Six strategies to help win the war against herbicide resistant ryegrass

19 March 2024

About

  • Date

    19 March, 2024

About

Date

19 March, 2024

Ryegrass is a very competitive weed with low populations economically reducing yield. Work by FAR and in the UK has demonstrated the devasting impact ryegrass can have, with just 5 plants/m2 capable of reducing yield by 5%.

If this wasn’t enough ryegrass germinates over a prolonged period, is a prolific seeder, and it tends to develop resistance to herbicides. It could be the perfect weed!

Recent surveys have shown ryegrass resistance to group 1 and 2 herbicides occurs throughout NZ and so wherever you farm there is a risk you have herbicide ryegrass resistant on your farm.

If you farm in South Canterbury the risk is much higher and unfortunately it is probable that you have herbicide resistant ryegrass to deal with.

Individual plants having a resistance to herbicides occur naturally in any population. Due to the open pollination method of ryegrass that involves pollen transfer between plants, and the high number of seeds produced by ryegrass, the potential for herbicide resistant populations to rapidly develop is high.

About

Date

19 March, 2024

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Dr Peter Boutsalis of Plant Science Consulting discussing the impact of herbicide resistance in Australia to a group of Bayer field staff and customers

Dr Peter Boutsalis of Plant Science Consulting discussing the impact of herbicide resistance in Australia to a group of Bayer field staff and customers

In NZ this risk is amplified by the area of ryegrass seed crops grown.

A ryegrass seed crop being grown in Canterbury

A ryegrass seed crop being grown in Canterbury

Controlling ryegrass is all about reducing seed return and there are several strategies you can adopt to do this. Each of these will effectively reduce seed return but individually none is likely to be sufficient. The trick is to stack strategies together to achieve a sufficient reduction in seed return to start reducing the seed bank in your paddocks.

Our Australian friends, who have been battling herbicide resistant ryegrass for many years, have needed to adopt strategies in addition to the ones outlined below. For instance, the use of seed terminators or growing a double break crop.

Seed terminators, fitted to the back of Australian harvesters, are an effective way of reducing the amount of ryegrass seed returned to the paddock and therefore reducing the seedbank

Seed terminators, fitted to the back of Australian harvesters, are an effective way of reducing the amount of ryegrass seed returned to the paddock and therefore reducing the seedbank

While these are not commonplace yet in New Zealand, they demonstrate the lengths that Australian farmers have found necessary to combat resistant ryegrass, and this emphasizes the importance of employing preventative strategies now to reduce ryegrass seed return in New Zealand.

1. Keep the seed within the top few centimeters of the seedbed. This encourages a more complete germination of weeds and allows pre-emergent herbicides to reach the roots of the germinating weed seeds, resulting in a greater level of weed control.

2. Produce a moist, firm, clod free seedbed to enable herbicides to work effectively and to aid rapid, even crop germination. Clods can physically shield soil from receiving herbicide and can also break down during the winter and release seed at a time residual herbicides are losing efficacy.

Time and care taken preparing a seedbed prior to planting and the application of Sakura pays dividends as the season progresses.

Time and care taken preparing a seedbed prior to planting and the application of Sakura pays dividends as the season progresses. The crop emerges quickly and evenly, weed seed is kept near the surface, and the firm, moist, clod free seedbed enables herbicides to work effectively

3. Plant on time to ensure vigorous crop competition. Crop competition from both wheat and barley very effectively controls the growth of ryegrass, and it can be more effective than delaying planting to create a stale seedbed.

4. Ensure you vary the herbicide modes of action you apply in any season, either in mixture or in herbicide programmes. Aim for a varied crop rotation to allow other modes of action to be applied in subsequent years.

5. Apply a herbicide programme to provide long lasting control to deal with the prolonged germination pattern of ryegrass. An effective programme for wheat (not durum wheat) is to apply Sakura® post-planting pre-emergence and Othello® OD in late winter. 

Weed control in cereals starts now

Caption Sakura applied post planting of the crop and pre-emergence of grass weeds followed by Othello OD applied in late winter has proved to very effectively control ryegrass weeds in wheat (not durum wheat)

6. Ryegrass escapes are inevitable. If possible, control these to prevent seed set. Depending on numbers and pressure this can include rogueing and cutting weedy areas such as headlands for hay.

Please remember controlling ryegrass is challenging and it doesn’t go right every season. It only takes one of the strategies you are using to suffer a problem and ryegrass control can get away. While everyone wants to control ryegrass 100% the important thing to remember is that any reduction in seed return is beneficial.

An Australian paddock in 2023 showing what can happen when even the best strategies to control ryegrass go wrong!

An Australian paddock in 2023 showing what can happen when even the best strategies to control ryegrass go wrong!