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 #1Stay ahead of the pack
Crop competition with weeds is a ‘winner-takes-all’ battle. When the crop wins their is higher grain yield plus lower weed biomass and lower seed set.
For the crop to win this battle it is very important to give it a head start with effective early weed control. Keeping the crop weed free for the first three to six weeks seems to be a practical target.
To maximise the effectiveness of using the crop as a weed control tactic, start planning the year ahead and do everything possible to reduce the weed seed bank using effective herbicides, weed seed burial, competitive cultivars and harvest weed seed control tactics or hay-making. Back this up with registered pre-emergents and as many non-herbicide tactics in-crop as possible.
Principle #2 Adopt at least one competitive strategy (but two is better)
There are six main avenues to increase crop competition:
1. Increased seed rate
2. Narrower row spacing – without changing seeding rate)
3. Row orientation – sowing east-west where practical
4. Crop choices – more competitive species and / or variety
5. Soil health – less compaction, fix pH and nutrient limitations
6. Time of sowing – early sowing is usually best
It’s hard to include all six in every crop or every paddock – the more you can do the better the odds for your crops to suppress weed growth and seed set.