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Older chemicals shine in weed resistance survey | Kenvos Biotech Co., Ltd.

Older chemicals shine in weed resistance survey

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Atrazine and Paraquat are still some of WA’s top-performing Herbicides, according to a recent Australian Herbicide Resistance Initiative’s (AHRI) Herbicide resistance in annual ryegrass survey. The project uncovered a substantial increase in resistance to a number of Group A and Group B Herbicides throughout the Wheatbelt but demonstrated only two per cent of ryegrass populations tested for Atrazine resistance had resistant plants and all tested for Paraquat resistance were susceptible.

Diclofop and sulfometuron on ryegrass were the main under-performers and AHRI senior researcher Mechelle Owen and her team collected 362 annual ryegrass samples from 466 cropping paddocks from the widest spans of the Wheatbelt to prove it.

When growers talk about Herbicide resistance in WA it’s usually Glyphosate which finds itself under the microscope.

But as Ms Owen explained, it was the Group B sulfometuron (or Oust, similar to Glean), whose test results showed that 98pc of populations tested in the AHRI survey had resistant plants.

Ms Owen said this was an increase of 10pc since 2003 and the rise had mostly occurred in southern cropping regions which experienced high rainfall.

Testing of the group A diclofop samples also showed that 96pc of populations tested in the State-wide AHRI survey had resistant plants, an increase of 28pc since 2003.

The area with the largest increase was also in the State’s southern cropping regions.

But perhaps the most astonishing result was that of the Group A Herbicide Clethodim (at its label rate of 250ml/L).

Sixty-five per cent of populations tested by AHRI in its survey had resistant plants which was an increase of 57pc since 2003.

Ms Owen said in 2003 only parts of the northern Wheatbelt ryegrass population had resistance to the Herbicide but its expanded use now meant resistance had become widespread throughout the State.

"In 1999 there was a 0.5pc resistant population," Ms Owen said.

"Of all our results Clethodim had the greatest change in resistance.

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