Avoid crop com­pe­ti­tion

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

THE photo is of a large barn­yard grass plant grow­ing in a 2018 grain sorghum block.

There was one of th­ese large echinochloa plants ev­ery 20 me­tres. Now this plant is sure to shed up to 30,000 seeds, of which even a ger­mi­na­tion vi­a­bil­ity of 30 per cent is likely to cause plenty of crop com­pe­ti­tion prob­lems and re­duced soil mois­ture lev­els over the next few years.

If this plant is Group M (glyphosate) or Group A (fop or dim) her­bi­cide re­sis­tant, the prob­lems be­come even more so in your pad­docks, as it be­comes more dif­fi­cult to con­trol.

Let us con­fig­ure th­ese seed num­bers into the equa­tion be­low with the knowl­edge that the prog­eny from th­ese HR grass plants will be HR as well.

I have of­ten heard it said that the most ex­pen­sive her­bi­cide ap­pli­ca­tion is the one that does not work and that is true. How­ever, we still con­stantly ap­ply her­bi­cides on our weeds and many times we do so with more a hope for sat­is­fac­tory con­trol than the ac­tual re­sult may be.

So the sce­nario goes like this, that the agron­o­mist in­spects the pad­dock and ad­vises the farmer to spray the en­tire block with one litre per hectare of glyphosate 450, plus some ad­ju­vant. The re­sult on two pre­vi­ous spray oc­ca­sions in the sum­mer fal­low has been rea­son­able, with well over 95 per cent con­trol on the weed spec­trum, es­pe­cially the barn­yard grass pop­u­la­tion.

A fairly cheap spray and the pad­dock can be done be­fore break­fast time. Now in that pre­vi­ous spray op­er­a­tion, the 95 per cent re­sult was fair, how­ever the five per cent sur­vivors that did not die went on to set seed.

Now th­ese few barn­yard grass sur­vivors did not die be­cause of what rea­son? Did the boom kick a bit and our cov­er­age droplets per square cen­time­tre on the grass tar­get was poor? Were they big­ger and drier due to the den­sity of th­ese barn­yard grass plants in var­i­ous places? Or could it be a combo of all things men­tioned here.

Th­ese days as soon as a plant does not die from a her­bi­cide ap­pli­ca­tion, the whole world yells her­bi­cide re­sis­tance. Yes, there is much more of this HR phe­nom­e­non around and we are all re­spon­si­ble for it, with the over-re­liance on the weed con­trol in a drum.

How­ever it may not all be her­bi­cide re­sis­tance prob­lems. The other prob­lems men­tioned that have plagued us for years in per­form­ing boom spray­ing could still be the is­sue.

Wouldn’t it be good if you could test for her­bi­cide re­sis­tance on your barn­yard grass? Well you can. My pre­ferred way is by us­ing your phys­i­o­log­i­cally ma­ture seed, so there­fore it takes some weeks’ du­ra­tion. Prov­ing you have her­bi­cide re­sis­tance can give you an ad­van­tage in de­sign­ing a spray pro­gram for next sum­mer.


SPREAD­ING ROOTS: Large barn­yard grass plants grow­ing in a 2018 grain sorghum block.

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