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Testing times for ryegrass resistance

Ryegrass
24.06.2021
Ryegrass seed heads

The Weed Resistance Action Group (WRAG), has warned that once resistance has developed in ryegrass, it’s not going to go away. Growers and agronomists are urged to spot resistance early, in a move reported to be more cost effective to stop the issue developing, compared to subsequent measures to resolve resistant populations.

Syngenta herbicide technical manager, Georgina Wood, advocates that to minimise the risk of resistance developing, growers should increasingly be looking at good practice of integrating cultural controls within their herbicide strategy.

Georgina Wood - Barton

“Where a resistance issue has been identified to contact chemistry, it further focuses the attention on cultural controls and making best use of Defy as a pre-emergence treatment,” she advised.

WRAG highlighted in a 10-point Action Plan that preventing the development of herbicide resistance is within growers’ control, and identifies resistance tests as a valuable management tool.

“A better understanding of the resistance status of ryegrass, along with testing and mapping of problematic populations, will help growers to develop a multi-year strategy to keep on top of the problem,” reported Georgina.

She suggested herbicide resistance could be indicated by a gradual decline in overall efficacy of control, or where patches of weeds remain uncontrolled, despite receiving applications. If some ryegrass has been controlled, but not all, that would also indicate that the application has been effective, but resistance is more likely an issue.

Ryegrass seed head

“Where resistance is suspected it is a really good idea to get ryegrass seed tested, and now is the time to be thinking about that,” she urged. It also helps to focus attention on the all-important autumn pre-emergence herbicide programmes for ryegrass.

Seed collection

Ryegrass seed may be mature for collection from early July, but more typically in mid to late July. Seeds should be sampled when they are brown and fall off the panicle when gently brushed with the hand; if they need to be forcibly rubbed off the plant, it’s too early.

Ryegrass seed for testing

Georgina highlighted that mapping areas of ryegrass during the growing season, with the Syngenta Protector scouting app, for example, makes it quicker and more accurate to return to the precise spot for sampling.

“The development of resistance isn’t necessarily ubiquitous across the farm, so where there is an issue developing in the corner of one field, for example, there may not be an issue in the field next door,” she advised.

“Mapping is one way to understand this detail, to help develop a targeted strategy for the future.”

Read more about mapping ryegrass populations

Resistance testing requires around a mug of seed (approx. 250 – 300 ml), which should be allowed to dry fully before being bagged to send for testing. Samples submitted to testing labs by the end of July, would normally have results back by the end of September, to aid agronomy decision making.

Application on target

For this season, Syngenta has introduced a new 3D ninety nozzle, proven to deliver more effective grass weed control from pre-emergence Defy applications – along with the potential to reduce drift, ensure more spray hits the target and optimise treatment timings.

3D90 application with Spray Assist icon

Find out more information about the 3D ninety and pre-emergence applicaions here