Article taken from Farmers Guide, October 2017.
Oilseed rape growers have traditionally based their initial grass weed control on a pre-em spray followed by a contact such as Falcon (propaquizafop) or Fusilade (fluazifop-P-butyl) to clear up volunteers.
It looks as though this will be a good strategy this season, with many crops in my area of Wiltshire going into good, moist seedbeds that should help optimise pre-em activity.
However, some growers are now omitting the pre-em spray, preferring to ensure they have a viable crop that has outgrown the attention of flea beetle and slugs before committing money'to chemistry.
In these cases, black-grass will be more difficult to control. Some plants will be too big for propyzamide to control adequately - that chemical needs to be applied when it is cold, so won't go on until mid November onwards. We will therefore need to apply something beforehand to keep black-grass in check.
I'll be recommending Centurion Max, which contains 120g/litre of clethodim. Applied at the recommended 1-litre/ha rate, this is active on black-grass that is resistant to other ACC-ase-containing products and it will take out volunteer cereals as well.
Centurion Max might not always result in a complete kill, but it will stunt the black-grass plants and slow subsequent growth, making them much more susceptible to the late autumn/early winter application of propyzamide.
However, there are several caveats to observe to ensure crop safety and to optimise performance. Crops should be robust, so need to be adequately waxed. A 10-day no-spray period should be observed before application. Crops should also be growing well, so adequate nutrition is necessary.
Centurion Max should be applied when the temperature is 8°C or more. Cold weather, particularly frosts, must be avoided.
The chemical should be applied in 200-litres/ha of water as a medium spray to optimise coverage. In hard water areas, be sure to add a water conditioner, such as Stingray at 200ml/ha, to improve efficacy.
A non-EC pyrethroid insecticide to control cabbage stem flea beetle can be tank-mixed if required. No other tank-mix partners are permitted. No herbicides or fungicides should be applied to treated fields for 14 days after application, while a 7-day period should be observed for nutrients and insecticides.
Timing is important. Centurion Max should only be applied once the crop has two true leaves. The cut-off date is the end of October, although crops drilled on or before 25 August and early flowering varieties (6 or above) should not be sprayed after the middle of that month.
Winter wheat
Winter wheat growers who struggle to control black-grass with their preem stack might want to consider an early post-em treatment. It won't be cheap, but it is likely to be more costeffective than allowing the infestation to flourish or writing the crop off.
Longer-term cultural controls will need to be considered. For now, however, an early post-em application ofTrooper (flufenacet + pendimethalin) at 2-litres/ha + Fence (flufenacet) at 0.25-litres/ha + Xerton (ethofumesate) at 0.6-litres/ha + Remix to keep the active ingredients in the top couple of centimetres of soil where they do most good, has done a fantastic job in trials and commercial situations.
Grassland growers who have not yet controlled perennial grassland weeds such as docks, thistles and nettles should consider doing so. These weeds will be returning nutrients to the roots in preparation for winter, so will translocate herbicide as well, improving control.
Doxstar (fluroxypyr + triclopyr) will do a good job where docks are the main problem. For additional thistle and nettle control, use Pas Tor (clopyralid + fluroxypyr + triclopyr), or ForefrontT (aminopyralid + triclopyr) + Companion Gold on grazing. I'll add Companion Gold in each case to improve efficacy.
Esme Shephard is an agronomist with Agrovista, based in Wiltshire (esme.shephard@agrovista.co.uk).