Dry soils in many areas are making follow-up herbicide decisions in cereal crops far from straightforward for Farmers Weekly’s Crop Watch agronomists.
Soil conditions have been challenging for pre-emergence herbicides, especially on earlier drillings, said Countrywide Farmers’ Gloucestershire agronomist Neil Donkin.
“Blackgrass is reaching the three-leaf stage apparently unharmed. It means that follow-up post-emergence treatments will be applied earlier than usual and we shall have to hope that all blackgrass has emerged by then.”
If pre-emergence treatments were having little effect on the weeds, it made it even more important to carry out the post-emergence follow-up in the autumn, rather than waiting until spring, when the blackgrass would be enormous, he added.
David Martindale of Arable Alliance in Yorkshire said he would turn his attention to using Atlantis (mesosulfuron + iodosulfuron) plus a residual partner when blackgrass had one to three leaves.
“This timing is proving to be tricky where crop emergence has been patchy as some parts of the field are ready to apply Atlantis now and in other areas the crop has only just emerged.”
In fields where sterile brome is a problem it would be best to apply herbicides such as Broadway Star (pyroxsulam + florasulam) in the autumn rather than spring to gain best control, he added.
VIDEO: David Martindale turns to Atlantis
Pre-emergence herbicides went on in less-than-ideal conditions in AICC agronomist Tod Hunnisett’s Sussex patch, with varying results.
“A few millimetres of rain a few days ago appears to have reactivated them, so in most cases I’m not rushing in with post-emergence follow-ups just yet.”
Farmacy’s Philip Vickers said large parts of his Lincolnshire area had received less than 25mm of rain this autumn. “As such the seed-beds are still relatively open, and the residual herbicides used to date are unlikely to have created as good a chemical seal as last year.”
Nevertheless, blackgrass was being affected by residuals. But delayed blackgrass emergence, earlier drilling and fewer stale seed-beds could result in a challenging year on some farms, he added.
“To help control annual grass weeds this autumn, I am eager to use a contact chemical such as iodosulfuron-methyl-sodium or pyroxsulam. Both these products will need to be applied with a residual partner.”
Oilseed rape was growing almost too strongly in some cases so a growth regulator will be needed soon to hold down some very leggy crops, said Mr Donkin.
Mr Hunnisett reported similar findings. “Winter rape, after a slow start, took off with a vengeance in response to the warm weather. Now all crops look very healthy – some would argue too healthy – but this is a problem I actually like. I’ve seen very little phoma and with some crops up to welly-boot level I think the risk is minimal this year.”
In the north oilseed rape phoma levels were well below the treatment threshold of 10% of plants infected, said Mr Martindale. “However, levels are expected to increase soon and a fungicide which also has activity against light leaf spot will be chosen.”