BRIEFING: Karl Geary
BRIEFING: Karl Geary

BASF’s Clearfield system of growing oilseed rape was launched in 2012/13 and has been doubling in area for the last three seasons, with more than 100,000 hectares expected to be planted this autumn. The company’s Karl Geary, right, explained how it works to reporter Wendy Short.

FOURTEEN Clearfield varieties of oilseed rape make up the BASF portfolio, with the range having been bred using conventional techniques to produce hybrids.

The company’s Karl Geary said the hybrid vigour helps to get the crop off to a good start and increases its resistance to common yield-robbers, including cabbage stem flea beetle.

The breeding programme has been designed to produce plants with tolerance to specific BASF herbicides, to allow the greater control of weeds. They are also resistant to any possible residue from sulfonylurea left over from the previous cropping pattern.

The varieties are tolerant to the imidazolinone group of ALS inhibitor herbicides. Key problems for oilseed rape growers in the UK include the limited timing flexibility for the control of weeds, with growers relying on the efficacy of pre and early post-emergence residual products, explained Mr Geary.

“Growers of oilseed rape face a wide germination window for broad-leaved weeds and an increasing challenge from cruciferous weeds,” he said.

“These infestations are having a negative impact on grain sample quality.

“Other problems which are common among growers are due to their dependence on seedbed conditions, coupled with their requirement for rapid crop establishment.

“There is also a heavy workload during the sowing period.”

One of the Clearfield herbicides that has been developed for the growing system is Cleranda, a product containing imazamox and metazachlor.

Designed for use on Clearfield winter oilseed rape varieties sown into all soil types and falling into LERAP category B, it is recommended for application from the expanded cotyledon stage until nine true leaves.

The other Clearfield herbicide is Cleravo, made up of imazamox and quinmerac and intended for use on winter and spring oilseed rape varieties only. It has similar timing to Cleranda and is also suitable across all soil types, with no aquatic buffer zone classification. It is recommended that DASH HC, a non-ionic surfactant, is added to both Cleranda and Cleravo, to improve leaf cover and uptake. Angled nozzles will also enhance coverage, if the crop is thick, while coarse spray patterns should be avoided.

“These two herbicides offer similar weed control and can be used as a one-shot option,” he said.

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“However, in cases where a high population of weeds are experiencing rapid growth, Cleravo will allow for an early application of a metazachlor based herbicide, in order to sensitise the weeds.

This would be particularly appropriate on farms which experience problems with crane’s bill or mayweed.

“For farms which are suffering from an infestation of black-grass, we would advise the addition of a product containing propyzamide, which will provide effective resistance management.”

Mr Geary offered some tips for ensuring that good quality Clearfield oilseed rape crops fill the barn at harvest.

“Attention should be paid to the combine’s real speed and depth; it is important to check that the drum is not running too quickly. High fan speeds should be avoided, which can lead to loss of seed, and the concave should be checked regularly, to ensure that it is clear and open. In order to reduce the mechanical transfer of seed to the following fields, the combine should be cleaned after use.”

Post advice included delaying cultivations or stubble treatments until rain had fallen, to encourage weed seed germination, and to wait until two to four weeks after harvest, to minimise the risk of secondary weed seed emergence after dormancy.

One element of the Clearfield system is that it may result in the emergence of oilseed rape volunteers with some tolerance to the Group B chemicals, he warned.

“These can be easily controlled through standard cultural and chemical means,” he said. “We also advise growers to keep detailed records of the management of their Clearfield oilseed rape crop, by adding the CL suffix to the field name, as a reminder to avoid the misapplication of Cleranda and Cleravo to non-Clearfield varieties,” said Mr Geary.


VARIETIES included in the Clearfield portfolio include DK Imperial CL, DK Impressario CL and Phoenix CL, all of which grow to normal height.

However, the variety, PX111CL, from Pioneer, is a semi-dwarf.

“One of the main cost-saving elements of the Clearfield system is time-saving in the spring,” reported Mr Geary.

“It does not require the grower to make any major economic changes to the standard agronomy practices, but only Clearfield herbicides should be applied to the specified varieties.”