Plan your attack on the weed seed bank

Here we summarise the key components of the WeedSmart Big 6 strategies and the principles that underpin them. There is even more detail in the GRDC’s Integrated Weed Management manual and workshop handbook. You can also test your plan using AHRI’s WIM decision support software for annual ryegrass, brome grass, barley grass, wild oats and barnyard grass.

1. Rotate crops and pastures

Short rotations cause herbicide resistance! This is because of the inherent lack of diversity.

Weed populations quickly respond to routine management practices – those that survive will set seed and their progeny have an advantage when the same control tactic is used again soon after.

Principle #1 Diversity in herbicide choices, diversity in cultural practices

Principle #2 Use double breaks, fallow and pasture phases to drive the weed seedbank down over consecutive years

2. Mix and rotate herbicide MOA

Before herbicide selection has taken place it is very rare for an individual weed to be resistant to two herbicides. Mixing herbicides at full label rates in a single application takes advantage of this fact.

Within an integrated weed control program, try to make sure there is rotation and mixing going on in each phase – in the fallow, pre-seeding, in-crop and for desiccation. When done in conjunction with a determination to stop seed set and remove survivors, it is possible to keep weed numbers low.

Principle #1 Rotating buys you time, mixing buys you shots

Principle #2 Rotate between herbicide groups

Principle #3 Use different groups within the same herbicide mix

Principle #4 Always use full label rates

3. Double-knock to protect glyphosate

The idea of a double-knock for weed control is to use one tactic, usually a herbicide, to kill the majority of weeds and follow-up with another tactic, usually a herbicide from a different mode of action group, to kill any survivors.

This can also be a herbicide followed by a non-herbicide tool (e.g. the ‘Canola Combo’ – crop top followed by HWSC or herbicide followed by tillage). All that really matters is any resistant survivors to the first herbicide are hit with another control measure so that the weeds don’t set seed.

Principle #1 Follow glyphosate with a high rate of paraquat to control survivors in a fallow or pre-sowing situation

Principle #2 Employ a non-herbicide tool after glyphosate to prevent seed set of survivors

4. Stop weed seed set

Reducing the weed seed bank is the ultimate goal of any weed management program and it becomes super-critical once herbicide resistance has gained a foot hold.

Principle #1 Take no prisoners and act early on weedy patches

Principle #2 Tactics that work to drive down the weed seed bank after a blow-out

5. Increase crop competition

A competitive crop will suffer less yield loss at the hands of the weeds, and will also reduce seed set of the weeds compared to an un-competitive crop. In other words more crop, fewer weeds.

Principle #1 Set your crop up to stay ahead of the weeds

Principle #2 Adopt at least one competitive strategy (but two is better)

6. Implement harvest weed seed control

Collecting and destroying any weed seeds as part of the harvest operation is rapidly gaining traction on Australian grain farms.

Principle #1 Collect and kill weed seeds at harvest

Principle #2 All the six HWSC options are effective – choose the one that suits your system best

WeedSmart Wisdom

• Never cut the rate – always follow label instructions
• Spray well – choose correct nozzles, adjuvants and water rates
• Clean seed – don’t seed resistant weeds
• Clean borders – avoid evolving resistance on the fence line
• Test – know your resistance levels

Key resources

Integrated weed management in Australian cropping systems manual

Integrated weed management (workshop handbook)

AHRI’s WIM decision support software

Case study – Curry family, Junee

WeedSmart Big 6

WeedSmart Wisdom