Help with agronomic decisions in Scotland during August

Early establishment crucial for oilseed rape

Early establishment, usually following winter barley for that reason, is key for oilseed rape in Scotland. If you haven’t grown it for a while on a field it is worth checking soil pH – oilseed rape is more sensitive to pH than many crops – ideally it needs to be 6.5 or above.

Min-till establishment into stubbles usually works well, while volunteer cereals can give a bit of cover from cabbage stem flea beetles. I’d always recommend using a starter fertiliser also to give the crop a quick start.

If you’re concerned about cabbage stem flea beetles, you could use one of our new Magic Traps to monitor for the pest. These are water traps with a camera attached, which autonomously identify numbers of pests, such as flea beetles, and send the information direct to your phone, providing a warning system to keep an eye on your crop and information about peak migration.

For varieties, look for fast autumn growth as a main trait. From the Deklab range, varieties such DK Extremus, DK Exsteel and DK Exstar are probably the top three for autumn vigour.

If you have a history of clubroot on the farm, then a clubroot-resistant variety will be needed. DK Pledge is an option from Bayer – it yielded the same as leading Recommended List clubroot resistant variety DSV Crocodile across four replicated NIAB and Scottish Agronomy trials in 2023.

Glyphosate can help with uneven crops

Plenty of Scottish growers call glyphosate ‘sunshine in a can’, and with a lot of uneven crops following a difficult winter and poor establishment of spring barley, there will be plenty that will benefit from pre-harvest Roundup (glyphosate) this harvest.

Check labels for latest timings – typically seven days for cereals, and always check with your end user to make sure they allow its use. It shouldn’t be used on seed crops, for example.

If you’re just using it to desiccate the crop, 360 g a.s./ha should be sufficient, but if you’re also looking to reduce a weed population then adjust rates for the target weeds, which could be up to 1440 g a.s./ha for perennial weeds such as couch and thistles.

Identify grassweeds to know how to best manage pre-drilling

Brome is probably the number one grassweed threat in Scotland, and it’s really important to know which species you have or which one is creating the biggest burden in a field to know how to best manage post-harvest.

If it is meadow, soft or rye brome, you should leave the seeds on the soil surface for a month to ripen before cultivating to encourage a chit. If it sterile or great brome, cultivate straight away and they’ll germinate within a week usually.

Other grassweeds, such as black-grass and Italian ryegrass will also benefit from a shallow cultivation.

Normally there should be time between harvest and drilling to achieve a stale seedbed to spray off with glyphosate. If you’re min-till establishing winter crops you can also use glyphosate in with pre-emergence sprays.

Application technique is crucial with glyphosate sprays to maximise efficacy. If you use hard water – perhaps from a bore hole – then reducing water volumes can help to reduce the amount of calcium ions that combine with the glyphosate molecule and result in reduced efficacy. Where you do use reduced water volumes remember to also check nozzle output and spray quality and perhaps travel more slowly.

Finally, also check rates and adjust for weed number, size and type. If applications are delayed then re-check rates with your agronomist to make sure the rate is adequate for what you are trying to control.

Keep an Infinito spray back for tuber blight

Blight pressure has been high and fungicides, including Infinito (propamocarb + fluopicolide) have been flying off the shelf.

Assuming you haven’t already applied the maximum total dose of Infinito of 6.4 L/ha, then it is worth considering keeping one application in hand for either the penultimate or last spray of the programme around the end of haulm destruction.

This is when it’s activity against zoospores helps reduce the risk of tuber blight, and there are limited alternative options.

Avoid creating weed or disease problems with cover crops

Where you are planning to grow a cover crop, choice of species is important. You don’t want to give yourself a weed burden for the future, or, with brassicas, a clubroot issue.

My choices would be based around forage rye, oats and vetch, none of which should create a weed burden and can all be grazed by sheep.

Whatever you choose, speed of establishment is critical as winter comes quickly up here as you will all know. So chase the combine with the drill and use a starter fertiliser, if necessary, to get the cover crop established for the winter and to maximise its benefit.