Weed control in oilseed rape this spring will not only rid the crop of direct competition, but often more importantly reduce the cost and aggravation of harvesting difficulties and the risk of higher admixture penalties.
"There are three weeds that are of major concern in this respect: cleavers, mayweeds and thistles (sow and creeping thistles). Their impact is not just as competitive weeds in their own right, but they complicate and make harvest longer and can contribute to admixture which will cost," according to Rene Pollak of Dow AgroSciences.
"Cleavers are the most aggressive broad-leaved weed competitors, impacting yield and decreasing final percentage oil content. Just one cleaver per metre squared can cause 5% yield loss. They continue to grow late into the season, climbing over the crop and can mesh with the crop at harvest, clogging or slowing down the combine. Both crop and cleavers can be harvested together, increasing the need for dressing and drying and increasing weed seed in admixture. All of this will cost time and money. For example a 2% admixture in a £250/tonne crop will be subject to a £18/tonne penalty and a 4% admixture a £37/tonne penalty," he says.
Similarly mayweeds also grow late in the season and may lead to uneven pod ripening and also seed in admixture.
Mr. Pollak explains that sowthistles are unsightly in the field and will make desiccating the crop prior to harvest difficult and more expensive. "The gummy sap in the stems clogs up cutter bars whilst the fluffy seedheads clogs up the combines radiators. You may need to return to the yard to clean up combines and tractors with an air compressor. Such action also costs money. John Nix Farm Management Book contract values show that a couple of hours a day down time equates to £160 of contracted combine time."
"The most effective way to control these weeds is an application of Galera, but timing is critical and the window in which it can be applied is fairly narrow," advises Rene Pollak. "To optimise the performance of Galera, stable air temperatures of 6oC and rising are required, but preferably it should be 8oC or higher. The warmer and more stable the conditions, the better the results are likely to be. Warm days and cold nights are likely to give poor results, particularly against cleavers."
Rene also points out that, despite the recent cold weather where many rape crops look very stalky with leaves either stripped by pigeons or lost to frost damage, the plants have established very well, with good root systems and an even establishment. "As the length of daylight increases and temperatures warm, these plants will grow very rapidly. It is important to plan applications of Galera now as the cut off stage for applications will be short this year. Once flower buds are visible above the crop canopy no further applications should be made."
Galera (267 g/L of clopyralid and 67 g/L of picloram formulated as a suspension concentrate) is recommended post-emergence in all varieties of winter oilseed rape for the control of broad-leaved weeds including cleavers, mayweed, sow-thistles and thistles. It can be applied from the 4 leaf stage of the crop up until before flower buds are visible above the crop canopy. It is recommended at a dose rate of 0.35 l/ha and is compatible with a wide range of graminicides, insecticides and fungicides. It is packed in a 1 litre container.
