Start grass weed battle now, Monitor Farm meeting hears

With grass weeds an increasing problem on farms, the battle for control should be starting now. Visitors at the East Lothian Monitor Farm summer meeting heard how cultural methods should be the mainstays of control, with work beginning now to map the extent of the problem before harvest.

Speaking to attendees at the event, Scottish Agronomy agronomist Stevie Gray said understanding what grass weeds were present on farm and mapping where they were should be done now. “Brome is an increasing problem, and understanding which type of brome or grass weed you have may not seem like a priority. Use the next few weeks before harvest to get out and identify which brome or grass weed species are present on your farm as that will impact what you do next.”

The East Lothian Monitor Farm, at Castleton near North Berwick has an increasing grass weed issue, with farmer Stuart McNicol facing high herbicide costs. Brome has built up on-farm for a variety of reasons, and this is now impacting on crop management decisions.

Stevie said: “Brome is being favoured by the increase in non-inversion tillage as its seeds are no longer being buried; we often find farms several years into a non-inversion tillage system running into problems with grass weed control.

“Sterile brome is the main problem at Castleton, but other farms could have multiple types of brome or blackgrass, and some have different bromes in different areas of their farms.”

He recommends growers use an online Rothamsted Research publication called ‘Which brome is that?’ which is available on the Monitor Farm Scotland website to help identify what species is on-farm. “It’s a good place to start as brome species can often look similar.”

Control should start by considering whether you can go for a stale seedbed in affected areas. “It’s not always possible, but if harvest is earlier this year, stale seedbeds mean you can get a good seed chit and spray off the emerged grass weeds with glyphosate. It’s a really useful cultural control, especially when using non-inversion tillage.”

Knowing the type of grass weeds present will help achieve the best results from stale seedbeds, he says. Sterile brome, blackgrass and volunteer cereals will chit best after a light, shallow cultivation, which will cover them lightly with soil. Where meadow brome, rye brome, soft brome and/or rat tail fescue are issues, no cultivation is needed as these seeds will germinate successfully on the soil surface.

The next step is to choose the most appropriate cultivation method for the crop and level of grass weed seeds in the seedbank. “Non-inversion tillage is driving the increase in grass weeds on-farm. Ploughing rotationally gives a great ‘leg-up’ with all brome species as it buries the seeds and will give a good level of control.”

He says the choice of tillage method is especially critical for winter barley as there are no post-emergence grass weed herbicides available. “Establishing winter barley with non-inversion methods where you have a brome issue is not good practice as you can’t do anything to control it - the weeds will come!”

Crop rotation and break crops should also be considered. “Oilseed rape offers the opportunity to use propyzamide which gives several months of activity against grass weeds. It can be applied in November once conditions allow and will still be active in February or March, giving a long window of control. It can also be used in winter beans.”

Growers may need to factor in lower margin break crops such as winter beans in order to continue to use non-inversion tillage, he says. “You can’t always be growing the highest margin crops with the lowest cultivation costs. Break crops can help with being able to use non-inversion tillage later in the rotation.”
Any farms considering home-saved seed should be particularly careful to exclude areas with grass weeds from this. “It’s crucial to identify where the grass weeds are before harvest, and to make sure there are no issues in any of the areas you plan to save seed from. Select your seed crops from the cleanest parts of the farm.”

Taking these cultural control steps now are crucial as spring herbicides won’t always be successful, he warns. “You won’t get out of a hole with chemicals alone – you have got to use cultural controls. This is the time to start taking control of grass weed problems and making the right choices.”

To view the report, visit: https://bit.ly/grass-weeds