Going in too early with an oilseed rape desiccant can hit the bottom line, advises Monsanto’s Barrie Hunt.
Holding-off on pre-harvest glyphosate spraying until the ideal timing can pay dividends for most oilseed rape growers at little or no additional risk.
That is according to Roundup technical specialist Barrie Hunt, who says too many growers are cutting their crop profitability for absolutely no gain by desiccating at least a week too early.
He says: “Each day of seed filling lost is known to reduce seed yield by 1-2%. So spraying a week before the optimum timing could mean losing half-a-tonne or more from a 4t/hectare potential crop. With most oil accumulated towards the end of seed fill, earlier-than-ideal spraying can seriously compromise oil percentages too. And excessive red seeds can further add to the cost.
“The fact that the main difference between the top and bottom yielders across last year’s entire YEN competition was an extra 10 days between flowering and desiccation underlines the importance of sufficient patience here,” adds Mr Hunt. “All the more so, as spraying too early will do nothing to bring forward the harvest. In most cases, crops will just take longer to dry down – especially if they’re thick.”
Sufficient patience in pre-harvest spraying is particularly important with well-structured, modern hybrids as Monsanto studies show their optimum timing for glyphosate spraying desiccation is significantly later than traditional, high plant population pure line stands, Mr Hunt adds.
This is because the greater branching of high output hybrids grown at today’s recommended plant populations means a much higher proportion of their yield comes from side branches which mature significantly later than the main raceme.
Crops with average populations of 30-40 plants/sq.m were typically found to carry 80% or more of their yield in the side branches and have seeds with a 5% higher moisture content than those on the main raceme.
“Under these circumstances, spray timing must be based on assessments of pods from the area of the crop where the lion’s share of the yield is being carried, not the traditionally recommended main raceme,” says Mr Hunt.
“The most effective glyphosate regime is equally important for the most rapid and complete crop ripening too because thick-stems are a lot more demanding to desiccate than those of the past due to their much higher stem volume to surface area; especially where they have profited from stay-green chemistry at flowering or late nitrogen for pod fill.
“A thicker 23mm diameter stem, for instance, has nearly two-and-a-half times the volume of a traditional 15mm stem. Overall, there’s a good 50% more internal plant tissue to deal with for every extra square centimetre of surface area, placing particular demands on the glyphosate.
“Unless the weather is ideal for rapid, even ripening, effective harvest management with glyphosate invariably allows earlier and more efficient combining than natural drying as well as giving good control over what can be very substantial weed burdens within and beneath the canopy,” he explains. “It can also be invaluable in evening-up crops with the sort of variability we so often see. But it has to be done right.”
In practice, glyphosate timing can only be determined by taking a representative sample of 20 pods and checking for the telltale change of seed colour from green to brown using the guidelines developed by Monsanto.
As well as using modern, high activity Roundups for the most reliable uptake and translocation under the particularly challenging conditions of a heavily-waxed and senescing crop, Mr Hunt recommends:
“Of course, it’s vital to use the correct dose rate and appreciate that the addition of an adjuvant cannot replace insufficient glyphosate for the job in hand,” adds Mr Hunt.
“For the fastest, most trouble-free and productive harvest, it’s also important to start combining only once stems as well as pods are fully fit. That way you get the best flow through the combine for the most efficient threshing and the easiest-to-deal-with trash.
“This fundamentally depends on the weather and may be up to three weeks after spraying under some conditions. So patience is again a virtue here.
“With all you’ve invested in the crop over the year and margins as tight as they can be, it’s important you don’t allow workload pressures and the overwhelming desire to get harvesting – spurred-on by neighbours out with their sprayers or combines – to compromise performance.
“Making a conscious effort not to desiccate or combine too early will definitely pay dividends. Shatter-resistant varieties and pod sealants can markedly reduce any extra risk of seed losses this may entail. They may even give you the flexibility to combine quality wheat ahead of your OSR as is often the case in continental Europe.”