Weed resistance management education critical
Jeshua Smith is used to having tough conversations with local farmers around weed resistance in his job as an Agronomist at Elders Young in New South Wales.
He hopes, in time, it’s a topic he won’t have to raise as often, as farmers get on top of the resistance challenge in a district dominated by wheat and canola. It’s a rotation that has taken a toll on chemistry as growers try to control annual ryegrass and wild radish.
“The prevalence of these weeds in our wheat/canola rotations puts a lot of pressure on older post-emergent chemistries, and a lot of those aren’t effective anymore,” Jeshua says. “In ryegrass, Group Bs have fallen over pretty well and so we have backed ourselves into a corner. In terms of post-emergents, we’ve really only got clethodim and butroxydim left, with clethodim being obviously the preferred option in canola.
“With pre-emergents, I haven’t come across any trifluralin resistance, but I know that with how hard it’s being pushed in the area, it’s not too far off.”
One of Jeshua’s philosophies is that the most expensive herbicide a farmer will ever use is the one that doesn’t work. “For a farmer to spray a crop or fallow and the chemistry not to work, you’ve got the potential there for a weed blowout to occur, which means more weed seed numbers for the following years,” he says.
“Research on annual ryegrass has indicated we’re able to get more than 90% germination of the seed bank within three years. If you’re able to stop the seeds entering that seed bank through good control, we can drive down those numbers really quickly, but if you have a blowout, you’re putting more pressure on the herbicides we have left due to increased populations.”
Jeshua says while many farmers don’t want to talk about resistance management, education is critical.
“It’s a topic that scares a lot of farmers and one of the biggest issues is a lot of the new chemistries that have some form of a unique molecule in them are all more expensive. I try and explain to farmers that by bringing these new chemicals into the rotation now, long-term we’re able to utilise some of those cheaper chemistries we still have.’’
A critical tool for Jeshua in spreading the message about resistance management has been the Diversity Can’t Wait website developed by Bayer. A valuable resource detailing the impact of chemical resistance, it includes a map section which shows how resistance has developed over time in individual districts.
“The website is really valuable to show growers, particularly those I know are going to have resistance issues because of their intensive wheat/canola rotations and the pressures we’re putting on some of the herbicides,” Jeshua says.
“I particularly use the map section to show farmers that resistance is coming. It’s imminent – for example, you can bring up results from 2010 indicating clethodim resistance in this area seven years ago, which sends a message to farmers using that intensive wheat/canola rotation.”
Jeshua is working hard with local growers to get on top of chemical resistance issues through a range of tactics, including resistance testing.
“I’ve been pushing resistance testing particularly for farmers who have either bought new country, which is happening a lot at the moment, or those who have been in those really intensive rotations.’’ The downfall of some older chemicals has increased the value of products such as Sakura® 850 WG herbicide, with Group K chemistry.
“Sakura has a really good t in this area because it is so effective, particularly in our wheat.
It’s product compatibility is also a big bene t, being able to put tri uralin in if we’ve got a slightly dry start or Avadex® if we’re chasing wild oats.’’
Jeshua says it’s a similar theme with post-emergent tactics, with Precept® herbicide (Groups I and H) and Velocity® herbicide (Groups C and H) introducing new, more effective chemistry.
“We don't have any Group C-resistant radish on the east coast that I know about yet, so we're pretty lucky with the combination of Group C and Group H in Velocity. It’s a really good fit, particularly as an early spray, as it’s pretty safe for use from the two-leaf crop stage,” he explains.
“Where we don't have a Group I issue, Precept is also going to be a really good fit to replace Tigrex®, it's a very handy tool to use in rotation.”
Mr Smith says incorporating these kinds of products into rotations will keep costs down and rotational flexibility up for growers.
“Some growers don't want to use something until they're backed into a corner, which is completely the wrong line of thinking. They're going to basically end up in a situation where they're going to be spending a mint year on year to keep their crops growing,” he says.
“Our biggest issue is educating growers about incorporating these tools strategically so we can keep as many herbicides as we can going for as long as possible.”