BYDV risk – South East Farmer – James White
The Barley Yellow Dwarf Virus (BYDV) risk is likely to be elevated this season as a consequence of several issues, says James White, Hutchinsons agronomist ...
James White, agronomist
He points out that crops are being drilled earlier because of the experiences of last year. Earlier drilling means an earlier or extended season at which crops are potentially at risk.
Warm soil conditions and seedbed moisture are ensuring that drilled crops are emerging rapidly, with some of the earliest drilled crops at leaf stage at the end of September.
Where moisture has been lost but crops have still been drilled, it is more likely that we will see an extended period of emergence. In these circumstances, if aphids start to colonise these plants early it is imperative to time insecticides to the earliest emerged parts of the field and not wait for full emergence.
We also know that warm air temperatures are conducive to early aphid flight, and we are now picking up from the trap data that aphids are already in flight.
With the loss of Deter to cover the early infection period, we are now solely reliant on the pyrethroids. Also remember that without Deter we have lost the additional early protection from slug hollowing it afforded us.
It’s important not to rely on variety tolerance in barley; it might mitigate some of the impact of any BYDV that gets into the crop but it shouldn’t impact on spraying decisions.
With regards to the variety resistance for the wheat variety Wolverine, be cautious as it is not yet fully proven as it is still in its first commercial year.
Where aphids are present in the variety, it’s important to still time the first insecticide as normal, but the likelihood of repeat applications is less likely.
There are also many fields that have not been treated to kill the green bridge, be it volunteers or grass weeds. A glyphosate treatment prior to drilling or mixed in with the pre-emergence treatment will be needed to reduce the risk of virus spreading to the emerging crop.
Once aphids have been seen in the crop, start counting from the 170 day degree spray threshold. The exception to this is if large numbers are seen feeding on a crop you should spray immediately then count once re-invasion occurs.
Spray timing prediction in Omnia
Knowing the right time to spray for optimum control is vital. The pest and disease forecast model within Omnia aims to tackle this by using weather data to make treatment timings as accurate as they can be, on a field by field basis, so predicted spray dates can be mapped out.
The risk level is presented in a graph and accrues degree days along the 170 degree-day model that’s frequently used. The graph counts up time, and as it reaches 150-day degrees it shows up as a warning period to alert growers when they’re reaching a key timing.
This email alert can be set by the user at a time dictated by themselves, say three days before for example.
The model tracks when crops are drilled, as with every different drilling date there is a different risk period. It can also be manually reconfigured, and treatments – plus treatment dates – can be added to reset the model.
This data can also be collated into a report to illustrate the levels of risk across the whole season and how they were treated, which will be very useful when it comes to making decisions in the future.
How many sprays will I need and when can I stop?
This is very dependant on the period that a crop is exposed to the aphids:
- Earlier drilled crops are at greater risk as more of the crop is emerging as aphid migration starts
- When migration occurs – reports at the end of September showed winged aphids moving into crops
- How quickly the aphids re-invade following treatment
- How mild the autumn remains – extending the potential period of infection later into the autumn
- The smaller the crop relative to being infected, the greater the yield
- To protect the efficacy of the pyrethroids they should be used with wetcit, as the first case of a shift in resistance status of R.padi was reported in 2020.
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