Annual rainfall: 300–310 mm Low rainfall zone
Weeds and herbicide resistance status: Annual ryegrass is the most prevalent weed across the Mallee cropping region, followed by sowthistle. In the northern Mallee, brome grass, barley grass and wild turnip are problematic on many farms. Herbicide resistance in annual ryegrass, sowthistle, brome grass, barley grass and wild turnip is challenging Mallee growers and agronomists to develop diverse weed control programs to avoid weed blow-outs.
Resistance to Group 1 [A] herbicides is common in several weeds across the region. Increasing resistance to Groups 1 and 9 [M] in barley grass is seen, particularly in long fallow systems.
Heavy reliance on imi-tolerant crops, mainly barley and lentils, has driven resistance in grass and broadleaf weeds in the Mallee through the increased the use of Group 2 [B] herbicides through the rotation. On the other hand, imi-tolerant barley provides an opportunity to sow into fields with a recent history of imi-herbicide application (soil residual), and to rotate to other modes of action in the weed-competitive barley phase.
WeedSmart Big 6 for integrated weed control programs on farms in the Mallee region.
Crop and pasture rotation
Continuous cropping and mixed farming operations in the Mallee have many opportunities to target weeds using different tactics. Common cropping rotations in the region are wheat, barley, pasture, or wheat, barley, pulse crop (lentils, vetch or field pea). Long fallow and hay production are also commonly included in the crop rotation.
Only small areas of canola are grown in the Mallee, mainly as an opportunity crop on a full profile of moisture. Barley is the most weed-competitive crop available to Mallee growers and generally has better productivity in dry years compared to wheat.
In mixed farming systems, brown manure pulses, pasture or hay crops are grazed early to prevent weed seed set and then either sprayed out or cut for hay.
Double knock to protect glyphosate
Optical spot spraying is widely used to double knock summer fallow weeds in the Mallee.
Double knock applied ahead of sowing is more opportunistic. Generally, the preference is to sow early rather than wait for rain to initiate a double knock spray event. The double knock often fits well ahead of sowing field pea, which is sown later in the season after the weeds have germinated.
Mix and rotate herbicide groups
Lower cost pre-emergent herbicides such as trifluralin [Group 3/D], metribuzin [5/C] and triasulfuron [2/B] are still widely effective in the Mallee and their continued use is sustainable within a diverse herbicide and cultural program.
Newer products such as Overwatch, Reflex and Ultro offer new use patterns and opportunities to rotate modes of action across the crop rotation.
Resistance to Group 1 and 2 (particularly imi) herbicides is driving crop choice and herbicide programs in the Mallee and generally requires a move away from an extended cereal rotation.
Stop weed seed set
The cleanest paddocks in continuous cropping systems usually include vetch, winter fallow or field pea, where a grass selective herbicide is applied early and then the crop is browned out and sown back to wheat the following year. Including a legume has the added benefit of returning nitrogen to the soil and the pulse phase provides multiple opportunities for weed control. Vetch is a versatile crop for Mallee growers, providing options for grazing, hay or seed for harvest.
Weed and crop maturity (particularly in field pea and lentils) at desiccation often coincides better in the Mallee than it does in some other regions. Some growers swath their barley crops to capture early shedding grasses prior to harvest.
Hay (vetch and oats) is also a great option for growers to stop weed seed set and provides excellent control annual ryegrass, or to salvage frosted crops.
A number of Mallee growers use shielded sprayers to control escapes before they grow too large or set seed. Weeds that emerge after the pre-emergent has run-out or where no post-emergent is registered can be controlled using paraquat, Sharpen or glyphosate through a shielded sprayer. This tactic was an innovation of Mallee growers and is used in both cereal and broadleaf crops.
Wider row spacing of 333 to 375 mm is generally used in the Mallee to avoid moisture stress. Strategic use of competitive barley varieties such as Commander and Compass is the most common weed-competitive tactic available to Mallee growers and effectively drives down grass weed numbers.
Early sowing, along with an effective pre-emergent package, is a very effective strategy for all crops in the Mallee.
Harvest Weed Seed Control (HWSC)
Herbicide resistance in brome grass has been a driving force for HWSC adoption in Mallee in recent years. Many growers have selected impact mills for their ‘entry’ into harvest weed seed control, having skipped over the other tools that have been available for many years. The abrasive soils typical of the Mallee region can cause significant wear and tear on impact mills. Other tools such as narrow windrow burning, chafflining and chaff carts are also used within the region.
Impact mills are used in all crops in the Mallee rotation, although additional patience is required when harvesting lentils.
HWSC has made a significant impact on brome grass, barley grass and annual ryegrass populations in crops across the Mallee region.