Identifying new pre-emergent herbicide options for brome grass

Sam Kleemann¹, Gurjeet Gill¹ and Chris Preston¹

¹University of Adelaide, School of Agriculture, Food and Wine

Funding: UQ00080

Key Words: pre-em, pre-emergent, brome grass

Key messages:

• Brome grass is becoming more problematic in the South Australian and Victorian Mallee due the absence of effective herbicides for its control in cereals, intensification of cropping (i.e. wheat on wheat) and introduction of conservation tillage (no-till).
• At present brome grass management is heavily reliant on group A and B herbicides, especially Clearfield™ technology.
• Growers need to be aware that overreliance on these herbicide groups is expected to eventually select for herbicide resistant biotypes.
• Research (GRDC project UQ00080) is being undertaken to find effective alternative herbicide options for brome grass.

Background

The use of pre-emergent herbicides in cereals can enhance the overall weed control and performance of grass selective herbicides such as Crusader®, Atlantis® and Intervix by reducing the amount of brome requiring in-crop control. Such combinations also help to delay onset of herbicide resistance as herbicides from several different MOAs can be used within a single cropping phase. However, achieving effective control of brome with pre-emergent herbicides has become more difficult due to selection for greater seed dormancy and extended seedling emergence during the growing season. These high-dormancy populations can escape weed control with knockdown herbicides and many plants emerge after the activity of pre-emergent residual herbicides has diminished.

In cereals, only Group B herbicides can be used for post-emergent control of brome grass. The over-reliance on sulfonylurea herbicides has increased resistance in this spp. in South Australia and Victoria (Peter Boutsalis, pers. comm.). Growers have responded by sowing Clearfield cereals and using imidazolinone herbicides for weed control. In recent years, resistance to the imidazolinone herbicides has been identified in some populations of brome from South Australia and Victoria. There is an urgent need to identify suitable alternatives to imidazolinone herbicides for brome grass control in cereals.

A field trial was undertaken at Balaklava (SA) in 2016 to identify alternative herbicides for managing brome grass. This trial evaluated the performance of several experimental pre-emergent herbicides and their mixtures with Terbyne and Avadex Xtra against brome in barley.

Of the herbicides examined Terbyne® provided excellent brome control (86%), whereas Avadex Xtra® (<58%) was ineffective in controlling the high weed infestation present at the site (495 plants m^-2). Furthermore, Terbyne and its herbicide mixtures with several experimental products provided season long control and the greatest reduction in brome panicles (<90 panicles m^-2); whereas brome grass recovered in treatments such as Avadex and had similar weed seed production as the untreated control (244 panicles m^-2). Unfortunately, Terbyne and its combinations with other herbicides, whilst effective on brome, were also the most damaging to barley. Finding herbicides with high efficacy on brome and good crop safety in cereals remains elusive. Some experimental herbicides have looked promising in early screening, and will be evaluated in wheat in 2017.

Acknowledgments

We are grateful to GRDC (Grains Research and Development Corporation) for providing project funding (project UQ00080), Phil Arbon for allowing us to undertake the trial on his property, and Jerome Martin and Alicia Merriam from UA for providing technical assistance.