“There are strengths and weaknesses of both alternatives,” he said. “But they have a role and will help growers to contain herbicide expenditure.”
Using chlortoluron instead of IPU would give better control of ryegrass and wild oats, he continued. “It’s also less prone to leaching than IPU and is more persistent. It’s safer in mixes too.”
The downsides with chlortoluron were varietal restrictions (see below), weaker blackgrass activity and less post-emergence contact activity, he said. “There’s also enhanced metabolism resistance to it in blackgrass and ryegrass.”
Dr Ellerton added that a bid swing to chlortoluron could give a rise in concentrations found in water, resulting in the herbicide having the same fate as IPU.
Replacing trifluralin with pendimethalin had advantages and disadvantages as well, he said. “Pendimethalin has a broader weed control spectrum and tends to result in less overspraying in the spring. It has stronger residual activity and greater contact activity, as well as being unaffected by target site resistance.”
It was also less affected by enhanced metabolism resistance than other actives and had a wider window of application, he said.
“On the downside, pendimethalin is gives variable results on blackgrass and is more seedbed sensitive. It can’t be used on stony, gravely soils and it’s more expensive.”
Dr Ellerton anticipated that the use of both chlortoluron and pendimethalin would rise this autumn. “At the same time, the pre-emergence herbicides will be relied on more, as will ALS chemistry.”
Wheat Varieties NOT Tolerant to Chlortoluron
- Batallion Gulliver Marksman
- Cordiale Humber Musketeer
- Deben JB Diego Riband
- Duxford Limerick Velocity
- Glasgow Malacca Xi19