Effective early-season weed control maximises winter cereal yields

UK - February 25, 2010



Controlling broad-leaved weeds in winter cereal crops early this spring could increase winter wheat margins by over £200 per hectare.

Cereals growers generally recognise that broad-leaved weeds compete with the crop but often don't fully appreciate their potential to adversely affect yields and profitability, or which species have the greatest 'yield robbing' potential.

"All broad-leaved weeds are bad news," explains Lincolnshire-based agronomist Stuart Jackson. "But cleavers (gallium aparine) is by far the worst, being seven times more competitive than blackgrass and 37 more than speedwells. Just one per square metre can reduce winter cereal yields by up to 3%, but most farms have far more and it can cost them 20% of the crop. Efficient control is critical to maximise profitability.

"Controlling cleavers is often left until later in the season when warm weather enables fluroxypyr to work quickly and reliably, but by then the yield potential is greatly reduced. Dow AgroSciences' trials between 2005 and 2009 highlighted an average yield benefit of 2.2 t/ha in winter wheat from early-season treatment, worth over £200/ha.

"Early control will be even more important in 2010 because many growers faced difficulties implementing autumn weed control programmes. In some areas, dry seedbeds reduced the effectiveness of pre-emergence herbicides and delayed the emergence of blackgrass, which reduced the opportunity to apply Atlantis WG (mesosulfuron + iodosulfuron). In others, the land was too wet. In many situations cleavers and other weeds have fared well, despite the extremely cold weather. The key is to hit them hard before Growth Stage (GS) 32, as most damage to yield/profitability occurs after this stage, which is also true of other broad-leaved weeds.

"To prevent yield loss and minimise seed return it is critical to choose a product which can deliver at least 95% - 98% control. Early-season applications need to control slow-growing cleavers and plants affected by autumn treatments, so they must work in a range of temperatures and conditions. After GS30-32 speed of control is essential to prevent cleavers from smothering the crop and competing for light. The most effective products for controlling cleavers before GS32 are based on the active ingredient florasulam."

"In winter wheat trials with high levels of cleavers infestation a 100ml/ha application of Boxer in March 2008 produced a yield of 8.8t/ha, compared with 6.6 t/ha for a late-season product applied in May at GS39. The message is very clear:  there is a significant yield benefit from attacking cleavers early! After GS32crop yield begins to drop off sharply if cleavers are left untreated to the later timing, with more than 2t/ha being lost between GS30 and GS39."

SUPPORTING EVIDENCE
North Lincolnshire-based Steve Portas, Masstock agronomist and Lincoln SMART Farm Co-ordinator, says that the company's own replicated trials, at Throws Farm Agronomy Research and Development Centre, where a range of treatments were applied from December 2007 through to May 2008, support these findings.
 
Barton (a highly concentrated, novel formulation of florasulam, the active ingredient in Boxer) applied in March, or two weeks' later in April, gave virtually 100 per cent control of cleavers. However, because cleavers compete for light and nutrients, crop yield was highest at the earlier timing, producing an extra 0.5t/ha due to its higher level of cleavers control in cool conditions, with good crop safety.

"It's clear that cleavers must be sprayed before growth stage 32 to avoid a yield penalty," Mr Portas explains. "Application in May, at GS37, not only gave poorer control but also a reduction in yield and specific grain weight. The highest bushel weight was almost 77kg/hl, achieved in March for the Barton treatment, 4kg/hl higher than from a straight fluroxypyr treatment in May. In economic terms, later control equates to a loss in income of £220/ha from a combination of a 2.2t/ha lower yield and reduced bushel weight."

One of Steve's customers, Elsham Hall Farms at Wrawby in North Lincolnshire, grows mainly winter oilseed rape, winter wheat, spring beans and winter rye. Manager Andy Radley says cleavers are particularly a problem on the heavy land, although numbers are gradually reducing each year in some fields due to early-season treatment

"We've been using Barton for three years and apply it much earlier than previous treatments because it allows us to spray for cleavers at GS30 when temperatures are lower. It's usually applied with a PGR, which comes with a wetter, and further enhances control of volunteer beans and large charlock.

"On several blocks of land this method has achieved an almost 100-per-cent kill of cleavers, with little or no seed returning to the seed bank. With hedge mustard a common problem in oilseed rape in some land we've taken on recently we look to use Barton to remove it in the preceding wheat crop. We're going in for cleavers anyway, so the extra cost is nil and using Barton has also reduced the amount of packaging we have to deal with."