Addressing the increasing challenges of OSR desiccation

With the climate as unpredictable as it’s proving to be, correct glyphosate use will be vital for the most reliable and effective oilseed rape desiccation this season, stresses Roundup technical specialist, Barrie Hunt, who urges everyone to be prepared for another year of snatched spraying opportunities and challenging summer weather.

He points out that the optimum glyphosate desiccation timing for well-structured modern hybrids is significantly later than for traditional, denser pure line stands and insists that growers should not be tempted to spray too early in an attempt to hurry the harvest.

At the same time, he explains that the thick-stemmed crops of today are a lot more demanding to desiccate than those of the past due to their much higher stem volume to surface area.

“A thicker 23mm diameter stem, for instance, has nearly two and a half times the volume of a traditional 15mm stem,” Barrie Hunt noted. “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 regime.

“Holding off with the sprayer will not delay combining and could make all the difference to maximising yields and oil contents,” he added.  “What’s more, today’s pod shatter resistant varieties mean this can be done without increasing the risk of seed losses in the run up to and at harvest.

“Our work clearly shows that earlier desiccation does not mean earlier combining. Desiccating too early just means stems take longer to dry down – especially if they’re thick.  It may also noticeably restrict output – primarily by limiting the oil which is formed relatively late in seed-fill – as well as increasing the risk of red seed at harvest.”

Monsanto studies also show that the far greater branching of modern hybrids grown at today’s recommended plant populations means a much higher proportion of the yield comes from side branches which mature significantly later than the main raceme.

Indeed, crops with average populations of 30-40 plants/m2 were typically found carry 80% or more of their yield in side branches and 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 bulk of the yield is being carried, not the main raceme.  In practice , timing can only be determined by taking a representative sample of 20 pods and checking for the tell-tale change of seed  colour from green to brown using the guidelines developed by and available from Monsanto.

As well as the right stage of maturity, Mr Hunt insists that the most effective glyphosate regime is crucial for the most rapid and complete OSR desiccation.

As well as the latest Roundup brands for the most efficient activity through more reliable uptake and translocation under the particularly challenging conditions of a heavily-waxed and senescing crop, he recommends:

• Using water volumes of 200-250 litres/ha in thick or leaning crops;
• Spraying early in the day in hot weather to take advantage of higher relative humidity;
• Adjusting the boom to ensure the best spray pattern coverage of the whole crop; and,
• Employing low drift nozzles wherever possible.

With their one hour rainfastness and superior performance in hot, cool, arid conditions, he stresses that modern brands like Roundup PowerMax and Roundup Flex will be especially valuable in helping to meet modern desiccation challenges, even where hard water is a problem.  In addition, their proven drift-reducing properties are valuable in spraying tall OSR stands in changeable conditions.

“Of course, it’s also vital to use the correct dose rate and appreciate that the addition of an adjuvant cannot replace insufficient glyphosate for the job in hand,” Mr Hunt concluded.