Weed control and late OSR drilling advice in the south

Article overview

Current situation (19 August)

Harvest stalled a little in early August with some showers, after the winter barley and oilseed rape were cut at quite a pace in July. But overall it is progressing nicely, with some cutting spring barley after wheat.

Yields are a mixed bag. Lighter soils have performed relatively better than heavier ground, with the latter suffering in the autumn waterlogged conditions.

Winter wheat yields are down on last year, which was also a lower-than-average year, and target grain protein contents has also been hard to achieve, despite nitrogen fertiliser levels and lower yields.

But considering conditions in February, many growers seem relatively happy.

Oilseed rape yields have been around the 3-3.5t/ha mark, with an average closer to 3t/ha, with some reports of fields achieving 4.5t/ha. Winter barley has been anywhere between 6-7t/ha to up to 10-11t/ha in Hampshire over chalks.

While I haven’t heard much feedback on spring barley yields, I imagine that could take the prize for best crop as they’ve looked pretty good all season, and we didn’t have a massive swing from cold and wet conditions into hot and dry.

1) Remove grassweeds before drilling cereals

A lot of growers are naturally looking back at last year and will be debating about moving drilling wheat crops forward. The consensus seems to be starting 7-10 days earlier to avoid any of the bad weather we seem to be copping in October.

Last year in the southeast we didn’t fare as badly as other parts of the country, soils are not quite as heavy, and a lot already drill in the last week of September or first week of October where they don’t have very high grassweed burdens. I don’t see that situation changing too much.

But where there are grassweeds, they will need managing and considered if drilling dates are brought forward. Regardless of drilling date the best possible herbicide approach starts with Roundup (glyphosate). Starting clean is the best start.

It’s been said many a time, but attention to detail is key when it comes to glyphosate applications. Identify your weed target and size, and then tailor dose, nozzle choice, forward speed and boom height accordingly.

The other consideration is your timing of application. As well as optimal weed control you're also trying to break the green bridge before the next crop. Studies at our field station in Hertfordshire shows that a minimum of 10 days before planting of the next crop is required to really break that green bridge so that dying vegetation which are hosting virus infected aphid species such as the bird cherry aphid and the grain aphid don't just hop from previous crop volunteers into the newly emerging crop.

That 10 days does create a little bit of a balancing act as it could allow weeds to still come up after spraying and before drilling. It's striking a balance between removing old volunteers for barley yellow dwarf virus control and getting the cleanest possible start to your weed control programme.

A possible solution to this dilemma is to scratch up stumbles now and then spray them off around 10 days before drilling and then following up with a second hit of glyphosate either pre-drilling or with the pre-emergence spray.

2) Options for pre-emergence sprays for early drilled crops

With growers considering drilling earlier attention to what residual herbicides are delivering in terms of persistency is probably going to be key for this season. You are likely to need active substances with the legs to last through to the peak of the black-grass germination in the middle of October.

Proclus (aclonifen) has a long-lasting half-life of 80 to 90 days. It is relatively unaffected by soil moisture which could be important when early drilling. The combination with Liberator delivers three different modes of action working on three different processes within the grassweed.

We've seen very good results over previous years where this has been deployed and the addition of an extra mixing partner can prove useful. We've seen benefits from the likes of prosulfocarb against Italian ryegrass, tri-allate against bromes and pendimethalin against black-grass. Diflufenican and aclonifen will also provide strong broadleaf weed control.

Another consideration if deciding to drill early is the likelihood of requiring at least two residual applications with the follow up likely to be applied 2-3 weeks after your pre-emergence application.

3) Tips for later drilled oilseed rape

Oilseed rape that has been drilled in August has come racing out of the ground thanks to good soil moisture and nice temperatures. So far there have been no reports of cabbage stem flea damage at this time. However we are approaching the end of August, beginning of September when we do tend to hit peak flea beetle migration.

An option that some growers are finding successful is to establish oilseed rape in September after the peak migration of flea beetles has passed. Bayer’s Magic Trap can help growers understand when that has happened. It is a water trap with a camera attached which monitors flea beetles and sends reports direct to your mobile phone.

Once you see a drop off in the migration curve then you can send the drill into the field knowing that you are over the peak. If you are using this tactic look at varieties with good autumn vigour. It does tend to lend itself to a hybrid approach. Our Dekalb varieties fortunately have many of these characteristics both in terms of good autumn vigour but also high spring vigour which can be useful too.

All DK varieties are now part of the Bayer establishment scheme. To qualify oilseed rape crops must be drilled by 20 September, registered by 30 September. If a block of 6ha or more fails a claim for compensation can be made up to 31 October.