Quick tips on herbicide use in cereals this autumn

Crop Progress

Wet weather has been both a boon and a hindrance in the northwest. It’s been good for oilseed rape establishment and growth, but has limited the opportunities to cultivate ground and obviously made harvest tricky.

For most harvest finally finished in mid-September, with only late spring oilseed rape and grain maize left for combines. Forage maize harvest is likely to start any day as this is written on 20 September.

Yields seemed quite soil type dependent. Light land suffered in May when it was dry, which impacted on yields. On heavier land yields were average, nothing special generally – not a bumper year and milling wheat quality was poor because of harvesting delays.

Andy’s agronomy tips for October

1. Consider timing of glyphosate to minimise BYDV risk

We’re unlikely given the weather and general lack of cultivation opportunities to have the chance to get two stale seedbeds this autumn.

Timing of spraying off volunteers and other weeds with Roundup (glyphosate) is important. According to trials work we’ve done, it’s imperative to spray off any volunteers that could create a green bridge for aphids to transmit barley yellow dwarf virus at least seven days, and preferably 10 days ahead of drilling.

BYDV pressure tends to be a bit lower in the northwest compared with further south, but with incentives to use no insecticides, cultural controls take on added significance.

2. Delay drilling if possible where grassweeds threaten

The latest growers want to be drilling wheat in the northwest tends to be the middle of October. After that, it’s easy to get paranoid about the weather closing in and not being able to drill.

Ideally though that’s about when you should be starting, if you have a difficult grassweed problem, but I appreciate practically it can be a challenging decision. Just be aware that earlier drilling can compromise grassweed control, as illustrated by some work carried out by NIAB (see chart).

3. Look for pre-emergence herbicide persistency

Residual herbicides with good activity and persistency are key elements to look for in a pre-emergence herbicide against grassweeds. In our portfolio that leads you towards using Proclus (aclonifen), which is both good in combination with Liberator (flufenacet + diflufenican), and persistent.

Where difficult grassweeds are not an issue, and you’re looking to control annual meadow grass and broadleaf weeds, Octavian Met and Alternator Met (both flufenacet + diflufenican + metribuzin) are potential options, alongside Liberator.

DFF is a good persistent molecule against broadleaf weeds, and flufenacet provides excellent control of annual meadow grass. Metribuzin provides a different profile to DFF, as it is mostly taken up by the roots rather than the shoots, and is more mobile. The complementary pathways into the weeds and the different mobility in soils helps the combination cope with most weather conditions.

Both Octavian Met and Alternator Met can be used at 0.5 L/ha for annual meadow grass and broadleaf weed situations, but we have a label extension that allows it to be used at 1.0 L/ha up until GS25 where it is being used to target grassweeds, perhaps as a follow post-emergence treatment.

5. Monitor for oilseed rape diseases

Monitoring of oilseed rape diseases through last season suggested there wasn’t much disease in the autumn, but come January almost every sample had a level of disease.

We think that spike of infection happened as a consequence of there being very few autumn fungicides applied in these samples.

My advice for this season would be, if you think you have a good viable crop, it’s probably worth considering applying an autumn fungicide depending on variety, especially if you’re going through with the sprayer to finish off any weeds, for example.