Don’t gamble with black-grass control

UK - October 15, 2012

Dow AgroSciences are advising growers not to gamble with their black-grass control in oilseed rape this year, especially as this weed is at higher levels following last years poorer control in wheat and also because of its prolonged germination this autumn. They are also warning growers of the importance of protecting water from potential contamination by residual herbicides, which will be compounded by mixing or sequencing residual herbicides.

The ADAS/BASF weed model has confirmed that black-grass dormancy is high this year and this means that black-grass will be germinating over a much longer period. This will mean that you need an effective and long lasting residual herbicide such as Kerb Flo 500 used at its new full rate of 1.7 l/ha applied at its optimum timing, says David Roberts of Dow AgroSciences.

“Many arable rotations are relying on rape to break the grass-weed cycle and, with high weed pressure this autumn plus later developing rape crops, a holding position is just not good enough. Using less effective products earlier at lower dose rates in warmer conditions isn’t man enough for the task in hand. You could also run the risk of increasing water problems as some residuals such as carbetamide are very soluble. I would also question the technical argument for earlier black-grass control, when it is volunteer cereals that are the early and more competitive weed issue in oilseed rape. Not many growers have had the opportunity to use stale seedbeds for volunteer cereals and, with the dreadful conditions at harvest, volunteer cereals are being seen at much higher levels this year. They are the priority weed to remove now with a straight forward contact fop or dim graminicide, to be followed up in November with Kerb Flo 500 for black-grass,” says David.

David reports that decades of trials and very wide field experience across the UK clearly demonstrate that using full-rate Kerb in November onwards gives the most reliable and most persistent control of black-grass year after year.  “Investments made in refining best advice mean that Kerb is much more reliable than it was, say ten years ago. We are seeing consistently high levels of black-grass control, much higher levels than any competitor residual.”

Black-grass trials show conclusively that Kerb Flo always outperformed carbetamide at any dose rate. The full dose rate of Kerb Flo consistently gave around 85% control of black-grass, whereas a full dose rate of carbetamide at 3.5 kg/ha gave 60% control and can be often as low as 30%. A second conclusion was that a tank mix of Kerb Flo with the contact herbicide Laser (cycloxydim) always gave control levels over 92%. In other trials a sequence of Aramo (tepraloxydim) and Kerb Flo gave 97% control of black-grass. Here the contact herbicide provided the “pre-treatment”, controlled the cereal volunteers and enhanced the overall level of weed control. With regard to contact graminicides, Kerb Flo 500 can be mixed or used in sequence with Laser and it can be used in sequence with Aramo.

David advises growers to focus on getting the best out of Kerb Flo 500 by timing its application correctly.  “To optimise Kerb’s performance, there are three areas to consider – temperature, soil moisture and weed seed depth. Soil temperatures need to be cooling - around 10ºC and falling, so that longer persistence is achieved throughout the germination period, particularly important this year. We are not there yet but it is usually around mid November. Good levels of soil moisture are needed to help the herbicide distribute evenly in the top few cms of the soil and facilitate uptake by the target weeds. Soil moisture deficit needs to be less than 50mm and falling. A rough guide to the soil moisture is 80% field capacity, before drains are flowing; soils must not be waterlogged or saturated. Care must be taken to avoid any risk of contamination to water and importantly all aspects of good Stewardship applied. With regard to weed seed depth, seed should not come from any deeper than 5cms as the black-grass would then be germinating below the zone where the Kerb Flo 500 concentrations are high enough to give good levels of kill. If application conditions are right, farmers can expect percent of black-grass control in the high 90’s, a level that very few herbicides can achieve.”

He also reminds growers that Kerb Flo 500 is a top class liquid formulation which is easy to use. “No problems with awkward powder formulations that don’t mix, just open up the non-foil sealed pack and pour. When the spray window is open, growers can be assured that Kerb Flo 500 will be quick and easy to apply with even fewer cans to dispose of.  For example, on a farm where 100 hectares of oilseed rape needs to be treated, you only need open and rinse 17 cans of Kerb Flo 500 10 litres, compared to 42 cans of 400g/l propyzamide in 5 litre cans.”

Dow AgroSciences have always taken Stewardship of propyzamide seriously. “We are very aware of the potential risk of residual herbicides getting into drinking water. With more oilseed rape being established with a subsoiler or drop leg, the potential for leaching is greater. If any of herbicide, including propyzamide or carbetamide, is found in water, then we could easily see additional mandatory measures such as dose rate reductions or restricted application timings being enforced or, the worse case scenario, a complete ban. Without herbicides such as propyzamide, growing a profitable oilseed rape would be very difficult, if not impossible.”

David argues that if you can achieve the same weed control using less residual at its optimum position and timing in the overall programme, it makes sense to go down that route and reduce any risk of water contamination.  “Maintaining careful Stewardship of residual herbicides in rape is vital to ensure long term availability of these herbicides and every manufacturer, agronomist and grower should be taking their responsibility seriously.”

New Kerb Flo 500 contains 500 g/litre propyzamide formulated as a suspension concentrate and packed in a new non-foil sealed 10 litre pack. In oilseed rape it is recommended at a dose rate of 1.7 l/ha for difficult black-grass situations. It is recommended at 1.0 l/ha or 1.4 l/ha to control annual meadow-grass, rye-grass, wild-oats, brome and volunteer cereals and a wide range of broad-leaved weeds including chickweed and speedwells. In oilseed rape Kerb Flo 500 has a wide window of application of four months, from the 1st October and when the crop has at least 3 true leaves, through to the end of January.