Ultimate guide to spring weed control in winter wheat

Check crop condition

Well-established crops are a huge benefit for weed control because they can compete with weeds effectively. Thin backward crops start at a big disadvantage and need more attention to produce a good return. Identify any problem areas with poor crop establishment and consider management options. 

Check weed populations

Autumn pre-emergence programmes typically control a broad spectrum of weeds but they are rarely give 100% control. In addition, there are spring germinating weeds to consider. Check which grass weeds and broad-leaved weeds are present in the crop and how they are distributed to plan the control strategy.  

Ground conditions

Weed control depends on being able to get out into the crop and spray. In early spring, wet, cold soils can be a big problem so herbicide treatments often happen when it is possible rather than at the optimum timing. Assess when it is feasible to travel on the field and consider how that may affect product use and tank-mix options. Likewise, if you are re-drilling with a spring crop, make sure that you don’t go on wet ground and seriously damage the soil structure for this and future crops

Comment for spring 2021

Compared to the beginning of 2020, most growers will be going into 2021 with the majority of the winter cereals drilled and well established. For those that drilled early, they will have had plenty of time to apply pre-emergence herbicides. This may have compensated somewhat if they did not have time to achieve as many stale seed beds as usual.

Where growers opted to drill later, many hit the wet mid-October period, which will have meant drilling into wetter, sub-optimal seed beds. In addition, due to the rainfall, they may have not applied any pre-ems, or had to wait and apply at peri-emergence. Parts of East Anglia which saw continued rainfall and wet land are facing a similar scenario to 2020, with a significant amount of crop still to drill.

Where pre-ems were applied on-time, overall they have done a good job. But, where they were missed or applied late, some black-grass and other grass-weeds may have come through. If it wasn’t possible to get a contact herbicide on before Christmas, these fields will require attention this spring.

Reduce seedbank

Reducing the seedbank is critical to long-term black-grass control and it is a similar story with other grass weeds. In any one season, there is often a compromise between minimising seed return and maximising yield because wheat can still yield well despite fairly high weed populations. However, allowing more seed to return to the soil each season will gradually make it harder to farm successfully so at some point, short term gain from yield has to be sacrificed to the long-term aim of reducing the seedbank. 

Maximise wheat yield

High returns will always be the overall aim when farming but how much long-term weed control are you willing to sacrifice to save money on herbicide spend in one season? The answer to this question depends on the specific situation on each farm with things like rotation options for following crops, land ownership and crop contracts all affecting the decision. 

Good entry for following crop

Where a crop fits in the rotation is also a factor in management. Does the crop need to be managed in a particular way to improve the potential of the next crop?

Comment for spring 2021

With most growers facing a more ‘normal’ start to 2021, the focus will be on monitoring crops for weeds that got through any pre-ems, and any post-em contact sprays before the end of 2020. As soil temperatures start to increase, growers also need to watch for spring-germinating grass-weeds including black-grass, and broad-leaved weeds.

Where fields have suffered from flooding over the winter, it will depend on the state of the crop and how quickly the land dries out, whether to nurse it through to harvest, or to re-drill in the spring.

Herbicides

In most wheat crops, a herbicide of some kind is needed to control weeds in spring to reduce seed return and improve yield. The exact choice depends on the weed profile and time of application. If grass weeds are the main target, Atlantis OD (mesosulfuron + iodosulfuron) is a good option in January. From 1 February, growers have the option of Monolith (mesosulfuron + propoxycarbazone) or Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron). Monolith is suited to situations where only grass weeds are a problem. Pacifica Plus has a good profile against broad leaved weeds as well so it is a good candidate to the mixed weed situations seen on many farms. If only one particular weed is causing a problem, there are a number of products available for example Othello (mesosulfuron + iodosulfuron + diflufenican) for annual meadow grass control.

As well as contact acting herbicides, residual herbicides such as 0.3 L/ha Liberator (flufenacet + diflufenican) can be applied until 31 March / GS23. Residual protection will help control any spring germinating weeds but is not likely to have much of an effect against large established weeds because they will have roots below the zone of activity in the soil.

Herbicide performance depends on good application conditions. Contact acting herbicides need active growth in the weed and fairly still, dry weather so that the herbicide can settle and be taken in by the target leaf.

Comment for spring 2021

Weed profile, field history and the extent of weed control in the autumn will drive herbicide choices this spring. There will almost certainly be a need to control some weeds to protect yield potential, and to manage seed return to reduce weed burdens in the longer-term.

With contact products it pays to hold your nerve and wait for good growing conditions, of both the crop and weeds, regardless of whether you’re targeting grass-weeds or broad-leaved weeds. Spraying too early when temperatures are low, and plants aren’t actively growing, will not be as effective.

In grass weed situations products such as Atlantis OD, Monolith or Pacifica Plus need active growth, typically after a few days of bright, mild weather. Where growers have sodden soils, it may take a while to dry out to enable sprayers to travel. In these cases, Pacifica Plus may be the better option with its wide-spectrum control of grass-weeds and broad-leaved weeds, including good activity against black-grass.

Crop management

Take steps to improve crop competitiveness in spring. Rolling encourages tillering and early nitrogen can improve growth. If crops are in very bad condition, re-drilling with a spring crop is also an option.

Patch management

Weeds are often concentrated in patches which are a starting point for infestations to spread across the field. Aggressively controlling patches can be a good way to get weeds under control by sacrificing some crop this season so that it is easier to crop in future seasons. You can spray off patches at any stage in the season before seed sheds so it is probably worth waiting until later in spring to work out the best area to spray.

If numbers are relatively low, hand roguing problem grass weeds like black-grass from late spring onwards is also a good option.