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Crop Advice & Expertise

West: Six October agronomy tips for the West

Gareth Bubb reports highest ever flea beetle pressure for OSR growers and offers some advice on how to keep weeds and diseases out of crops this October

This month’s key messages

  • Monitor oilseed rape for foliar disease and treat with a broad-spectrum fungicide such as Proline where risk is identified
  • Delaying wheat drilling deep into October is advised to reduce pressure from grassweeds, virus-carrying aphids and Septoria
  • Use appropriate pre-emergence herbicide stacks in wheat to control problem grassweeds, but do so with crop safety in mind
  • Where pre-emergence herbicide timings are missed, consider an early contact post-emergence spray to control emerged grassweeds
  • Use all available tools to correctly inform cereal insecticide treatments for BYDV control
  • A Redigo Pro seed treatment is advised in late-drilled wheat crops at greater risk of microdochium and fusarium infection

Crop progress

A summary of the autumn so far would be “really dry, then really wet”. Growers were crying out for rain and then most in the region had about 80mm in nine days towards the end of September.

In the West, we have seen more cabbage stem flea beetle in oilseed rape this year than we’ve ever had, and it has been compounded by the dry weather. The recent rain has really helped, with crops looking like they might not survive getting the moisture they desperately needed. Some crop’s survival is still in the balance, but my advice is don’t write them off too early. Give them every opportunity to survive, as they can recover.

Some cereal crops were drilled before the rain at the end of September, but not any significant proportion. Once the forecast improves as we move into October, the pace of drilling will increase rapidly.

 

Gareth’s agronomy tips for October

 

 1. Look out for two key oilseed rape diseases

Up to now, we have not had enough rainfall to increase phoma disease risk in oilseed rape crops. However, growers should remain vigilant and use forecasting tools and the ADAS SpotCheck service to monitor disease progression. Treat with a fungicide when the threshold of 10% of plants infected is reached.

Remember that if treating for phoma in the first half of October, most crops will require a second treatment in early November to protect against light leaf spot. If only planning a one-spray programme, ensure a broad-spectrum fungicide such as Proline (prothioconazole) is used later in the autumn window to control against both diseases and see crops through to spring.

 

2. Delay wheat drilling for weed, pest and disease control

The earlier you drill wheat, the more grassweeds you are likely to have. Crops will also be exposed to higher barley yellow dwarf virus infection risk and Septoria pressure will be higher.

Where possible, delay drilling into mid- to late-October to maximise pre-drilling grassweed control. This will also see crops emerging in cooler conditions when BYDV-carrying aphid pressure is lower. Early Septoria infection will also be minimised.

Where growers are forced to drill earlier, they should consider planting a variety that has a high Septoria rating. In the West, if you sow early with a dirty variety, you will struggle to keep it out in the spring.

 

3. Stack pre-emergence herbicides to tackle key grassweeds

If drilling wheat into fields with populations of blackgrass, ryegrass or brome species, a pre-emergence herbicide stack is a very important component of control strategies. A Liberator (flufenacet + diflufenican) base is recommended and then look at bringing in additional actives, depending on target weeds. Extra diflufenican is the most cost-effective addition and prosulfocarb will also help boost control of all the main grassweeds.

There is a caveat to stacking extra actives. Although they will improve weed control, it also increases the risk of herbicide damage to the crop. The likelihood of damage increases on light, stony soils and if there is heavy rainfall shortly after application to a crop just poking through the ground. Try and avoid large stacks in high-risk these situations.

 

4. Consider early contact herbicide if pre-em herbicide missed

Where pre-emergence herbicide timings are missed and grassweeds have emerged with the crop, consider an application of a contact grassweed herbicide such as Atlantis OD (iodosulfuron + mesosulfuron) to kill any grassweeds already at the 1-2-leaf stage. Adding a residual herbicide such Liberator into the tank will also help control any late emerging grassweeds yet to come through.

 

5. Use decision support tools to manage BYDV in cereals

This year is the first without Deter (clothianidin) seed treatment to protect against cereal aphids carrying BYDV. Growers should utilise T-Sum calculations – accumulated day degrees above 3C from crop emergence – to work out timings for pyrethroid insecticide sprays, which are now the only tools for control. Once a T-Sum of 170 is reached, it is time to check crops for colonising aphids and the need for treatment. The AHDB have a BYDV management tool to help.

 

6. Use Redigo Pro seed treatment for microdochium

For late-drilled wheat crops after crops such as maize and potatoes, it is wise to use a fungicide seed treatment such as Redigo Pro (prothioconazole + tebuconazole) to protect against microdochium and fusarium seedling blight. These diseases are exacerbated by cold, wet soil conditions and slow emergence when crops are planted in late autumn.   

 

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