Read time: 6 minutes

Is crop rotation an economic option for managing weeds?

With Tony Swan, Senior Experimental Scientist, CSIRO Agriculture

While wheat is the dominant commodity in Australia’s grain production systems, sowing consecutive wheat crops results in reduced production and profitability due to the effects of diseases, pests, weeds and declining nutrition.

Adding a broadleaf break crop to the cropping sequence helps keep wheat profitable in a sustainable cropping system.

3

Tony Swan, CSIRO says their 5-year GRDC funded project illustrated that adding at least one break crop, and preferably two, to the crop rotation was beneficial for weed control and nitrogen management, and can be as profitable or more profitable than continuous wheat. A series of experiments were established to challenge the idea that break crops are risky and not profitable.

“Many farmers in south-east Australia are sceptical about growing break crops such as pulses and canola,” says Tony. “The problem is, once high populations of herbicide resistant annual ryegrass become apparent, the profitability of continuous wheat significantly reduces.”

“Rotations that include a break crop in paddocks with high populations of resistant annual ryegrass were more profitable than continuous wheat and had significantly less ryegrass numbers after three years, provided all the available tactics were used to reduce germination and prevent seed set,” he says. “Our experiments demonstrated that it is cheaper and more effective to control ryegrass using one of the many break crop options than attempting to achieve control in wheat using expensive herbicides.”

What break crop options did you trial?

Short answer: RR canola, TT canola, lupins for grain, field peas for brown manure, fallow and wheat cut for hay.

Longer answer: The combination of a fallow or break crop in year 1 followed by a second break crop in year 2 resulted in the greatest reduction in annual ryegrass seed bank population and panicle number after 3 years. This sequence was significantly more profitable than continuous wheat, but not as profitable as a RR canola–wheat (high input) –wheat rotation.

What was the most effective option in a weedy situation?

Short answer: A 2-year break crop option.

Longer answer: The double break rotations of lupins grown for grain followed by RR canola, or RR canola followed by wheat cut for hay provided a very high level of weed control while also generating high average annual 3-year gross margins of $790/ha/yr and $834/ha/yr, respectively. This compared to the most profitable 3-year sequence of RR canola followed by wheat (high input) / wheat of $883/ha/year. However, this sequence did not achieve the same reduction in annual ryegrass and grass herbicides cost over $140/ha in the wheat crops. Sequences that included fallow or brown manures followed by RR canola were extremely effective at reducing the annual ryegrass seed bank but were not as profitable as continuous cropping.

Where herbicide resistant annual ryegrass is a major problem, an alternate three year sequence of wheat-hay (sprayed afterwards) in year 1, pulse-grain (spray topped) in year 2, and RR canola in year 3 can be profitable and also reduce the seed bank to extremely low levels.

A two-year break crop can break the weed cycle without breaking the bank.

A two-year break crop can break the weed cycle without breaking the bank.

What is the key recommendation from this trial work for annual ryegrass control?

Short answer: Two consecutive years of total annual ryegrass control using break crops and implementing all available weed seed control options.

Longer answer: Break crops work and can be profitable. Two or more years of effective ryegrass control using break crops and other management options including strongly competitive crops, rotating herbicide groups, pre and post emergent timing and prevention of seed set using crop topping, hay making and brown manuring along with fallow management and harvest weed seed control such as narrow windrow burning.

How to ask WeedSmart a question

Ask your questions about using break crops to manage annual ryegrass on Facebook or Twitter @WeedSmartAU or leave a comment below.

Related Articles

Related Articles

View all
Article
Ask an Expert

How does crop competition support other weed control tactics?

Crop competition is a quiet achiever in weed control that also has a synergistic effect when applied with other tactics. Read More...
Article
News

WeedSmart Big 6 for Mallee farms in NSW, Vic and SA

Get started with the WeedSmart Big 6 tailored for the Mallee region. Read More...
Article
Ask an Expert

Can faba bean crops outcompete sowthistle?

Faba bean crops have the potential to significantly curb common sowthistle, a problematic weed with widespread resistance to key herbicides. Read More...

Webinars

View all
Video
Webinar

How faba beans pack a punch against sowthistle

Research shows there are opportunities to alter the agronomy of faba beans to suppress sowthistle growth and seed production in crop. Read More...
Video
Webinar

Combat Velocity® resistant wild radish with the WeedSmart Big 6

AHRI researcher Dr Roberto Busi explains in this webinar how he discovered Velocity® resistant wild radish populations in two paddocks in the northern Wheatbelt of Western Australia. Read More...
Video
Webinar

No survivors – weed control in cotton, what does it look like in 2022?

Research Agronomist Eric Koetz and WeedSmart Northern Extension Agronomist Paul McIntosh discuss key weed control challenges cotton growers are facing. Read More...

Videos

View all
Video
Webinar

How faba beans pack a punch against sowthistle

Research shows there are opportunities to alter the agronomy of faba beans to suppress sowthistle growth and seed production in crop. Read More...
Video
Webinar

Combat Velocity® resistant wild radish with the WeedSmart Big 6

AHRI researcher Dr Roberto Busi explains in this webinar how he discovered Velocity® resistant wild radish populations in two paddocks in the northern Wheatbelt of Western Australia. Read More...
Video
Webinar

No survivors – weed control in cotton, what does it look like in 2022?

Research Agronomist Eric Koetz and WeedSmart Northern Extension Agronomist Paul McIntosh discuss key weed control challenges cotton growers are facing. Read More...

Factsheets

View all
Fact Sheet

Windrow burn chute for CASE harvester

CAD designs for a narrow windrow burning chute suited to a CASE header – suitable for adaptation to other harvester makes. Read More...
Fact Sheet

Wild radish factsheet

Increasing resistance to multiple herbicide modes of action is forcing growers to adopt diverse strategies to control wild radish. Read More...
Fact Sheet

Farm Practices Survey Report 2021

The report provides information on the adoption of a range of weed management practices on Australian grain farms. Read More...

Subscribe to the WeedSmart Newsletter