How can I make the most of spring planning sessions?

Spring is a critical time to evaluate the current season’s weed management program and revise plans for the next season.

Growers and their advisors can make the most of these planning sessions using the WeedSmart Big 6 as a framework for the discussions to maximise the diversity of herbicide and non-herbicide tactics employed.

Anna Hose, agronomy advisor with Premier Ag in the high rainfall zone (HRZ) in Victoria’s south-west, says the spring planning sessions she has with growers are vitally important to keep ahead of weeds and herbicide resistance.

“Ryegrass is our biggest challenge in the HRZ, and we can’t manage what we haven’t measured. Identifying paddocks for resistance testing is critical to planning herbicide programs for the season,” she says. “Any newly acquired paddocks or paddocks that have had ryegrass escape the planned program for the season are obvious candidates for herbicide resistance testing.”

“Before harvest, usually in November or December, we will return to those selected paddocks and collect weed seed for testing,” says Anna. “We send the seed to Plant Science Consulting, and they run the resistance testing over summer.”

Anna says once the results are available in January or February, she revisits the herbicide plans for the affected paddocks and makes any required changes.

Growers can also send weed seed samples to the CSU and UWA herbicide resistance testing services.

What actions can be taken following a herbicide resistance test?

In brief: Knowing what works and what does not work is very valuable information and can save growers from wasting money on a herbicide that won’t do the job.

The details: The herbicide resistance test helps make decisions around double-knock strategies. With increasing glyphosate resistance, paraquat followed by paraquat may be the most effective option.

The results will also highlight the best options for the pre-emergent herbicide package and the in-crop weed control. For instance, we see a synergistic effect by mixing glyphosate and clethodim, so if glyphosate resistance is evident, this is an important mixing option for use in RoundUp Ready canola.

With the pre-emergent herbicides, there has been heavy reliance on Sakura and Treflan because of their versatility, so to preserve these herbicides, it is necessary to rotate away from them as much as possible across the crop rotation.

The new suite of pre-emergent herbicides allows growers to add more diversity to their herbicide program. Final product selections sometimes have to wait until just before planting to take into account the conditions at sowing, such as the amount of stubble cover, the timing of operations and weather conditions (e.g. dry vs wet sowing).

What are the main levers for weed control in the HRZ?

In brief: Good drainage, strategic crop rotation and sustainable herbicide usage.

The details: Poor drainage is a key concern for weed control in the high rainfall zone. The last three years have been particularly wet and clearly demonstrated the value of good paddock drainage.

There are two things that ryegrass loves, and crops do not – wet feet and acidity. Raised beds and well-designed drains have proven their worth throughout the HRZ.

Effective drainage also allows timely access to paddocks for seeding and spraying operations. Time spent on drainage works over summer will invariably pay off with better weed control and improved crop yield.

Drainage programs go hand-in-hand with rotation planning. When cultivating paddocks, we bury weed seed and must ensure we have spray topping options for later-germinating ryegrass in the crop that follows a renovation. Canola fits well in such situations.

Why have long-term goals for weed control?

In brief: Sometimes, it is necessary to accept a slight yield reduction in break crops to achieve long-term dividends.

The details: Planning the crop rotation is an important tool in minimising ryegrass blowouts. In the HRZ, it is common for ryegrass seed to shed well before the wheat crops are ready for harvest, so canola and faba beans are useful in ryegrass management because of the pre-harvest weed control options.

Growers can use crop topping in canola or desiccation in faba beans to stop ryegrass seed set. Getting the time right for these operations is critical and needs to be based on the ryegrass maturity and product choice, aiming to achieve 100 per cent control.

Depending on the season and the variety’s length of maturity, it is sometimes necessary to cap the yield potential of a break crop to ensure ryegrass doesn’t set seed. In such situations, it is important to remember the long-term weed control goals.

After harvest, it is beneficial to recheck the paddocks for ryegrass survivors and apply a second knock of paraquat if necessary.

Break crops also provide early grass control options, so don’t underestimate their value in the weed control program. Including break crops often equates to significant cost savings and improved yield in the cereal phase.

It is beneficial to take a long-term view across the rotation when considering using more expensive herbicides to increase the diversity in the program and increase the longevity of some less expensive herbicides.