31 October 2024

Time to get weeds in autumn cereals under control

Ciaran Collins, Tillage Specialist, discusses autumn weed control strategies for winter cereals, focusing on effective herbicide applications for high-priority weeds like annual meadow grass and brome.

This autumn has given tillage farmers a favourable window for planting winter cereals, a welcome change from the challenges of recent years. Now that crops are in the ground, it is time to focus on weed control. For the best results, tackle weeds early with a pre-emergence or early post-emergence herbicide application, especially for tough grass weeds.

The target of autumn weed control is to control weeds that are most damaging to yield and weeds where spring herbicide application will be least effective. In particular, sterile brome in winter barley and annual meadow grass (AMG) in both wheat and barley are high-priority weeds if they are present in your fields.

No herbicide offers full control of brome in winter barley, but early post-emergence application of products containing Flufenacet/PDM can help if no pre-emergence treatment was applied. If you did apply a pre-emergence herbicide, a follow-up can boost control, though you can typically expect about 50-60% effectiveness in winter barley.

The strategy for brome control in winter wheat is different. Flufenacet/PDM can give some control but there is a spring follow-up option of Broadway Star/Pacifica. Therefore, the best strategy is to target annual meadow grass in the autumn and follow up with alternative products for brome.

Applying residual herbicides (Table 1) to control AMG up to early tillering of the weed stage offers the best chance of success. Once AMG starts to tiller, it becomes more difficult to control. Be cautious with post-emergence spring options in wheat, as AMG is increasingly resistant to certain herbicides like ALS-Pacifica Plus. Testing by Teagasc has confirmed resistance, making timely autumn applications even more critical, especially for AMG that thrives in open, wet conditions like those experienced last year.

Getting on top of weeds now will help ensure a cleaner crop and better yields come harvest.

Table 1: Pre- or early autumn post-emergence (Winter wheat & winter barley)

*Alternative options to these products are available that can offer rate flexibility and savings to growers.