Alternative methods to combat herbicide resistance
Herbicide resistance begins with the failure of one or two herbicides but can quickly escalate as the reliance on a smaller pool of active ingredients increases the selection pressure on weeds to develop resistance to the remaining herbicides. This growing resistance poses a significant threat to food security, as weeds compete with crops for essential resources like water, sunlight, and nutrients.
The loss of effective herbicide-based weed control can render crop production uneconomical due to decreased yield, lower quality, and the higher costs associated with non-chemical alternatives, such as tillage. In Australia, the rise of herbicide resistance during the late 1990s and early 2000s contributed to a significant decline in the number of grain growers, as noted by Dr. Michael Walsh, a professor of plant sciences at Charles Sturt University.
Dr. Walsh highlighted that herbicide resistance is more severe in Western Australia compared to other regions in the Australian wheat belt. This is largely due to the region’s focus on intensive crop production with less emphasis on livestock. In contrast, growers in the eastern wheat belt, who typically integrate crop and livestock production, have managed to slow the development of herbicide resistance.
Surveys conducted every five years reveal that since 2010, approximately 90% of ryegrass populations in Western Australia have developed herbicide resistance, with 95% of these populations resistant to multiple modes of action. Other regions, such as South Australia, Queensland, and New South Wales, show resistance in about 70% of ryegrass populations, while Tasmania has a resistance rate of 46%.
Weed Seed Control Innovations
The challenge of herbicide resistance has led Western Australian farmers to rethink their weed management strategies, resulting in the development of Harvest Weed Seed Control (HWSC) systems. These systems, which include chaff carts, narrow-windrow burning, direct baling, chaff-lining, chaff tramlining, and impact mills, aim to prevent weed seeds from returning to the soil seedbank during harvest.
For these systems to be effective, proper harvester setup and operation are crucial. Dr. Walsh’s research indicates that a correctly configured harvester can ensure that weed seeds exit the machine in the chaff, rather than being scattered back onto the field.
Comparing HWSC Systems
Different HWSC systems treat chaff in various ways. Narrow-windrow burning, for example, involves concentrating straw and chaff into narrow rows that are burned in autumn to destroy weed seeds. While highly effective, this method is not recommended as a long-term solution due to the need for specific climatic conditions and the potential for nutrient loss.
Chaff carts, originally designed for livestock feed collection, have been used in Western Australia since the 1980s to collect chaff and target the weed seed-bearing fraction. The collected chaff is later grazed, burned, or baled.
Chaff lining and tramlining concentrate chaff into narrow rows or wheel tracks, creating an unfavorable environment for weed seed germination. While these methods are generally effective, they can be “messy” and may still allow some weed seedling emergence.
Impact mills, which align with conservation farming principles, return and spread all harvest residues to the field. These systems, though expensive, have proven effective in reducing ryegrass emergence.
Innovations in Weed Control
As weed populations decrease, farmers can transition from whole-field herbicide applications to targeted spot spraying, using systems like WeedIT and WeedSeeker. These technologies, which use reflectance sensors to detect and target weeds, represent a non-chemical alternative to traditional methods.
Strategic tillage is another approach gaining traction among farmers using conservation farming methods. This practice addresses issues such as nutrient stratification and shallow weed seed banks by inverting the soil and significantly reducing weed seed emergence.
Dr. Walsh emphasizes that no single method can fully address weed problems. A combination of strategies, including the complete destruction of resistant weeds, is essential for successful long-term weed management.