Arable growers and agronomists should now be paying as much attention to developing an integrated approach to control Rye-grass as they do Black-grass, if they are to prevent the problem escalating to a worse situation in the future.
Rye-grass can be more competitive in the crop, faster to spread and more difficult to control than the problems caused by Black-grass, warned Syngenta Field Technical Manager and grassweed specialist, James Southgate.
Speaking at Tillage-Live in Lincolnshire last week (Langworth, 14 September), he said: “Whilst herbicide control has, hitherto, been relatively successful, there has been increasing recorded and anecdotal incidences of reduced efficacy in Rye-grass populations.
“Agronomists should be looking to intervene with a robust integrated approach, if we are to better protect the chemistry options that we have available,” he advised. “Fortunately, many of the cultural measures adopted and proven to counter Black-grass are also applicable and effective to target Rye-grass too.”
Issues with Rye-grass are also widely prevalent in areas where growers may not have encountered Black-grass – or more pertinently problems with herbicide resistant Black-grass, he pointed out.
The aggressive growth habit and extensive tillering of Rye-grass can have serious effects on cereal crop yields, even at relatively low plant populations; a density of just five plants per m2 is widely recognised to cause a 5% loss in potential yields. Furthermore, it can produce high seed yields of over 5000 seeds per plant that would lead to its rapid spread.
James advocated a stale seedbed is especially important, to trigger early seed germination and kill-off with glyphosate before the crop is sown. “This season the rainfall and warm soils have been ideal for encouraging weeds to chit, and the real chance to target grassweed seedlings,” he added. “Whilst Rye-grass will germinate rapidly on the surface post-harvest, it tends to have an extended germination throughout the autumn and early winter, which growers need to address.”
Ploughing can effectively bury grassweed seeds including Rye-grass, but with a dormancy of five to eight years there is the risk of bring previous season’s seeds back to the surface. Min-till establishment techniques have potentially increased the threat from grassweeds, but James pointed out the cost implications and effectiveness of other techniques have to be considered in part of each farm’s overall cultural package.
“Delayed drilling, to facilitate greater cultural control of grassweeds, has proven extremely effective in reducing weed populations. Techniques to enhance establishment and rooting, such as cultivations; soil improvement; variety vigour and the boost from Vibrance Duo seed treatment can all help to mitigate the effects potential yield loss from later plating.”
Trials at the Syngenta Black-grass Innovation Centre, in Cambridgeshire, have highlighted the potential for a practical integrated cultural controls programme to reduce grassweed pressure, and enable the herbicide programme to work more effectively.
James advocated the best solution for Rye-grass is to follow the lessons learned from Black-grass control. That means a combination of at least three ai’s in a pre-em stack, along with early post-emergence removal to stop competitive weeds establishing and tillering.
He advised Defy as being especially effective for Rye-grass in the pre-emergence residual stack, in tank mix with a flufenacet base and at least one additional active, such as DFF.
“Sequencing with an early post-emergence application is especially useful to address the prolonged germination of Rye-grass and extend the residual control,” he added. James’ preferred option would be to use Axial targeted at grassweeds at the one true-leaf stage in the autumn, with the options to include pendemethalin in the mix.
He pointed out that the Axial mix would be especially useful where growers have delayed drilling to improve cultural control, and soil conditions could be too cool for good sulfonyl-urea herbicide efficacy with the post-em application. This approach also leaves the option for an S/U herbicide in the spring, when conditions warm up, if required.
“The aim is to remove small weeds more effectively in the autumn. This approach combines a stack of different actives with different modes of action, which could help to minimise the issue of herbicide resistance,” he advocated. “Resistance has been identified across the UK, with the enhanced metabolism mechanism most prevalent.”
Where growers had suspected reduced levels of Rye-grass control from herbicide treatments in the past, James urged they should have seed or plants tested and change their approach accordingly: “It’s crucial that we quickly build up a picture of the incidence, effect and area of each resistance mechanism.”
He cited instances where applications of the same product combination appear to give different performance – typically influenced by effects of weather conditions, seedbed and especially application technique – irrespective of potential resistance.
“Following best practice for pre-emergence application, including the maxim for Go Low; Go Slow; Get Covered, is equally important for Rye-grass treatments as Black-grass this autumn,” he advised. “With the post-emergence treatment to target small grassweeds, low and slow is still key. However, nozzle choice and water volumes will need to be different.”
