Cereals LIVE 2020 - Grass weeds

Successful grassweed management relies on developing a strategic approach that combines a long-term view and proactive tactical control. Syngenta grass weed research at the Barton Black-grass Innovation Centre and Doncaster Ryegrass Innovation Centre is combining innovative and practical integrated control solutions to manage grass weed populations at economically and agronomically sustainable levels – and it is working. Use this page to explore how you could incorporate various techniques into your on-farm strategies.

An integrated approach to grass weed control is critical, taking into consideration cultural control options, herbicide strategy and application technique.

The key insights from Barton come from overlaying weed control tactics over multiple years, and monitoring both weed control and margins. The site is now in its fourth year and we have begun to establish some interesting principles.

Seed dormancy is the term used to describe when a grass weed seed will not germinate even when all of the necessary conditions for germination are met. 

Weather conditions during maturation influence the dormancy of black-grass: a hot, dry year results in low dormancy in freshly shed seed, whereas a cool, wet year triggers a higher level of dormancy.

At Barton, dormancy tests have shown high dormancy in all seasons except 2018/19, following the hot summer of 2018.

Watch the video and listen to our dormancy soundbite to find out more about grass weed seed dormancy. 

At Barton, in our matrix field, we have crossed both cultivation technique and crop species to look at the effect of population, resistance and dormancy across the rotation. The work spans 5 years to enable effects of the rotation to become evident, for both grass weed control but also margin over input costs across the rotation.

Use our Cultivation Insight Tool to visualise the effect of different combinations of cultivations on black-grass distribution in the soil. 

As you can see the cultivation strategy that has given the best ‘control’ (or reduction) in black-grass over the 3 year period is DD/Plough/DD. This is despite the Plough giving the best control on average in both years one and two when considered as individual seasons. Best control was seen in a situation where the previous year’s plough offered a ‘re-set’ before direct drilling, meaning there was only one season’s seed return to contend with. Due to the low dormancy of that freshly shed seed residual herbicides worked well where that seed was on the surface in the direct drilling. The position of the plough in the multi-year strategy is something we are interested to understand further as the project progresses.

The best margin came from a DD/Min-till/DD strategy where there was a balance of moisture retention in undisturbed soils in dry summers and good establishment in the wet autumn of 2017.

At Barton, in our matrix field, we have crossed both cultivation technique and crop species to look at the effect of population, resistance and dormancy across the rotation. The work spans 5 years to enable effects of the rotation to become evident, for both grass weed control but also margin over input costs across the rotation.

Cultivation method, drill date and soil type all have an impact on when black-grass seeds will germinate. This has implications for your stacking versus sequencing approach and timing of herbicide application.

1. Map where you predict grass weed seeds are based on previous cultivation strategies.

2. Monitor weather at weed flowering to help understand dormancy for the coming season.

3. Adapt your herbicide strategy accordingly, using stacks or sequences for best control.

4. As a guide, aim to apply pre-em within 48 hours of drilling; apply sequences 3 weeks later. Adequate soil moisture is important for good performance of residual chemistry.

5. Start spring cropping in the autumn by preparing seed beds to achieve good crop establishment.

The ryegrass Innovation Centre at Doncaster is part of a network of trial sites across the country, providing practical solutions for farmers. The site is in its second year, and is starting to generate useful insights into the short- and long-term impact of cultural, chemical and application methods on grass weed control and yield.

At Doncaster, we have found that greater competition gives fewer grassweed tillers. Hybrid barley is showing consistently higher levels of competition and a lower number of ryegrass tillers than winter wheat or conventional barley. Hybrid barley is also demonstrating a reduced number of weed ears, due to a greater proportion of weed ears remaining below the crop canopy.

Pre-emergence herbicide treatments create one of the biggest challenges for effective application. With no crop to intercept the spray, extra care must be taken to avoid drift, and to achieve even distribution of droplets on the soil surface to maximise efficacy. Trials at Barton and Doncaster last autumn have reconfirmed our previous findings around techniques to balance efficiency, efficacy and environmental impact.

1. Consider crop competitiveness when choosing your crop.

2. Get your pre-emergence application on as quickly as possible.

3. Ensure 50cm boom height and maximum speed of 12km/h.

4. Adopt 90% drift reducing technology.

5. Map your fields with a traffic light system - most 'tough' sites will need 200l/ha water volume for best grass weed control. Where timing is under pressure, balance efficacy by using 100-150l/ha on lower pressure fields.

6. Download the Spray Assist app.