Time to re-think weed plan

Re­sis­tance to glyphosate a grow­ing prob­lem that needs fresh think­ing

South Burnett Times - - RURAL WEEKLY -

THE weather is not good for us­ing her­bi­cide for weed con­trol is it?

The weather is not even good for ger­mi­nat­ing weed seeds over this sum­mer, so when they do ger­mi­nate af­ter the next sig­nif­i­cant fall of rain, there will be thou­sands of them and they will be a mix­ture most likely of sum­mer and au­tumn weeds ger­mi­nat­ing all over the place.

Also many of them may have a real per­cent­age of her­bi­cide re­sis­tant species in amongst them.

In our fal­lows then with­out doubt, the main her­bi­cide used is glyphosate, plus you may add other her­bi­cides to give you bet­ter con­trol across your weed spec­trum.

Noth­ing wrong with this plan as we have do­ing it for over 30 years.

Maybe that is a cause for con­cern the 30 year long pe­riod of min­i­mum or zero till prac­tices, we have all en­gaged.

Just be­cause we only used 1L per ha of Roundup 450 CT in 1985 on elon­gated milk this­tle plants for ef­fec­tive con­trol, as it was fairly ex­pen­sive at $23/L and then her­bi­cide costs were a real con­cern.

Th­ese days we still have elon­gated milk this­tle in our pad­docks and how much glyphosate do we ap­ply th­ese days?

I would haz­ard a guess we are closer to 2–2.5L per ha for ef­fec­tive con­trol with a much cheaper glyphosate 450 at $4 per litre.

So what would this tell us with re­spect to milk this­tle over the last 30 odd years about get­ting harder to con­trol?

Some­thing is go­ing on if we were killing milkies in 1985 with 1L per ha and now we are need­ing to ap­ply 2–2.5L per ha.

Surely that may tell us about this rate creep or maybe we should say rate gal­lop of our bril­liant fal­low her­bi­cide in glyphosate.

That word re­sis­tance gets bandied about a fair bit th­ese days doesn’t it?

Her­bi­cide re­sis­tance is the in­her­ited abil­ity of a plant to sur­vive and pro­duce seed, from a pre­vi­ously nor­mal lethal rate of her­bi­cide.

So if we were us­ing 1L per ha of glyphosate in 1985 and now are us­ing au­to­mat­i­cally 2L per ha or above, that would sug­gest to me that we have a rate creep and in­di­cates that we have con­trolled suc­cess­fully all the least re­sis­tant plants of milk this­tle and now we are com­ing up against the more dif­fi­cult ones.

Sure, we have all ob­served the weeds in the paddock that are made sick from a her­bi­cide ap­pli­ca­tion and they re­cover to set and drop seed, how­ever we have al­ways as­sumed it was poor coverage, bad en­vi­ron­men­tal con­di­tions, a more stressed milkie from me­chan­i­cal dam­age of wheels or dust and the list goes on.

Our def­i­ni­tion of her­bi­cide re­sis­tance is the ac­quired abil­ity of a weed pop­u­la­tion to sur­vive a her­bi­cide ap­pli­ca­tion that used to con­trol it.

Pop­u­la­tion is an im­por­tant word in this def­i­ni­tion of my short­ened ex­pla­na­tion of re­sis­tance.

Her­bi­cide tol­er­ance is used around our crop safety as­pects and an ex­am­ple would be the old Di­camba broadleaf prod­uct reg­is­tered for over the top spray­ing of many grass crops.

Di­camba has some good as­pects on weed con­trol, how­ever crop safety on some older bar­ley va­ri­eties was not one of them and as I re­call my fa­ther, Alec, many years ago de­nounc­ing Di­camba to all and sundry that it “wrecked” one of our sown bar­ley va­ri­eties’ yield by about 70%.

Then you have the other side of weed con­trol, where I have been rec­om­mend­ing for many years, glyphosate plus a com­pan­ion prod­uct for buck­wheat con­trol.

Glyphosate on its own has never been good on buck­wheat or wire­weed and only claims sup­pres­sion on la­bels.

So where does all this wordage leave us.

It leaves us won­der­ing how long am I go­ing to be able to use a vi­tal prod­uct like glyphosate and other her­bi­cide ac­tives in my weed con­trol hand­book, un­less I

change my ways.

It may not be next week or even next year for the glyphosate prod­uct to run out of use­ful­ness in your pad­docks.

How­ever it is com­ing, un­less you di­ver­sify your weed con­trol meth­ods.

So you and your agri ad­viser need to run some “what if” plans, and feel free to call your neigh­bours in as well.

If you get enough tak­ers feel free to give me a call also.

PHOTO: CON­TRIB­UTED

GROW­ING IS­SUE: Prickly let­tuce is an in­creas­ing prob­lem.

PAUL MCIN­TOSH

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