By Bill Crabtree Agronomist and General Manager of 4Farmers – Feb 2025
There’s been 75 million tonnes of grain grown in the last 4 years in WA, despite two challenging starts. Obviously, our farmers have a love affair with cropping, and rightly so – as our modern tools and farmers are doing a great job. We are now averaging 19 Mt/yr which is up 30% from 10 years ago. We are also cropping more land as the Federal governments pressure on sheep remains, sadly.
With less sheep and pasture, we need excellent weed hygiene, especially for ryegrass. Many wheat farmers are managing to keep their paddocks reasonably clean of rye with a mix of pyroxasulfone at 118 g/ha (also known as Sakura®) and trifluralin at 2 L/ha. Now that pyroxasulfone is more affordable, this combination is more affordable ($35/ha), even in dryer areas.
When I was farming at Morawa, Sakura® was new and very expensive. I would rush out and in one day hit all the hot rye spots on my farm with the full rate of Sakura. This was only 1-2 ha here and there, sometimes 5 ha. Then I would come back with trifluralin and other pre-emergents and go seeding for the next few weeks. This was both efficient and affordable.
Now that the price has dropped, farmers can afford to do whole paddocks and then consider coming back with prosulfocarb post-emergent on the hot spots. These are usually either lower lying areas that get a bit more water, gravel ridges or water repellent soil patches.
Many farmer groups have done trials that show that 2 L/ha of trifluralin might give 75% control and pyroxasulfone might give 92% control. But when you mix these together you might get 98% control. You could say that 98% control is 4 times more effective than 92% control. How can I say this? Well, think of what percent is left behind? With the combination only 2% of ryegrass is left behind and with pyroxasulfone alone 8% is left behind. So, 2% times four (times) is 8%.
When thinking of weed hygiene this makes a lot of sense. This will also be much more economic than the other more sexy ryegrass pre-ems in wheat. I would argue that it is also more effective – again, perhaps four times more effective. But, says the shop-connected agronomist, this will cause resistance by constantly using trifluralin. I’d say, as long as you have good hygiene and grow say a glyphosate or glufosinate tolerant canola following and keep throwing in atrazine, propyzamide or clethodim then I think you will be just fine.
Of course, a fallow will do much the same and store some water and lower risk as well. Another trick with these small areas is to put 10 L/ha of Aquifer on them in April and at $5.60/L get all these weeds up on the first rain. This is quite affordable if it is only a few hectares here and there and creates good hygiene over the whole paddock.