New registration for Trezac® Arylex® active helping graziers extinguish fireweed

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Livestock producers have greater ability to control the highly invasive fireweed, with Trezac® Arylex® active now registered for use in grass pastures via boom application.

One of only a few products registered for boom application to control fireweed, Trezac was already registered in pastures as a spot spray application for the control of many other weeds.

Corteva Agriscience ANZ Marketing Director, Dan Dixon, said the recent approval by the Australian Pesticides and Veterinary Medicines Authority (APVMA) was a win for producers looking to bolster their integrated weed management (IWM) plans.

“Trezac® Arylex® active herbicide has been registered in Australia since 2020 and has been widely used in winter cereals and fallow for the management of some of the hardest to control broadleaf weeds,” Mr Dixon said.

“In late 2024, the APVMA approved the registration for Trezac to be used in grass pastures via a boom application for the control of deadnettle, Mexican poppy and, most importantly, the control of fireweed.

“This use pattern will allow graziers to effectively manage this weed, which even at light infestation rates, is capable of producing more than one million seeds and can rapidly decrease the productivity and stocking rate of pastures.”

In addition to its highly invasive nature, fireweed contains pyrrolizidine alkaloids which can cause severe liver damage if consumed by livestock. The damage is irreversible and gets worse the more fireweed an animal eats.

Hay, silage or grain contaminated with fireweed plants or seeds can also poison livestock.

Implementing an effective IWM strategy

Corteva Territory Account Manager for coastal NSW, Jon Dadd, said minimising the health risk to livestock and increasing the overall productivity of pastures requires a multi-year and multi-tactical approach by graziers.

“Trezac is an excellent first choice in a fireweed management strategy, to bring plant numbers down in year one of the plan,” Mr Dadd said.

“In particular, we see Trezac fitting at the beginning of a pasture rejuvenation program to get a large fireweed population under control without the use of soil disturbance or slashing, which can actually increase fireweed numbers.

“It’s not an easy weed to manage because seeds are easily dispersed by wind and animals, in stock feed and via mud on vehicles, and its competitiveness means it will easily get a stranglehold on a pasture, and productivity in that paddock will decrease considerably.”

Trezac contains the most effective amount of Arylex® and aminopyralid that is required to control many of the key target weeds in pastures, and has the added benefit of offering graziers the ability to create a robust herbicide mix to control broadleaf weeds in pastures.

“The product is compatible with other grass and broadleaf herbicides and in many cases, the addition of a mixing partner such as Starane Advanced or MCPA will be required to control the wider weed spectrum,” Mr Dadd said.

“Having the ability to alter the rate of the mixing partner will give growers the choice to dial up the control levels to suit their individual needs.”

How to get the best out of Trezac

Trezac is a Group 4 (Auxinic) herbicide with active ingredients from the pyridine and arylpicolinate sub-families, and the molecules work by interfering with the normal growth and developmental functions within a target weed.

“Trezac’s strong action on legume species means any legumes in the pasture sward will likely be severely impacted following application,” Mr Dadd said.

“We’d suggest graziers set about building their pasture back up by introducing new grass species following the application of Trezac in the first year of the management plan, then spot spraying any fireweed in the second year with Trezac or Grazon Extra.

“Once the fireweed is under control, legumes can be introduced back into the pasture to provide a diverse sward for grazing.”