Black-grass often grabs the weed control headlines but there are several other grass weeds that cause problems for farmers across the country. Here we summarise the main management techniques for some of the most problematic weeds.
Italian ryegrass is probably the most significant grass weed problem affecting cereal crops apart from black-grass. It can thrive in a range of conditions and crops as well as producing large quantities of seed which can quickly build up the seedbank. In addition, it has a well-known capacity to develop resistance to a wide range of chemistry, including most of the common grass weed actives. Consequently, ryegrass management has to be based on integrating a wide range of cultural and chemical controls – there is no quick fix.
Ryegrass is also widely believed to have a much more protracted germination window than black-grass. Farmers and agronomists report that it germinates in significant quantities throughout the season although research on the topic contradicts this.
Two studies involving Dr Stephen Moss have found that in autumn sown cereals, ryegrass germination and emergence mainly occurs during autumn in win. Approximately 80–90% by the end of December, the remaining germination occurs in spring.
Dr Moss has suggested that the perception of greater spring germination may be due to very small ryegrass plants being difficult to spot and identify. Consequently, when patches become obvious in late spring this is attributed to spring germination. Dr Moss admits that long-term trials based in working fields would help to understand this better. In any case, it indicates there is something in ryegrass’ life-cycle and development that is not fully understood. Learning more about this may help improve ryegrass control methods.
Delaying drilling and a robust autumn herbicide programme is very important for ryegrass control. Research has found some degree of resistance actives like pendimethalin and flufenacet when used as straights. But in co-forms and mixtures the actives still deliver good levels of control. What’s more, the new active aclonifen found in Proclus is showing very promising results against ryegrass in its first season on the market when used in a mixture with Liberator (flufenacet + diflufenican).
In spring, farmers can either use contact-acting chemistry or eliminate patches with Roundup (glyphosate) or by hand. Products such as Pacifica Plus (amidosulfuron + mesosulfuron + iodosulfuron) are effective on ryegrass depending on resistance status. Farmers need to consider whether to use it on a field-by-field basis. As it also eliminates many other grass weeds and several important broad-leaved weeds, the decision to apply may not be entirely determined by rye-grass pressure.
The majority wheat is treated with pre-emergence herbicides which effectively deal with annual meadow-grass. But where pre-ems are missed due to weather or cannot be used due to soil type, annual meadow-grass can cause problems at harvest and reduce wheat output.
AICC agronomist Peter Cowlrick advises some farmers on greensand soils on land to the north of the South Downs. Farmers are reluctant to use pre-ems because ruts and wheelings can potentially lead to erosion of these shallow soils. Consequently, Othello (mesosulfuron + iodosulfuron + diflufenican) is used to control annual meadow-grass and some other weeds which cause problems on these soils.
Farmers facing an annual meadow-grass problem this season can tidy up with Othello or other mesosulfuron based products such as Pacifica Plus or Atlantis OD if there are other grass weed targets in the weed spectrum.
Even at low densities of 3–5 plants/m2, brome species can cause yield loss and interfere with harvest. Brome produces fewer seeds per plant than ryegrass or black-grass so infestations develop more slowly but preventative cultural control backed up with chemistry is important.
Autumn management is based on stale seedbeds, delayed drilling and pre-emergence herbicides such as Liberator. Farmers also have to be aware of the differences between brome species when planning cultivations.
In some places, farmers have noticed an increase in rye-brome and meadow brome populations because of a reduction in post-em use and an increase in low disturbance establishment for black-grass control.
Despite isolated instances of resistance, post-em herbicides are still very effective. Both Pacifica Plus and Monolith (mesosulfuron + propoxycarbazone) provide excellent brome control. In five trials in 2016, Monolith provided 99.5% control of sterile brome compared to 85% from a rival product based on florasulam and pyroxsulam.
Brome grasses can develop into yield-robbing infestations if not closely managed. With harvest coming up, it is worth considering what you can do before, during and after combining to keep brome grasses in check.
Conditions and application accuracy are crucial to ensure the best grass-weed control results, says Bayer’s Jack Hill. Here are his 5 tips to optimise grass-weed control.
While many growers appear to be making encouraging progress in getting on top of black-grass and brome, Italian ryegrass problems are growing across the country, according to the latest in a 20-year series of national grassweed management studies. Noticeable increases in resistance have also been seen in the past four years, in particular.