Horticulture Development Board (AHDB) in the UK has been researching how farmers might manage without neonicotinoid seed treatments.

Pest researcher Charlotte Rowley says the yield loss from BYDV in wheat averages 8% but can be as high as 60%.

It’s estimated that 82% of the UK crop area could be at risk from infection, if untreated, implying a potential crop loss of £136 million/year.

And rising global temperatures could allow aphids to be more active in the winter, further increasing the risk and spread of BYDV.

According to the AHDB, insect pests in crops will rise by at least 50% by 2050, with associated yield reductions of (on average) 22%.

To cope with the BYDV threat to cereals, farmers will, in basic terms, have to fall back on use of old-fashioned pyrethroid insecticides to control aphids.

But they will need a more integrated pest management (IPM) approach, to avoid unnecessary crop spraying for aphids, which would increase the already moderate levels of pyrethroid resistance seen in the Sitobion avenae grain aphid, which is a principal vector of BYDV.

That means field monitoring, to assess when the risk of BYDV rises enough to justify spraying.

Already, this aphid monitoring information comes from the Rothamsted Research network of suction traps, but it doesn’t cover the whole of the country.

Researchers have done the detective work necessary to know the behaviour of the grain aphid, and the bird cherry-oat aphid (Rhopalosiphum padi) that carry the BYDV virus.

They either migrate into crops from surrounding habitats, or survive from the previous crop, between the harvest and the next planting.

Putting “sticky traps” in grain fields has revealed much information on aphids behaviour.

A sticky trap in a grain field, which researchers use to monitor arrival of aphids in a crop, as part of the investigation into how growers will protect crops from BYDV, without using neonicotinoid insecticides.
A sticky trap in a grain field, which researchers use to monitor arrival of aphids in a crop, as part of the investigation into how growers will protect crops from BYDV, without using neonicotinoid insecticides.

It was found most of them land around the field edges, with three and a half times as many in the headlands compared with further into the fields.

“Aphids are weak fliers and it’s likely they’re deposited downwind of hedgerows and woodland edges by wind currents flying over them and down into the crop,” says Professor John Holland, head of farmland ecology at the UK’s Game and Wildlife Conservation Trust.

“This gave rise to a clear boundary effect, with more aphids found within 10m of landscape features such as hedges or woodland edges.”

BYDV levels are generally found to be higher near uncropped land such as grassland, moorland and wasteland, than where arable crops are dominant.

“Grasses, including maize, provide an alternative site for the BYDV vectors, with a consequent increase in numbers,” says Professor Holland. “Traditionally, western regions of the UK have been at higher risk of BYDV, because there is more grassland than in the East, but a recent study in France has shown that having more maize in the landscape increases the numbers of aphids infesting wheat crops.”

Therefore, more maize being grown in the UK for anaerobic digestion could cause extra grain crop damage by aphids carrying BYDV.

Researchers in the UK have also studied how many aphids carry BYDV.

Aphids weren’t carrying it at one site, yet 5.4% were infected only two miles away.

“Generally only a small proportion of the aphid population carry the virus,” says Professor Holland.

“Many perennial and annual grasses are infected with BYDV, but wild grasses are generally considered to be a poor source of virus.”

It is also suspected that minimum tillage or no-tillage systems may have less BYDV, because they are less attractive for aphids, and the extra debris in min-till system may be suitable for web-spinning spiders that can help control aphid infestations.

However, autumn-applied pyrethroid insecticide for BYDV control will also kill the spiders.

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