Autumn control is key for rat’s tail fescue

Early action is key to preventing rat’s tail fescue from becoming established, writes Teagasc Researcher, Vijaya Bhaskar.

Rat’s-tail fescue is an unusual grass weed that is becoming an increasing problem in non-inversion crop establishment systems. The weed is naturally tolerant to some post-emergence herbicides, making effective autumn management particularly important.

Glyphosate

For most grass weeds, targeting small plants at the 2-4 leaf stage is important for effective glyphosate control. However, with rat’s tail fescue, even the maximum glyphosate rate may not provide complete control at this growth stage (Figure 1).

Effective control was achieved when larger, tillering plants with a dense canopy were targeted at higher rates, with the maximum rate of 1440 g/ha (now the recommended label rate for annual and perennial grass weed control in stubble or pre-sowing applications) providing the best results (Figure 1).

Figure 1. Rat’s tail fescue 30 days after application of glyphosate products. When small plants were treated, surviving green plants, including some that were severely damaged remained in all pots and subsequently recovered. In contrast, treatment of larger, tillering plants provided better control, but only at higher rates (1440 g/ha for both non-Roundup and Roundup brands).

Residual herbicides

Getting residual programmes right is more important than ever. Residual herbicides provide broad-spectrum weed control, but the results presented here are specific to rat’s-tail fescue and cannot be used to predict responses in other weed species (Figure 2).

Pre-emergence application gave the best results, with all seven products providing effective control (Figure 2). Most products also provided control or useful growth suppression when applied at the 1-leaf stage. Efficacy declined significantly when applications were made at the 2-4 leaf stage, with differences between products becoming more pronounced. Applications at the early tillering stage were largely ineffective, providing poor suppression.

Tower, which contains multiple active ingredients, delivered consistent and effective control in these experimental conditions across all application timings.

Figure 2. Effects of residual herbicides on rat’s tail fescue 30 days post-treatment, applied at the recommended label rate across different application timings. Products Fundatis and Luxinum are not currently registered for use in Ireland.

Key message

With winter cereal harvest now fully complete, stale seedbeds can be used to encourage rat’s-tail fescue emergence before drilling, with glyphosate applied once the plants have developed sufficiently for effective control.

Combining pre-sowing glyphosate application with a pre-emergence herbicide (applied 24 to 48 hours after drilling), will provide the best chance of achieving control.

Other actions, including spring cropping and delayed autumn drilling, can also reduce populations, while deep ploughing can provide a useful reset where infestations have become established.