As cereal growers approach the first autumn without support from neonicotinoid seed dressings, we examine what this means for controlling weeds, slugs and aphid vectors of Barley Yellow Dwarf Virus (BYDV).
The European ban on neonicotinoid seed treatments means products such as Redigo Deter will not be available to protect cereals from aphids and slugs this autumn. As well as its direct effects on pests, the seed treatment was a valuable tool to help manage autumn workloads for many. The impact of its loss will vary from farm to farm, but the key is to prepare well and not let added pressures compromise crop management.
|Autumn activity with Deter||Autumn activity without Deter|
|Deter treated seed – sown mid-October||SPD treated seed – sown mid-October|
|Pre-em treatment||Pre-em treatment|
|Residual top-up (if required)||Insecticide|
|Residual top-up (if required)|
|Insecticide (if required)|
For many farmers, autumn cereal establishment has become dominated by grass weed management, particularly black-grass, so late drilling followed by a robust pre-emergence herbicide programme is the mainstay of weed control.
Prime Agriculture agronomist Andrew Blazey does not foresee radical changes to autumn workloads where farmers are already drilling later, although says BYDV is an added concern.
Advising clients in Essex, Suffolk and Cambridgeshire, he witnessed the problems caused by the withdrawal of seed dressings in oilseed rape. But he is optimistic the impact on cereals will not be as significant, providing growers are aware of the dangers and use the agronomic tools available to decide when to treat.
Without protection from Deter, farmers are likely to have to spray at least twice for aphids in earlier-sown crops and once in later-drilled crops:
“Most farmers with a black-grass problem are already late-drilling in October which is also an effective cultural BYDV control. Aphids are less active in cooler weather and it takes longer to accumulate the necessary degree days before you need to apply an insecticide.”
It will take time to fully understand the consequences of losing neonicotinoid seed dressings, and Mr Blazey says it should not distract attention from effective weed control.
“The biggest thing is not to compromise herbicide timings for aphid control and visa-versa.
“Pre-emergence herbicides must be applied at true pre-em timing and the same with a peri-emergence top-up. The top-ups are where I see most danger of farmers compromising control by combining a herbicide and insecticide spray, but timings often have to be different to get the best results.”
For the pre-emergence application, he prefers Liberator plus pendimethalin or Crystal with some diflufenican. Where farmers can use tri-allate at pre-emergence, a peri-emergence top-up is not always necessary, but where tri-allate is not used, it should be considered, he says. Mr Blazey recommends applying peri-emergence top-ups to just-emerged crops for best control.
In contrast, a pyrethroid spray to control aphids will probably be needed a little later at around the two-leaf stage of wheat, depending on the T-Sum calculation. Separating herbicide and insecticide applications also maximises efficacy and crop safety.
Rothamsted entomologist Dr. Steve Foster agrees that timing and thresholds mean everything for additional sprays:
“Pyrethroids are relatively cheap so there is a temptation to put them in the tank with a herbicide because you’re spraying anyway, but this is bad for resistance management. There is already some resistance to pyrethroids in grain aphid and unnecessary sprays increase the probability of it becoming more of a problem.”
Dorset sprayer operator Iain Robertson is well aware of the dangers of BYDV. Based at David Foot Ltd., near the south coast, he is in a high-risk zone for aphid activity.
“Three years ago, we were hit badly with BYDV because the weather was conducive to aphids and we couldn’t spray in time.”
With seed protection no longer available, Mr Robertson thinks it very likely he will need to apply insecticides after drilling and up to three more times during the autumn.
“Later drilling is an option to manage BYDV, but I’m not sure it’s possible on our heavier land as there is a good chance nothing would get drilled. Our wheat goes in after maize from late September onwards, but thankfully we don’t have the same black-grass pressure as other farms.
“Farmers with black-grass still need the full pre-emergence herbicide programme and sort out aphids after that.”
Black-grass, slugs and aphids are all concerns for Alex Borthwick who farms 880 ha near Market Rasen, Lincolnshire.
“The loss of Deter is in the back of our minds but black-grass remains at the front. I see aphids and slug pressure both having potential to cause problems depending on conditions.”
Mr Borthwick believes this season will be about learning because he is not certain how the lack of Deter will affect crop establishment, particularly early-drilled crops.
He thinks the biggest addition to workload will be time spent walking crops and monitoring problems, not on the sprayer:
“Deter meant we didn’t really need to worry about what was happening in the field because it was protected. Now we need even better attention to detail to keep crops healthy.”
Seed hollowing from slugs is a risk that he is still deciding how to manage:
“We may need to do baiting before drilling to get an understanding of slug pressure. We could then increase seed rates and apply ferric phosphate pellets straight after if required.”
He also expects to control slugs through ploughing which is his standard cultivation and should result in fewer problems than min-till systems.
Currently, 30% of his land goes into spring cropping with a mixture of wheat, barley, potatoes and sugar beet that is usually drilled around late February or early March; the other 70% is autumn-sown.
Barley is drilled in late September, first wheats in early October to maximise potential, and second wheats last. In recent seasons, second wheats were not treated with Deter so he is used to going back into crops during November to treat for aphids when necessary.
If timings and thresholds match, he combines this with the herbicide programme. Wheats receive a pre-emergence stack based on Liberator or Crystal followed by a residual top-up and Atlantis OD depending on black-grass.
“We host some trials which have convinced me autumn Atlantis is worth the effort because you get much better control than spring.”
Late drilling wheat is standard practice for black-grass control, but can you drill barley later to get a double boost of black-grass and BYDV control?
Oxfordshire farmer Richard Davey is challenging the notion that barley should be drilled in late September by testing whether it is possible to drill hybrid barley in late October:
“We’ve got used to drilling, rolling and applying the pre-emergence herbicide and then leaving the field until spring. Having to come back with an insecticide wouldn’t be ideal so hopefully, late drilling can help with this as well as black-grass.”
In autumn 2017 and 2018 he drilled hybrid barley late on 28 and 26 October respectively. Yields held up well at around 7.5 t/ha, with better areas at 9 t/ha. Winter barley also helps spread harvest workloads and provide timely entry for oilseed rape.
Mr Davey is mindful that good conditions in recent autumns have helped late drilling, including a 19 November sown second wheat in 2018. But because controlling black-grass is so important, he is convinced he has to push back drilling dates and run the risk of wet weather forcing him to drill a spring crop.
This blog is based on an article from the autumn ‘19 issue of Crop Focus magazine. The magazine is packed full of insight, advice and research from the world of arable farming to help you grow the most profitable crops possible. Over 90% of readers find Crop Focus an interesting read – it’s free to subscribe so sign-up today!
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