Managing annual ryegrass in the High-Rainfall Zones of Victoria, South Australia and Tasmania

What’s challenging in the HRZ?

Managing annual ryegrass in an economical and sustainable way has been a significant challenge for many years in the high-rainfall zone (HRZ) cropping paddocks of the south-eastern grainbelt. However, the challenge has increased in recent years.

There is now widespread resistance to post-emergent herbicides and increasingly to other important herbicides such as glyphosate, which places heavier reliance on pre-emergent herbicides. However, annual ryegrass germinates throughout winter into spring, which challenges the ability of early season herbicide strategies to control it.

Key messages

• Annual ryegrass in the high-rainfall zone (HRZ) is as competitive as in lower-rainfall environments, with each ryegrass plant reducing cereal yield potential by about 0.3 per cent. There is no benefit to tolerating more weeds in the HRZ than in other environments.
• Pre-emergent herbicides are important tools for annual ryegrass management in the HRZ and are more effective when used in mixtures and sequences than when used alone.
• Crop competition is an important tool for ryegrass management in the HRZ in canola and cereals. Reduced competition results in large annual ryegrass seed production.
• Double-breaks aid in the reduction of annual ryegrass seed production through the ability to include additional tactics to target the weed in consecutive years.
• With a large number of missed weed seeds due to later harvests, harvest weed seed control (HWSC) is less effective in the HRZ. However, it can still play an important role when integrated with other tactics. Ensure extra costs are less than $34 per hectare.
• The best results in terms of both annual ryegrass control and profitability come from stacking multiple tactics each season over several seasons. Extra income from better weed management is obtained in favourable years and more than compensates for less-favourable years.