Crop Watch: Patience pays off with late weed flush

Seed-bed conditions across the country are reported to be almost perfect following the dry conditions, although for those growers who took advantage of conditions early, blackgrass is already a problem.

Those who managed to hold their nerve until last week were rewarded with a late flush thanks to storm Callum, with rain also improving the activity of robust pre-emergence stacks already applied.

Levels of phoma and less light leaf spot remain low, but where light leaf spot is a problem, fungicides should be prioritised over plant growth regulators.

Iain Richards

Iain Richards

South: Iain Richards

Agrii (Oxfordshire)

It took nerves of steel but the last week of October gave us just the wheat drilling opportunity we were waiting for on bad blackgrass ground.

A good two inches of rain from storm Callum was exactly what the low-dormancy blackgrass needed. With such dry conditions up to this, we were beginning to despair of a decent weed flush.

But within a week we had a great glyphosate target to spray-off immediately ahead of drilling in a nice, settled weather window.

See also: Crop Watch: Rising aphid threat to OSR and cereals

The prolonged wait since post-harvest cultivation meant the soils had weathered down really nicely too, allowing us to drill up large acreages rapidly and evenly with the minimal soil movement we want to avoid waking up more weed seed.

Those who ran out of patience before this have seen plenty of blackgrass coming through where they least want it – with the crop.

Here we’ve had to beef-up the peri-ems with some extra contact activity, looking to “old faithful” clodinafop, although it can be rather hard on the crop.

With fine, well-consolidated seed-beds and sufficient moisture, our flufenacet, DFF and prosulfocarb pre-ems should work much better on the later drillings; especially with the colder weather extending their persistency.

As soon as we can see the drills we’ll be going in with a top-up of extra flufenacet with pendimethalin plus picolinofen, where necessary.

Flea beetle

Providing it proves more than just a brief snap, the onset of cooler weather should help hold back the recent worrying build-up of aphids. So Deter treatment should see our later drillings through – unlike our September-drilled wheats on low-risk blackgrass ground, which we will be spraying within the week.

Thankfully we’ve survived the worst flea beetle season we’ve ever known, with the majority of our OSR surviving the onslaught.

Despite continued concerns over a number of small crops struggling to pull away, the large amount of blackgrass coming through has forced us to bite the bullet and invest in clethodim in the hope they’ll make it.

They will, of course, still have to get over what is set to be a very substantial larval burden, which we can do little about where pyrethroid resistance is at high levels.

Crops that get away quicker in the spring are better able to compensate for larval damage, so first-class early spring management – including nutrition and light leaf spot control – will be especially important; not to mention essential to justify all the investment that’s already gone into the crops to get them this far.

Stephen Harrison

Stephen Harrison

West: Stephen Harrison

AICC/Southwest Agronomy (Avon)

Autumn drilling is now complete except for a few fields of winter beans. I cannot recall a drilling campaign where seed-beds have been so uniformly excellent.

Slug pellet use has been minimal, even after oilseed rape, crops have established rapidly and uniformly.

Everything has been rolled in ideal conditions and this has contributed positively to pre-emergence performance.

Emergence has slowed down with the later drilled crops, but they have plenty of time before the worst of the winter sets in.

High-yielding years such as 1984 and 2011 were preceded by dry autumns, we now have strong foundations in place for the coming growing season.

There’s still a long way to go until next harvest, and as a few of my clients delight in telling me, there’s still time for crops to get a kicking.

Winter oats

One crop that has already had some savage treatment is a piece of winter oats riddled with blackgrass. We took the decision to run a spring tine grass harrow through it.

It looks drastic, but the oats are largely undisturbed, and a lot of the blackgrass has been ripped out.

Watch this space. It is becomingly increasingly difficult to find clean ground for winter oats; so the spring acreage will only increase.

It is possible to find mildew and net blotch in advanced winter barley. If damp, mild weather returns we may consider treatment.

I have almost as many establishment systems as I have clients. This autumn it is very hard to pick out the best and worst. Not a year for drawing too many conclusions. On kinder soils, a fiddle drill and garden rake would have sufficed.

Winter rapeseed is a complete mixed bag. The further west you go, the less flea beetle damage is apparent. Over in south Wales, even crops established in the dry have pulled through.

Andy Goulding

Andy Goulding

North: Andy Goulding

Hutchinsons (Cheshire/North Wales)

This time last year many cereal crops in Cheshire were only just emerging with few farmers able or willing to apply a residual herbicide. Now as I write, all my cereals are drilled and have received residual herbicides, aphicides and manganese where necessary.

Problem ryegrass fields are now receiving post-em herbicides as they have reached the two-leaf stage, and with the good temperatures and shallow-till now adopted on farm, I’m hoping for some good results.

Moisture is now ever present but conditions for travel have been good for the continuing aphicides.

The long, dry summer has really helped keep the slug population in check as they lay torpid in the depths trying to remain hydrated; only now are they beginning to cycle.

Weed emergence has been slow, but the return of moisture will drive an influx of germination and activate the residuals that I have largely based on Pendimethalin and DFF with their long half-life.

Light leaf spot

Oilseed rape has never looked so clean of disease, but now is the time to apply fungicides. Phoma has not been the driver this season so one fungicide to cover that and light leaf spot will be a good foundation for spring fungicide success and keep the pressure lower.

No one wants to find themselves in a crop full of disease come the time when we will be able to travel again up here in the North West.

While going through the crop, it would be worth using any planned propyzamide applications. If we wait much later then the risk of it getting into water will be great and blackgrass could be getting large and rooting deeper out of the chemical uptake zone.

Better to apply when the weeds are active, up-taking chemical from nearer the surface and smaller in size. For those farms practising surface tillage or less, onward flushes will be of lower concern as the requirement to rely on persistency is vastly reduced.

Forage brassicas are looking excellent after the large flush of volunteers were taken out early on and are now starting to be grazed.

Grass re-seeds have generally all been a roaring success and livestock farmers are continuing to cut grass and will do late into the year to try and restore low stocks.

Sean Sparling

Sean Sparling

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

Wheat drilled in the first half of October is pushing GS12 and, in those blackgrass fields that went in a week too early due to drillably dry weather, some blackgrass is at a similar stage.

Most growers held their nerve and therefore have only wheat emerging, and on those worry fields where robust pre-emergence stacks were applied shortly after drilling, we appear to be in control, with recent rain improving activity – no post-drilling glyphosate needed yet.

BYDV remains a concern in non-deter dressed fields. The recent run of sharp frosts will do little to bother aphids, unlike the insect predators that are now suddenly conspicuous by their absence. We continue to monitor populations closely and treat as necessary.

In earlier drilled cereals, some of which are now GS23, mildew has been widespread thanks to the mild conditions, but the frosts will deal with that problem, as it always does.

Oilseed rape disease levels remain low, with little phoma and less light leaf spot. With fungicides only giving three weeks protection against light leaf spot at best, timing is everything so “calendar date” or routine applications should always be avoided.

Prioritise disease control

Where light leaf spot is the target, prioritise the disease control over perceived plant growth regulator activity, because with many OSR canopies now almost up to the knees, it’s worth remembering that until the crop hits stem extension, it’s only the root system that will respond to a PGR and reductions in canopy height are unlikely.

I have OSR plants 40cm tall but not close to stem extension (that happens when the distance between the leaf axils becomes greater than the distance around the circumference of the stem) but, in those canopies, the roots are a similar length – we are therefore still holding off fungicides for now.

Still too warm for propyzamide – why apply it too early and risk losing efficacy?

I have never seen so many peach potato aphid in OSR, nor have I seen so much parasitisation of them by wasps and fungi – unfortunately, insecticides control both parties.

In the more backward crops, damage by huge numbers direct feeding still poses a threat, but the TuMV threat decreases if infection occurs after four leaves – so if your OSR is bigger than that and if TuMV is already in, you’re wasting your time and money spraying for it.

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