Agron­o­mist Paul McIn­tosh dis­cusses the im­pact of weeds in broadleaf crops

Pro­tect­ing broadleaf crops

The Western Star - - RURAL WEEKLY - PAUL MCIN­TOSH

.THERE are many of us still wait­ing for sig­nif­i­cant rain to plant a sum­mer crop and oth­ers who have good crops af­ter the heavy mid-De­cem­ber rain.

Whatever your sit­u­a­tion, weeds may still be play­ing a detri­men­tal part in your farm­ing sys­tem.

My thoughts for this week are con­trol­ling weeds in crop, specif­i­cally in the hard­est sit­u­a­tion is con­trol­ling broadleaf weeds in broadleaf crops.

The photo at­tached is of a mung­bean crop in the ex­treme hot and dry times of March 2017. All crops around this area were un­der a lot of pres­sure and even think­ing about spray­ing weeds was a low ne­ces­sity. As you can see the medium width rows of mungs had very few weeds grow­ing how­ever not all crops are so lucky .

A lot of our her­bi­cide la­bels ad­vise to ap­ply to young ac­tively grow­ing weeds and that is what we all try to do, how­ever we have this en­vi­ron­ment fac­tor, where very lit­tle rain­fall in crop oc­curs and the air tem­per­a­tures in sum­mer can reach the of­fi­cial 40 de­grees, but can be much higher on bare soils.

We know in our mung­bean, soy­beans and other reg­is­tered broadleaf sum­mer crops that the her­bi­cide ac­tive in­gre­di­ent Aci­fluro­fen (orig­i­nally Blazer when first re­leased in 1980) needs ex­cel­lent cover­age on small sus­cep­ti­ble ac­tively grow­ing broadleaf plants.

Noth­ing has changed much in these spe­cific needs apart from the mung­bean rate with Has­ten crop oil, be­ing re­duced to 1L/ha. Of course, not only do the weeds need to be ac­tively grow­ing, but so does the crop for crop safety an­gles. Tem­per­a­tures above 30 de­grees C and low hu­mid­ity at ap­pli­ca­tion time, can also play havoc on soft broadleaf crops with an oil based ad­ju­vant.

Even with the in­creased ef­fi­cacy of this has­ten oil be­ing added, the end re­sult on large blad­der ket­mia (wild cot­ton), noo­goora burr, bell vine and the goose­berry fam­ily are go­ing to be less then good. Sup­pres­sion only maybe your best re­sult for many of the broadleaf weed spec­trum. So be aware of this less than per­fect re­sult.

The to­tal in crop post emer­gent broadleaf her­bi­cide list for mungs is a fairly short list of two only, with only some Imazamox prod­ucts like Rap­tor and Claw, also al­lowed to be ap­plied un­der the per­mit 82490. All these post emer­gent Imi prod­ucts need to be ap­plied to any ac­tively grow­ing crop plants, even lucerne crops, to pre­vent any crop dam­age. This safety an­gle is brought about by the crop plant be­ing able to metabolise or grow out, the ap­plied her­bi­cide into a form that does not im­pact the crop plant. Any­thing that puts the crop un­der stress such as dry and hot con­di­tions, wa­ter­log­ging or frost can re­duce the crops abil­ity to ef­fec­tively metabolise the se­lec­tive her­bi­cide ap­plied.

Along with these crop safety prin­ci­ples, you also have your WHP or with­hold­ing pe­riod to ad­here too. These days are not like the 1980s and 1990s, where WHP were treated with lit­tle con­cern with our in­sec­ti­cide and her­bi­cide prod­ucts. You re­ally need to be mind­ful of your WHP, es­pe­cially with our fop and dim grass her­bi­cides in your pulse crops. Stat decs, that you fill out at de­liv­ery time, are there to pro­tect you and our en­tire ex­port in­dus­try. Please obey the rules and if a mis­take has been made. Do not just cross your fin­gers and hope for the best, you are best ad­vis­ing your pre­ferred mar­keter to make the best de­ci­sion with you and for you.

PHOTO: PAUL MCIN­TOSH

NOT-SO-COOL BEANS: March 2017, in a very dry/hot time, a crop of mung­beans in south­ern Queens­land. Paul McIn­tosh says mungs are tougher than they look.

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