Weed control challenges loom for farmers

Inevitably there are a few knock-ons from this season, however, that need to be factored in to crop agronomy plans.

Harvest and been a stop-start affair, with winter wheats and spring barleys in particular slow to come fully ripe. That later harvest makes the placing of oilseed rape crops for next year tricky, especially in areas of Scotland where it commonly follows spring barley. Oilseed rape would ideally be drilled before the end of August and anything much beyond the first week into September can be very challenging.

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Wheat crops

On the plus side, soils are moist (often too moist) so emergence will be fast, but everyone is mentioning the number of slugs so emergence and pest challenges could be pretty severe. The slugs risk pertains to all winter crops so checking fields with bait traps and managing accordingly would be well advised.

It is striking how green and weedy harvested stubbles are looking and that gives a warning that weed control for autumn crops will need a bit of extra help.

There are a number of reasons why we are seeing extra weed pressure. Thin open cereal crops this year have left plenty of opportunities for weeds to thrive, and there is also the legacy of the difficulties with getting autumn herbicides on a year ago playing their part in this. Grass weed – rye in particular – are competitive and hard to manage in cereals.

Reports of black grass in Scotland continue to tick upwards and it is a statement of the obvious that if you spot this then it is worth nailing early before numbers explode. Based on current weed pressure it is likely that more people will aim to use pre-emergence herbicides this season compared to last season, but where this can’t be done then peri-emergence options can be pursued.

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The other key feature this season will be that, after 2024’s autumn experience, no-one will hang about and delay autumn cereal drilling where they have an option to go. The memory of last year where later drilled crops waited endlessly for suitable weather windows for drilling, and were then really vulnerable to flood damage, is still with us.

Early drilling obviously adds to grass weed pressure, but it also increases some disease pressures like septoria in wheat.

We just need to recognise those risks and factor it in to plans. It is another reason to select more resilient varieties. It’s been really evident how dirty some of the older less resistant varies have been this year. SRUC trials suggest a few good options for winter wheat and winter barley for you to consider. Winter wheat varieties Bamford and Blackstone have septoria scores of 6.7 and 6.2 respectively and have both looked significantly better in trials than some of the older varieties like Skyscraper. We also have RGT Stokes, RGT Bairstow and KWS Zealum in our ‘top six’. For winter barley, mildew and rhynchosporium pressure will be that much greater when early drilled, so varieties like Bounty, Belter, and Firefoxx, which score 6 or more for rhynchosporium and are all ‘8s’ for mildew, will build in a bit of resilience. SY Tennyson and Diviner also make it in to our top 6 but are that bit weaker for rhynchosporium (5 and 4 respectively).

Both are good for mildew though (Diviner is a 9 and SY Tennyson an 8).

Certified seed comes with a certain guarantee about some of the seed-borne disease health risks, and with a known germination rate you can adjust seed rates to get consistent target plant counts.

If home-saving then always ask for gemination but it is also worth asking for other seed heath risks to be assessed. After a very wet harvest season it is very likely that fusarium and microdochium levels will be elevated and these can lead to seedling blights, which can be managed through seed treatments.

Aphid risks also increase where there is plenty of green bridge and a lot of early drilled new crop coming through. BYDV levels in cereals continue to climb, so as a final point remember to monitor crops and react if you see aphids start to invade.