With the climate as unpredictable as it’s proving to be again this season, correct glyphosate choice and timing will be vital for the most reliable and effective oilseed rape desiccation, 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 go in with the glyphosate 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.
“Holding off with the sprayer will not delay combining and could make all the difference in maximising yields and oil contents from high potential crops,” Barrie Hunt advised. “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 are thick. It may also noticeably restrict output – primarily by limiting the oil that 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 crop 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 which had seeds with a 5% higher moisture content than those on the main raceme.
Under these circumstances, spray timing needs to 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 available here.
While desiccation will be more rapid and complete when undertaken at the right stage of crop maturity, Mr Hunt is adamant it will continue to demand the most effective glyphosate regime.
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 or formulations wherever possible.
He adds that the latest brands, like Roundup PowerMax and Roundup Flex, will also be valuable in helping to meet the weather challenges with their one hour rainfastness and superior performance in hot, cool, arid conditions, even where hard water is a problem. In addition, their proven drift-reducing properties are especially useful in spraying the tall OSR stands in difficult weather.