Weeds just wait­ing for rain

Dry weather means no weeds... for now

Warwick Daily News - South West Queensland Rural Weekly - - News - PAUL MCIN­TOSH

WITH the cur­rent run of dry weather we re­ally do not have too many weed is­sues.

We are not even re­ceiv­ing those an­noy­ing 5-6mm falls of rain that do very lit­tle for soil mois­ture lev­els and in­vari­ably just bring up a few grass and broadleaf weeds.

So why would I be talk­ing about weeds this week?

It is sur­pris­ing how quickly the whole sit­u­a­tion can turn around in the rain­fall depart­ment and there­fore weed ger­mi­na­tion and emer­gence.

Many of us have ob­served this be­fore with an ex­tended dry time, when along comes some sig­nif­i­cant rain and you then get eight months of weeds emerg­ing over the next cou­ple of weeks.

So your im­pec­ca­bly clean fal­low blocks can get very dirty, very quickly.

In the last 15 years or so gone by, we would grab some glyphosate her­bi­cide and load up the spray rig with 2L or more per ha of this bril­liant knock­down prod­uct to re­gain con­trol of our pad­docks.

No need for any other mix­ing prod­uct as it was cheaper to use more and more glyphosate per hectare and I was as guilty as any­one of overus­ing in these cheap glyphosate her­bi­cide years.

Orig­i­nally in the early 1980s with the price of $23 per litre equiv­a­lent for Roundup CT, we had to mix com­pat­i­ble her­bi­cides to keep the cost per hectare down, es­pe­cially for broadleaf weeds, which un­wit­tingly gave us dif­fer­ent modes of ac­tion in the tank.

The price per litre for gly dropped down to around $15 per litre in the mid 1990s and still we mixed and matched her­bi­cides to bring down the cost to the farmer. Not that we re­ally wor­ried too much about modes of ac­tion, it was more the cost per hectare we were all con­cerned with.

So then the glyphosate-only band­wagon had re­ally kicked in by the early 2000s and that is when we re­ally started to select for her­bi­cide re­sis­tance.

You have all seen re­search fig­ures of her­bi­cide re­sis­tance lev­els climb steeply af­ter five or 10 ap­pli­ca­tion events or shots.

That has al­ways in­trigued me for va­lid­ity, as one thing ex­pe­ri­ence can do was to make you more cyn­i­cal on her­bi­cide re­sis­tance oc­cur­ring at all. How wrong I was.

So where does the phrase “ro­tat­ing buys you time, mix­ing buys you shots” come from and how does it ap­ply to us?

Is this how we have held off re­sis­tance weed in­creases, un­til this decade in some species, be­cause we were mix­ing com­pat­i­ble her­bi­cides to­gether at full rates?

Over­seas re­search and here in Aus­tralia also has stated and graphed out that hav­ing 2.5 modes of ac­tion in each and ev­ery ap­pli­ca­tion on weed co­horts per year, can make you 83 times less likely to de­velop glyphosate re­sis­tance.

So mix­ing ef­fec­tive her­bi­cide part­ners as we have done and are con­tin­u­ing to do is very im­por­tant.

By ef­fec­tive, I mean it is a waste of time if your pad­dock has a very high level of re­sis­tance and you con­tinue to ap­ply this tank mix , which may leave only one prod­uct do­ing the work.

More next week on ro­ta­tion and mix­ing of our her­bi­cides.

Re­mem­ber we need to stop seed set at all costs to take back our pad­docks from wors­en­ing weed is­sues.

Weed re­sis­tance lev­els in a pad­dock should not con­trol our fu­ture eco­nomic crop­ping de­ci­sions.


we need to stop seed set at all costs.” — Paul McIn­tosh


GROW­ING PROB­LEM: Times have changed when it comes to weed con­trol, with plenty more tools in the box be­sides glyphosate.

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