Wheat yields are showing increasing variability, according to analysis of this year’s crop.

Land agents Strutt & Parker, which tracks crop performance through its annual harvest survey, said over the past decade, farmers had seen greater variability in winter wheat yields than they did in the previous five years.

While average winter wheat yields have slowly climbed since its survey began 19 years ago, growers are now seeing a wider range in yields from year to year.

Agronomist George Badger said while the yields low of 2012 and the highs of 2014 and 2015 had a lot to do with the fortunes of rainfall and sunshine, his team believes there is another factor at play.

“Our survey data, which this year covers 58,000ha, is largely gathered from farms in the East of England and the Midlands where blackgrass is an issue. It is our belief that part of the explanation is a shift to later drilling, as part of a strategy to tackle blackgrass once resistance to contact post-emergence herbicides became more evident from 2010 onwards.

“Late drilling is an essential grass weed management tool, but it does result in smaller root structures which leave crops more vulnerable to weather extremes than they were when people could reliably drill in September.”

Delayed drilling (after October 15) remained the right course of action on the worst-affected fields, he stressed, but the firm’s data suggests farmers need to make a field-by-field decision, rather than whole-farm.

According to Strutts’ provisional results for Harvest 2017, the most significant change in crop performance was seen in winter oilseed rape yields which rose 27%, from a disappointing 2.9t/ha in 2016 to 3.7t/ha in 2017.

“Part of the reason for the improved yields is that only those crops with good potential were taken through to harvest,” said Mr Badger. “In the eastern region, a large area was lost shortly after establishment due to the dry conditions, with Cabbage Stem Flea Beetle (CSFB) damage a secondary problem. Our estimate is that about 80% of the crop was lost in Essex at that point. However, elsewhere CSFB larvae pressure seemed to be lower and the OSR plants benefited from higher June sunshine Overall winter wheat yield for 2017 was 9.1t/ha, which was up 2% on the previous year’s average of 8.9t/ha.