Knock down weeds

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

HERE we are again in early sum­mer at the start of an­other sum­mer crop­ping regime.

Once again the rain­fall pat­terns have been very stag­gered and se­vere in places from hard-to-pre­dict storms. So by my rec­ol­lec­tion, in the past 11 months we have had two solid sig­nif­i­cant rain­fall events in gen­eral and, of course, some of our num­ber have not even had those amounts.

These top­soil-wet­ting events do bring up a huge bulk of weeds as the photo shows. Small falls of rain bring up some sur­face-dwelling weed seeds like sowthis­tle (or milk thistle), how­ever usu­ally never in big weed num­bers like above. It is a fact that good soak­ing rain after an ex­tended dry time cer­tainly brings up a plethora of weeds, both sum­mer and win­ter ones.

In this photo there are vol­un­teer wheat plants, black oats, urochloa, barn­yard grass, blad­der ket­mia, cal­trop, buck­wheat, red pig­weed, turnip and, of course, sowthis­tle. A fair se­lec­tion isn’t there? And thank good­ness this coun­try was not planted to any sum­mer crop.

It is a clas­sic case of let­ting those ini­tial weed strikes emerge after good rain and con­trol­ling them to­tally with ap­pro­pri­ate knock­down prod­ucts.

This use of knock­down her­bi­cides pre-plant is good prac­tice, in­stead of just leav­ing the weed con­trol to­tally up to any pre-emer­gent resid­ual her­bi­cide ap­pli­ca­tions. It is more than a num­bers game of weed-seed bank lev­els in your pad­docks, it also in­cludes weed-seed po­si­tion­ing depth in the soil pro­file when us­ing resid­ual-type her­bi­cides.

Our range of sum­mer resid­ual her­bi­cides are mostly root ad­sorbed, apart from meto­lachlor, which is ba­si­cally shoot ad­sorbed as a short de­scrip­tion. There is an aw­ful lot of this Group K grass her­bi­cide be­ing ap­plied these days to get on top of our grass is­sues. I have ob­served through the years that grass seeds sit­ting on the sur­face are not well con­trolled at ger­mi­na­tion time solely by us­ing meto­lachlor prod­ucts.

Mind you, I have been called out to many break­outs or as­sumed prod­uct fail­ures in the past 38 years that meto­lachlor (Dual was the orig­i­nal name) has been around. So these days it is more dif­fi­cult to as­sess any prod­uct com­plaint with gen­eral her­bi­cide re­sis­tance, so in­creas­ingly preva­lent across all modes of ac­tion.

Not that I have been ad­vised of any her­bi­cide re­sis­tance lev­els to this handy resid­ual sum­mer grass prod­uct in meto­lachlor. How­ever, her­bi­cide re­sis­tance or not, hav­ing some atrazine or other root-ad­sorbed tri­azine combo prod­uct does as­sist in get­ting an in­creased per­cent­age of grass con­trol.

For ex­am­ple we have al­ways recog­nised that our nor­mal atrazine-only rates are not bril­liant on an­nual grass is­sues in sorghum or maize pad­docks. Add some meto­lachlor to the mix and in­vari­ably con­trol lev­els in­crease. Two modes of ac­tion and two sites of ac­tion with some steady rain just after ap­pli­ca­tion onto level soil and you have a good plan for grass con­trol.

So all the best for weed con­trol and I re­alise it is only one of the many tasks you need to com­plete in this busy time. The spring rain has been fair, how­ever we all need a good top up of soil mois­ture now for not only our thirsty crop plants but to also in­crease our resid­ual her­bi­cide weed-con­trol ac­tiv­ity.

PHOTO: PAUL MCIN­TOSH

SPROUT­ING WEEDS: A plethora of weeds in south­ern Queens­land farm­ing coun­try this month.

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