Crop Watch: Effective residual chemistry leaves crops clean

As we head towards the new season, our Crop Watch agronomists report surprisingly few blackgrass plants, despite many later-drilled not receiving a full autumn herbicide programme.  

Crops on all but the heaviest land are looking surprisingly well despite a wet winter, but susceptible wheat varieties are showing yellow rust, with septoria also visible.

See also: How to fight fungicide-resistant ramularia in spring barley

ben pledgerEast: Ben Pledger

Farmacy (Bedfordshire/Hertfordshire)

Weed control from residual chemistry has benefited from the high soil moisture since my last article in November.

Both flufenacet-based products in cereals and propyzamide-based ones in oilseed rape, winter beans and lucerne have produced good levels of control.

Where propyzamide was applied for blackgrass control in oilseed rape and winter beans, field assessments are being made about whether a follow-up of carbetamide is needed to take out any healthy blackgrass.

Fortunately, on the whole this hasn’t been necessary, especially as a lot of the heavier land in the area is so wet it probably won’t travel until after the end of the February cut-off.

Seed still in the shed

On the lighter land there are still a few fields sitting after late-lifted sugar beet destined to go into wheat with the seed still in the shed.

Just a reminder – winter cereals sown after the end of January should be legally considered as a spring cereal and only approvals for the spring crop should be applied.

Later sowing of winter wheat varieties also produce the risk of low or no vernalisation, which in turn can lead to significant or total yield loss.

Check varieties against the latest safe sowing date information in the AHDB Recommended Lists.

Driving through Suffolk and Cambridgeshire last week, there were signs of spring seed-beds being made, and if the rain continues to stay away, I expect to see drills running in the next few days.

Spring cropping on light land in the South East is a balancing act between allowing the land to dry enough to be able to get on without causing damage to soil structure and not leaving it until drier periods, when too much soil movement sees precious seed-bed moisture lost.

This loss of soil moisture will possibly lead to a reduction in both seedling germination and effectiveness of residual weed control.

david martindaleNorth: David Martindale

Arable Alliance (Yorkshire)

Heavy land cereal crops are showing the most dramatic stress symptoms, with persistent wet areas of wheat now looking brown rather than green, while some winter barley crops have turned yellow.

The wet autumn conditions that made seed-bed preparation and sowing very difficult also made soil compaction difficult to avoid. This is apparent in oilseed rape, with small, stunted plants and short taproots and quite obvious yellow wheelings running up the barley fields. 

In a few weeks, some nitrogen and warmer weather should improve these areas, but it is worth noting the compacted areas to be rectified in the autumn. 

Nitrogen fertiliser will soon start to be applied to oilseed rape, but with a much higher percentage of the crop already having a large canopy, there will be no rush to apply the first nitrogen. Instead, target the smaller crops or where there has been significant pigeon grazing.

Don’t be complacent over yellow rust

Light leaf spot levels are currently low in crops that received an autumn fungicide, but where this was not applied, symptoms are at much higher levels and a fungicide will be required as soon as conditions allow.

Particularly large oilseed rape canopies will also warrant some growth regulation.

Yellow rust is evident in the more susceptible varieties of wheat. Levels are quite high in some cases, so do not be lulled into thinking that a few frosts has killed off this disease. As temperatures begin to rise, disease levels could soon increase rapidly.

Blackgrass control in winter wheat has been good where the full autumn herbicide programme was applied. However, far too few crops received the full programme.

The “Plan B” approach will be to use more contact-acting herbicides once soil temperatures rise enough. This timing can be tricky due to some blackgrass plants now having several tillers and being more able to survive. 

od-HunnisetSouth: Tod Hunnisett

AICC (Sussex)

Happy new year! This is the first Crop Watch of the new season for me and I’m afraid to say not a wheel has turned since the last one.

In terms of quantity, we haven’t actually had excessive rain – the springs, ponds and lavants have only just risen – it’s just that we haven’t had anything longer than a three- or four-day period without rain to allow the fields to become traversable.

I have some later-drilled crops that haven’t had a tractor in them since the drill pulled out of the field.

Where crops managed to get a double autumn herbicide, weed control has generally been good. Later-drilled cereals that only had one application are holding a few blackgrass survivors, but I’m not seeing many fresh emerging plants.

Residuals prove effective

This must mean the residuals have hung on well, because there is plenty of blackgrass at one to two leaves on overwinter plough and cultivated stubbles.

Where oilseed rape has had propyzamide it has worked superbly – another reminder of how important these residual actives are in difficult grassweed situations.


Blackgrass © Tim Scrivener

A result of last autumn’s enforced late drilling is that I don’t have many crops that wouldn’t benefit from early nitrogen. Anything after oats, nearly all the winter barley and other second cereals (except oats) and lots of rapeseed crops look as if they could do with a helping hand.

Nitrogen recommendations have been put in and as soon as they can sensibly travel the fertiliser spinners will be in action. The irony is, at this time of year, the fields that will travel first are usually the ones that need their nitrogen least.

It will soon be time for the spring grassweed survival walk. Once that happens, we know the season has well and truly started.

Neil PottsWest: Neil Potts

Matford Arable (Devon)

It seems as if it has been raining constantly since July last year, but despite this, many crops are looking surprisingly well at present. Fields are at saturation point and beyond. They will soon need to dry out to allow timely field operations and crop applications.

Winter wheat crops are well-structured, but not forward. Disease is present, predominantly septoria, but there are a few fields with yellow rust present where susceptible varieties are being grown.

With many crops having been planted using a power harrow and drill combination last autumn due to the damp soil conditions, there is now quite a lot of manganese deficiency in evidence.

This will need to be rectified at the earliest convenience and certainly no later than the T0 timing, which will soon be on us.

Winter barley crops are looking well and are generally well-tillered without having a huge canopy. Rynchosporium and brown rust can be readily found in many fields.

Very variable rapeseed

Many of the barley crops are due a first top dressing imminently, but the ground conditions are going to have to improve before this can happen.

Winter rapeseed crops are very variable and range in green area index from 0.4 up to 3.4. The worrying thing is that on occasions this range is found in the same field, which is going to make nitrogen management a touch challenging.

Autumn fungicides appear to have done their job well, as there is little evidence of either light leaf spot or phoma.

Residual herbicides appear to have worked well, but I suspect the continuous wet soil conditions have also suppressed weed seed germination as some untreated fields are looking surprisingly and unexpectedly free of weeds as well.

With the season about to kick off, I wait with interest to see what it throws at us.

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