Get­ting on top of weeds

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

BACK onto weeds this week and look­ing at fence lines and even coun­cil road­sides, where the eas­i­est course of veg­e­ta­tion con­trol is to use a heavy spot spray rate of knock­down her­bi­cide, with one part of glyphosate to 100 parts of wa­ter be­ing com­mon.

That equates to roughly 10L/ha.

It is cheap, not the worst op­tion in drift or sen­si­tive plant sit­u­a­tions, rel­a­tively safe to the op­er­a­tor and fairly ef­fec­tive at keep­ing un­wanted veg­e­ta­tion un­der con­trol for sit­u­a­tions of elec­tric fences, pad­dock boundaries, road­side sig­nage and cul­vert edges.

Ex­cept when her­bi­cide re­sis­tance comes along and the hard-to-kill species just grow right through these pre­vi­ously suc­cess­ful her­bi­cide ap­pli­ca­tions.

We of­ten ob­serve a plethora of weeds in the cul­ti­va­tion pad­docks when the planter fails to drop crop seed and we have a bare spot of maybe 2sq m or 2ha, that has no use­ful crop grow­ing on it.

De­spite some of our best ef­forts in us­ing se­lec­tive her­bi­cides as the sole weed con­trol agent, that very re­duced crop den­sity still gets more weeds than you can poke a stick at.

So my point is that crop or de­sir­able plant com­pe­ti­tion is a great way to re­duce our weed count.

So are our road­sides and prop­erty fence lines try­ing to be too clean?

The bare earth prin­ci­ple. What I am sug­gest­ing, or should I say chal­leng­ing ev­ery­body with, is to achieve some non-her­bi­cide weed con­trol by en­cour­ag­ing de­sir­able plants to grow as com­peti­tors for weeds.

For ex­am­ple, many years ago I saw some strag­gly buf­fel grass, over a pe­riod of many months, out-per­form and there­fore out­grow some gal­vanised burr clumps.

Now buf­fel is a strong com­peti­tor, how­ever so is gal­vanised burr in over­grazed sit­u­a­tions.

The patch of about 1000sq m went from a gal­vanised burr patch to a stand­out patch of buf­fel grass. All the buf­fel needed was some en­cour­age­ment and that was done by a sim­ple method of re­mov­ing all live­stock and lo­cal roos by a tem­po­rary fence erec­tion.

My cur­rent thought project is to find ways to leave es­tab­lished pi­o­neer or com­mer­cial rhodes grass grow­ing and pre­vent feath­er­top rhodes from pro­lif­er­at­ing along fences and road­sides. Too of­ten I have ob­served that the pi­o­neer rhodes is killed by heavy glyphosate spray­ing and the feath­er­top rhodes then be­comes ram­pant.

It struck me that we all need to fig­ure out our own ways to in­tro­duce some de­sir­able plant com­pe­ti­tion to those pesky weed sites.

My re­cent trip to CQ cer­tainly saw plenty of parthe­nium weed out-com­pet­ing both buf­fel and leu­caena plants, af­ter Cy­clone Deb­bie’s pow­er­ful rain event.

Apart from not over­graz­ing in drought, an un­re­al­is­tic call, what else could you do for parthe­nium con­trol in buf­fel-only pas­tures?

Well in this case I would use some very eco­nom­i­cal and se­lec­tive her­bi­cide in met­sul­furon methyl that would clean up the parthe­nium and leave the es­tab­lished buf­fel well enough alone.

This her­bi­cide, orig­i­nally called Ally, would kill or se­verely sup­press any legume plants present at time of spray­ing by the way.

This Group B mode of ac­tion prod­uct could be mixed with many other se­lec­tive op­tions de­pend­ing on weed spec­trum iden­ti­fied and pas­ture species present.

So it needs some thought for a her­bi­cide pack­age here.

So here I am talk­ing non-her­bi­cide meth­ods at the top and re­sort­ing to a lib­eral rate of met­sul­furon methyl at the bot­tom of the ar­ti­cle.

I am merely point­ing out that we may need a com­bi­na­tion of ideas for the weed con­trol we want.

We need to im­ple­ment both cul­tural and chem­i­cal con­trols with­out los­ing our pre­cious top soil down the creek.

This would there­fore pro­long the use­ful life of our cur­rent her­bi­cide pack­ages.

I have not heard of any weed species that can to­tally re­sist other de­sir­able plants’ com­pet­i­tive na­ture, how­ever I cer­tainly know many plant species that can re­sist her­bi­cides we are cur­rently overus­ing.

Her­bi­cide re­sis­tance is a com­mon phrase these days and it does not have to be a life sen­tence. We just need to chal­lenge our­selves to ob­tain weed con­trol by other means.


SPARSE COM­PE­TI­TION: Agron­o­mist Paul McIn­tosh checks weed num­bers in a patchy grain sorghum crop last sum­mer.

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