Withoilseed rape drilling now complete and in some areas crops at 45 leaf stage,combined with low black-grass dormancy, oilseed rape growers should grab theopportunity to begin carbetamide-based black-grass control programmes asquickly as possible.
Theaim must be not only to maximise control levels but also to help protect theactives future by minimising the risk of water pollution by adopting a newsequence of control measures this year.
Earlierspraying targets smaller, shallow-rooted, actively-growing black-grass, pointsout Jonathan Brooks, technical manager at Makhteshim-Agan UK.
Theweed at this growth point is more vulnerable and susceptible to the effects ofthe herbicide, in essence applying the lessons learned in cereals to theoilseed rape crop, he says.
Applicationaccuracy is also greater than it would be at a later stage because spraying istaking place when the soil is accessible through an open canopy, rather thanbeing applied in a more closed crop which shelters more of the target weeds.
Theinherent physico-chemical characteristics of Crawler (carbetamide) means thatit can be applied much earlier than traditionally used, resulting in a higherpercentage control of black-grass, explains Mr Brooks.
Becauseit readily dissolves even in low moisture situations, and has a low affinity toorganic matter, it transfers from the soil into even low levels of water beingheld in the soil profile and starts to control the black-grass when it is atits most vulnerable, even under quite dry soil conditions. Thesecharacteristics also allow it to move through the soil profile and controlblack-grass emerging from depth.
Butthe other key benefit to be gained from earlier application is thesignificantly reduced risk of the active ingredient reaching watercourses,points out Mr Brooks.
Sprayingat this stage of the growing season, as long as the weather remains relativelydry, can help to protect carbetamides future, as the peak periods of rainfalland high water content soils that occur later in the season will be avoided,and the active will have more time to break down before the weather becomeswetter. With low rainfall across much of the country in September, and fewfield drains flowing significantly as a result, now is the best time forapplication.
Carbetamideis being detected in drinking water at levels exceeding those approved, and asa result is under scrutiny, Mr Brooks explains. With 40% of the national OSRarea affected by black-grass, losing the ability to control it through productrestriction or tighter regulation could cut yields by over 1t/ha and reduce thenational OSR gross margin by 43%, according to ADAS figures. The rotationaleffect could also reduce the gross margin in winter wheat by 40%.
Soits essential that we do all we can to protect what is an invaluable grass weedcontrol tool in oilseed rape, with no known black-grass resistance to it, and awide range of possible tank mixes. Using it in the correct manner, in the rightconditions and at the right timing as part of a new sequence, will help toprotect its future by ensuring that the industry is doing as much as possibleto keep it out of water.
Bestgrass weed control results are achieved through a sequence of 2.5kg/ha Crawlerat the 35 leaf stage of the OSR crop, before mid-October, followed by 2.1litres/ha of Cohort (propyzamide).