Crop Watch: Blackgrass battle being waged through this autumn

Oilseed rape is at the front of our agronomist minds with Kevin Knight looking at blackgrass control as the grassweed’s emergence has been protracted during this autumn.

Sean Sparling in Lincolnshire is looking at phoma disease levels and slug problems in rapeseed crops, and is planning his strategy for the first emergence of light leaf spot.

In the South West, Stephen Harrison says soil temperatures are still too high to consider propyzamide herbicide applications, while many of his oilseed rape crops have received a phoma fungicide.

See also: Light leaf spot risk higher in the North

Further north in Cheshire, Andy Goulding is looking at ways of reducing soil damage in his high rainfall area to increase the number of days for cultivation work.

Kevin Knight

Kevin Knight

South: Kevin Knight

Zantra (Kent)

When I mention weather in this column it has the effect of producing the opposite to that described between writing and publication. This worked perfectly for my late-drilled oilseed rape with soil temperatures rising a treat.

Now I’m stuck between wishing for rain on growing wheat, rapeseed and field vegetable – and wanting heavy land to dry up at drilling depth to finish planting second wheats and winter beans.

As ever patience is key. It’s far better to drill late into decent conditions than muddle a crop into wet ground and be playing catch-up all season.

On oilseed rape, flea beetle pressure has been low while slug damage is surprisingly high as it has largely been dry and indeed dusty over October – but with dews overnight.

Emergence protracted

Blackgrass emergence has been protracted – the earlier flowering varieties of oilseed rape received Clethodim (Centurion Max/Chellist) by 8 October for grassweed and volunteer cereal control.

Beware applying this too late as, once bud initiation begins, it can cause some distortion especially if a frost follows.

On late flowering varieties, that were late drilled, it’ll be fine for a while yet. If in doubt, switch to carbetamide (Crawler).

Winter wheats are establishing well. Disease wise, I am seeing powdery mildew on stressed plants, with some varieties, such as Basset, more susceptible than others.

Ensuring decent foliar nutrition is applied should go some way to mitigating this, and add a mildewicide (cyflufenamid) if severe mildew is present – unless a frost is likely which will clear it up for free.

Sean Sparling

Sean Sparling

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

Dry old do up here in Lincolnshire with only 12mm rain so far this October, but coming off the back of 86mm, 71mm and 81mm in July, August and September – we really needed it to be a dry old do.

Oilseed rape has surged away over the last 10 days, thanks to wet soils and a three-day 23C “heatwave” that hit last week – outgrowing the last throes of cabbage stem flea beetle grazing, but alongside we saw a huge hatch of slugs and rapidly increasing phoma levels.

The 1-in-10 plant phoma threshold is being easily hit in some fields therefore suitable fungicides are being applied. There is little or no sign of light leaf spot but that may well change over the next few weeks.

So it’s worth taking advantage of the free Adas/Bayer disease analysis “SpotCheck” initiative to see what’s actually going on, and please don’t confuse downy mildew, fertiliser or leaf miner damage with light leaf spot.

Also, remember you will only protect not cure when light leaf spot is the target – three weeks’ protection at most – so know what you’re dealing with before you spend.

Questionable seed-beds

Winter wheat is being drilled… although into some very questionable seed-beds on some sites. Call me old-fashioned but clods the size of Wayne Rooney’s head don’t constitute a seed-bed and plasticine lumps the size of my head don’t constitute a tilth.

It’s still far too soon to panic yet on seriously blackgrass-infested fields, where at least one good flush of the grassweed has yet to appear.

Being the first to blink and simply getting on “before the weather breaks” just because your neighbours are going, makes the likelihood of that devastating flush appearing.

The timing of the drilling and application of pre-emergence herbicides is crucial. So use glyphosate pre-drilling, drill, roll and then spray, all within the three to four days following drilling.

West: Stephen Harrison

Stephen Harrison

Stephen Harrison

AICC/Southwest Agronomy (Avon)

Autumn storms have hampered spraying this week, and so a few planned pre-emergence cereal treatments will be forced into peri emergence.  Where pre-ems have gone on the effects on blackgrass are noticeable, with characteristic bleaching of the emerging leaf.

Cereal crops also have a little whitening, which never worries me as it is a sure sign that herbicides uptake is good. Unsurprisingly, the best response is being seen in the better seed-beds.

On cloddier seed-beds, blackgrass is pushing through relatively unscathed, and we will need to keep our fingers crossed for post-emergence backup here.

The mild and damp weather means crops have emerged rapidly and evenly, and so the upshot of this should mean even crops next spring which will greatly simplify management.

Soil temperatures for mid to late October are above average, therefore take-all risk in second wheats already drilled will be high.

Mild conditions

Oilseed rape is relishing the mild conditions and even crops which looked suspect a month ago look in good order. It has been a good autumn for Centurion Max herbicide treatments, while it is clearly far to early for propyzamide.

 Adult cabbage stem flea beetle is receding but larvae are being found in petioles. Treat when the threshold of five per plant is reached.

Peach potato aphid is difficult to find, and we will monitor until the aphid migration season ends in mid-November. Many crops have reached phoma threshold and they have had a half-rate fungicide.

From early November, we will be targeting light leaf spot. If propyzamide timings are delayed, do not be tempted to delay the fungicide.

Winter bean establishment is under way. Herbicide applications based on propyzamide, pendimethalin and clomazone are planned.  This is expensive but has proved very successful.

North: Andy Goulding

Andy Goulding

Andy Goulding

CAS/Hutchinsons (Cheshire)

Many of us were on the home stretch of autumn drilling and some were lucky enough to finish, but as I write the rain has come lashing down.

Hopefully by the time you are reading this it has dried out enough for the soil to become friable again and we can finish drilling.

It is after this heavy rainfall that our soil’s resilience is put to the test. Aggregates in over-worked soils lacking in biological glues and organic matter will break down rapidly.

Sediment will have started to produce a cap on the soil surface, reducing the infiltration rate and resulting in surface ponding.

With better soil health and structure we can increase the number of days available for cultivation, which is essential in a high rainfall area such as here.

Couple that with slashing establishment costs, better conditions for machinery to work, grassweed control, increased worm numbers and subsequent nutrient cycling, we should all be looking to reduce tillage in conjunction with residue management.

Excellent cob fill

Most crops have passed the opportunity for their residual herbicides to be applied pre-emergence, but this will not be detrimental to the vast majority of land (being grassweed free) and will coincide with manganese applications on light land – and an early pyrethroid on the few non-Deter treated crops.

On average, maize crops are well into being harvested with excellent cob fill and dry matter, which should clamp well and provide a good quality winter forage.

With the high level of risk to soil damage, erosion and penalties that  ensue, surely it is time we adopted practices such as undersowing to reduce that risk to the benefit of all parties.

No grower wants to see their fields in a mess and no contractor wants to spend a large proportion of their time pulling one another out of sticky situations.