Weed control in winter cereals has undergone fundamental change over the past few years because of the loss of isoproturon (IPU) as an active and the increasing prominence of a range of very troublesome grass weeds.

This has led to a significant change in the main actives that are now commonly used and also a general move from post-emergence to pre-emergence herbicide application.

This has added to the challenge of getting timely weed control done in the autumn when there is also pressure to get crops sown, especially in a back end with awkward weather.

To do this requires greater organisation through the autumn to get some spraying done in the windows where planting may not be possible due to unsuitable field conditions.

The options available for crops differ, with very few actives cleared for use pre-emergence on winter oats while there are quite a number that can be used on wheat and barley and there are also limited options for rye and triticale.

In general, early application will work best against most weeds and pre-emergence treatment is often superior for grass weed control.

For this reason, pre-emergence herbicides are important where they can be applied. But there are also several post-emergence options that can be used but it can be difficult to get the correct timing married to optimum conditions for spray application.

In barley, most of the standard broad-spectrum products can be used pre-emergence but there are relatively few options, particularly for grass weed control, post emergence.

Some of the options that can be used include DFF, Firebird Met and Tower. But as is the case generally, grass weed control can be compromised if the plants are well-emerged and hardened off at the time of application.

Products differ in the spectrum of weeds that they control and this can differ depending on the rate used and pre- or post-emergence application.

The information compiled in Table 1 provides some help with the choice of products or actives to target weeds that may be specific problems in individual fields.

Pre-emergence options

The 2022 autumn-drilling campaign has been pleasing so far. Dry weather and higher-than-average soil temperatures are enabling growers to get crops sown in excellent conditions. Once this is completed, or interrupted by broken weather, the focus should switch to autumn herbicide strategy and application.

With field conditions remaining quite good across the country, a pre-emergence or early post-emergence herbicide application should be a real option for most growers.

As always, herbicide programmes should be tailored to individual fields as much as possible to target the weeds present in that field.

So knowing your field history is vital in order to know your target weeds and especially your most troublesome weeds.

A sequence of herbicides will always be needed for the control of difficult grass weeds like sterile brome.

Products containing flufenacet, such as Firebird, Navigate, Griffen, etc, have good residual control on grassweeds, especially annual meadow grass, and are also good on broadleaved weeds.

Be mindful that rates vary between individual versions of what may seem to be the same product.

Firebird Met is new to the market this year and contains metribuzin as well as the flufenacet and diflufenican (DFF) which are in Firebird.

But the active concentrations differ in both products so be conscious of this when targeting a specific weed spectrum.

It can be used as a pre- or post-emergence treatment and the Met product gives good control of groundsel and some other broadleaved and grass weeds.

Prosulfocarb, ie Defy, Roxy 800EC etc, is a good option for situations where annual meadow grass pressure is high but be careful when using it at the peri-emergence stage on winter barley.

Add DFF for additional broadleaved weeds control. Remember that high annual meadow grass infestation may also be associated with local patches of low pH.

Pendimethalin-based products (PDM) such as Stomp Aqua, Most Micro (various rates), etc, have good residual activity for pre-emergence situations and the active is good on annual meadow grass.

This active is better on fumitory than DFF but it is weak on groundsel.

Tower, which contains chlorotoluron, PDM and DFF, is good on annual meadow grass control plus a good range of broadleaved weeds. Be mindful that a 9m buffer zone is required along by watercourses when using standard nozzles.

Baraca Triple, which contains metribuzin as well as DFF and flufenacet, is good on annual meadow grass and a range of broadleaved weeds with different application timings for different crops.

It can be applied pre- or post-emergence to winter wheat but application is confined to post-emergence for winter barley and triticale.

Avadex Factor, which contains tri-allate, is effective at targeting grassweeds as a part of a programmed approach. It may be one of the few options to use where weeds like blackgrass show resistance to multiple actives. It must be used as part of a programme and follow-up sprays will always be required.

Diflufenican – Hurricane, Stride, etc – is a very useful ingredient for broadleaved weed control with a good weed spectrum. However, it is poor on fumitory.

Pendimethalin and picolinafen, ie Flight, is good on cleavers, poppy and fumitory but it is weak on groundsel. It should be used pre-emerge for best control of annual meadow grass.

Pendimethalin plus diflufenican mixes, such as Adept and Bulldog can control a broad spectrum of broadleaved weeds.

Application rates need to be adjusted for post-emergence application.

Fence or Flosset contain Flufenacet at 0.5l/ha or 0.4l/ha respectively. This active is good on grass weed control when used early and it is generally used as a tank mix partner with DFF or PDM mixes to enhance broadleaved weed control.

Tidy-up sprays

There are many other herbicide actives that can be used to tidy up problem weeds or weeds that escaped the earlier autumn treatments. Examples would be Thor, tribenuron-methyl, Pixxaro, Zypar or products that contain fluroxypyr, such as Binder, Hurler or Reaper. These are good mixers and they can be used, generally in springtime, to tackle weeds that escaped previous treatments. Some, like tribenuron, might be used in autumn or winter to tackle bad volunteer bean or oilseed rape problems.

Problem grass weeds such as sterile brome will generally require a follow-up treatment of a product like Broadway Star to get good control but this too really needs to follow an earlier treatment to control annual meadow grass.

In short

  • Pre-emergence herbicides offer the best control options for broad-spectrum weed control in winter cereals.
  • The are many options that can be used on winter wheat but fewer on barley, wheat and rye and DFF is really the only option on oats.
  • Many fields will require a sequence of products to achieve adequate control.
  • Control of blackgrass and wild oats has become increasingly difficult due to the presence of herbicide resistance.