United Kingdom
September 4, 2015
East Anglia based agronomist Andrew Blazey of Prime Agronomy says that most of the larger farms in his area will be sticking with oilseed rape in their rotation, because of logistics and spreading fixed and operational costs. “I think that most will stick with what they know, but will have to make some tough decisions with regard to flea beetle.”
Andrew reports that, in his view, the availability of neonicotinoid insecticides in counties where a derogation has been given for use against flea beetle on rape seed has been handled well. “I look after farmers in South Suffolk, East Cambridgeshire, East Hertfordshire and Essex. So some will be in the protected counties and will benefit from these seed treatments. Last year in east Hertfordshire around 20% of the rape was lost. We can agonise over standing power and disease resistance but in some areas it is the availability of neonicotinoid insecticides that clinches seed decisions this autumn. Seed treatments are important as flea beetles are suspected to be resistant to pyrethroids.”
He says that last year half of the rape was hybrid, namely Extrovert, Incentive, PW21, Harper, and half conventional, Charger, Cabernet, Trinity, Vision and Picot. “I can foresee a move back to more conventionals, mainly based on seed costs and the fact that you sow more plants m2 of a conventional variety.
“In rape the major weed problems are black-grass, cleavers, mayweeds, Shepherd’s purse, sow thistle and hedge mustard. Cleavers and black-grass are the driver weeds. In the past I have used a pre-emergence herbicide based on metazachlor + quinmerac, with or without clomazone if cleavers or hedge mustard are a particular problem. I am moving away from this strategy, because of flea beetle and the possibility of the crop being damaged or even lost. I don’t want to spend on a pre-emergence treatment and then the crop not make it. A less risky approach is to establish the crop, wait for it to have 2 leaves and then use 500 gm a.i./ha of metazachlor to start the black-grass and broad-leaved weed control. If necessary, a fop or dim is applied for volunteers and then AstroKerb® is applied post-emergence later in the autumn. The opportunity to use Galera® (clopyralid + picloram) in the autumn has been taken away from us now, so with the exception of high numbers of cleavers, AstroKerb will do what Kerb® and Galera would do and is less expensive.”
“In my experience AstroKerb worked well last year. It did all that it was expected to do; in particular it did a good job on mayweeds and poppies. It does take a long time to work however,” Andrew warns.
Peter Waite of Dow AgroSciences explains that AstroKerb can be used from the 1st of October up to before the 1st of February. “Soil temperatures at 30 cm depth need to be down to at least 10ºC and falling. Good levels of soil moisture help distribute the herbicide in the top few cm of the soil. Germinating grass-weed seed should not come from any deeper than 5cm, as the black-grass would be germinating from below the zone where the propyzamide concentrations are high enough to give good levels of weed kill.”
“If application conditions are right, farmers can expect levels of black-grass control from AstroKerb frequently in excess of 90%, a level that very few herbicides are currently achieving in any other crop,” he says.
Peter reminds growers that careful Stewardship of residual herbicides in rape is vital to ensure long term availability of these herbicides.
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