Five tips around drilling, BYDV and weed control for growers in the south

Crop Progress

Harvest was definitely more frustrating this season, after a couple of years where it has been relatively plain sailing. All-in-all, though, harvest has progressed and a lot of growers with the good weather before the August bank holiday have or were not far from wrapping up by that weekend.

Most yields have been pretty average. Some areas and crops have done okay – down in Hampshire it seems to have been a good year for wheat yields as well as winter barley yields. But there’s also the coastal areas that have been affected by barley yellow dwarf virus, while more marginal land hasn’t fared that well either.

There was already oilseed rape in the ground and up by the middle of August, so fingers crossed it has survived any flea beetle attacks. At this time, as we approach the bank holiday weekend, there had been no reports of damage from either flea beetles or slugs, but as we know that weekend does seem to be the one where it all starts.

Richard’s agronomy tips for September

1. Is it too late for oilseed rape drilling in September?

It’s not too late to plant oilseed rape, although I would think a lot of the planned area will have been planted in the preferred window of August. But previous years have shown it is possible to achieve really good yields from September drillings, with some growers actively targeting post adult cabbage stem flea beetle migration.

You do need to pick your fields for September plantings carefully – avoid north-facing exposed fields where temperatures will drop more quickly and ones prone to pigeon damage later in the year. A fine, consolidated seedbed becomes even more important in September too.

Also choose a variety that has speedy autumn growth and vigour, as it is all about getting a good tap root down. If it has that, almost regardless of what’s happening on top, it can recover in the spring – we’ve all seen crops looking very sad in February or March that have sprung back really well.

Typically the varieties with the exceptional autumn vigour tend to be hybrids. In trials comparing hybrids and conventional open pollinated varieties, the hybrids germinate more quickly and push the tap root down. Our variety DK Exstar is one option – it is a good all-rounder that has good speed of germination, and early spring vigour you can rely on.

2. What about cover crops?

In a similar vein, it’s not too late, at least in the first part of the month, for cover crops. Later in the month you are probably starting to push it with some of the species you’re trying to establish, but ones drilled in the first week or so of September have the chance to establish and capture as much nitrogen and other nutrients as possible.

Tailor your species mix according to drilling date. As you get later, there will be fewer options that you can guarantee will establish successfully.

3. Break the green bridge for BYDV

The weather has probably helped create good conditions for both correcting areas of compaction or drainage, and also running a set of discs through stubbles to help encourage grassweed germination.

Achieving two stale seedbeds seems to be the optimum before drilling, but you don’t always need to rush to cultivate post-harvest.

Last season was reminder about the need to break the green bridge, having seen plenty of barley yellow dwarf virus in crops, and suction traps are already finding winged aphids carrying virus.

Trials last season highlighted that waiting until one- or two-days pre-drilling to spray off volunteers isn’t long enough to prevent aphids moving on from feeding on a dying volunteer to transmitting virus to the emerging crop. Instead, the optimum was 10 days to remove volunteers before drilling.   

One option for a programme would be to scratch the surface post-harvest, spray that off three weeks later, scratch it up again to mechanically destroy any survivors and promote a further chit, and spray off 10 days before drilling to make sure there is no green bridge and remove any grassweeds.

Alternatively, you could cultivate post-harvest, follow up with another cultivation to mechanically destroy the first flush, before spraying off with glyphosate 10 days before drilling.

If there is any more grassweed emergence in that 10 days between glyphosate and drilling, it’s possible to then either spray glyphosate just before drilling or with the pre-emergence herbicide, but hopefully with a decent early flush that might not be required.

4. What to drill and what not to drill in September

Last year’s experiences with grassweeds, as well as BYDV and Septoria, might at least put some caution in the minds about drilling wheat in September. Early drilling was not beneficial for some, especially with it being so dry and not achieving much of a flush of grassweeds before drilling.

The majority of grassweed emergence probably occurred from the second week of October onwards leaving growers a problem with control that was all too evident in June.

It’s obvious advice but if you are going to drill in September try to target cleaner fields for grassweeds, and postpone dirtier ones as late as you possible can.

But it’s likely that certainly winter barley will be drilled in late September, and no doubt some wheat too – just remember the above points about breaking the green bridge.

5. Herbicide options for early drilled crops?

Last season was the first season where Proclus (aclonifen) was an option in winter barley, and in combination with Liberator (flufenacet + diflufenican) worked well. It probably lends itself to those higher grassweed situations. Remember in winter barley the maximum dose of Proclus is 1.0 L/ha, compared with 1.4 L/ha in wheat.

It’s also imperative it goes on pre-emergence of the crop and weed, ideally within 48 hours of drilling to maximise both efficacy and minimise any potential crop damage. With warmer soils in September, crops can be emerging within five days so don’t delay.

In barley we don’t back the mix with any additional partners in the tank, but you can top up with a residual 14 to 21 days later, or if you’re under a lot of weed pressure, with bromes for example, tri-allate is worth considering as a separate application just after drilling.

In wheat, the higher 1.4 L/ha dose of Proclus plus Liberator has shown good success in previous years. It’s possible to also add in other residuals in wheat, depending what weeds you are targeting. Prosulfocarb seems a good addition for Italian ryegrass, while in blackgrass the addition of pendimethalin up to 1200g a.i./ha will give you a mix of four different modes of action.

Tri-allate is also a benefit when tackling grassweeds in wheat, but be prompt with applications.