In the current cropping and grazing industries, control of weeds is an ever-evolving challenge faced by many farmers across the country.
Weeds use valuable moisture and nutrients from the soil and can cause issues at sowing time and harvest. They are also often toxic to stock and can carry diseases and insects.
According to the Grains Research and Development Corporation (GRDC), weeds are estimated to cost Australian agriculture $2.5 billion to $4.5 billion per annum. The cost of weeds to the winter cropping system is $1.3 billion, equivalent to approximately 20% of the gross value of the Australian wheat crop.
With the increasing herbicide prices and the rise in herbicide-resistant weeds, it is paramount that we continually look at new methods of controlling weeds and maximizing the effect of herbicides.
Herbicide Resistance
Herbicide resistance is a growing threat across Australia’s grain region. There are over 50 weed species currently identified as herbicide resistant in Australia and many more are at risk of developing resistance, particularly to glyphosate.
The zero-till principles used by many growers over the last decade have caused significant changes to the types of weeds found throughout Australian farms. The spectrum is now dominated by weeds suited to surface germinating and the reliance on herbicides for weed management is causing herbicide resistance to rapidly evolve.
Key herbicide resistant weeds include fleabane, feathertop Rhodes grass and windmill grass.
Fleabane:
Glyphosate resistance in fleabane is confirmed and widespread. The weed produces high volumes of viable seed per plant, although over 90% of the seed loses viability within 18 months. Therefore, the key to managing fleabane is an aggressive focus on preventing plants from going to seed over 2 years, thus reducing the seed bank. The control of larger weeds, however, is difficult as they quickly develop a large tap root. The points below provide general information on fleabane.
Upright annual weed found throughout all states of Australia.
Confirmed and widespread glyphosate resistance.
Surface germination is preferred, and the weed does not germinate greater than 20mm below the surface.
Major flushes occur in spring and autumn, but it does not commonly germinate in summer.
Prefers lighter soils but will grow anywhere, especially when there is little competition.
Seed production of up to 110,000/plant.
Feathertop Rhodes Grass:
Feathertop Rhodes grass has a short persistence of approximately 1 year. Due to this, a concerted effort over 12 months to prevent seed from going back into the soil should drastically drive down numbers. Glyphosate has always been a poor herbicide to use on feathertop Rhodes grass as it is unlikely to provide effective, consistent control. The points below give a further outline of the characteristics of the weed.
Short-lived tufted grass, usually growing 15 – 100cm tall.
Widely found throughout mainland Australia.
Shallow germination between 0 – 20mm.
Ideal conditions for germination are over 10mm rainfall, a temperature of approximately 25°C, and light.
First to establish on bare soil.
Seed production of up to 6,000/plant.
Short dormancy of 6 – 10 weeks.
Only persists for approximately 12 months, even when buried.
Windmill Grass:
A 12-month effort to prevent windmill grass seed from going back into the soil is likely to drive down large numbers due to the short persistence (approximately 1 year). Glyphosate has never had a good effect on controlling windmill grass and therefore is unlikely to provide effective and consistent control, even when used in a double knock strategy.
Short-lived prostrate perennial that is present throughout Australia.
Prefers lighter soils and is often found in heavily-grazed, higher fertility areas.
Germinates between 0-20mm below the surface.
Germinates summer to autumn after rain event with greater than 20mm.
Is a prolific seeder.
Individual plants continue to set seed during the year.
Seed heads are blown by the wind.
Only persists for approximately 12 months, although burial will increase short-term persistence.
Management:
Traditionally, controlling weeds has been dealt with through heavy tillage and excessive herbicide application. While these will still continue to play a large part in weed management strategies, the mindset that glyphosate can be used for ‘just about anything’ has to change. The use of the double knock program is becoming more popular as a strategic weed management program.
Slashing and mulching have also been used for many years, but the benefits of strategically using these methods have only recently been widely recognized within the farming community.
Slashing and Mulching:
Slashing and mulching crop residue and pastures maintains ground cover while limiting the effect of soil erosion and provides greater access in wet weather. As the Department of Primary Industries (DPI) have mentioned, continual slashing and mulching may provide control if a desirable pasture species is present and encouraged to replace the weed, but slashing will not eradicate a weed, and can't be used for weed control in crops.
Slashing can:
Prevent tall weeds from flowering and seeding
Remove unpalatable or inedible weeds left after stock have selectively grazed a paddock
Temporarily control weeds until they re-shoot
Control vegetation and weeds along roadsides
Slashing and mulching allow sunlight to access and rejuvenate stock-friendly pastures and provide early prevention in stopping taller weeds from seeding. Leaving a mulch on the floor of the paddock limits regrowth of the weeds, thus allowing for a more effective kill when spraying. Keep in mind that the timing of slashing and mulching is crucial in weed management. Ideally, mulching before the weeds seed has the greatest effect.
Conclusion:
As recommended by GRDC and DPI, fighting these herbicide resistant weeds is best done through multiple different avenues of control, be it strategic tillage, mulching, burning, or spraying.
With the benefits of slashing and mulching listed above, providing machines that suit these applications is a key component to the success of your weed control. Our machines are built to suit this type of work with high tip speeds, a fine cut from high quality blades and the ability to reduce residue size with a mulching kit. Control over cutting height and easy setup of the machines are also key points that we focus on in our designs.
Our particular machines that assist in weed control are the AlphaCut, TurboTopper and Bravo Twin Spinner. Be sure to check out the details on our website, and if you have any further questions, contact us to speak to one of our salesmen.