Glyphosate can­not be lost

US farm­ers hav­ing big trou­ble with re­sis­tance

Central Queensland News - - RURALWEEKLY - PAUL MCINTOSH

APOLO­GIES for talk­ing about weeds again when it is so very dry in all ar­eas of Queens­land.

I be­lieve it will break even­tu­ally and as we get closer to sum­mer­time, then our sum­mer storms could well be large and rapid.

Th­ese storms, with some sig­nif­i­cant rain in them, will bring up a heap of weeds and in days gone by we would rush out about seven to 10 days af­ter the rain has stopped and ap­ply a ro­bust rate of glyphosate with pos­si­bly a com­pan­ion prod­uct, if fu­ture crop se­lec­tion al­lows it with plant backs.

We all know that glyphosate forms the back­bone of our spray­ing pro­grams in trait crops and fal­lows, so while los­ing a group A fop or dim would make it fairly dif­fi­cult for grass con­trol in broadleaf crops, we could prob­a­bly live with it. We re­ally can­not af­ford to lose glyphosate.

That comes from one of my bosses, Pro­fes­sor Steve Powles from AHRI in Perth, and I re­ally do agree with him.

As much as I can con­clude, there are maybe six mech­a­nisms of glyphosate re­sis­tance in Aus­tralia now.

The one mech­a­nism I wish to com­ment on is gene am­pli­fi­ca­tion.

If you are still re­cov­er­ing from my state­ment of six mech­a­nisms of glyphosate re­sis­tance in Aus­tralia, you can breathe a lit­tle eas­ier know­ing they are not all present in Queens­land... yet.

Right, the gene am­pli­fi­ca­tion re­sis­tance story.

Glyphosate con­trols plants by in­hibit­ing a crit­i­cal plant growth en­zyme called EPSPS.

So for years we have been us­ing la­bel rates of 500ml to 3L/ha of glyphosate and th­ese mil­lions of mol­e­cules of our favourite knock­down her­bi­cide pen­e­trate the leaf sur­face and make their way to the plant growth en­zyme called EPSPS to halt fur­ther growth and the plant dies.

A good re­sult and ex­plains a lot from over the years of us­ing too low a rate at times and get­ting a poor re­sult.

Many of us have heard the Yanks are hav­ing mas­sive prob­lems with palmer ama­ranth, which is evolved to glyphosate-re­sis­tant sta­tus.

Af­ter many years of spray­ing glyphosate in fal­low and over cot­ton, corn, soy­bean crops etc, this tall ama­ran­thus species in the US has be­come glyphosate-re­sis­tant due to this newish mech­a­nism of gene am­pli­fi­ca­tion.

So all the eas­ier-killed plant lines of palmer ama­ranth have been taken out through the years and now, through lack of di­ver­sity in her­bi­cides, the sur­viv­ing ama­ranth weeds that are left have a pe­cu­liar­ity of be­ing able to pro­duce mas­sive num­bers of EPSPS en­zymes that ba­si­cally soak up the glyphosate.

With the glyphosate mol­e­cules soaked up into a molec­u­lar sponge, the re­main­ing plant EPSPS en­zymes carry on inside the weed to al­low its nor­mal meta­bolic func­tions to con­tinue through to seed set.

This is not a new, mind­bend­ing oc­cur­rence, as in­sects like aphids have done this as well else­where and we sure have had some prac­tise con­trol­ling var­i­ous re­sis­tant in­sects through the years.

What is not good is that this type of re­sis­tance is her­i­ta­ble, mean­ing it is main­tained and ap­par­ent in fu­ture seed­ing gen­er­a­tions.

Now, this gene am­pli­fi­ca­tion “unique­ness” is present in an­nual rye­grass.

The years-ago-planted live­stock feed so­lu­tion is now a num­ber one her­bi­cidere­sis­tant plant in our south­ern farm­ing sys­tem.

The GA pres­ence isn’t as high as palmer ama­ranth, how­ever th­ese cred­i­ble re­search find­ings should teach us all that weeds have abil­i­ties to re­sist our hu­man at­tempts to con­trol them.

PHOTO: CON­TRIB­UTED

HOLD­ING OUT: Queens­land ama­ran­thus is yet to be­come her­bi­cide-re­sis­tant in Aus­tralia, un­like its Amer­i­can coun­ter­part, palmer ama­ran­thus.

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