Pot tests needed to find weeds

06 Mar, 2018 04:00 AM
 Presenters at the Bayer Crop Science Innovation Update, Alan McKay (left), Friedrich Kerz-Moehlendick and Peter Boutsalis with Bayer's head of product development in Australia Sue Cross.
Presenters at the Bayer Crop Science Innovation Update, Alan McKay (left), Friedrich Kerz-Moehlendick and Peter Boutsalis with Bayer's head of product development in Australia Sue Cross.

MORE cereals seed testing and plant sample “pot trials” are needed to monitor herbicide resistance and maintain cost-effective management of cropping weed pests, such as wild radish and annual ryegrass.

That was the message for about 120 agronomists, researchers and agriculture advisors attending the Bayer Crop Science Innovation Update at Optus Stadium, Burswood, on Sunday.

It was delivered by Peter Boutsalis, an Adelaide University researcher monitoring herbicide resistance and investigating new mode of action (MoA) herbicides.

From the outset Dr Boutsalis acknowledged a vested interest in promoting more testing – he also runs Plant Science Consulting (PSC) specialising in commercial herbicide resistance testing and herbicide and weed trials covering all of Australia.

In the 1990s, Dr Boutsalis developed a-four week Quick-test to check herbicide resistance of grass and weed samples, which is used by PSC as part of its commercial testing.

He also said Bayer sponsored hundreds of tests a year to make the data available to farmers.

The baseline information gathered from seed and plant resistance testing was critical, Dr Boutsalis said, for agronomists and farmers to make informed decisions on what combinations of herbicides to use, under what conditions and at what application rates to control weed pests and, importantly, slow the development of genetic and mutational resistance.

There are already concerns about resistance in wild radish to Group A chemicals – different brand-name herbicides with the same active ingredients are grouped by their MoA – and in WA current testing showed glyphosate (Group M) resistance in annual ryegrass at 31 per cent and needing to be watched, Dr Boutsalis said.

“We need to be proactive and try to combat resistance before it gets to significant levels,” he said.

“Why resistance test?

“Because it makes your job a lot easier, when you sit around the table at this time of year with your clients you can make suggestions a lot easier than when you are guessing,” he told attendees.

“It’s so you know which herbicides are going to work.

“Only 1-2pc of cropping paddocks have actually had a (resistance) test, so there’s a lot of unknowns out there and a lot of guessing games.”

Dr Boutsalis pointed out factors, including environmental and application timing and rate, could affect performance of particular groups of herbicides against specific weed targets and create perceptions of their effectiveness that were not entirely accurate.

“Because there is a very low or no resistance to new pre-emergent herbicides – farmers are relying on Sakura, Boxer Gold and others, which is great – but we are starting to see unnecessary selection pressure through overuse of them,” he said.

“We shouldn’t be seeing that if they are rotated more (with herbicides from different MoA groups to knock down individual plants which survive an initial herbicide spray).

“We are missing out on the opportunity to use some older chemistry which are excellent herbicides that still work, for example the Group As - particularly in southern regions where Group As work quite well - and in WA, the Group Es.”

Weed seeds taken from plant survivors, misses or delayed germination samples, or separated out of soil and grain samples, across paddocks could be tested for resistance to provide an accurate picture of what was happening and help to develop a management strategy for properties.

Reports on the results of testing are generated through plantscienceconsulting.com.au Dr Boutsalis said, which provided information on a variety of weed pests across Australia.

The weedresistance.com.au website, compiled from data collected from PSC and Charles Sturt University, also enabled agronomists and farmers to identify what weed species have been identified near their towns or postcodes and to evaluate the latest weed management strategies, he said.

“You have to assume your worst patch (of pest weeds) is the whole paddock and treat accordingly – more aggressively,” Dr Boutsalis said.

“With low level resistance, sometimes increasing the rate (of application) can be the solution.

“Are you gambling on a litre or do you want to go up – spend a little bit more money, a few more dollars per hectare – and make sure you do the job right?

“In some cases however, increasing the rate doesn’t help.

“This is where a pot test can help determine where you are in the spectrum, not only for glyphosate, but also for trifluralin.”

Dr Boutsalis said multiple resistance in wild radish had been detected in WA and other States by testing.

It was relatively difficult to combat without increasing the risk of resistance because, like ryegrass, it was genetically diverse and cross pollinates so resistance genes are transferred.

Also, only half its seeds germinate every year and it had a seedbank life of six to eight or more years when exposed to the same MoA chemicals.

“That’s very important to remember,” Dr Boutsalis said.

“The seeds last for a long time and if you are rotating herbicides every year you may still be exposing the original populations to the same MoA.”

Bromoxynil worked effectively against wild radish, atrazine still worked as dis glyphosate and Velocity, he said.

Using full application rates, rotating MoA groups B, C, F, H and I herbicides “even if cheaper herbicides are working” and spraying early produced best results.

“Some individual resistant weeds can be killed at early growth stages – an extra couple of weeks and they’re invincible,” Dr Boutsalis said.

Against ryegrass, atrazine worked with some low-level resistance and trifluralin also worked in WA but was less effective in South Australia because of resistance, he said.

Test samples had shown ryegrass had least resistance to prosulfocarb and Boxer Gold, Sakura and Paraquat.

Dr Boutsalis said testing had shown emerging trends of resistance detected in fleabane to glyphosate, an 80-90pc resistance in south-east Australia in sowthistle to Group B herbicides and to a lesser extent to groups I and M, very strong multiple resistance in mustards to groups B, I, F and C and some resistance in Rhodes grass to Group M herbicides.

The update also heard from Alan McKay, South Australian Research and Development Institute (SARDI) principal scientist, who had a similar message on increased testing to manage root diseases in cereal crops.

Dr McKay advocated the use of Predicta B, a DNA-based soil testing service available through SARDI accredited agronomists, prior to seeding to identify which soil-borne pathogens pose most risk to their crops.

Bayer Germany’s head of product and project support, research and disease control Friedrich Kerz-Moehlendick also gave an overview of herbicide use and resistance development in Europe.



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