Crop weeds: controlling small weeds

Page last updated: Friday, 29 June 2018 - 9:49am

Herbicides for different situations

Herbicide tolerant crops

Herbicide tolerant crops have a tolerance to herbicides that normally would cause severe damage (for example, Group B imidazolinone in Clearfield® canola). Herbicide tolerant crops provide additional crop choice, enabling implementation of alternate weed management tactics to target specific weeds whilst maintaining crop sequences.

Herbicide tolerance traits are introduced into crops either by conventional breeding methods (and include triazine tolerant (TT) canola introduced in 1994 and imidazolinone tolerant (IT) wheat, introduced in 2001) or by genetic modification (GM), where genes are introduced from another organism. Genetically modified (GM) herbicide tolerant (HT) cotton has been commercially grown in Australia since 2000, while Roundup Ready® (RR) canola was first commercialised in some states in 2008.

For more information refer to Information on genetically modified (GM) crops and the Genetically modified crops and herbicide resistance.

Winter fallows

Fallow spraying

Winter fallows are becoming more popular in Western Australia especially in the drier areas. They are usually incorporated as a one-year rotation into cropping programs to reduce weeds and retain moisture profiles. A fallow period on its own, or in sequence with a number of crops, can be highly effective in reducing the weed seedbank (by utilising non-selective herbicide etcetera).

An alternative is a 10 month fallow. These suit either 100% cropping enterprises or those with stock where there is value in grazing early feed. In this system, the first spray is not applied until there is stem elongation and some woodiness. This achieves soil stabilisation and a mulch effect to reduce summer evaporation provided the fallow is not grazed afterwards. Growing canola after the fallow can increase the reliability of the canola and broaden the opportunity for good weed control.

Both fallow systems give an opportunity to do deep-ripping or liming on those paddocks while they are out of cropping and if weed numbers are kept low then crops can be dry sown the following season. It is important to have a zero seed set policy for fallows to achieve this objective.

Controlled traffic or tramlining for optimal herbicide application

Controlled traffic or tramlining refers to a cropping system designed to limit soil damage by confining all wheel traffic to permanent lanes for all field operations, including seeding, harvesting and all spraying activities.

A traffic lane can increase the health of the crop due to improved soil characteristics which in turn can improve the competitive ability of the crop. They can also provide guidance and a firmer pathway for more timely and accurate application of herbicide. This will help to improve weed control and reduce input costs.

For more information refer to Developing a controlled traffic (tramline) farming system.

Weed detector sprayers

A weed detector spray unit

Weed detector sprayers are for the control of scattered weeds in crop fallows. Weed detector-activated sprayers detect the presence of weeds using infra-red reflectance units linked to a single nozzle. When a weed is detected, a solenoid turns on an individual nozzle and the weed is sprayed. In action, light-emitting diodes (LEDs) point two different light sources, infrared and near infrared, towards the ground. Green weeds have a different reflective signature to stubble or soil. The system can operate at speeds up to 20 kilometres per hour (km/h), requiring a stable boom to aid operational efficiency.

One advantage is a lower risk of drift as coarse droplets are used and only a low percent of the paddock is sprayed.

Grower experience using this technology has been that in most summer spraying and winter fallow situations, less than 10% of the entire paddock is sprayed. For greener paddocks, with more ground cover from weeds, it is often more economical to blanket spray the entire paddock given the low glyphosate prices at present.

Contact information


Sally Peltzer