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Crop Advice & Expertise

Cultivations grass-weed control and oilseed rape establishment advice for Midlands growers in August

Oilseed rape establishment and grassweed control advice Ben Giles’ top tips for August in the Midlands.

Ben’s agronomy tips for August

1. Check if the soil is wet!

The best way to establish oilseed rape is to out in the field and see if the soil is wet. It doesn’t matter what the date is, it is purely about whether it is good conditions for a seed to come through the ground quickly to avoid adult cabbage stem flea beetle attack. If the answer is yes, go and drill it, if it isn’t – don’t.

But be careful with seed rates, especially from early drilling. If you pile on the seed you better hope it doesn’t all come because otherwise if you get a larval attack on stems smaller than your little finger because you’ve planted far too many seeds then you’re in serious problems.

I understand why and have no problem with growers who want to go down the route of taking seed out of the barn, but it’s not reducing risk, it’s reducing cost – and they are two different things.

Aiming for a sensible population coming out of the ground quickly, particularly if partially insured under various schemes such as the Dekalb Establishment Scheme is fairly low risk – higher cost, yes, but lower risk.

If you are establishing oilseed rape, then whatever you do with cultivations don’t remove moisture from the soil.

Direct drilling and Autocast are options because they can be done quicker and if you have an opportunity not long after harvesting a cereal won’t remove moisture from the soil. The caveat, and especially following the storms we’ve had recently, is that there are combines rolling on fields that are moist and there is potential for compaction. So before you go direct drilling be careful about what you have done to the soil while harvesting, and is that conducive to direct drilling? We know oilseed rape hates any degree of compaction.

If you want to reduce cost from your system while not increasing your risk, consider varieties such as DK Exstar that potentially allow you to reduce your fungicide programme in the autumn. With its double eight for Phoma and light leaf spot resistance I don’t think I would be too worried about Phoma and I wouldn’t be looking too hard for light leaf spot until the spring rather than the autumn.

The other benefit from DK varieties is the in-built pod shatter resistance in all bar the HOLL varieties, which as we’ve just seen in July, can be extremely useful.


2. Watch out for spring brome species

There’s a good chance I might get put in a Wicker man at next year’s Groundswell, but there is a definite need in some situations for cultivations and one of those is where you have spring germinating bromes.

I cannot see control of meadow and rye brome being sustainable longer term without the use of steel, having seen yet another year where the chemistry is middling at best in the spring. I know many won’t want to hear it, but at some point the plough has to be considered, and that’s probably one of the easier decisions to be made with cultivations.

If the situation isn’t that bad, you would hope the delaying tactic of leaving the seed on the surface as they need light to break dormancy, and then doing something about them would help.

Bear in mind that the pre-emergence residual herbicides will struggle as they are applied too far in advance of the main flush, and the post-emergence chemistry is often more a suppressant than control agent on some of these populations. There are probably more difficult populations out there than we probably want to believe.

So if you’re coming into a cereal crop and you know you have a problem it’s about deciding whether that will do a good enough job for you? I think there are situations now where the answer is no and a harder reset is needed.


3. Stale seedbeds useful for other grassweeds

For other grass-weeds, such as black-grass, rye-grass and autumn-germinating bromes (sterile and great) early cultivation after harvest can help trigger a flush.

Timing of spraying weeds off will depend a little on your plans. You can go twice, but more than twice is not good practice according to the latest WRAG guidelines. Try not to let the weeds get overly big – if you cultivate and get a significant flush that starts tillering, you’re probably going to want to spray that off.

If we are doing the right thing and delaying drilling until mid-October for drilling, then the chances are you’re going to spray it off again just in advance of the drill going in.

The problem is that might scupper for some the desire to put more glyphosate in with the pre-emergence. So there could be some that will let it flush, flush, flush and then spray off 10 days before drilling, and then put a second glyphosate in with the pre-emergence, which has worked quite well. But if you do this, please make sure it is properly pre-emergence of the crop.


4. Think about how catch crops will effect grassweed emergence

Catch crops planted after early harvest and lasting until autumn drilling are usually there for soil cover rather than any soil improvement as such, but are worth considering particularly on vulnerable soils.

If you’re putting one in, think about how it might impact grassweed emergence – will it stop grass-weeds coming up, out competing or making them dormant and then only coming up in the following crop? Or if you do slightly move the soil when establishing the catch crop it could be that you get quite a lot of weed come up in the catch crop, which shouldn’t be a problem as you’re probably going to spray it off anyway. But in that case use sensible doses of glyphosate tailored to the species of cover.

The other consideration is whether it will reduce the efficacy of the pre-emergence herbicide. We’ve done one or two trials, and while it is difficult to think that it won’t, it’s quite difficult to prove, which might mean it doesn’t do it quite as much as you might think.

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