Presenting an Arable Weed Week Resistance Management Masterclass, Steve Dennis, head of business development at BASF, said managing the black-grass population was key to control. “If you are not getting 97 per cent control, you won’t be reducing the population.
“The key challenge is to control the resistant population to at least the same degree as the sensitive population. If you leave 20 per cent of the black-grass population, and only control the sensitive ones – that 20 per cent will be the resistant population and increase the problem for future years.”
Any control approach needs to kill resistant as well as sensitive strains, he said. It should include delayed drilling, use of stale seedbeds to allow germination and glyphosate to reduce the population. Using spring cropping is the greatest example of delayed drilling there is, he added.
Apart from rogueing and patch spraying, in-crop black-grass control means using herbicides, he said. There are two types: low risk herbicides in terms of resistance, with performance gradually reducing over many years, tend to be pre-ems. Most can be used post-em but their performance drops. They include pendimethalin, flufenacet and new active, Luximo, explained Mr Dennis.
“If you’ve used cultural control with all the IPM tools and you’ve used a low risk chemical in a pre-em situation you may have achieved sufficient control that you don’t need to use a high risk herbicide. The more years you can get away without using one, the longer it takes for resistance to develop.”
In high risk ALS and ACCase inhibiting herbicides resistance is more ‘black and white’, says Mr Dennis. “It gets quickly to the point of no value. That’s why it needs to be protected. Only use it in a way to manage numbers and, as much as possible, only in mixtures with other actives. Use under good conditions and achieve good spray coverage.”