Crop Watch: Purple OSR leaves but better wheat drilling

Wheat and bean drilling continues, with much better progress than during last year’s monsoon. However, the forecast wet means rolling is increasingly unlikely for some crops.

Barley yellow dwarf virus risk continues to give agronomists a headache, but there are also plentiful numbers of beneficials like money spiders being reported.>

See also: Late drilling and companion crops works for Dorset OSR crop

In oilseed rape, purpling is being seen in oilseed rape leaves, which is due to the crop being unable to take up phosphate in the wet conditions.

West: Stephen Harrison

AICC/Southwest Agronomy (Avon)

A few dry days last week brought some relief from the rain, allowing further good progress with the remaining cereal drilling.

Wheat seed rates have been increased to 400/sq m to allow for reduced tillering from a November sowing. Depth of drilling has been maintained to ensure seed is protected from residual herbicides, which should perform well in the current cooler and moister conditions.

If seed-bed quality is compromised, herbicide treatments are best left to the 1 leaf cereal stage. Rolling will not be possible, especially as showery weather looks set to persist into next week. 

Unfortunately, those fields drilled close to the early October deluge are often struggling, sandier land has capped severely.

Barley yellow dwarf virus transmission by aphids continues to cause headaches. Not all fields that have reached T-sum 170 have aphids present, careful inspection is needed to avoid indiscriminate insecticide use. 

Last week’s foggy mornings revealed fields carpeted in predatory spiders’ webs. Improved decision-support systems that consider migration, levels of virus in the aphid population and numbers of colony-forming aphids are much needed. 

The only sustainable way forward is through decision support, tolerant varieties, local knowledge and field inspections, not necessarily in that order. A wholly integrated approach is required.


Winter beans are now being ploughed down or direct drilled where appropriate drills are available. 

We place great reliance on powerful pre-emergence mixtures based on propyzamide, pendimethalin and clomazone as post-emergence broad-leaved materials are limited to bentazone, which is becoming more expensive and has a very narrow weed spectrum.

Winter rape looks like a different crop to the last couple of years. Growth regulators applied to advanced crops in early October look to be helping create a more compact canopy, but will need a spring follow up.

Little evidence of cabbage stem flea beetle larvae can be found. Soils are much too warm for propyzamide applications, but where samples indicate light leaf spot presence, do not delay fungicide treatment and apply the herbicide later.

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

From 10 October to 10 November 2020, I recorded 39.5mm rain, so drilled winter cereal areas are back to expected levels. Compare that to 136.9mm for the same period 12 months ago when we’d mauled in 10% of the target area and we are understandably counting our blessings.

As bean and wheat drilling continues, wheats range up to growth stage 25 in late September sowings. Recent wet mild conditions have encouraged flecks of yellow rust and mildew, but the winter months will deal with these.

Second-generation barley yellow dwarf virus vectors are now appearing following 170C  degree days cumulative totals, but they’re much harder to find than money spiders, which visibly outnumber them 100:1, hence integrated pest management and spiders are managing aphid control for now.

Some of the blackgrass land that was panic drilled before the end of September, didn’t make it to the end of October – thank God for glyphosate!

In the main, however, fields drilled more sensibly due to rain stopping play and allowing stale seed-beds to do their job (thank God for glyphosate again), and where tailored pre-emergence were applied within two to three days, are thankfully impressively clean.

Oilseed rape disease levels have increased during recent mild wet conditions, phoma in particular flourishing and light leaf spot is now showing.

OSR fungicide

Clearly, fungicide choice depends upon diseases present and whether lodging control and canopy manipulation is necessary so, with several crops above my knees and very frothy, tebuconazole is in the mix.

Thankfully, no crops have been lost to cabbage stem flea beetle this autumn and larval numbers are a tiny fraction of 2019 levels, but RWSW (rape winter stem weevil) may yet be an initialism with more relevance to this season’s OSR crop, so don’t forget about it.

With soil temperatures over 14C at 30cm, it’s too warm for optimising the efficacy of propyzamide applications.

The guide of 10C at 30cm gives propyzamide a half-life of 100 days, apply it at 14C at 30cm and you lose about 40 of those 100 – patience, patience.

If 10C at 30cm doesn’t happen until early December, applications made then should give reliable control beyond the end of February.

With sugar beet viruses crippling both yields and sugars, Covid-19 lockdown and a looming no-deal Brexit – I find myself longing for those simple times when it was just the rain we worried about!

South: Iain Richards

Agrii (Oxfordshire)

This October was even wetter than last for us; the wettest on record for many, in fact, with anywhere from 190–230mm in the rain gauge across my geography.

A brief respite in the middle of the month allowed us to get some drilling done. So we’re now 90% drilled up with just a few fields of wheat on the worst blackgrass ground and with maize still to go in.

Learning from last year, we took advantage of the earlier weather window to drill some of our heaviest land first. This means we only have the lightest of our difficult ground ahead.

Knowing how much wheat we were able to drill decently well last November and how rapidly crops are coming through in the continued warmth, we’re far from concerned yet.

While rolling is looking increasingly unlikely, we’re well geared up to cover a lot ground as soon as conditions allow us to both drill to a decent depth and get a pre-emergence on. We simply won’t compromise on either of these essentials.

My worries about pre-emergence performance on some earlier-sown cereals have been dispelled by the good activity we’ve seen from our robust peri-emergence approach and pre-emergences beefed up with Avadex (tri-allate) on the heaviest ground where the likelihood of any peri-emergence was slim.

We are much more concerned about barley yellow dwarf virus just now. Winged aphids are easy to find and, with night-time temperatures set to remain at up to 10C, we’ll need to spray our barley and earlier wheats again as soon as we can.

It’s proving to a real challenge without Deter; especially with so few spray days available to us.

A solid autumn fungicide is fast becoming a priority too in our generally well-established OSR, as phoma levels have built up in the warm, wet weather – even in reasonably resistant varieties.

Broad-leaved weeds

Good grassweed control in the spring barley ahead of most of our oilseed rape means broad-leaved weeds – especially poppies, thistles, cleavers and groundsel – are much more problematic than blackgrass this autumn.

To deal with these we’ll be combining the fungicide with Astrokerb (propyzamide + aminopyralid) wherever necessary.

In the past we’ve always held off on our propyzamide for as long as we can for the best grassweed activity, but earlier Astrokerb always gives us better broad-leaved control.

Not being tempted to drill our OSR too early means we haven’t seen the sort of cabbage root fly problems being reported by some down here – purpled plants that look to be short of phosphate but are carrying four to five larvae in their roots.

Profiting from good growing conditions, even our September-sown crops are well-rooted and going into the winter without the sort of growth likely to cause canopy management headaches.

After last autumn, we’re thankful to have got our maize off with the least possible soil damage. We have been seeing some worrying European corn borer problems, though. So, flailing off the stubbles before cultivation to expose and damage the larvae has been vital.

North: Helen Brown

Hutchinsons (Cumbria)

The last month has brought a serious amount of rain, which has brought an end to any field work.

Thankfully September and October allowed for almost all the winter crop acreage to be drilled and autumn residuals applied, so we are in a much better position than this time last year.

Autumn crops are in general emerging well, although the usual headlands and wetter areas are starting to suffer with the recent wet weather.

Oilseed rape is looking well with most crops around six to seven leaves. The extended period of wet weather has caused some purpling of leaves due to the plant being unable to uptake phosphate from the soil in these conditions.

Our maize trial plots have now been harvested with yields varying from 40.5-55.3t/ha of fresh weight.

The key findings included an increase of 4.4t/ha dry matter where the same variety of maize was grown under film compared to in the open.

A key part of this year’s maize trials was starter fertilisers and as early as six weeks post-drilling early vigour was visibly increased in some of the starter fertiliser plots.

Often in trials these early observations don’t equate to yield increases, however where Primary P was applied, dry matter yield and starch levels were increased at harvest, despite being on a site with high levels of phosphate, showing the benefit of placement fertiliser.

Our regional trial site was drilled on 29 September near Carlisle into good conditions and despite the heavy rain in the week following this is now nicely established.

We have 33 winter wheat varieties including new hybrid wheats and a plot with a mixture of four winter wheat varieties as a blend after recent research and increased interest in variety blends.

Also at the site are 27 winter barley varieties, winter wheat seed rate work and various tramline sized trial plots working with various bio-stimulant and micro-nutrition products. I will share insights from our trial site as it progresses in spring.

Tip of the Week

With soil temperatures over 14C at 30cm, it’s too warm for optimising the efficacy of propyzamide applications in OSR.

Sean Sparling

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