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Arable

Herbicide tolerant beet a significant addition to weed management options The first ALS tolerant sugar beet varieties are in recommended list trials across Europe and a recent conference held in Malmo, Sweden saw researchers come together to present work on this new innovation. Independent weed consultant Dr Gillian Champion sent this report. Weed control in sugar beet is known to be challenging, requiring multiple applications of tank mixes of herbicides and little has changed in recent years, but a new development in the form of herbicide tolerance is soon to be introduced to this sector which could transform the way weed control is achieved. The new technology has been christened Conviso Smart and combines two ALS herbicides (from Bayer) already used in maize, with a sugar beet variety (from KWS) which has been selected to tolerate these herbicides. “We were searching for a natural variation of the gene encoding the ALS enzyme resulting in a tolerance to ALS inhibiting herbicides,” said KWS’ Dr Carsten Stibbe. “And one single tolerant individual out of 1.5 billion screened formed the basis for the development of the new system,” he commented. The system uses a mix of herbicides as an oil dispersion formulation. One of the active ingredients (foramsulfuron) works mainly on the leaves as a contact material and the other (thiencarbazone-methyl) works both via leaf and soil for a residual effect. According to Bayer’s Dr Martin Wegener (right), the herbicide is to be used at 1.0-litres/ha as a single spray

or as two treatments of 0.5-litres/ ha, approximately 14 days apart, depending on the weed emergence and growth stages.” The first varieties to come to market are likely to be slightly lower yielding than the current List leaders but this is common when varieties with new traits first appear, as was the case with BCN resistant varieties. The yield lag may last for some years but gradually the gap closes. Speakers also mentioned that, to some extent, the additional selectivity (lack of crop damage from the herbicides) will offset part of these differences.

Trials results Ms Barbara Manderyck (right) of IRBAB (Belgian sugar beet institute) presented results on behalf of COBRI (Coordination Beet Research International) a collaboration of sugar beet institutes in Germany, Belgium, the Netherlands and Denmark. A total of 12 trials were conducted in which single and split applications were compared. Other treatments within the series of trials included standard (three application) programmes and FAR programmes (five low dose applications). Some of

the Conviso treatments also included an oil. “The selectivity of the Conviso system is high,” she said, “and better than the standard treatments in the COBRI trials. But it depends to which standard you compare and in which conditions you compare them.” She concluded that timing of the herbicide will depend on weed growth stage (especially when applying the 0.5-litres/ha rate) and the key species for determining this will be fat hen. “The maximum size for fat hen using the split programme is 2-leaves whereas the maximum size for the single application is 4-leaves,” pointed out Ms Manderyck. In some situations, with continuous flushes of emergence the weed control efficacy of the standard treatments was as high as the Conviso split treatments by catching the weeds at a vulnerable stage, she added. As a herbicide group the ALS inhibitors are particularly prone to selecting for resistance and French trials examined the use of conventional herbicides in programmes, and in particular in relation to control of ryegrass. Cedric Royer of ITB (the French sugar beet institute) stressed the importance of knowing

the resistance status of the weeds in fields and in relation to results from known ‘dirty’ fields. “In these fields, the ALS product will not be the solution because some weeds are already resistant to the ALS group.” He advocated the use of ALS herbicides with existing products as a sustainable weeding strategy. “ALS plus traditional products increases efficacy, enables simplification for farmers, reduces the treatment frequency interval and the number of treatments, and prevents resistance problems.”

Hit weeds hard Dr Christophe Delye from INRA (French National Institute for Agricultural Research) echoed the resistance message and recommended hitting major weeds hard, to treat them early when they are most sensitive and at a time which most protects the yield, and to carefully monitor the creep of resistance in any minor weeds. “ALS tolerant crops are effective but fragile tools,” he said. “Do not use an ALS tolerant crop alone to control heavy weed infestations, combine it with non-chemical practices and other herbicide modes of action. Including ALS tolerant crops in the rotation must be carefully considered and avoid ‘allcontinued over...

Can I grow ALS tolerant beet now? Before ALS tolerant sugar beet can be grown, several hurdles have to be overcome. Besides requiring that the variety is registered in the country of use there are also two herbicides which have to be registered, and these each have different re-registration deadlines. Commercial production of the ALS tolerant sugar beet can begin in a few countries such as Sweden in 2018, with more to follow in the subsequent years. The UK is unlikely to be able to grow it before 2020 and varieties are currently being evaluated in Recommended List trials.

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