The graminicide Centurion Max is regarded by many agronomists as the best fop/dim herbicide for grass-weed control in oilseed rape. It has been successfully integrated into many weed control programmes since its launch two years ago. But it needs to be used sensibly so that its efficacy is maximised and risk of resistance is minimised, according to Nufarm UK Ltd.
With more commercial experience, new stewardship guidelines have been issued to ensure that users get the best from Centurion Max in terms of weed control, without increasing the risk of resistance or without exacerbating crop effects, says Simon Bishop of Nufarm UK Ltd.
“We have had many reports of excellent weed control from early applications of Centurion Max in winter oilseed rape. There is no question that it works well, better than other contact graminicides, but we have also learnt some practical lessons in the last two years of commercial usage. These guidelines take into account our wider experiences.”
Simon emphasises that the effective dose rate of Centurion Max must be 1 L/ha. “We recommend this dose rate is not reduced. In trials Centurion Max applied at 1 L/ha gave 98% control of black-grass and 96% control of annual meadow-grass, a weed that few other ACCase graminicides can control. In over 40 trials in Europe and the UK, good activity was shown on other grass-weeds too; 97% control of wild-oats, 97% control of rye-grass and 92% control of brome.”
“Centurion Max should be applied from the 2 true leaf stage of the oilseed rape and not after the end of October. After this time, it is colder; with mean temperatures below 7°C and this means that weeds are no longer actively growing. The herbicide works best at temperatures between 8°C and 25°C. Periods of frosty weather before application will reduce uptake and translocation. Any situation where target weeds or crop are under stress e.g. drought, frost, waterlogging or other environmental conditions could interfere with the herbicide’s activity and crop safety,” warns Simon.
Observations made over the last two years indicate that later applications, after mid-October should be avoided on rape varieties that are early flowering or maturing – those with a 6 rating or above – or on crops drilled before the 25th August.
The Centurion Max label states that it should be applied when black-grass has 3 leaves. “This fits in well, as Centurion Max is then unlikely to be the first graminicide used; an earlier fop being applied for cereal volunteers. Because it is the best “dim” for black-grass control, it should be saved for more difficult situations. Only one application of Centurion Max is permitted in each crop, but growers can use two different ACCase herbicides, a fop in this case, provided they are targeted at different weeds.”
Simon Bishop also points out that the guidelines advise a minimum of 14 days between Centurion Max and other chemicals, before or after application, with the exception of some insecticides for Cabbage Stem Flea Beetle control or water conditioners. “Following a data review last year, we now support a mix with a non-emulsifiable concentrate pyrethroid, if needed for CSFB. The addition of a water conditioner, which was not encouraged last year, has now been found to improve the herbicide’s efficacy in areas where water has a high pH. When it comes to fungicides for Phoma or Light Leaf spot, tank-mixing is not supported as many autumn-applied triazole fungicides have growth regulating activity, which also affect grass-weeds. Nor are we supporting the use of adjuvants as the product is already formulated to give maximum control.”
Growers and advisors should integrate Centurion Max into a programme with herbicides with different modes of action. “You can sequence Centurion Max with propyzamide (Kerb), propyzamide + aminopyralid (AstroKerb) or carbetamide (Crawler). It is important that clethodim is not the last herbicide treatment in the programme. Any survivors from a clethodim treatment will then be controlled by the other herbicide, so reducing weed seed return. This helps to minimise or prevent the development of resistant weed strains.”
Black-grass screening has proven that clethodim has much less resistance pressure than other ACCase chemistry. ADAS black-grass screening work in 2013 showed that 84% of the 122 weed samples had a specific gene mutation Ile-1781 which conferred resistance to cycloxydim, whereas just 4% of the samples had the gene mutation Asp-2078 which confers some resistance to clethodim.
“Apart from intrinsic efficacy, this could be an additional reason why clethodim outperforms all other fop and dim graminicides in the field,” explains Simon. “Most farmers are pleased with the level of black-grass control achieved by Centurion Max. Our guidelines are on the cautious side, but we want to ensure excellent results with no crop issues this autumn.”