PEST WEED: Common sowthistle is rapidly becoming a wide-spread and persistent problem for grain growers in southern Queensland and northern NSW.

How to tackle common sowthistle

The Northern Grower Alliance has developed three tactics for controlling the problematic weed common sowthistle.

COMMON sowthistle is increasingly becoming a problematic weed in the grains industry.

What was once considered a winter problem has become an issue all year round and is now one of the most widespread, broadleaf weeds in southern Queensland and northern NSW.

For the past 18 months the Northern Grower Alliance (NGA), as part of a GRDC research investment project, has been investigating the challenges of safe, effective and economical control of common sowthistle or Sonchus oleraceus. 

NGA research manager Lawrie Price said the increasingly common sowthistle problem was largely because its seed is readily dispersed by wind. Growers are also now starting to battle glyphosate resistant populations.

“In recent years, weed control in summer fallow has become an increasingly difficult and expensive component of northern farming systems,” Mr Price said.

“This is in part due to a heavy reliance on glyphosate, which has led to the selection of weed biotypes which are glyphosate resistant.

“So we now need to develop non-glyphosate-based management strategies to effectively, safely and economically control common sowthistle.”

GRDC’s most recent investment into this weed has seen NGA researching weed management using residual, knock-down and double knock approaches.

1. Residual herbicides (fallow or in-crop)

Products currently registered for residual control of common sowthistle in fallow include Balance and Terbyne Xtreme. Balance, Terbyne Xtreme and simazine are all registered for in-crop residual control.

2. Herbicide double knock 

Using a double knock of glyphosate followed by paraquat can be an effective tool on small common sowthistle (e.g. four to eight leaf).

However, the level of control can be variable on larger weeds (rosette) and at more advanced growth stages. Evaluation of alternative first knock candidates indicates that Group I products followed by paraquat are providing improved levels of efficacy compared to glyphosate followed by paraquat on larger rosettes.

Many of these options are used for fleabane control and often provide a level of residual activity for common sowthistle. Screening is also underway for alternative second knock herbicides to paraquat. 

3. Knockdown control 

Mr Price said there were limited knockdown (single knock) options for common sowthistle.

“Sharpen (saflufenacil) is registered for use in mixture with glyphosate. This can be an effective tool but needs to be applied on very small weeds for consistent control,” he said.

“Basta is also registered for use in some situations and maybe an option. It can be used in fallow for the control of common sowthistle at the two to six leaf stage.”

Mr Price said when it came to problematic weeds like common sowthistle, effective management could have an impact on crop profitability. Growers needed to focus on individual paddocks and adjust rotations to suit environmental conditions and also allow for residual herbicide use in fallow or in-crop.

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