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When ryegrass becomes glyphosate tolerant

HOT TOPIC: The ryegrass population is becoming glyphosate resistant according to Paul McIntosh.
HOT TOPIC: The ryegrass population is becoming glyphosate resistant according to Paul McIntosh. Contributed

IN MY last article in Rural Weekly I talked about annual ryegrass (ARG) now becoming a plant out of place, or a weed basically.

I gave a brief explanation of plant fitness with the extra possibility of possessing the double mutation (that little bit of internal difference in some ARG plants' make-up) and about having large amounts of ryegrass survivors after a cropping sequence, especially after using a Group A clethodim selective grass herbicide product and not controlling them in crop.

I did say it can get worse and it can when you are dealing with a plant like annual ryegrass, which we originally planted as a livestock feed crop. So the next considerable blow to the southern farming systems is that these same ryegrass populations can "easily” get glyphosate resistant. So you cannot control them with our Group A dim or fop grass products and then you also get survivors from our once-in-a-lifetime Roundup product, more commonly known as glyphosate these days.

Even if they are only glyphosate-resistant plants, that is still a huge blow to our farming systems in those southern areas. Now do not assume "thank goodness it does not grow up here” as it can sneak in and really we have our own problems developing similar glyphosate resistance in our farming system.

Let us look at some disturbing characteristics that annual ryegrass has that make it a number one herbicide- resistant weed in my eyes.

All stages of growth can be gly resistant. Resistance can be transferred by pollen and seed and the progeny from survivors after a herbicide application can be more resistant.

That is enough to make your eyes water to know that with an outcrosser (pollen is exchanged with other nearby ryegrass plants) like ryegrass, that if you have two resistant ryegrass plants next to each other in a field, their progeny can be even more resistant to the particular herbicides you have used.

Thank goodness we do not have acres of ryegrass, however we do have wild radish here in the north and that can go the same way as ARG has done. Perhaps the only practice saving us from paddocks of white-flowered (yellow faded actually) resistant radish plants is our summer and winter farming system.

Another slight benefit in our favour is that some samples taken of glyphosate-resistant ARG plants show a reduced fitness level. In other words, they are less competitive than other non-resistant ryegrass plants. By less competitive I mean they can produce less seed. So hence why one of the major tips or tactic to be considered in our developing herbicide-resistance war is crop competition to stop or reduce seed set by our species of weeds in the north.

The continuing bad news is that this ARG plant and others can have a double glyphosate- resistant mechanism, by both translocation and target site resistance, and that is a story for another day.

So, on your property what changes to practice can you make that will reduce future resistance problems with your own weeds. Sure, continuous cultivation kills weeds and can bury the weed seed bank, however do you really want to go back down that path and lose all the soil and moisture conservation benefits of zero or min till, plus your valuable time to go over the paddock several times at 10km/h.

Start planning if you haven't already. Herbicide resistance is not going to fade away and while you may get tired of hearing about it, do not assume someone will come up with another miracle herbicide that will take care of all our weed problems.

The silver bullet was glyphosate and we have overused and overexposed that product or Group M mode of action so that our barnyard grass, our liverseed/urochloa grass, our milk thistle plus others, are now at our front gate with herbicide resistance in their natural make-up.

Topics:  column farming news glyphosate paul mcintosh weed control