The element plays an important part in the development of pollen and in regulating flowering, so any deficiency should be corrected as soon as possible, he says.
“People will be going through with fungicides or insecticides at the green bud stage, which is a good time to include boron if it’s needed.”
Rape has a high boron requirement a 4t/ha crop typically needs about 350g/ha throughout the season, compared with just 500g/ha for a 50t/ha sugar beet crop.
Boron is a key element for regulating oilseed rape flowering, so any deficiency must be corrected now, says Chris Bean.
Boron is a mobile element in the soil, so can be relatively easily leached in wet seasons, Mr Bean warns.
Light, coarser, sandy or stony soils are therefore at greatest risk from deficiency, but he says it can also be an issue where the pH is high.
“Calcium antagonises the lock-up of boron, so on chalky soils, or where lime’s been applied to correct potential club root problems, deficiency can be an issue.
“Years ago we didn’t see as many boron problems when using the old boronated fertilisers. But the more modern products don’t contain the old boron impurities, so this could be adding to soil deficiency.”
Mr Bean thinks soil testing is generally the most accurate way to detect boron deficiency and any soil with levels below 1ppm is potentially at-risk.
“Low, or deficient is generally classed as anything below 0.8ppm.” Tissue analysis can also be used to measure boron, but the crop needs to be actively growing to avoid inaccurate (very low) results, he notes.
There are a number of powdered and liquid boron formulations available and one to two applications at the 3-5kg or litres/ha rates are generally sufficient to meet the crop’s requirement, Mr Bean says.