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Wet Weather Demands Revised Oilseed Care Strategy

Date Added: 04/09/2008

The lessons learned over the past two growing seasons have shown that crop management techniques must be adapted in order to counteract changing climatic conditions. And the wet weather conditions going into this autumn will make it even more essential that crops are given the proper level of care if they are to achieve bumper yields next summer.

The wide variation in soil and climatic conditions that UK farmers have experienced over the past two autumns has given rise to two very different crop establishment periods. In 2006, most oilseed crops were sown in near perfect conditions, with plants growing very quickly and establishing vigorously prior to winter. In contrast last year, many crops did not emerge until early October due to overly dry soil conditions which delayed germination.

This year, the exceptionally wet conditions across the UK have resulted in the delayed drilling of many crops, with some farmers still left wondering if they will ever finish combining their wheat. As a result, it is undoubtedly going to be a challenge to manage oilseed crops and to keep disease under control.

According to Richard Elsdon, technical manager at United Oilseeds, vigorous establishment is critical in ensuring that crops do not fall behind. But he also claims that farmers who have sown their crops later than anticipated should not be disheartened. "Oilseed rape has the ability to surprise even the most experienced growers," Mr Elsdon claims. "Those crops that start poorly often out-perform crops which initially seem more vigorous and more likely to perform well.

"But that does not mean that the crop does not need to be carefully managed to give it a fair chance of success. There are a number of disease threats that can and should be addressed during the autumn so that crops go into the winter as strong and healthy as possible."

The first disease to be aware of is Downy Mildew. This posed a serious problem last autumn with many crops seriously affected. The disease rapidly reduces the area of leaf that is available for photosynthesis and limits the plant's ability to grow. "This can result in some very small plants going into the winter," Mr Elsdon explains. "My advice for those growers whose seed was not treated with Cruiser prior to sowing would be to apply either mancozeb or chlorothalonil as soon as the crop has developed its first true leaf."

Mr Elsdon continues to explain that where crops do develop well, with plants showing four true leaves during October, there is an opportunity to manipulate the plant to produce more root tissue and prevent the formation of an overly lengthy stem. "By increasing the size of the root, the plant becomes more efficient at scavenging nutrients as well as supporting itself later on. And minimising stem growth keeps the leaves as a flat rosette going into the winter. This reduces the likelihood of stem splitting which can allow phoma spores to enter the plant structure. When this happens no amount of fungicide will stop the effects of phoma infection," he adds.

The most effective way of achieving this kind of manipulation is by applying a formulation of metconazole which can also delay the requirement for fungicide applications. Last year's dry conditions meant that one fungicide treatment was sufficient for many crops. However, Mr Elsdon urges farmers to think back to the wet and mild conditions in 2006 which allowed spores to be released over a longer period. "Prolonged wet spells often mean that a second fungicide application is necessary to control disease effectively. Needless to say, the wet weather that has disrupted many arable activities so far this year means that it is likely that two fungicide treatments will also be required this time around."

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