Barley Grass trials

The GRDC ‘Maintaining profitable farming systems with retained stubble - upper Eyre Peninsula’ project aims to improve farm profitability while retaining stubble in farming systems on upper Eyre Peninsula (EP). Weed control in stubble retained systems can be compromised where herbicide efficacy is limited due to higher stubble loads, especially for preemergent herbicides. Current farming practices have also changed weed  behavior with later germinating barley grass genotypes now present in many paddocks on the Minnipa Agricultural Centre (MAC) (B Fleet, EPFS Summary 2011). Several MAC farm demonstrations  were undertaken in 2014 to address barley grass weed issues including later germinating types and barley grass resistance to Group A herbicides. An integrated approach to weed management aimed at lowering the weed seed bank can make use of diverse techniques such as cultivation, stubble burning, in-crop competition using higher sowing rates and possibly row orientation. The weed seed bank can be reduced within the break phase by hay making, or green or brown manuring. Other techniques used effectively in WA on ryegrass and wild  radish have been narrow windrows and chaff carts. However there is limited information on the effectiveness of these tactics on barley grass in part because it is believed that most seed is shed well before harvest, limiting control. In 2015 the monitoring of farm paddock demonstrations in low rainfall farming systems to  assess control methods for grass weeds, mainly targeting barley grass, were undertaken by;
• Monitoring of narrow windrows in MAC paddocks N1 and N6W, and Bruce Heddle’s paddock CE42 (windrows and chaff dumps).
• Spray topping after oat and vetch hay (MAC paddock S4) using both crop competition (high seeding rate) followed by spray topping after the hay cut.

Barley grass continues to be a major grass weed in cereal cropping regions on the upper Eyre Peninsula (EP). Swathing a cereal crop involves cutting and collecting the cereal crop and weeds into windrows at 20 to 40% grain moisture and allowing it to dry. Having the weed seeds cut and in the windrow before the seed heads shatter and before tillers fall over (lodging), may allow greater weed seed collection when using a chaff cart or windrows. Swathing early then harvesting for weed seed collection needs further evaluation as it may provide farmers with another tool for integrated weed management, especially for barley grass that matures and sheds seed before crops ripen.

Barley grass possesses several biological traits that make it difficult for growers to manage it in the low rainfall zone, so it is not surprising that it is becoming more prevalent in field crops in SA and WA. A survey by Llewellyn et al. (2015) showed that barley grass has now made its way into the top 10 weeds of Australian cropping in terms of area infested, crop yield loss and revenue loss.

The biological traits that make barley grass difficult for growers to manage in low rainfall zones include:

• early onset of seed production, which reduces effectiveness of crop-topping or spray-topping in pastures,
• shedding seeds well before crop harvest, reducing harvest weed seed control effectiveness compared to weeds such as ryegrass which has a much higher seed retention,
• increased seed dormancy, reducing weed control from knockdown herbicides due to delayed emergence, and
• increasing herbicide resistance, especially to Group A herbicides, used to control grass weeds in pasture phase and legume crops.

Barley grass management is likely to be more challenging in the low rainfall zone because the growing seasons tend to be more variable in terms of rainfall, which can affect the performance of the pre-emergence herbicides. Furthermore, many growers in these areas tend to have lower budgets for management tactics, and break crops are generally perceived as more risky than cereals. Therefore, wheat and barley tend to be the dominant crops in the low rainfall zone. This project is undertaking coordinated research with farming systems groups across the Southern and Western cropping regions to demonstrate tactics that can be reliably used to improve the management of barley grass.

Why do the trial? 
Barley grass possesses several biological traits that make it difficult for growers to manage it in the low rainfall zone, so it is not surprising that it is becoming more prevalent in field crops in SA and WA. A survey by Llewellyn et al. (2015) showed that barley grass has now made its way into the top 1 O weeds of Australian cropping in terms of area infested, crop yield loss and revenue loss. 
The biological traits that make barley grass difficult for growers to manage in low rainfall zones include: 

- early onset of seed production, which reduces effectiveness of crop-topping or spray-topping in pastures,
shedding seeds well before crop harvest, reducing harvest weed seed control effectiveness compared to weeds such as ryegrass which has a much higher seed retention,•    increased seed dormancy, reducing weed control from knockdown herbicides due to delayed emergence, and
•    increasing herbicide resistance, especially to Group A herbicides, used to control grass weeds in pasture phase and legume crops. 

Barley grass management is likely to be more challenging in the low rainfall zone because the growing seasons tend to be more variable in terms of rainfall, which can affect the performance of the pre-emergence herbicides. Furthermore, many growers in these areas tend to have lower budgets for management tactics, and break crops are generally perceived as more risky than cereals. Therefore, wheat and barley tend to be the dominant crops in the low rainfall zone. This project is undertaking coordinated research with farming systems groups across the Southern and Western cropping regions to demonstrate tactics that can be reliably used to improve the management of barley grass. 

Why do the trial? 
Barley grass possesses several biological traits that make it difficult for growers to manage in the low rainfall zone, so it is not surprising that it is becoming more prevalent in field crops in SA. A survey by Llewellyn et al. (2015) showed that barley grass has now made its way into the top 1 0 weeds of Australian cropping in terms of the area infested, crop yield loss, and revenue loss. In this survey, barley grass was ranked as the 7th most costly weed to control by the growers in SA and VIC Mallee and Mid-North, Lower Yorke and Eyre Peninsula. In a previous random survey in SA in 2012, Shergill et al. (2015) identified resistance to quizalofop in 15% of barley grass populations from Upper North and Eyre Peninsula. Additional herbicide-resistant populations have been identified since the previous survey. Growers in these regions have observed many control failures and have been collaborating with this GRDC-funded project to confirm the resistance status of their barley grass populations. 

Barley grass continues to be a persistent grassy weed in low rainfall farming systems and current farming practices have selected for increased seed dormancy. This change in seed dormancy has resulted in Barley grass germinating later, and being much harder to control with knockdown and pre-emergent herbicides. In 2018 a range of herbicide strategies was tested for their effectiveness on a high density population of Barley grass.

To evaluate the impact of spray drift reduction strategies on grass weed efficacy.

A recent N LP2 investment, Adapting cropping systems to changing climatic conditions to reduce inputs and maximise water use through improving crop competitiveness, is a demonstration and extension project which started in late 2019. An initial grower survey of current management practices and attitudes towards barley grass was undertaken in March 2020 to be used as the baseline to assess changes in grower attitudes and changes in practices at the completion of the project. 

Barley grass weed density was monitored in three paddocks on upper EP (Minnipa Agricultural Centre (MAC), Heddle’s at Minnipa and Wilkins’ at Yaninee using an UAV during the 2017 (EPFS Summary 2017, p 83) and 2018 growing seasons at three different timings, with paddock transects conducted to verify grass weed density in paddocks.

Barley grass is now one of the top 10 weeds of Australian cropping in terms of area infested, crop yield loss and revenue loss (Llewellyn et al. 2016). Barley grass has several biological traits that make it difficult for growers to manage it in the low rainfall zone, so it is not surprising that it is becoming more prevalent in field crops in SA and WA.

Through recent GRDC investment, the research project ‘Demonstrating and validating the implementation of integrated weed management strategies to control barley grass in the low rainfall zone farming systems’ (hereby referred to as GRDC Low Rainfall Barley Grass) has commenced. An initial grower survey of current practice and attitudes towards barley grass was undertaken in 2019 to be used as the baseline to assess changes in grower attitudes and any change in practices after the completion of the three-year project.