Managing spray timings for aphid and black-grass control
Growers should resist the temptation to combine autumn weed control with aphid control in the same spray pass unless it is appropriate.
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The ban on use of clothianidin (Redigo Deter seed treatment) last December means growers are facing the first autumn drilling period without it for many years.
It seems inevitable that its loss will mean greater use of aphicide sprays to control aphids potentially carrying barley yellow dwarf virus (BYDV). However, knowing when to spray is key, according to Ben Coombs, Bayer campaign manager.
“There is a danger that if the timing of herbicide treatment and aphicide treatment does not line up, one of the sprays may be pulled out of synchronisation from when it should be applied.
“If it is a warm autumn T-Sum may be reached early. There is a risk that the grower does not want to travel through the crop twice, applying the insecticide then the herbicide. Instead they may make one application that is good timing for the insecticide but compromises the herbicide timing and grass-weed control.
“Alternatively, they may wait until they go through with the herbicide before putting in an aphicide and compromise aphid control.
“With Deter you could treat and forget about aphids and when drilling late, were unlikely to reach T-Sum until after it had run out of steam.”
Mr Coombs advises growers to apply herbicides and aphicides at the correct timings, even if this means more than one pass.
“The one piece of advice to control all those challenges is to delay drilling, which is good for grass-weed control and for aphids. The temperature is getting cooler and it takes longer to reach T-Sum, so may eliminate the need for some or all aphicide sprays.”
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Farm case study: Iain Robertson, Dorset
Iain Robertson works as sprayer operator and trainee arable manager for David Foot, a 2,900ha mixed farming business near Dorchester.
“There is a massive risk of BYDV here. We are under pressure. We are looking at variety selection and later drilling. At the moment we drill between the end of September and the end of October. We will probably drill about a fortnight later.”
In autumn 2017, when windy conditions meant Mr Robertson was unable to apply a follow-up aphicide to Deter in a spring barley crop, he estimates there was a 10% fall in yield due to BYDV.
Black-grass only affects one of the company’s farms, on heavy clay. “We aim to drill at the end of October on this farm but if the weather is likely to break we go earlier.”
On this farm, for grass-weed control he applies a Liberator (diflufenican + flufenacet) pre-em within 24 hours of drilling followed up with 0.3 litres/hectare of flufenacet later in autumn if necessary. On the rest of the farm only the first pre-em spray is applied.
While a lot will depend on the weather, he expects to have to potentially apply three or four aphicide sprays.
Regarding synchronising spray timings, he says: “We can not compromise on spray timing but, if a timing is delayed because of the weather and they are within a day of each other, it would be silly not to amalgamate them.”
Farm case study: Alex Borthwick, Lincolnshire
Alex Borthwick is farm agronomist for R M Cottingham, an 880ha farm on the Lincolnshire Wolds.
Being 350ft above sea level, the farm generally has a slightly lower risk of BYDV, says Mr Borthwick. “In recent years we have managed it by using Deter seed treatment and pyrethroid sprays when the risk has been there.
“In future we will have to pay more attention to aphid activity within the crop from emergence, through more field walking, and utilise cultural controls and risk management tools such as aphid forecasts as a guide to when the pressure will be greater. We will then spray an aphicide if required.”
Black-grass is a significant issue on the farm and wheat drilling starts at the end of the first week in October where fields are clean of black-grass, but most starts from mid-October due to black-grass.
Mr Borthwick says: “It is vitally important with regards to black-grass control to ensure the pre-em and post-em herbicides are applied at the correct timing as part of the black-grass control strategy.
“With regards to aphicides, in the past these have been applied separately and, to make the most of the spray pass, we add manganese to help with plant health through the winter. However, if there was deemed to be a risk building near to the post-em herbicide timing, we would add the aphicide to this treatment.”
T-Sum
The timing of production of the second (potentially most damaging) generation of aphids can be approximated by accumulating daily average air temperatures above a baseline temperature of 3degC. It takes around 170 day degrees C from the day of emergence of untreated crops. Visit cereals.ahdb.org.uk/media/1438720/BYDV-management-tool-September-2018-.pdf for more information.
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