Despite the heavy cost of chemical resistance for Western Australian farmers, the vast majority
still don’t test to see how effective their herbicides are.
The reasons are many, from a lack of time through to cost, but the fact remains,
a lack of knowledge about the effectiveness of herbicide programs is costing growers money.
Weed and Spray Management Consultant Andrew Storrie says the cost of failed herbicides
needs to be better appreciated.
The problem that growers have with herbicide resistance is that they don’t really know
what they’re dealing with in the paddock unless they’ve tested.
And I prefer to call it herbicide susceptibility testing, because really what they want to
know is what herbicides still work.
One of the problems is that they’re spending 80, 100 dollars a hectare and they have no
guarantee that those herbicides are going to be effective.
So that could be wasted money.
Thankfully for growers, there are a number of options available to them to test for herbicide resistance,
or susceptibility, with the choice depending in part on the time of the season.
Growers have two testing options available to them, the quick test and the seed test.
The quick test is done at this time of year, where you collect live plants to send off
for testing and you get a turnaround in about six weeks.
The seed test is done at the end of the season and the problem is you’ve got to collect
the seed in a very busy time of year and often when the weather is unpleasant.
So faced with a choice of the seed test and the quick test to determine herbicide susceptibility,
what should growers do?
Andrew Storrie says aiming to get a quick test done during mid-season is ideal as it
provides valuable information in time to make important management decisions.
The quick test is, you would do it now, and probably for the next two months, the beauty
of it is that you get the results back within six weeks and you can make management decisions
this year before your weeds set seed, which means you stop them in their tracks.
The seed test can only be done after the weeds have set seed, so that means that seed is
going back in the paddock’s seed bank and creating a problem for next year.
So you can’t actually do anything about your resistance problem until next year,
so that puts you behind the eight ball.
The weeds in this Roundup Ready canola crop showed signs of herbicide resistance after being sprayed
with Glyphosate a month earlier.
In this case, the quick test is an ideal option for gathering information mid-season,
however it’s critical the samples are taken correctly.
So the important thing when collecting the samples for a quick test is that they have roots on them.
So we need about 100 plants minimum, and the more herbicides you will test for,
the more plants you will need for the test.
So we dig the plant up, shake a bit of soil off,
rinse them so we don’t have too much soil on the roots,
then the other thing is we need to wrap them in a bit of paper towel.
We don’t want them too wet otherwise they’ll go rotten,
we put them in a zip lock bag,
then we send them by express post to the lab.
This must be done on a Monday.
If you’re collecting these plants later in the week, keep them in the fridge until the Monday,
get them in the mail so they’re spending the shortest amount of time in the mail
before they get to that lab – you’ll get the best results that way.
Resistance testing should be part of every growers’ management package - we test for soil fertility,
we should be testing for herbicide susceptibility,
otherwise you’re going to be wasting lots of money
and wasting lots of time.
The Department of Agriculture and Food WA website offers comprehensive information about on
how to perform a seed test and a quick test for herbicide susceptibility.
In addition, you can links to lab testing services on the DAFWA website.