Clear Thinking on Weed Control
The need for the most targeted and cost-effective autumn broad-leaved weed and volunteer control without any risk of setting-back OSR establishment is driving a dramatic increase in the uptake of the Clearfield production system across the country.
To such an extent that the latest industry figures show the area planted to varieties bred to be resistant to imazamox herbicides has more than doubled in the past year to some 30,000 ha. What is more, it’s predicted to do so again in the coming year as existing growers build-on their success with the latest high performance Clearfield varieties and more growers appreciate the value of what is fast becoming a mainstream system.
“Effective weed control is vital to winter OSR profitability,” explained Frontier crop production specialist, Paul Cartwright. Difficult-to-control weeds like charlock, runch and hedge mustard can make profitable rape growing almost impossible. Their growth can seriously interfere with harvesting. And we need to guard against any risk of them elevating erucic acid levels in rapeseed at harvest.
“But the weed control challenge doesn’t end here. It’s important to prevent OSR volunteers from compromising the most productive canopies; to limit autumn competition from a wide range of other broadleaves and cereal volunteers; and to hold grassweeds back until soil temperatures decline enough for the best propyzamide activity.
“Importantly too, we only want to control the weeds that actually need controlling and don’t want to do anything that gets in the way of the vigorous crop establishment so crucial to combatting early flea beetle and slug pressures, not to mention less-than-ideal sowing conditions. We also need to have the greatest flexibility in our early crop management.”
This makes the post-emergence autumn weed control focus of the Clearfield system so valuable, according to BASF agronomy manager, Clare Tucker who points out that it allows weed control to be undertaken only once crops have safely developed to 2-4 true leaves.
“As well as excellent activity against broad-leaved weeds in general and both cereal and non-Clearfield OSR volunteers, Cleranda, Clesima and Cleravo will control any bromes, wild-oats and ryegrass present at spraying,” she said.
“They need to be applied at between one and four true leaves of the weeds, ensuring good spray coverage and sufficient leaf drying time. But within these essentials they provide great early season flexibility and widely compatible for tank-mixing.
“The imazamox resistance of Clearfield varieties also protects against any SU residues from previous cereal crops having a negative effect on establishment,” she added. “And the vigorous, high performance varieties now available make the whole system that much more attractive.”
The first full set of independent trials assessing the UK performance of Clearfield oilseed rape undertaken by NIAB-TAG last season has highlighted the particular performance abilities of today’s leading CL varieties.
Topping the three-site average with gross outputs of 108% and 107% of the very reasonable 3.54 t/ha trial mean in a difficult OSR year were DK Impression CL and DK Imperial CL, comfortably ahead of the six non-Dekalb varieties tested.
These two varieties also demonstrated their consistency by out-performing all the others at both the highest and lowest yielding sites. At the same time, their average oil contents of 44.3% and 44.6% were noticeably ahead of the rest.
As well as their leading performance in the independent trials, DK Impression CL, DK Imperial CL and newly-introduced DK Impressario CL from the same stable stand out for their combinations of other valuable Dekalb yield-protecting traits. These include vigorous establishment and strong standing power with double phoma, good light leaf spot and pod shatter resistance – the latter being particularly important in minimising Clearfield volunteers.
Keeping on top of the charlock and hedge mustard that were previously threatening the viability of his OSR has become a simple matter for David Lord at Earls Hall Farm on the Essex coast near Clacton-on-Sea, thanks to the Clearfield system.
Problem fields are now routinely sown with Dekalb CL varieties, 32 ha of which averaged
3.6-3.7 t/ha last harvest against 4.1t/ha from the best field of rape on the farm. Treating them with a single autumn application of Cleranda has proved to be cost-neutral thanks to the savings possible in other herbicides, he notes.