We know that growing oilseed rape can be challenging so we have gathered together everything you need to know about oilseed rape here. From establishment to harvest we can provide insight about crop management and protection to help maximise yields.
Posted 2 years ago
May
Crops had been growing slowly due to the relatively cold and dry start to 2021, which extended into April. As a result, crops are behind and the flowering period has been prolonged.
This has also delayed fungicide timings, with the later developing crops not having received a Sclerotinia fungicide by the start of May. While the Sclerotinia risk has remained low, the risk from Light Leaf Spot has persisted, with infections seen in crops in late April.
With crops continuing to flower well into May, fungicides should be applied where required this month. It’s likely that most crops will only warrant a one-spray approach for Sclerotinia, though crops should be monitored since warm and wet weather, that is forecasted this month, will increase disease risk.
An application of 0.75 L/ha of Aviator 235Xpro will provide excellent control of Sclerotinia and Light Leaf Spot, both of which will knock yield if not controlled. Two different modes of action in Aviator support good resistance management, and the bixafen element provides valuable physiological benefits which has shown an increase in yield in the absence of disease.
Growers should monitor for Cabbage Seed Weevil once temperatures increase during flowering. The larvae of this pest leaves a hole when it emerges from the seed pod, which opens the door to a more damaging secondary pest, the Brassica Pod Midge. Control of Cabbage Seed Weevil is only necessary if populations exceed thresholds. For most of the UK, the threshold is one weevil per plant, but in the north of England and Scotland it increases to 0.5 weevils per plant.
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April
During April many crops will move quickly through growth stages from green bud to yellow bud and into flowering.
Even crops that were knocked by the cold snap in February are starting to bounce back, although where Cabbage Stem Flea Beetle Larvae are present in the stem in high numbers, they are continuing to hinder spring growth. Unfortunately, there is no control option at this stage but plants that are less affected may compensate for those struggling from pest attack.
The focus for pest control activities will be around the green bud and yellow bud phases where it’s important to monitor for pollen beetle, especially during warmer periods of weather (above 15 degrees centigrade) which will break the pest’s winter dormancy. Monitor beetle levels against thresholds and only apply insecticide if thresholds are exceeded but bear in mind that there is widespread resistance to pyrethroids. Other modes of action are available if required. Remember, once the crop is flowering, pollen beetle are beneficial in helping pollination and the crop will no longer be at risk of damage.
Most crops will have been treated for light leaf spot if the disease was present, but growers should continue to monitor the crop through its growth stages and into flowering. It’s important to keep light leaf spot off the developing pods so a further treatment may be required if disease is visible on leaves.
Sclerotinia is the main disease risk as the crop comes into flower. The optimum timing to spray for protection of this disease is at early to mid-flowering before any significant petal fall. Most fungicides used at three-quarters dose rate offer around three weeks’ protection against Sclerotinia. The requirement for a follow up spray will depend on disease risk linked to weather as well as the length of the flowering period.
Aviator offers excellent disease control over straight azoles when targeting both Sclerotinia and light leaf spot. Bayer trials have also seen valuable physiological effects, from the bixafen element of the product, which has shown an increase in yield in the absence of disease in the last two years. Having two different modes of action in one product also supports a good resistance management strategy.
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March
Increasing day lengths and warmer temperatures in March means that oilseed rape crops will begin a period of rapid growth and stem extension.
The snow and frost over winter has caused defoliation, and some crops are coming out of winter looking weathered. In some places this is no bad thing, since crops were looking quite forward coming out of autumn and many will grow away strongly with the improving weather. Some crops which struggled to get established, or have suffered significant winter damage, may benefit from an application of nitrogen as a priority, to help them grow away.
Stem extension is a key timing for light leaf spot infection, so growers will need to closely monitor crops for the tell-tale tiny sugar-like spores on the leaf surface. It’s important to intervene quickly if disease is present, to prevent spores moving up the stem to the pods via rain-splash.
If you’re unsure of disease symptoms, use Bayer’s SpotCheck service to help identify whether disease is present, and justify any subsequent fungicide decisions. This initiative is helping to identify high levels of light leaf spot across the county, with 92% of the 195 samples assessed in February, showing signs of disease.
Choose a robust fungicide, that targets light leaf spot, such as Proline. This is particularly suitable for any backward crops, since Proline doesn’t have any plant growth regulation effect and therefore won’t provide any check to crops struggling to catch up. For those crops requiring some PGR activity, tebuconazole can be added to Proline where necessary.
With crops entering a rapid growth phase it’s important to use sufficient water volume to penetrate the canopy and provide adequate coverage for disease control.
There have been reports of Cabbage Stem Flea Beetle larvae in stems and damage from Rape Winter Stem Weevil larvae. The two species differ by Cabbage Stem Flea Beetle larvae having legs. Any stunted plants with side shoots may be affected. At this stage there is nothing to be done to control the larvae, but fields should be monitored, and noted for future cropping.
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February
The main focus during February for oilseed rape growers is monitoring for disease. Not much spraying was achievable in January, but light leaf spot in particular may continue to infect crops if the weather remains wet.
Phoma re-infection is less likely in February, so attention should turn to monitoring crops for signs of light leaf spot. If temperatures rise going into late winter and rainfall continues, this will provide the ideal conditions for light leaf spot infection and spread.
At the early stage of infection it is very difficult to find visible signs of light leaf spot on leaves. Small, sugar-type spores can occur on the top or underside of leaves, but may be sporadic through the crop and are easily missed.
Growers can make use of Bayer’s SpotCheck service to aid their crop monitoring, and is particularly useful in more susceptible varieties. Samples of leaves are incubated to speed up the visible expression of disease, which helps to justify fungicide decisions.
There is no threshold for light leaf spot until stem extension and fungicides only work as protectants. Any autumn-applied fungicides will have run out of steam by now, so growers should aim to spray as soon as infection is identified and ground and weather conditions allow.
Proline will protect against light leaf spot, and any remaining Phoma.
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