February 15, 2013
Care in Winter OSR Decision – Making
Don’t give up on any winter oilseed rape too early this spring. Judge each crop field-by-field, area-by-area. Take account of weed as well as crop status in your decision-making. And base your agronomy on what is below the ground as much as what you can see.
This was the timely advice from senior Agrii agronomist, Andrew Richards at the company’s Brackley demonstration farm last week (February 8) where Lawrence and Anthony Bonner currently have 160 ha of winter rape as variable as any in the country.
Around 40% of the crop on the clay loam over brash farm is in reasonable shape, with the rest very small, backward and in many cases questionable.
“Vigorous hybrids like Excalibur and DK Excellium have been a real boon this year as the bulk of our crop couldn’t be drilled until the second week in September,” Andrew Richards pointed out. “But even these have struggled in the battle against slugs and pigeons in wet ground which went cold very much more rapidly than normal.
“Add to this the fact that the persistent wetness prevented much of crop receiving any propyzamide and there’s far too much black-grass and chickweed about for comfort in many places. Thankfully, though, pre-ems did a good job in our more backward crops so these are relatively weed-free.”
Where weeds present particular problems in their reasonably established crops, Andrew Richards will be using an early dose of Crawler (carbetamide), followed by Galera (clopyralid + picloram) or Fox (bifenox) to deal with cleavers and cranesbill. However, Crawler cannot be used on waterlogged soils or after the end of February.
“These restrictions, the fact that all three herbicides can be harsh on crops and very limited effective alternatives, mean weed problems in small and backward crops may be the key factor in any decision over their future,” he suggested. “The fact that they haven’t had either propyzamide or carbetamide, of course, leaves the greatest flexibility for replacement cropping.
“Our backward crops will be receiving Nutri-Phite PGA through the sprayer as soon as we can get on the ground to stimulate root development and help address the problem of very low P availability with poorly rooted crops in cold, wet ground.
“Then we’ll get on with 40-50 kg/ha of N in a sulphur compound and delay any decision on their viability until mid-late March. We may not have the leaf area yet, but we’ve got 15-20 plants/m2 and a reasonable 6” of root in most cases. Providing they’re well enough rooted, we know we can get much better yields from vigorous hybrids with only 12 plants/m2 than we can from spring rapes. So we’re giving them every opportunity to recover if the season relents. After all, we’ve invested a good £70/ha in them to get them to this stage. And 3t/ha is a much healthier proposition at £400/t than it ever was at £250”
For their reasonably established crops with a decent leaf area, 30-40 plants/m2 and a good 1-2 cm diameter tap root, Andrew Richards will be delaying the first dose of N and S until they’ve dealt with the grass weeds (to avoid feeding them as well as the OSR). Nutriphite PGA will also be applied to encourage root development, together with foliar manganese and boron to correct specific imbalances.
To keep on top of phoma infections wherever they’re evident he’s also planning an early spring prothioconazole spray, pointing out that small plants are acutely vulnerable to stem canker development as the fungus has such a short distance to travel from leaf to stem.
“Thankfully, our best looking crops are DK Excellium which has excellent stem canker resistance,” noted Andrew. “But it’s still better safe than sorry. Especially as we’ll be managing them for a good 4.5-5t/ha and they’ll need a decent bit of input to develop a good canopy from their current 0.75 GAI.
“Although regular organic matter additions mean N-Mins on these fields currently stand at 110 kg/ha, we need to account for the fact that the cold, wet conditions mean lower levels or microbial activity so only around 30% of this is likely to be immediately available to the crop,” he added.
And what of any land currently under OSR which doesn’t make the grade in March ? It will be too late for beans; Andrew and Laurence have ruled out both spring OSR and peas from past experience; and both consider fallow a very last resort.
Their alternative is a crop of Westerwolds ryegrass. This will provide at least one if not two cuts of silage for the farm’s beef rearing enterprise before being ploughed out to give a good timely wheat entry. Now that’s the sort of extra value that’s really useful from a cover crop.