Decision support tools needed for aphid control

The focus of the morning session of this year’s Irish Tillage and Land Use Society’s winter conference was on BYDV, with a number of Irish stakeholders making presentations.

John Mahon of Teagasc explained that “BYDV is our worst enemy from a virus point of view, we can have up to 80% yield loss,” but with a typical level of infection, it can reduce yield by up to 30%.

Teagasc research has shown that a 3.7t/ha yield loss in winter barley and 1.99t/ha in spring barley is possible.

As most farmers will know, the nearer a field is to the coast, the less frosts and cold temperatures it will experience, leading to a higher aphid pressure.

The level of wind, rain, light and humidity all have an effect, leading John to note that weather monitoring tools are vital.

The aspect of the field, whether it is south-facing or not, and sowing date can influence aphid numbers too.

Min- or no-till has been shown to confuse aphids based on colour; they cannot identify the plants to land on them.

Climate change could also play a role in the spread of BYDV. John told the attendees that there is little to no movement by aphids when temperatures are under 4°C.

However, these low temperatures are becoming less common as our winters become milder.

John confirmed that Teagasc is seeing higher number of aphids on field headlands than in the middle of field.

He said that this brings into question whether headlands can be sprayed with an insecticide, but to leave the remainder of the field unsprayed.

John said that Teagasc is constantly monitoring aphid numbers through suction towers, yellow traps and manual in-field checks, hoping that the continued research can help them to give better advice to farmers.

Reduce

With pressure being applied to reduce insecticide use, and the risk of resistance build up in these insecticides now at a high level, John discussed some of the ways in which insecticides can be used in a controlled and targeted manner. To do this, farmers must know when exactly they need to apply an insecticide.

Thresholds are one method of achieving this. John said that there are no robust, verifiable aphid thresholds available to farmers at present.

This means that farmers do not know if they need to apply an insecticide whether they see one or seven aphids on a plant.

A decision support tool called Acrobat created by ADAS in the UK is currently under review by Teagasc.

John explained that it is based upon environmental factors and agricultural practices, but it mainly focuses on the bird cherry-oat aphid, as this is the main BYDV vector in England.

Research is being carried out on a plot-scale and tramline-scale here to see whether it can be a benefit in Irish conditions where the grain aphid is the main vector.

Referring to the tool, John said, “That’s the place we want to get to in Ireland, protecting our chemistry, using less of it, and only using it when we need to.”

Resistant

Louise McNamara, an entomologist with Teagasc took part in a panel discussion on the day.

She described how the new BYDV tolerant and resistant varieties are in trial on a number of different sites.

Some plots are planted very early in the middle of September to drive aphid activity and the amount of virus in the crop.

She said that while results are promising, they will need another couple of years to take conclusions from the trial as BYDV levels are variable; if there is little or no BYDV in a certain year, the trial does not provide useful data.

Louise noted that while there has been no research done on the topic, in theory crop diversification and crop rotation should help to reduce the likelihood of a host being present to pass the pests from one crop to the next, similar to how it is recommended to terminate volunteers six weeks before a new crop is planted.

However, grass can also host aphids, and as there is so much grassland in Ireland, there are still plenty of reservoirs of aphids available.

George Blackburn, agronomist with the Cooney Furlong Grain Company, explained that he sometimes applies a graminicide to cover crops once cereal volunteers have emerged.

This has a dual benefit; it will get rid of a host for aphids and disease over the winter months, and it will allow for a better cover crop to grow as it will have less competition for nitrogen.

He explained that BYDV is a big issue in Wexford. However, with the increase in the amount of BYDV tolerant varieties available, it is now easier to choose winter barley as a crop.

“It’s a testament to the breeders that they’ve brought it on so much, that we have some mitigation for that [BYDV], it was putting a lot of people off [winter barley].”

Covered

Due to a large amount of acreage needing to be covered on the Cooney Furlong farm, George said that the planting of winter cereals needs to start on 20 September.

He accepted that this may not be an optimal agronomic date, but with a large acreage and a minimum tillage system, planting has to begin early, and BYDV tolerant varieties give confidence and peace of mind when doing this.

He said that yields have been very good so far, and he wondered whether there had been sub-clinical BYDV in some non-tolerant varieties in previous years.

Ramularia

The only negative that George can see is that some BYDV tolerant varieties seem to be slightly more susceptible to ramularia.

However, some members of the panel disagreed with this, and there has been no research to back up the claim.

Spring barley is a very important crop for George. He uses a lot of sulphur on it, approximately 50kg/ha. George said that this means that the barley emerges very green, and BYDV then does not seem to be an issue on the crops with extra sulphur, but this has not been studied.