ADAS, BASF and Dow AgroSciences have joined forces to optimise grass-weed control strategies and to provide tools to support these strategies on farm.  "It is recognised that herbicides are a critical component of grass-weed control, but correct timing is a crucial consideration as herbicide efficacy can become much more variable as weed size increases," says Sarah Mountford-Smith of BASF.

To optimise herbicide timing and performance, it is important to know how much black-grass and other grass-weeds is likely to germinate, as well as when the majority of these weeds will be present.  BASF and Dow AgroSciences are funding the necessary research to clarify both these important factors, says Sarah.

Sarah Cook from ADAS reports that the results from this year’s BASF-funded research have shown that dormancy in black-grass seed samples this autumn is high. "The level of black-grass likely to germinate depends on the weed seed dormancy. Weather conditions during maturation influence dormancy. Cultivation and drilling decisions can then be made to maximise seed losses pre-drilling and so reduce black-grass incidence in the crop."

Blackgrass dormancy

According to Sarah Mountford-Smith, following an extended dormancy more black-grass could be expected over a longer period of time during autumn 2011. "The residual activity of pendimethalin in Crystal is ideally suited to manage short or extended periods of black-grass germination. It perfectly complements the short half-life of the flufenacet. This has been evident last year where Crystal consistently outperformed Liberator (flufenacet + DFF), clearly demonstrating the value of pendimethalin over DFF. In our trials Crystal alone has given an average control of black-grass of 64%, compared with Liberator which gave 59%."

She also claims that pendimethalin at 1200 g ai/ha gave an average black-grass control of just under 40% compared with straight DFF at 60 g ai/ha at just 22%, reinforcing that pendimethalin is the preferred partner to flufenacet. "Pendimethalin is more long-lasting in the soil – after 100 days the predicted level of active remaining in the soil for pendimethalin is 64% compared with 27% for flufenacet and just 0.5% for prosulfocarb."

"The addition of DFF to Crystal provides 3 complementary ingredients for optimal black-grass control. The pendimethalin is equally active on the growing points of emerging weed shoots and on emerging roots. The flufenacet also acts on both these sites, but with 80% on emerging roots, whereas the DFF acts mainly on shoots as they emerge. In fact residual stacking of other herbicides with Crystal delivers the most consistent level of black-grass control and provides a great start to any weed control programme."

The second crucial step to achieving successful control of grass-weeds – black-grass, rye-grasses and sterile brome – is to monitor when grass-weeds emerge, so that post-emergence treatments can be applied as soon as possible when the weeds have appeared and are actively growing. To help growers and their advisers understand growth of these weeds, Dow AgroSciences is funding an ADAS monitoring scheme for a second year.

Monitoring Grass weed emergence

At five sites across England including Cambridgeshire, Worcestershire, Humberside, Kent and Oxfordshire, the emergence of grass-weeds will be monitored every week during the autumn (late September to mid-December) and in early spring (February to late April).

"This information is proving invaluable for identifying the best time to apply post-emergence treatments," says Dow AgroSciences Stuart Jackson. "Last year, it was clear that the key grass-weeds all emerged by late October and farmers who delayed treatments gained no benefit. In fact, later treatment of more established weeds is likely to be less effective."

The sites will monitor two different drilling timings - mid-September and late October drilling. "With a geographic spread of sites and two sowing timings, the monitoring project will provide a truly representative picture of how grass weeds are emerging," said Mr Jackson.

Dow AgroSciences will convey information from these monitoring sites through crop advisors. The aim will be to ensure information is available as soon as possible to optimise herbicide timing in practice.

Dow AgroSciences markets a range of products based on its innovative active ingredient pyroxsulam, which is proving successful around the world in tackling both grass and broad-leaved weeds with its contact activity. "Broadway Star (pyroxsulam + florasulam), Broadway Sunrise (pyroxsulam + pendimethalin) and our recently introduced GF-2070 (pyroxsulam + flupyrsulfuron-methyl) offer the best results when applied to small, actively growing weeds. By monitoring weed emergence, agronomists can choose the optimum timing to tackle the headache grass-weeds such as black-grass, bromes and rye-grasses," says Mr. Jackson.

To illustrate this point, Stuart reports on a programme approach for the control of rye-grass and brome. "The research has indicated that these two weeds germinate predominantly in the autumn, rather than in the spring, as had been previously thought. Our trials clearly support this premise as the best efficacy on sterile brome and rye-grass came from herbicide treatments applied in the autumn. Efficacy appeared to decline or become more variable as the weeds get bigger."

He reports that Dow AgroSciences trials have also shown that a programmed approach integrating other herbicides such as Crystal and Stomp Aqua results in the best levels of control. "Trials show that the addition of Stomp Aqua to Broadway Star lifted the level of sterile brome control to well over 90%. Starting the programme with Crystal pre-em at 4l/ha followed by Broadway Star at 265 g/ha plus Stomp Aqua at 1.75 l/ha post-emergence in the autumn at the 2 to 3 leaf stage of the brome resulted in even better control of 100%. Our trials found that the use of Crystal pre-em is marginally superior to flufenacet plus DFF pre-emergence."

Similarly a Crystal pre-em followed by Broadway Star post-em programme has given excellent control of around 98% control of rye-grass.

Stuart concludes that, irrespective of grass-weed species, a programme delivers best performance. Always use robust residual partners at recommended rates and ensure that pre-em partners are applied as true pre-ems. For contact materials make applications to small actively growing weeds and complete the programme in the autumn.