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Early weed control can help with the flea beetle challenge With oilseed rape growers looking to increasingly squeeze their input costs on crops across the country, agronomists are rightly concerned that both pre- and post-emergence herbicides are used to their optimum efficacy and that money is not wasted on crops that either are not viable or do not have enough yield potential. Independent AICC consultant, Richard Cromie (right) of Hampshire based Crop Management Partners is adamant that caution must be exerted when planning an autumn herbicide strategy, where costs can run away if crops are not managed appropriately. “I actually aim to spend as little as possible,” he explains. “With the constant threat of flea beetle, not only at emergence but at the larval stage in the spring as well, the need to balance weed control with expenditure can often be a difficult

task. “The aim is get crops as quickly as possible to the three-leaf stage. To ensure this happens, the plants don’t need to be put under extra pressure and some mixes of herbicides, either applied pre- or early postemergence, can induce a lot of stress and leave the emerging crop exposed to further pest damage, or if the active ingredients are ineffective due to weather or soil conditions, weed competition.” In order to mitigate the effects of early herbicide-induced crop stress or even damage, Mr Cromie advocates a single pre-emergence application of Centium 360 CS (clomazone), which is highly immobile in soil and less likely to leach out, compared with other products. When applied at 0.25-litresha, this level of active ingredient is sufficient he believes, to control major competitive weeds such as cleavers and hedge mustard, as well as having additional, good broad-spectrum suppression of

annual meadow grass, chickweed, shepherds purse and fool’s parsley. Clomazone can also suppress blackgrass, sensitising it for follow-up applications. “The application of Centium 360 CS has little or no effect on emerging crops and that is vital if the flea beetle situation is going to be managed. Growers may see some cosmetic (chlorotic) bleaching of leaves, especially on overlaps, but that will grow out,” Mr Cromie explains. “We have been using the product very successfully for many years now and the bleaching, although visible, has never affected the crop’s ability to yield.”

Cost-effective Centium 360 CS works by inhibiting photosynthesis and the same symptoms can be identified on target weed species which lead to plant death, whereas in the crop the symptoms are transient and do not cause a yield penalty. “I find that a cost-effective dose of clomazone at this stage is sometimes all that’s needed,” he says. “Occasionally I might follow up

with an application of metazachlor in situations where there are populations of black-grass that need controlling, but generally it’s enough. If the crop then fails because of whatever reason, you haven’t spent the earth on it.” Mr Cromie has also had good results using companion crops to assist the rape establishment on certain farms, with clover, buckwheat and white mustard being the main species that ‘bank’ nutrients for the crop to use later on in its growth stages, although other anecdotal benefits have included reduced slug and flea beetle pressure. “Generally, most companion species we use have also proved to be tolerant to Centium 360 CS,” he adds. “This is even better news as they can develop properly, equally benefiting from reduced weed competition and allowing the emerging rape to be protected. We look to drill the rape approximately 7–10 days after the companion crop and to be honest, the results have been very encouraging and Centium 360 CS now appears to be an integral part of that strategy.” ■

Imagine… An autumn sown break crop that can deliver a gross margin of over £580 per hectare Imagine… A viable autumn sown alternative to Oilseed Rape that doesn’t suffer from flea beetle Imagine…

Winter Linseed For more details call Premium Crops on 02392 632883 a division of Cefetra Ltd

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Farmers Guide July 2019