The use of hormone herbicides for resistance management and control of difficult weeds in cereal crops in the UK (with special reference to Scotland)

This paper reviews the importance of phenoxy herbicides (hormone herbicides) in Scottish Agriculture with specific reference to the spring barley crop, the most important cereal crop in Scotland. In 2013 the agricultural census figures showed that to 296,000 hectares of spring barley were planted in 2013. Of this area pesticide usage surveys estimate that 72% of the spring barley crop was sprayed with a metsulfuron-methyl, (sulfonylurea/ALS inhibitor), the most common sulfonylurea in Scotland in 2012. There was a similar area of crop sprayed with a phenoxy herbicide, a figure that has remained fairly constant over the last 10 years. The phenoxy herbicides are important as standalone products but they also have an important use in resistance management of the sulfonylurea herbicide group. Sulfonylureas are the foundation of herbicide use in the spring barley crop in Scotland. The use of phenoxy herbicides in spring barley has not prevented the development of resistant to the sulfonylureas in the Stellaria media (common chickweed) population in the Scottish spring barley crop. Sulfonylurea resistant chickweed is not confined to the spring barley crop but is a problem in other crops in Scotland such as potatoes and maize where sulfonylureas are used. Resistance to the sulfonylurea group of herbicides has been shown to be target site occurring as result of a single mutation. The multi site mode of action of the phenoxy herbicides are useful anti-resistance options with the sulfonylureas offering control of sulfonylurea resistant Stellaria media. The phenoxy herbicides are also particularly useful in increasing the weed spectrum of the sulfonylureas and the use to control difficult weeds such as Fumaria officinalis (common fumitory) in spring barley crop.