Don’t give up on backward oilseed rape yet
Oilseed rape establishment and growth may be painfully slow and slug damage acute in many parts of the country, but even the most backward crops shouldn’t be written off just yet, according one expert.
Vigorous hybrids, in particular, have picked-up noticeably as waterlogging pressures have eased in the past two weeks. And both trials and experience show that spring populations of well below 20 plants/sq m can deliver yields comfortably over 4t/ha.
“There couldn’t be more contrast with the well-developed canopies we had on our sites last season,” said Agrovista technical manager, Mark Hemmant, at a Growcrop Gold Discussion Group meeting at Harper Adams University College. “But vigorous varieties like the DK Extrovert we’re growing this year are getting their feet down well despite the wetness on even our least promising sites. So, providing we keep our management up to scratch and don’t have a very cold winter it looks like being well-placed to develop strongly in the spring.
“Three years of our field-scale studies show we get the best performance from 20-30 established plants/sq m in the spring. With the 50cm row width we’re working on as our standard these days, this means 10-12 plants/m in the row.
“For drilled crops our work with very low seed rates, however, also shows much lower plant populations than this can deliver every bit as well. Last year, for instance, across four sites we averaged 4.50t/ha from mean populations of 14.5 plants/sq m against 4.57t/ha from a more optimal 26.5 plants/sq m.
“With ground conditions as wet as they remain, there’s nothing most growers can do to reliably replace a crop this side of 2013,” said Mr Hemmant. “So they might just as well wait until early February and see how it develops.
“What they cannot afford to do in the meanwhile, though, is abandon it. Especially not in the face of the serious phoma infections we’re seeing this season, not to mention grassweed levels and the pigeon threat. Backward crops really need nurturing if they’re to pull through. Small, slow-growing plants can easily be wiped out by phoma leaf spot as well as pigeon grazing. And they’re highly vulnerable to weed competition.”
Mr Hemmant advised all those not growing a highly phoma-resistant variety to apply an autumn spray – two, if necessary – immediately the 10% threshold is reached. While DK Extrovert and other particularly resistant varieties offer more leeway in timing, he still suggests as least one spray given the scale of the threat and the extra value of early light leaf spot control.
To this he recommends adding the amino acid stimulant, Terra-Sorb Foliar to boost root development, following the 20% increase in root weight seen from autumn spraying in last year’s trials.
With the particular sensitivity of smaller, shallow-rooted crops to propyzamide, he favours an early dose of low rate carbetamide to hold grassweeds at bay. This will allow as much time as possible for root development before the main winter herbicide is applied.
“Since early N will be particularly important with backward crops in the spring, it will be vital to have sufficient stocks on farm,” Mr Hemmant added. “Transport shortages and ordering delays mean it will not be a year to not rely on just-in-time delivery.”
