Dow AgroSciences are advising growers to check which of their oilseed rape crops are infested with weeds that reduce yield, complicate harvest or contribute to admixture penalties and be ready to treat them with the herbicide Galera.
Variable results from pre-emergence residual herbicides applied in autumn 2009, combined with open crop canopies after the severe winter weather, have resulted in oilseed rape crops with high levels of broad leaved weeds remaining – difficult weeds such as sow-thistles, thistles and cleavers. Spring herbicide treatments need to be well-planned to allow these crops to reach their true potential, according to Rene Pollak of Dow AgroSciences.
"Cleavers are the most aggressive broad leaved weed competitors, impacting yield and, just as significantly, decreasing final percentage oil content. As yield robbers, mayweeds, groundsel and thistles, follow closely behind. All these weeds impact harvesting flexibility and carry potential admixture penalties," he says.
With such obvious populations of broad leaved weeds present in oilseed rape crops, the temptation is get out early and treat with Galera, but caution is required. To optimise performance, stable air temperatures are required of at least 6oC and rising, but preferably 8oC or higher. The warmer and more stable the conditions, the better the results are likely to be. Warm days and cold nights (high diurnal variation) are likely to give poor results, particularly against cleavers, advises Rene.
Rene Pollak also points out that wet leaves could also be an issue with which to contend. "For best results Galera needs six hours drying time after application to a dry leaf. A breeze to dry the plants off in the morning and a planned application during the warmest part of the day is the approach most likely to give good results."
"That’s why having the appropriate fields identified and the required amount of Galera on farm and ready to apply is so important. With the cut off of flower buds visible above the crop canopy, the opportunities to spray can be limited, but the benefits of ridding your crop of these damaging weeds will pay dividends now and at harvest," concludes Rene.
He summarises the key points to remember.
1. Identify in advance which fields will benefit from treatment with Galera
2. Make applications as soon as conditions are suitable
3. Specifically for cleavers, avoid applying Galera until large variations in day/night air temperatures have passed (i.e. no frosts)
4. Make applications to a dry leaf and allow for 6 hours of drying
5. Control of cleavers is maximised when applications are made just before crop canopies close.
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.
