Weeds are a significant threat to all farming systems in NSW. Glyphosate tolerant cotton has been rapidly adopted by the Australian cotton industry since its introduction 18 years ago and currently accounts for about 99% of all cotton crops sown. This has led to a change in weed management practices with growers moving away from applying residual herbicides in anticipation of a weed problem, to dealing with known weed issues in fields using predominantly glyphosate to control surviving weeds.

These changes have resulted in a shift in the weed species found across cotton growing regions. Increasingly the broadleaf weeds: flax-leaf fleabane and sow thistle, dominate weed spectrums in cotton crops, and with increasing weed burdens in the non-cotton component of the rotation. Other important weeds include: the emerging threat of awnless barnyard grass and increasing problems with feathertop Rhodes grass and windmill grass. This project undertook a number of weed surveys to get a baseline measure of the level of glyphosate resistance in hard to control weeds of cotton farming systems.

This project aimed to develop increased weeds research capacity within the cotton industry and improve the knowledge and understanding of critical areas including:

• The current herbicide resistance status of weeds in the cotton system including awnless barnyard grass, feathertop Rhodes grass, windmill grass, fleabane and sowthistle.

• The impact of tillage operations for pupae busting on weed control in cotton systems

• Controlled environment studies to better understand the role of temperature, rainfall, growth stage and different populations on the survival of important weeds, especially awnless barnyard grass.

The project also incorporated the role of Technical Lead for Weed management within the CottonInfo team, as lead researcher. The project has worked closely with CottonInfo Regional Extension Officers (REO’s) to deliver extension messages and communicate results from herbicide resistance testing.