Tackling annual ryegrass in broadacre cropping systems

Garry Onus, Senior Agronomist at Nutrien Ag Solutions, Moree recently spoke on the topic at WeedSmart Week forum at Dalby, commenting that early control and stacking weed management tactics is the key to prevention of seed set. 

“Annual ryegrass is becoming increasingly prevalent in broadacre cropping systems and with a wide emergence window (from late autumn to spring), we’re seeing widespread resistance to post-emergent herbicides and increasingly to other important herbicides such as glyphosate, which places heavier reliance on pre-emergent herbicides.” 

“There are many ways to attack the problem, and the key is to use as many methods as possible.” 

Know your enemy 

“It’s important to understand where the ryegrass has come from – for example hay, a roadside weed or creek,” said Garry. 

“A resistance test will help to understand what will control it rather than playing Russian Roulette with herbicides and potentially missing opportunities.” 

Stop seed set in fallow 

“If using glyphosate in fallows be prepared to do a double knock with Paraquat, Voraxor®, Sharpen® or similar products but be aware some products come with plant-back restrictions. Don’t create a bigger monster by developing glyphosate resistance,” said Garry. 

“It’s also important to focus on the areas adjoining the crop (e.g., fence lines, gullies, creeks) as these can feed seed into the paddocks. The use of optical sprayers enhances the ability to control annual ryegrass as more robust product rates are normally used.” 

“Don’t be afraid to get the hoe out if necessary for scattered plants and light infestations, and if it’s really bad and herbicides are failing, conservation tillage can help get populations under control.” 

Stop seed set in crop 

“In defined areas of annual ryegrass, consider a non-selective spray or cultivation of that area and if weeds are scattered, chipping is likely to be your best option,” said Garry. 

“If growing wheat, be prepared to use herbicides with residual activity such as Sakura and Luximax® and plan rotations accordingly. If possible, use combinations of residual chemicals so you are not relying on one mode of action. For example, mixing pyroxasulfone (Sakura®) and prosulfocarb (Arcade®) can increase control in wheat crops by 11% and 29% compared to each product alone. Even when using residual chemicals, be prepared to also use post-emergent chemicals as well. For example, using Sakura® and then AXIAL® XTRA to clean up escapes later.” 

“Most new residuals require an IBS treatment which moves the herbicide away from the seed trench, leaving the plant line with no protection.” 

Spray topping and crop topping 

“Spray topping is the late application of selective herbicides to prevent seed set, usually for broadleaf weeds, but can be used for annual ryegrass during flowering. A similar strategy, crop topping is the late application of non-selective herbicides to kill weeds and prevent seed-set, and works best in feed barley and pulses,” said Garry. 

It’s a numbers game 

“Don’t underestimate annual ryegrass resistance,” said Garry. “Use as many of the WeedSmart Big 6 tactics as possible to stop seed set at the beginning and stop the spread once in crop. Practice good hygiene to capture weed seed survivors and be prepared to chip or cultivate if necessary.”  

About WeedSmart 

WeedSmart Week brings together a wealth of knowledge and experience from local and interstate growers, agronomists, and technology experts – putting the spotlight on herbicide resistance and weed control. Designed to engage growers and advisors on the WeedSmart Big 6 messages, WeedSmart Week offers a unique opportunity for growers and industry stakeholders to hear first-hand about innovative and practical weed solutions. 

Nutrien Ag Solutions has recently signed up as a silver partner of the WeedSmart herbicide stewardship program to spread the WeedSmart Big 6 message amongst growers and advisors to tackle herbicide resistance in Australia.   

For more information about sponsorship opportunities and implementing the WeedSmart Big 6, please visit the website: www.weedsmart.org.au