The ability to rotate crops and herbicides plays a critical role in reducing the threat of annual ryegrass at Wyalkatchem, in the central wheatbelt of Western Australia.
Nutrien agronomist, Bernie Quade, said the area grew a range of winter crops including wheat, barley, canola, lupins, and oats, with weeds such as annual ryegrass and wild radish providing the major challenges. He said they were trying to keep weed numbers down through crop rotations and different herbicide (mode of action) groups, although it could be challenging depending on the seasonal conditions and other factors. "Every business is different,” Mr Quade said. "As far as a rotation, if people can do a double break, and that might look like lupins followed by canola, or fallow followed by canola – that will get our numbers down a bit." He said the wheat crop could be two in a row or even three or four in a row depending on the paddock and when the season starts. "If we have a wet summer and a nice early break then our break crop area will naturally go up. If we have a dry summer, a late break, then our break crop area will go down.”
Canola has been an excellent option as a key break crop going from a break-even option to a profitable crop, that, in some years, competes well with cereals. "We are seeding earlier, and we know that there is a yield upside to that,” Mr Quade said. "We've changed from open pollinators to hybrids and using higher rates of N in the right circumstances." He said they were using crop rotations, initially to try to get weed numbers down and then utilising a range of herbicides to stay on top of the annual ryegrass and wild radish numbers. "The knockdown herbicides have to be bang-on. We can't have any survivors once the crops are getting seeded. We're very fortunate with pre-emergents that there are a lot from different herbicide (mode of action) groups to pick from.”
There are challenges, however, with some populations of annual ryegrass showing resistance to a range of pre-emergent herbicides. "There are problems with Treflan*, the old group Ds, (Group 3) and it is emerging in the Group Ks (now Group 15) which includes prosulfocarb, Boxer Gold*, Sakura* (pyroxasulfone). We really want to hang on to that group of chemistry so naturally we need to diversify to do that." Mr Quade said there were some newer products available in single or multiple crop types which should be utilised as part of the herbicide rotation. There are options other than a Group K (now Group 15) in the wheat program that provide very good annual ryegrass control which will also prolong the life of all our other herbicide groups."
Overwatch® Herbicide from FMC is one herbicide that has been utilised in recent years in both canola and wheat. "Initially It was a very good way for us to use it in canola to break up our propyzamide use,”Mr Quade said. "We then realised we had developing issues with prosulfocarb and pyroxasulfone and we now have had to use more of it in our cereal crops."
Overwatch® can show some transient bleaching in certain circumstances, and he said they made sure their farmers were aware of how it should be used. "We just made sure anyone that was using it, used it in the right way so that we're getting good crop safety,” he said. "We were very happy with not only the performance on the annual ryegrass, but also crop safety.. We navigated our way through the difficulties earlier on in the piece, to a point where everyone's very comfortable with it as a product both from a crop safety and performance point of view.”
He said the majority of farmers in the area had precision seeders and were planting their cereals at depths of 30 mm and not driving too fast. The bleaching challenges with Overwatch® Herbicide were an indication to get the seeding right. "Overwatch® has these symptoms that we can see straightaway, but they could have been causing damage with other herbicides, that are not so visual," Mr Quade said. "It's probably been a good indicator for them that they need to fix something, not just from that Overwatch® point of view, but from a range of other products they are using as well."
He said each season trials are conducted in the area to develop knowledge around new products and see how they perform against farmers' standards. In 2023 a wheat trial compared different pre-emergent and early post-emergent treatments for the control of wild radish and annual ryegrass. The trial had good numbers of both weeds, so they were able to get a good assessment around the different herbicide options. Mr Quade said the best performing treatment was Overwatch® Herbicide up-front followed by Mateno* Complete, early post-emergent. "This was considerable upfront investment but it ended up being the highest-yielding treatment and also the most profitable treatment," he said. "It's not just about that financial result. By throwing what we did at that plot, we're also trying to get that weed seed bank down and prolong the life of all our products. They're all supporting each other."
