Growers are being urged of the need for vigilance in this season’s spring barley to ensure a timely start of post-emergence weed control strategies over the coming weeks. Rotam technical manager James Anderdon is warning that the favourable seedbed conditions at drilling, combined with recent changeable weather conditions, could risk ill-timed herbicide applications and subsequently difficult to control weed populations. "Planting has been off to a good start, particularly in the midlands and south east. The considerable period of reasonably fine, dry weather has enabled the majority to complete drilling before the end of March, planting into good seedbeds without delay," explains James. "But recently we have seen considerably more rain, particularly in the south east. This, together with much warmer soil temperatures compared with this time last year, means conditions are likely to stimulate a scenario of strong crop growth and rapid weed emergence. "There is a risk of weeds coming through more strongly than usual," he notes. This current period of unsettled weather comes at a time when crops are still at risk, explains James. "They are still to pass the stage of growth where they are able to out-compete arising weed populations. He therefore advises vigilance to time herbicide treatments correctly and to be ready to treat post-emergence, considering the use of a sulfonylurea as either a straight or in a mix," notes James. "Sulfonylurea herbicides based on metsulfuron, such as Savvy Premium, Ergon and Boudha offer attractive treatment options with a high level of effect against a number of key target species including spring germinating mayweed and polygonum species such as knotgrass, redshank and bind-weed." According to James the timing of post-emergence applications are paramount to deliver cost effective control of key weed species at their most susceptible growth stages. "Too late and the effectiveness of the treatment will wane as weeds develop reduced sensitivity. But too early and you risk later emerging weed flushes which miss the treatment entirely," he explains. "Treatment timing will be largely dictated by the species present which will have varying rates of growth. Applications to weeds at the 4 leaf stage up to the 6 leaf stage is ideal. Beyond this timing, the sensitivity of some weed species will be lost, and they become more difficult to control."