Big benefits from early-season cleavers control

UK - February 24, 2010

Controlling broad-leaved weeds early this spring could boost winter wheat returns by over £200/hectare according to trials which investigated the best time to tackle these major 'yield robbers'.

Cereals growers generally appreciate that broad-leaved weeds compete with the crop for water and nutrients, and can harbor insect pests. However, some still do not fully appreciate their potential to adversely affect yield and profitability, or which species have the greatest impact.

"All broad-leaved weeds are bad news, but cleavers (gallium aparine) is by far the most competitive, seven times more than blackgrass and 37 more than speedwells. Just one cleavers plant per square metre can reduce yield by up to 3%, but many farms have far more and are losing over 20% of their crop. Efficient control is the key to maximising profitability," explains agronomist Stuart Jackson.

"Some growers leave the job of controlling cleavers until late in the season when warm weather enables fluroxypyr (Starane 2) to work quickly and reliably, but by then the damage will have been done - yield potential will have been lost and financial penalties incurred. Over a four-year period Dow AgroSciences highlighted an average yield loss of 2.2 t/ha in winter wheat, worth more than £200/ha, which far outweighs any cost differences between the most and least-effective programmes.

"This spring, early control will be even more important than normal, because many growers faced difficulties in implementing weed control programmes during the autumn. Dry seedbeds reduced the effectiveness of broad-leaved weed control from pre-emergence herbicides and delayed the emergence of blackgrass, which reduced the opportunity to apply Atlantis WG (mesosulfuron + iodosulfuron). Consequently, in many situations cleavers and other weeds have fared well, despite the extremely cold winter, and if not treated early will pose a considerable threat.

"To minimise the adverse impact of cleavers they must be hit hard before Growth Stage (GS) 32 when they really start to compete, because if left untreated until the later timing yields really begin to drop off. Starting a broad-leaved weed control programme earlier could prevent significant yield losses and maximise the crop's agronomic/financial performance.

"The two priorities for selecting a cleavers control product are final level of control and 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 regardless of the climatic conditions. Early-season applications must control slow-growing cleavers and plants affected by autumn treatments, so they must work in a range of temperatures and weather conditions, especially when it is cold and weeds are growing slowly.

After GS30 - GS32, in addition to the level of control, speed of control is essential to prevent cleavers from smothering the crop and competing for light, as most damage to yield/profitability occurs after this stage, which is also true of other broad-leaved weeds. The most effective products are based on active ingredients such as florasulam, which is included in Boxer and Starane XL."

GO IN EARLY
"The application of Boxer to winter wheat, winter barley and winter oats will provide useful control of some key autumn-germinating weeds, such as common chickweed, mayweed and volunteer oilseed rape, together with broad-leaved weeds in cereals.

"Where Atlantis will be used in the spring it is possible to tank mix it with 50 or 75ml/ha of Boxer (florasulam. This is cost-effective, very compatible and approved by CRD, with no additional restrictions to the following crop beyond those of Atlantis.

"Where Atlantis was not used in the autumn growers should use a T0 timing of Boxer at 100ml/ha, or a T1 timing of Starane XL (florasulam + fluroxypr) at 1.25l/ha to control cleavers before GS32. If, at the T0 timing, cleavers still appear blue, increase the dose rate of Boxer to 150ml/ha or wait until active growth begins, then use 100ml/ha.

"Trials in winter wheat with high levels of cleavers infestation during 2007-2008 showed that a 100ml/ha application of Boxer in March produced a yield of 8.8t/ha, compared with 6.6 t/ha for a late-season product applied in May. This significant yield benefit confirmed the results of earlier trials in a crop with fewer cleavers (37 per square metre) which produced an untreated yield of 5.25t/ha, compared with 8.96t/ha where Boxer was applied at GS30 and just 7.16t/ha where a late-season product was applied at GS39.

"The message is very clear. There is a significant yield benefit from attacking cleavers early, before GS32! After that stage crop 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."

MAKE THE MOST OF SPRAY DAYS
In addition to the benefits of early treatment of broad-leaved weeds, Dow AgroSciences' research during the last five years has shown that an average of 24 extra spray days could have been utilised during March, April and May by applying Starane XL (florasulam + fluroxypyr) to control cleavers, compared with its fluroxypyr-only stable-mate Starane 2.

"Starane XL provides robust control independent of temperature or speed of cleavers growth, offering increased flexibility compared with the straight fluroxypyr. It should be included at 1.25l/ha in a T1 tank mix, when the sprayer is in the field anyway, ensuring that cleavers are controlled before they compete with the crop from GS32. It also controls a wider range of broad-leaved weeds than fluroxypyr and is compatible with fungicides. The co-formulation is ideal for farms where there is a threat of cleavers and big acreages to cover.

"Starane 2 is more suited as a 'late rescue' treatment if earlier broad-leaved weed control applications were missed, or where a further application of an ALS inhibitor herbicide is not permitted."