Conditions in recent weeks, and this week in particular, have been on the chilly side. For several crop types, including fruiting trees and food crops from flowering plants these cold temperatures at flowering can be linked to higher yields.

Could this also hold true for oilseed rape, as cold temperatures this year coincide with crops flowering in earnest?

According to Dr Pete Berry, a crop physiologist and oilseed rape expert at agriculture consultancy ADAS, this is far from a given. Dr Berry said cooler temperatures can be expected to lead to a longer flowering period, but OSR crops will need good filling conditions to realise that yield potential.

He said that, if conditions remain cool - as expected over the coming days - and if this continues a good way through flowering, then this should allow more grains/m2 to be set. So cool weather and a longer flowering period could lead to more seeds/m2 set, but crops then need good seed filling conditions to fill seeds and yield highly.

One other possible benefit noted by Dr Berry is that cool temperatures could give some relief from pests; pollen beetles will be less likely to fly, as they prefer temperatures above 15oC. Although pollen beetles have been known to fly at lower temperatures, this year’s cool temperatures appear to have suppressed migration to such an extent that most crops are now flowering and so beyond the green/yellow bud stage, at which they are susceptible to the pests. 

In Fact the latest Bayer Pollen Beetle Bulletin, released on 19th April, shows a clear north-south divide. Met stations in England now range from ten to 50% complete with migration most advanced in the southern counties, but there has been hardly any movement in Scotland over the last week, and met stations there have shown eight to 19% migration.

Although the OSR area is down again this year, conditions for the crop look good, if a bit dry. Again, this could carry some benefits. OSR can deal comparatively well with drier conditions and lower relative humidity, combined with cool nighttime temperatures (dropping below 7oC) can also make sclerotinia less likely; the fungal infection requires the right temperature and level of humidity (80% RH) for almost a day to affect crops.

Ultimately, though, as Dr Berry noted, the deciding factor in OSR yield is not likely to be temperature durning flowering, though low temperatures and dry conditions could provide some benefits. Louisa Dines, senior lecturer in agronomy at Harper Adams said sunlight is likely to have a larger role to play, as the amount of photosynthesis that occurs during flowering will have the largest influence on yield.

Dines said, “Seed number is the critical factor determining yield in oilseed rape and this is determined by the amount of photosynthesis during a period of 300 day degrees after mid flowering. In cool periods it takes longer to achieve this and therefore the amount of radiation received increases and there is potential for a higher number of seeds to be set. 

“However, interactions with canopy size will also affect this and ultimately yield will also be affected by conditions during seed fill so at this stage it is hard to predict the impact of current weather conditions on yield.”