Detailed weed control advice for Midlands’ growers this September

1) How to tackle increased grassweed pressure this season?

With the wheat area likely to return to a more normal 1.8m ha or more this season after the big drop last season, generally poor grassweed control last season leading to a significant seed return, and with farmers planning to mitigate difficult autumn establishment conditions by drilling earlier, there is likely to be much more pressure on grassweed control this season.

I fully appreciate why growers are planning to drill earlier – most will say that making sure having a crop in the ground even with a level of black-grass that will deliver a half decent yield is probably going to be better financially than a poor performing spring crop.

But that has to be tempered against moving from mid-October to mid-September drilling on some fields is akin to agronomic suicide.

From a grassweed control perspective, there has to be a balance, and it will be vital to do as much as possible, whether through using glyphosate or steel to control grassweeds out of the crop. I know the changing fashion is to use as little steel as possible.

For weed control, there are effectively two cultivation strategies – either keeping all weed seed on or very near the surface or completely inverting the soil and burying it. Clearly growers will have different views on what cultivation is needed to create a seedbed, but, particularly for bromes, then properly inverting soil is the best way to minimise the amount you will have in the crop.

I’m also a big fan of using steel within the rotation to prolong the effective life of glyphosate, particularly as we get more and more problematic Italian ryegrass populations. That’s the weed I’m most concerned about for growers who are not killing weeds with steel. I think it is in direct drilling situations where we are mostly likely to see an issue with resistance, when it comes.

Anyone who thinks continued use of glyphosate in those situations without other methods of controlling Italian ryegrass is living in cloud cuckoo land.

Glyphosate timing could need to be a balance between optimum weed control and destroying green bridge for aphids transmitting barley yellow dwarf virus. For the latter, which might be important if you have grown a summer cover crop or catch crop with cereals in the mix, then allow at least 10 days before drilling for your glyphosate application.

That gives 10 days before drilling and around another 10 days before the new crop emerges for the cover crops to have died off and the aphids to have moved on or died. Otherwise, they move straight into your nice newly emerging crop.

Unfortunately, that timing might not be ideal from a black-grass control timing, as you’re giving time for another flush to start emerging. In that situation you might need to come back either just before or as part of the pre-emergence application.

But remember there are some restrictions on dose when you’re withing 48 hours of drilling – a maximum of 540g a.s./ha which, if this is the only application and there are any bigger weeds, might be a problem.

2) Weigh up the benefits and costs of early drilling

Before drilling in September consider what it might both save you and cost you, so at least you go in with your eyes open. The main thing it will save you is that you will more than likely get a crop established, plus a small saving on seed costs as you can go with a lower seed rate.

Agronomically, earlier drilling will mean more grassweeds, greater risk of barley yellow dwarf virus, and reduction in the varietal resistance score for Septoria.

AHDB’s Recommended List ratings are based on a 7 October sowing date. If you decide to drill two weeks before this then you have reduced a variety’s score by 0.6. So if you do decide to drill a more Septoria-resistant variety, such as Typhoon (7.2) which is slow and steady enough to be drilled early, don’t expect to spend £60/ha on it in the spring. Effectively you’ve turned it into Graham (6.6).

From an autumn perspective, drilling earlier means more grassweeds will come up in the crop than outside because more of the germination curve is occurring after you’ve drilled the wheat.

That means don’t expect a single spray of herbicide, however much you stack, applied at drilling in September to see you through to the end of grassweed germination. If you have an Italian ryegrass problem, for example, germination could last well into November.

Instead, you’re committing yourself to a two- or even three-spray strategy, because September soils tend to be warmer and therefore what you apply will tend to break down more quickly.

The half-life of the two most effective actives against black-grass, flufenacet and cinmethylin, are both relatively short-lived, so they might have dropped below an effective dose after a month, which will only take you to the third week of October. Hence why you will need a top up to ensure you maintain control after that.

Do you have the spray capacity to do that? Will you be able to travel? These are other points to consider before embarking on this strategy.

Of course, in certain areas where there isn’t high grassweed pressure, drilling early won’t create such problems, but in our region these areas are few and far between.

Within this two spray programme approach, I think there are many farms where there will be a place for both the main BASF and Bayer herbicide offers. We’ll just differ in opinion on which one to apply first.

My suggestion is to apply Liberator (flufenacet + diflufenican) + Proclus (aclonifen) first, because Proclus will last – it has greater persistency, it has to be applied pre-emergence to comply with the label and it is less likely to cause crop effects. Autumn 2023 has shown cinmethylin is still very effective and is safer at the second spray timing, but in many cases when earlier drilling you’re going to need all the chemistry, maybe even including tri-allate in the programme.

3) Watch drilling depth in winter barley

More care needs to be taken with drilling depth in winter barley, where you’re going to use grassweed herbicides. With the speed that barley can come through the ground when drilled into warm soils makes the crop inherently more sensitive to herbicides.

And if it does rain that can exacerbate potential sensitivity, particularly on lighter soils where some products can get washed through, so ensuring crops are drilled to 32mm depth is important.

With cinmethylin not approved for winter barley, Liberator + Proclus will be the strongest available base, but you want to be careful with some mixes to make sure you don’t reduce crop competitiveness.

4) Drilling tips for later sown oilseed rape

Some growers are now choosing to delay oilseed rape drilling into September beyond the peak of cabbage stem flea beetle migration.

It will be interesting to see the data from Magic Trap this autumn. These water traps with a camera attached are designed to give an almost real-time indication of when flea beetle numbers spike, which can be used to delay drilling until after that period has passed.

If you are drilling in September, it is obviously one month closer to winter than when drilling in early August. The crop needs to be at least four true leaves and hopefully slightly bigger by the time the weather closes in to ensure survival, if we have a cold winter.

Therefore, look for a variety with good vigour, probably a hybrid. Some of the Dekalb range are pretty rapid. Pick one that is vigorous, has decent disease resistance and pod shatter resistance if that’s important to you.