Three agronomy tasks to consider this October in the north

Crop Progress

Yorkshire and northeast growers are drilled up with oilseed rape. The downpour in August helped restore soil moisture and ease establishment concerns. Unfortunately cabbage stem flea beetle seems to be back with a vengeance in the area, with some damage being done to crops.

Winter wheat, as well as winter barley, drilling started in September understandably with moisture in seedbeds and concerns over workloads. In some cases, this will have been in fields where grassweeds are a concern, so these will need managing carefully.

Adam’s agronomy tips for October

1. Spray off stale seedbeds as close to drilling as possible

Most growers will probably try to only spray off stale seedbeds once, although Weed Resistance Action Group guidelines allow for a maximum of two glyphosate sprays to stubbles.

Low black-grass dormancy could play into the hands of those looking to go twice, but remember the guidance states that any surviving weeds from a first application should be destroyed by an alternative method before a second spray to minimise the risk of resistance development. In practice, that’s most likely through some form of mechanical intervention.

The final application of glyphosate, whether it is a first or second dose, should be as close to drilling as possible. Use the correct dose for the weed type and size. Ideally grassweeds will be treated before tillering with a minimum dose of 540g a.i./ha. If any have reached tillering then increase the dose to a minimum of 720g a.i./ha.

Application technique is important. Think about going no faster than 10 km/h when applying glyphosate – this will make it easier to keep the boom stable and at the correct height of no more than 50cm above the target, and reduce disturbance to the spray pattern that can be created at faster speeds. Glyphosate remains a key pillar of control strategies so it’s vital to maximise its efficacy.

To that end, also consider using a branded Roundup product rather than a generic glyphosate formulation. Bayer trials have highlighted the Roundup products give better efficacy than generics, increasing reliability from the application.

2. Apply pre-emergence sprays in cereals within 48 hours of drilling

Agronomically it makes sense to delay drilling of wheat into the latter half of October, where grassweeds such as black-grass or Italian ryegrass threaten, although farm logistics and weather might make this difficult.

Delaying drilling maximises the time for the grassweeds to emerge before drilling allowing them to be controlled outside of the crop. It also means pre-emergence residual herbicides efficacy is likely to be improved as there should be more soil moisture to activate the active substances.

Where drilling is taking place in October, consider upping seed rates to maximise the competitiveness of the crop against the grassweeds, and hopefully you have chosen a variety that will also grow vigorously and compete well.

It’s important to apply pre-emergence residual herbicides as soon after drilling as possible – preferably within 48 hours. For most commonly used options, including Liberator (flufenacet + diflufenican) + Proclus (aclonifen), make sure seed is buried to at least 32mm depth to protect it from the herbicide layer applied to the soil surface.

Concentrate on setting up the drill correctly including the pre-emergence markers to avoid unnecessary overlaps when spraying which can also exacerbate any crop safety concerns.

In wheat, Proclus can be used at 1.4 L/ha in conjunction with 0.6 L/ha of Liberator, while it is also now registered for use in winter barley at the lower rate of 1.0 L/ha. It has a different mode of action to other residual herbicides, helping to diversify activity.

Where wheat has been drilled in September, it will be worth considering a residual top up where grassweeds are an issue. Our metribuzin-containing products Alternator Met and Octavian Met (flufenacet + diflufenican + metribuzin) fit well into this slot. From 1 October they can be used at a maximum rate of 0.5 L/ha.

3. Monitor for oilseed rape diseases

Most oilseed rape varieties have decent genetic resistance to Phoma and / or light leaf spot, which reduces early season risk, but it is still important to monitor for both diseases during the autumn.

Our SpotCheck service will be running again this autumn, allowing you to send sample leaves to ADAS to be analysed for key oilseed rape diseases. If you would like to use this service, please get in touch with me for a sample pack.

The threshold for treatment for Phoma is when 10-20% of plants are showing symptoms. Treat varieties with lower varietal resistance scores first (7 or below), or more backward crops. Varieties with a varietal resistance score of 8 or higher should only be treated when at least 20% have symptoms.

Proline (prothioconazole) or Prosaro (prothioconazole + tebuconazole) are potential product choices for Phoma control.

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