Making farming systems WeedSmart

This is where the WeedSmart Big 6 can help guide discussions about weed management within the broader farming system. Dealing with herbicide resistance can be frustrating, but if you get good advice and use the WeedSmart Big 6 checklist, you will soon be on track with an integrated plan to keep weed numbers low.

Based at Wallaroo, SA, Chris Davey, WeedSmart’s southern extension agronomist, says crop competition is a quiet achiever in weed control that also has a synergistic effect when applied with other tactics.

Chris says that if you do nothing else different except increase crop competitiveness, there will be fewer weeds in the crop and fewer weed seeds added to the seed bank. Increasing crop competition often reduces weed seed production by around 50 per cent.

“When there is a competitive crop growing, the herbicides work better and harvest weed seed control works better,” Chris says. “By suppressing weed numbers, growers can avoid the difficulties that come with herbicide resistance and weeds have less control over crop choices.”

“Everyone has seen weeds flourish in a bare patch in-crop,” he says. “The quicker the crop can cover the inter-row space, the better. This is where pre-emergent herbicides and varieties with rapid early growth work well together. More competitive crops also assist with holding weed seed heads in the canopy ready for destruction with harvest weed seed control tactics.”

The WeedSmart Big 6 integrated weed management program starts with maximising crop competition to suppress weed seed production. Then, add the other strategies, such as a diverse farming system, mixing and rotating herbicide modes of action, preventing weed seed set and implementing harvest weed seed control, to reduce the impact of herbicide resistance on your business.

Strategy #1 Increase crop competition

A competitive crop will suffer less yield loss at the hands of the weeds and will reduce weed seed set compared to an un-competitive crop. Use competitive crops and varieties that suppress weed growth through shading and resource competition. This includes selecting crops with good early vigour and canopy closure.

There are at least six ways to boost crop competition – increased seeding rate, narrower row spacing, planting east–west, addressing soil constraints, choosing vigorous or competitive varieties and correct sowing time.

Strategy #2 Rotate crops and pastures

Short rotations speed up herbicide resistance evolution because weed populations quickly respond to predictable management practices. Implement a crop rotation system that includes different crops and pastures, with differing planting and harvest times, to disrupt weed life cycles and reduce weed pressure. Double-breaks are an effective tool to drive down the seed bank of aggressive weeds like annual ryegrass.

Strategy #3 Mix and rotate herbicides

Any herbicide program that relies heavily on one or two herbicide modes of action for a target weed is bound to fail eventually. Rotate modes of action to keep herbicides working longer and use compatible herbicide mixes to safeguard each mode of action. Test weeds for resistance and susceptibility to individual modes of action and mixes. Always apply each herbicide at the full label rate.

Strategy #4 Optimise spray efficacy

Use the correct herbicide application techniques and equipment to optimise spray efficacy. This includes using the correct nozzle, spray pressure, and spray volume for the target weed species. Ensure the full dose of every herbicide hits the target.

Strategy #5 Stop weed seed set

Avoid replenishing the weed seed bank in your paddocks. Prevent weeds from producing viable seeds by implementing early weed control, preventing weed escapes, and managing weed patches effectively. Swathing, crop-topping, brown manuring and cutting for hay are all very effective ways to nip a weed problem in the bud.

Strategy #6 Implement harvest weed seed control

Implement practices to capture and destroy weed seeds during harvest. Consider harvest timing and height, aiming to get maximum weed seed into the header. Six highly effective harvest weed seed control tools, including chaff carts, chaff lining, and impact mills, are available. Choose the one that best suits your operation.

Test-drive your strategy

You can also test your plan using AHRI’s Weed Integrated Management (WIM) decision support software for annual ryegrass, brome grass, barley grass, wild oats and barnyard grass.

Controlling weeds is an ongoing task and requires determination and persistence. Having a great plan of attack is essential. By incorporating the Big 6 strategies into your weed management program, you can effectively reduce weed populations and minimise the impact of weeds on your crops.