Adam Hinchcliffe offers some guidance on weed control in cereals and disease control in oilseed rape

Crop Progress

Some oilseed rape crops have been hit by cabbage stem flea beetles, which appear to have been turbocharged, just as it came through. In many cases emergence coincided with the warmer weather in early September, moisture disappeared which slowed growth, and then the flea beetles attacked. So there’s been a lot of crops taken out.

Some growers have also been drilling early winter wheat and winter barley – some of it very early. I can understand why farmers want to get on, but there’s also a little bit of madness to it too.

Adam’s agronomy tips for October

1. Think smart when using glyphosate

The ideal would be to get two stale seedbeds before drilling cereals, but realistically in the north that’s not going to happen. Most will be able to get one though where they are drilling in October.

Think smart when you use glyphosate. If barley yellow dwarf virus is a risk, especially if you’re going down the no insecticide Sustainable Farming Incentive route, then our trials suggest spraying off at least five and preferably 10 days before drilling to make sure you destroy the green bridge carry over for aphids.

If grassweeds are the biggest threat, then spraying off as close to drilling is ideal for weed control to minimise any weeds emerging before the pre-emergence can be applied.

Ultimately it will be important to manage expectations and target what you’re trying to control.

2. Herbicide options depend on drilling date

With winter cereals crops already in the ground there’s a range of different weed control requirements likely during October.

For those who haven’t drilled, especially on land with grassweed issues, delaying drilling as long as possible, albeit sometimes practically difficult, is a good start to weed control programmes.

Applying a pre-emergence residual herbicide within 48 hours of drilling will help maximise that cultural control. We’d suggest using Liberator (flufenacet + diflufenican) + Proclus (aclonifen) as the base in wheat. A sequence with tri-allate is a decent additional option for most grassweed situations or tank mixes with prosulfocarb, especially Italian ryegrass and black-grass, or pendimethalin are alternatives.

For any winter barley still to receive a pre-emergence, note the rate of Proclus is reduced in this crop to 1.0 L/ha and we don’t recommend mixing any partners other than Liberator because of the increased risk of crop damage.

In both crops make sure crop seeds are buried by at least 32mm of soil to minimise crop damage risk and avoid spraying when heavy rain is immediately forecast.

Those who have drilled in September and need some top up grassweed activity, our metribuzin products, Octavian Met and Alternator Met (flufenacet + diflufenican + metribuzin) have had a change on the label that now allows the full 1.0 L/ha rate to be applied up until GS25, rather than there being a cut off date. Ideally you’d be looking to apply these when grassweeds reach the 1-2 true leaf stage.

Where easier-to-control weeds are present, such as annual meadow grass and broadleaf weeds, the metribuzin products could also represent a good option either pre- or post-emergence.

3. Monitor oilseed rape crops for survival and disease

After the difficult start for many oilseed rape crops, survival is probably the first thing growers will be monitoring for, but for those that have come through and there are some out there, especially early drilled crops, then in October start monitoring for diseases such as Phoma and light leaf spot.

Phoma is usually the first to show, and with the wet weather and smaller crops, could be a greater risk this season, although most varieties now have good varietal resistance. If you suspect light leaf spot infections, sample some leaves, put in a plastic bag and leave for a few days in an airing cupboard for symptoms to develop to confirm.

Fungicides, such as Proline (prothioconazole) or Aviator (prothioconazole + bixafen) are possible treatments which will cover both diseases.