Newwork on oilseed rape is revealing how improved canopy greening delivers extra yield and by how much.
Trials carried out by ADAS on behalf of BASF during 2014 and 2015 show clearly that applyingPictor (boscalid + dimoxystrobin) during mid-flower can push yields above and beyond what would be expected from disease control alone.
Leavesin particular are staying greener for longer and work harder, intercepting more sunlight to boost seed size and number. For the first time in oilseed rape, the study is also attempting to quantify this effect.
Thework stems from a Sclerotinia trial established in 2014 in Herefordshire in what turned out to be a very low disease year, says ADAS plant pathologist JulieSmith.
Despitea lack of disease we did see a yield response of around 0.22t/ha when Pictor was applied at mid flower, and around 0.29t/ha when sprayed at yellow bud and mid flower.
This prompted her to review earlier ADAS trials carried out between 2012 and 2014 on other low-disease sites. This revealed a similar average increase of 0.23t/ha over untreated plots across eight sites, close to the 0.28t/ha achieved across a further 48 BASF trials.
Thistold me these responses were real but could not be explained through disease control there was something else going on, says Dr Smith.
Thekey difference is that Pictor-treated plots retain more green leaf, she explains. The actual green leaf area index (GLAI) in 2014 trials was about 0.15larger from the two-spray Pictor program over untreated plots, an effect that persisted from the start of flowering to the green seed stage (see graph 1).The effect was seen again in 2015, albeit less marked.
Although leaves make up a relatively small amount of the canopy at this stage and appear insignificant, being low in the crop, it appears they have a key role in intercepting light and building yield, says Dr Smith.
Toquantify this effect, the ability of the canopy, particularly green leaves, to intercept light has to be measured over the key yield-building phase between mid flower and green/brown seed, she explains.
This is done by destructive sampling of plots every 7-10 days between to record the green area index of the leaves (GLAI). The total GLAI over this period is called healthy area duration (HAD). HAD is given a notional score to help researchers link the degree of greening over time with increased yield.
The2014 the two-spray Pictor programme that gave the additional 0.29t/ha translated into an increase in HAD of around 35 units. A single mid-flower spray (+0.22t/ha) delivered a HAD increase of about 25 units. (As a comparison,a single yellow bud spray (+0.11t/ha) produced a HAD score of 20 units, while untreated plots averaged around 17 units.)
However,the relationship between HAD and yield is not as straightforward as it first appears, says Dr Smith. Although it was linear in 2014 (see graph 2), it plateaued in 2015 (see graph 3).
Westill saw an increase in GLAI in 2015, although it was larger to begin with.From this already high baseline HAD level we got to the point where increasingGLAI no longer added yield.
This happened when the HAD value reached 50+. The result tells me that Pictor still did its job but the crop reached a point where it couldn’t work any harder, and couldn’t respond any more.
However,one of the 2015 trials did show Pictor-treated plots produced higher yields compared with untreated plots with the same HAD scores. This suggests that green leaf area treated with Pictor is working harder the treated canopy wasa darker green and we found the photosynthetic rate was slightly higher, saysDr Smith.
Boththese effects from Pictor (the increase in total HAD and each HAD unit working harder) could act as a buffer if plants come under stress during the key flowering period, she adds. We know OSR is not good at coping with a lack of moisture.