CONTROLLING WEEDS early this spring could boost winter wheat returns by more than £200/ha, according to trials conducted by Dow AgroSciences.

“Broadleaved weeds compete with the crop for water and nutrients, and can harbor insect pests,” says Stuart Jackson, its customer agronomist. “To minimise their impact it is advisable to implement effective control measures before they compete significantly with the crop, which means hitting them hard in the spring, before Growth Stage (GS) 32.

“The fact that the wet autumn provided few opportunities for pre-emergence herbicide control means that cleavers and other broad-leaved weeds will pose an increased threat this spring. Making the most of available spray days could be vital.

“Cleavers is the most competitive weed in cereals, being seven times more competitive than blackgrass and 37 times more than speedwells. Even one cleavers plant per square metre can reduce yields by up to 3% and our research has demonstrated significant yield benefits from attacking them early,” says Mr Jackson.

Dow’s trials in winter wheat between GS30 and GS39 suggest a loss of 2.2 tonnes per ha can be expected by sticking with later weed control programmes.

“The two priorities for selecting a cleavers control product are the final level of control and the speed of control. To prevent yield loss and minimise seed return, products need to deliver consistent 95%-98% control, whatever the time of year and whatever the climatic conditions,” he said.

“After GS 30-32, in addition to the level of control, speed of control is essential to prevent cleavers from smothering the crop and competing for light. Most damage to yield and profitability is done after this stage. This is also true of other broad-leaved weeds.

“Early-season applications, ie before GS32, consistently produce better yields and margin-over-inputs than late-season application. From then on cleavers really start to compete and if left untreated until the later timing we see yields really begin to drop off.”

He reckoned that for early control measures, the most effective products are based on active ingredients such as florasulam, which is included in Boxer and Starane XL.

Dow trials in winter wheat with high levels of cleavers infestation during 2007-2008 showed that Boxer applied in March at 100ml/ha produced a 2.2t/ha yield benefit (8.8t/ha) compared with a late-season product applied in May (6.6t/ha).

Earlier (2005-2006) Dow trials in a crop with fewer cleavers (37/m²) produced an untreated yield of 5.25t/ha. But, where Boxer was applied at GS30, it produced 8.96t/ha, compared with 7.16t/ha when a late-season product was applied at GS39.

“Typically 2t/ha was lost between GS30 and GS39, so we’re definitely seeing a significant yield benefit by attacking cleavers early,” adds Mr Jackson.