Dry Sowing: Do We Wait For A Knockdown Or Go In With Pre-Emergents

Dry Sowing: Do we wait for a knockdown or go in with pre-emergents?   Each year Autumn rain seems harder to get, and each year…
March 12, 2020Seed Back to All

Dry Sowing: Do we wait for a knockdown or go in with pre-emergents?


Each year Autumn rain seems harder to get, and each year there seem to be fewer weeds germinating for a good knockdown at seeding time, which leaves us with a question: Do we delay seeding to get a knockdown? Or do we go in without a knockdown? 

In most cases, research supports that we go straight in and not wait. Just ensure other weed management strategies are organised.


Chris Preston, and his team from The University of Adelaide, has shown that early sown crops can compete better with weeds. This is because they are growing in warmer conditions and putting pressure on ryegrass and other weeds. Their research shows ryegrass will set a similar amount of seed regardless of whether sowing was early or delayed to get a knockdown. The key points are this: Sowing your crop in the right sowing window for the variety will maximise yield and help boost crop competition. Don’t worry about knockdowns. We can fight weeds with a robust pre-emergent herbicide package. Preston’s trial results demonstrate how sowing early maximises yields regardless of ryegrass seed below. 



Table 1: Ryegrass density in crop, headcounts in spring and wheat yield for two times of sowing at Hart, SA 2014, where Sakura was applied pre-sowing (118g/ha). (Australian Herbicide Resistance Initiative 2019) 




So, if you take away one thing from this article, make sure it’s this – don’t let weeds determine when you sow. Sow to benefit your variety. And if that means going in without a knockdown,then go for it. Your yields will be better for it. Just ensure you have a pre-emergent herbicide plan to tidy up any weeds.

If you start letting weeds call the shots in your system, you’ll lose money. Working around weeds means changing rotations, delaying sowing, and even leaving paddocks out—all to the detriment of our profits. 

Remember that the factor that allows us to get away without a knockdown spray is the use of a robust pre-emergent herbicide package. Mix at least two herbicides, and make sure they’re herbicides which suit the situation. For example, trifluralin (where there is no resistance) could be a better option in drier conditions than Sakura, as Sakura requires some rainfall to activate it. 

The money saved from skipping a knockdown could be used on pre-emergent herbicides that may even do a better job. Just remember to keep rotating chemistry to stop resistance. 

Also, try to maximise the growth of a competitive crop with the following; utilise narrow row spacings, use higher seeding rates, try east-to-west sowing, competitive cultivars, and improving healthy soils. 

If you’re still itching for a knockdown spray, remember if you miss the knockdown at the start of the season, you can always try to get one at the end of the season. You can stop the weed set cycle with crop topping, or hay cutting if appropriate, and by using harvest weed seed control techniques when harvesting. 

We wish everyone the best of luck seeding this year!