OSR success, weed control and blight protection from our regional expert in the South

Richard's September Advice

1) From flea beetle timing to tap roots: winning late OSR strategies

Most oilseed rape growers in the middle of August were holding off planting any more crop until there was some rain, and with the current forecast suggesting that was unlikely we could see a big split in drilling dates between late July established crops and September-sown ones.

September isn’t too late to be successful though, with this year’s new World Record oilseed rape yield by Lincolnshire farmer Tim Lamyman achieved from a September-sown crop.

With the low pressure so far from flea beetles, more growers will take a chance when there is rain but perhaps the best way to understand whether peak flea beetle migration is happening or passed, is to use one of our MagicTraps, available to buy in our online store.

Usually, the start of the second week in September is a good bet for the migration to have passed and I think many growers in the south will be waiting until then to drill OSR. At that point, choosing a hybrid variety is a good bet due to their fast establishment and rapid autumn growth.

Successfully getting plants to develop a good tap root so they can access all the nutrition required in the spring for growth is one of the keys for successful oilseed rape crops. It matters more than having lots of top growth, as most varieties can bounce back from pigeon, spring flea beetle or slug damage in the spring.

Most DEKALB® varieties, including DK Exstar, have strong vigour characteristics making them good choices for September-sown oilseed rape.

2) How to use Roundup^® to tackle BYDV risk and grass weeds together

Before getting the next cereal crop in the ground, it’s important to make the most of the best herbicide available – Roundup^®.

Objectives for the coming season are likely to be two-fold: minimising BYDV risk via green bridges and grass weed control.

Off the back of the warm, dry spring and summer, aphid numbers have been high and Rothamsted continues to catch bird cherry-oat and grain aphids in suction traps indicating a continuing risk of BYDV infections. Minimising that risk will involve killing off any green bridges in fields far enough in advance to allow green material to die fully and aphids to move on.

Bayer trials found that at least 10 days was needed for that to happen and there to be reduction in BYDV. I think it is an area growers will need to pay more attention to this year.

For grass weed control the ideal timing is for the period from two days before to two days after drilling. For the latter glyphosate can be mixed in with pre-emergence herbicides.

The two objectives don’t need to be mutually exclusive, with two applications of glyphosate possible under stewardship guidelines.

I wouldn’t be rushing out with stubble rakes or cultivation equipment unless we’ve had some rain, but they can help stimulate that initial flush of volunteers and grass weed emergence. Remove that green bridge around two weeks before planned drilling date, and then come back with a second application around drilling.

Monitor results of the first spray carefully, especially if you have high populations of Italian rye-grass on the farm, and if there are any survivors use cultivations to destroy them for resistance management.

Pay attention to application technique with any glyphosate application also to help minimise the risk of resistance build up, as well as to maximise efficacy. Use the correct dose for the target weed and size – 540g a.s/ha for 1-2 leaf grass weeds, a minimum of 720g a.s/ha for grass weeds that are starting to tiller – apply at sensible forward speed of around 12km/h, and use the right nozzles, boom height and water volumes.

3) From field selection to chemistry choice: getting September drilling right

Off the back of two very challenging autumns for drilling cereals, it’s highly likely growers will want to drill earlier this autumn, assuming decent conditions. Ideally, there will be some moisture to benefit establishment and also help residual herbicide chemistry to work effectively. I suspect many growers will be targeting mid-September for a start date for drilling wheat, moving it forward a good week to 10 days from previously.

The evidence just from last year when growers were forced by the weather to delay drilling into late October and November is that it does pay off for grass weed control, and that won’t change.

Targeting on a field level across the farm and start with the lowest pressure grass weed fields, while holding your nerve for the worst fields until October that will give a greater benefit for grass weed control than using any chemistry. But the financial implications and risk from delaying drilling and not getting a crop in make even that compromise one that’s difficult to stomach.

Assuming you are drilling in the early part of the window, understanding what chemistry will work best in what most likely will be drier conditions is important. Proclus®, for example, is a different sort of residual chemistry. A number of other residual herbicides, such as cinmethylin and flufenacet, work by root uptake. For them to be most effective you need good moisture in soils so that the spray can move into the zone where grass weeds roots are growing.

On dry soils is where aclonifen comes into its own. It’s essentially a contact residual, by which I mean, it binds tightly to the soil surface and is taken up by the weeds shoots when it grows through the herbicide layer. It is then translocated to the meristems of the plant, disrupting the photosynthetic pathway, causing bleaching and ultimately plant death.

That’s what makes Proclus® a good base for any crops drilled in that September and early October window. It’s also unaffected by ultraviolet light. The one caveat is it works best when you can create a good, consolidated seedbed. Poor quality seedbeds disrupt the herbicide layer for weeds to grow through, reducing effectiveness.

Partnered with Liberator® and potentially another active, such as pendimethalin or tri-allate and you have a strong start to a residual programme. Tri-allate, in particular, is another good option in dry conditions because of the way it works.

In winter barley, Proclus® at the lower rate of 1.0 L/ha in combination with Liberator® will also get you off to a good start, but in warm soils we do see hybrid barley, in particular, emerge very quickly.

With Proclus® restricted to pre-emergence of the crop only, an alternative approach could be to use a metribuzin co-formulation such as Alternator® Met, Cadou® Met or Octavian® Met. These give an extra 10% black grass control due to the contact activity from the metribuzin over flufenacet + diflufenican products and extra flexibility in timing over Proclus® in being able to be applied both pre-emergence and early post-emergence.

The metribuzin co-forms also pick up a wider range of difficult-to-control broadleaf weeds, such as groundsel, crane’s-bill and bur chervil. Applying them at GS11-12 when these weeds are at cotyledon to first true leaves gives really good results, especially against bur chervil.

4) Managing blight risk at the end of the season

Potato crops are two to three weeks ahead of usual but where crops are still in the ground it will be coming up to last sprays of what’s been a low-pressure blight season.

As night-time temperatures begin to fall, more dews form and blight risk increases in denser canopies. Tuber blight, along with foliar blight, is a risk, especially for crops going into longer term storage.

In these crops, Infinito® comes into its own at the back end of programmes. Assuming you haven’t used the 6.4 L/ha total maximum dose for the season, an application or two of Infinito® with its dual mode of action has shown in trials to be of great benefit in controlling both forms of blight.

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Alternator® Met, Cadou® Met and Octavian® Met contain diflufenican, flufenacet and metribuzin. Infinito® contains fluopicolide and propamocarb. Liberator® contains diflufenican and flufenacet. Proclus® contains aclonifen. Roundup® contains glyphosate.

Alternator®, Cadou®, DEKALB®, Infinito®, Liberator®, Octavian®, Proclus® and Roundup® are registered Trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist. Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information, including contact details, visit www.cropscience.bayer.co.uk or call 0808 1969522. © Bayer CropScience Limited 2025