Top tips on grass weeds, vigorous varieties & blight prevention in the NE & Scotland

1) Early harvest provides opportunity for stale seedbeds

We continue to be more fortunate than some with the weather, with some rain in mid-August likely to help to encourage weed germination in stubbles where crops have been cleared.

Use a little bit of shallow cultivation to 5cm and consolidate with a press or roll to conserve moisture to create a stale seedbed by maximising seed-to-soil contact and encouraging germination of grass weeds – predominantly bromes with a bit of black grass and Italian rye-grass in this region.

Stale seedbeds can also help where you are using a direct drill or min-till establishment system to remove volunteers of the previous crop, such as volunteer wheat in winter barley crops, or barley in oats.

Ideally, aim for two stale seedbeds before drilling if possible – one initially when stubbles green up and one just before drilling. Make sure you use a good quality Roundup® formulation and tailor rates to the toughest target weed species and size. It shouldn’t be a problem at this time of year, but avoid spraying grass weeds during stem extension when efficacy can be challenged.

Application technique is important – limit forward speeds to optimise coverage and to reduce drift. It will also help keep the boom stable with the aim of 50cm above the target. Choose the correct nozzle to produce a droplet size and spectrum to match the size of the target weed. If you have one leaf grass weed plants, you need a small droplet to get the chemical onto the target as opposed to a big droplet that will bounce off it. Lower water volumes can be effective in helping to avoid run-off when targeted small grass weeds, but if you have big broadleaf weed targets then you probably want higher water volumes for coverage.

Between sprays, use mechanical cultivation to both encourage a further chit and also to remove any survivors from the initial spray to reduce the chance of resistance development.

2) Drill dates, weed pressure and weather concerns – is there a sweet spot?

The quickest way off any farm as an agronomist is suggest to farmers to delay drilling and then not being able to get crops in. Technically, it does help with grass weed control, especially black grass, and evidence is starting to suggest that, if anything, the germination period is widening. Previously, starting to drill in mid-October would help hit that reduction in germination, but over the past couple of years with the weather patterns, there’s a shift that could push that even further back into winter.

But giving advice to drill in late October or November can quickly make you look silly, even if it is correct technically.

In reality, growers will want to crack on with drilling in late September if weather is decent. Ideally try and drill fields with more difficult grass weeds later, and use seed rates and variety choice to create a crop that will be competitive against grass weeds.

Where weeds like black grass, Italian rye-grass and bromes are present, a pre-emergence of Alternator® Met, Cadou® Met or Octavian® Met + Proclus® is a good base to any programme, giving four different modes of action. Proclus® works well in both good moisture and dry situations.

Using Alternator® Met, Cadou® Met or Octavian® Met can bring a little extra efficacy against grass weeds, and broaden the broadleaf weed spectrum to include groundsel and bur chervil, among others. Liberator® + Proclus is an alternative option that has been widely used in previous seasons.

Where additional punch is needed, tri-allate is a good addition to the mix for bromes, while prosulfocarb helps against black grass and Italian rye-grass.

3) Why vigorous varieties are key for September-sown OSR

Establishing oilseed rape in September does have its risk the further north you are, but where you are planning to use this window, using a vigorous variety is crucial.

Fortunately, that’s a trait you will find in all DEKALB® varieties, including varieties like DK Exstar and DK Excentric, which is very vigorous. Other options include perhaps my favourite DK Exsteel and the brand-new variety DK Exedge, although the small amount of seed for the latter this season has sold out – but it’s one to keep an eye on in variety trials for next season.

Using a tool such as Bayer’s MagicTrap to monitor the cabbage stem flea beetle migration is worth considering. Peak adult migration is usually around the August bank holiday, but using a MagicTrap can help monitor whether that is the case this year, and whether levels are reducing when you plan to drill.

4) Consider tuber blight risk for potatoes

While late blight risk has remained low all season so far in potatoes, don’t be complacent as the season draws to a close. Irrigated crops, where risk will be higher, and crops due to go into storage, in particular, should benefit from at least one or two applications of Infinito® towards the end of programmes to control foliar blight and reduce the risk of tuber blight, assuming you haven’t already used your four applications for this season.

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