United Kingdom

Weather will determine product choice for controlling cleavers

UK - April 21, 2010

Growers must be on their guard against a late flush of broad-leaved weeds and cleavers now that weather conditions are warming up, according to crop protection specialists Hutchinsons, who operate a team of over 130 arable agronomists throughout the UK.

"Cleavers have such a negative impact on winter wheat yields that growers simply cannot afford not to control them effectively. April is generally the most cost-effective time to do so because temperatures are rising and weeds are growing quickly. However, the continued cool weather this year has created a very complex situation because cleavers and other broad-leaved weeds remain slow to develop. Correct product selection therefore becomes the key to effective control," emphasises Technical Support Manager Duncan Connabeer.

"In many of the major grain-producing areas very few growers, probably less than 10 per cent, were able to apply the broad-spectrum grass weed herbicide Atlantis WG (mesosulfuron + iodosulfuron) during the autumn. Following the prolonged spell of cold spring weather, crops in most regions have really only begun to develop during the last two or three weeks. There has been a flush of broadleaved weeds over the last 14 days, but few cleavers at present.

"The need to apply fungicides, particularly on varieties which are susceptible to the 'Solstice' strain of yellow rust, is driving farmers towards using multiple product tank-mixes. But I would urge caution so as to avoid applying too many products at the same time. This need to prioritise makes it likely that many growers will delay cleavers control until late April or May. Each situation will then need to be assessed on its own merits, products selected according to the weather conditions prevailing at the time of application and rates managed accordingly. If, as they are now, cleavers are stressed and slow-growing it is vital to use the full recommended application rates. When they start to develop more rapidly it might be possible to adjust the rate."

"Cleavers are three times more competitive than wild oats and seven times more than blackgrass, which leads to very high levels of crop losses if they are not controlled effectively," emphasises Stuart Jackson of Dow AgroSciences. "However, cleavers' prolonged emergence pattern makes it difficult to determine the best control strategy. The precise timing of emergence and balance between the autumn and spring flushes does vary, while the timing and abundance of the spring flush is difficult to predict because it varies between individual sites and from year to year. If you attempt to control cleavers too early in the spring you run the risk of missing later-emerging plants, but leave it too late and the risk is of crop damage from early weed-crop competition, potentially poorer control and significant yield loss.

"During February and March it is essential to select a product which delivers consistently high levels of control. It must take out slow-growing cleavers together with plants that have been affected by autumn treatments, and which will work in a range of temperature/weather conditions. Speed of control is not important at this stage, so products based on florasulam, such as Boxer*, are most effective.

"By April, speed of control becomes more important, so products must control both fast- and slow-growing cleavers and work in a range of conditions, especially when daytime temperatures are relatively high, but the nights are cool. It is also essential that they can be tank-mixed with others that are applied at that time. Products such as Starane XL* which combine florasulam and fluroxypyr will achieve that.

"After GS32, speed of control becomes essential to get on top of fast-growing cleavers, preventing them from smothering the crop and competing for light. They can be controlled successfully by later applications, but the longer that they are left after that time the greater will be the yield penalty. Products based on fluroxypyr again provide the best solution under fast-growing conditions because they deliver rapid control.

"A successful management strategy for cleavers, and indeed any other weeds, must address long-term population dynamics of the species and be based on a sound understanding of the biology of the weed over the course of the complete rotation. To control or reduce the cleavers population in winter wheat, for example, a herbicide must be 95%-100% effective and, just as with grass-weeds, cultural control methods can help to take the pressure off herbicide programmes."

More information on achieving effective control of cleavers is available at www.dowagro.com/uk