Do not blame your agronomist for low yields this year weather factors have conspired to undo any yield enhancing techniques they may have advised you to apply. 

Wheat yield as determined by grain number and grain size is established mainly during the period around anthesis (flowering), a stage in development known to be sensitive to high temperature stress. Anthesis for many wheat crops in the UK occurred during the second week of June this year. Temperatures during this period for the main wheat growing regions were around 20 - 22 °C. These temperatures alone will not have influenced grain set but exceeding a temperature threshold five days after anthesis will have reduce the potential grain size. The temperature threshold is set at 27 °C.  

Therefore, wheat crops in areas where temperatures exceeded 27 °C during the last half of June are likely to see a reduction in individual grain size. Temperature records show that this occurred in many wheat growing regions this June. 

The high temperatures in early July coupled with the dry conditions have reduced the active photosynthetic canopy in many crops and consequently shortened the grain filling period. Weather data shows temperatures in early July reaching a maximum of 31 °C in many southern regions and these temperatures will have increased the speed of leaf senescence, irrespective of soil moisture deficits. 

In experiments in Australia, plants were transferred into controlled rooms with high temperatures 7 days after the first anthers appeared, showing that a temperature of 27°C and above could substantially reduce the maximum grain size of several Australian wheat cultivars, resulting in substantial yield losses. This is particularly relevant for our spring sown crops this year as they will have flowered later and consequently have been at a more critical development stage when the high temperatures hit the UK.

Dry soils.

CEH’s UK Drought Portal  shows June as being so dry in many parts of southern England that it was off the scale used to report rainfall deficits in the portal. For the UK as a whole, end-of-June 2018 soil moisture was the driest on record (from 1961). It was also the driest soil moisture for any month since August 1995. Little wonder then that crops are maturing earlier than usual and that initial harvest results show below average yields. 

However, this will become more apparent as harvest continues and expect some disappointing spring crop yields. This will of course all make decisions for next seasons planting more difficult. Those that have adopted a higher proportion of spring sown crops as part of an integrated approach to black-grass control may take some persuading to continue with this practice.