ISOLATED cases of ryegrass and blackgrass resistance to the herbicide flufenacet is not an immediate cause for concern.
However crop protection specialists Bayer Crop Science are urging farmers to continue their use of integrated weed management programmes, to minimise future risk.
Testing on ryegrass and blackgrass has revealed the presence of resistance to flufenacet on a small number of farms in the UK, as well as in several other countries around the world, according to Dr Gordon Anderson-Taylor of Bayer.
The results were found following testing to determine the quantity of active ingredient that is required to provide 50-90 per cent of control within the population.
He said: “In the ryegrass, some UK populations needed more than 300g/ha of flufenacet to be applied pre-emergence to achieve 50 per cent control and more than 3kg/ha for a 90 per cent control rate.
“These figures are well above the label rate of 240kg/ha for flufenacet.
“The results are of particular concern on farms which are already experiencing problems with ryegrass resistance, but I would emphasise that the issue is unlikely to be widespread.”
He added: “It is worth noting that the research has focused on the most resistant samples that are available. Resistant strains of ryegrass have also been identified in Germany, France and in the USA.
“Understanding the ryegrass population on your own farm is essential and a resistance test will provide valuable information about the status of the farm population.”
When it comes to the control of blackgrass, Dr Anderson-Taylor does not expect the research results to prompt a radical change in the management of blackgrass on UK farms.
Many growers are already taking steps to prevent the spread of resistant strains, he said. Nevertheless, he advised producers to continue their vigilance, in terms of product stewardship.
The three methods which can be adopted to reduce the risk of the development of chemical resistance are cultural control, crop rotation and the use of herbicides with varying modes of action, he explained.
The cultural control programme should be based on reducing ryegrass populations before the main crop is sown.
“Delayed drilling can be a useful management tool, as the majority of ryegrass plants germinate in the autumn. Rotational ploughing, higher seed rates and an aggressive approach to weed patch control are also important,” he said.
“In common with all problem weeds, the aim is to reduce populations down to manageable levels to allow herbicide applications to work effectively.”
Another option is to adopt wider rotations which include spring crops and non-cereal crops, he added, with the latter permitting a broad range of chemical programmes with varying modes of action.
OTHER HERBICIDES – RESISTANCE ISSUES
THE research also highlighted potential resistance issue with two other herbicides: pendimethalin and prosulfocarb, added Dr Anderson-Taylor.
“When applied as single active ingredients, these two chemicals both showed lower efficacy on blackgrass, although the research has not investigated their performance when applied in mixes and sequences,” he said.
“No active ingredient is immune from the risk of resistance. As well as using varying modes of action, programmes should be carefully planned and the use of pre-emergence products should be considered.
“Another tool is to eliminate survivors of the herbicide programme, wherever possible. Glyphosate can be used for larger patches, while smaller populations should be hand-rogued.
“This will help to stop the shedding of resistant strains of seed, which may germinate the following year.”
ARABLE OPEN DAYS
THE National Institute of Agricultural Botany’s annual Croft open day will take place on Thursday, June 28 at Grange Farm, Croft-on-Tees.
Speakers include Clare Leaman and Ian Midgley, who will be giving advice on winter wheat, while Simon Kightley will be manning the oilseed rape plots.
Bill Clark will be offering tips on cereal disease management and the subject of wheat genetics will be covered by Fiona Leigh.
Elizabeth Stockdale and Nathan Morris will be available to answer questions on soil management and rotations. The site will be open from 10am, with the final field tour at 3pm.
Meanwhile, DKB Crop Protections annual open days will be on June 18-19 (10am-5pm) near the company’s headquarters at Walworth.
