Couch grass is a common and invasive perennial grass with creeping under leaves stems known as rhizomes. It spreads rapidly to form dense mats of underground stems. Grows among cultivated crops and competes for water, nutrients and also harbors pests and diseases. Host plants includes citrus maize, sugarcane and cotton among other crops.
The only sure answer to Couch Grass is to apply glyphosate in the fallow period. In my experience the dose rate needs to be at least 1,500 grams of active ingredient per hectare, so 3 litres/ha for most quality glyphosate formulations.
It is best applied when the Couch Grass is actively growing which means soil moisture and not too hot or cold days. Good coverage is essential so avoid dusty conditions, and the use of an adjuvant will improve retention and penetration on the leaf. As always, use ammonium sulphate to condition the water before putting the glyphosate into the sprayer tank, and acidify to improve activity.
I tend to use either Flat Fan nozzles for this type of spray, or 3D type nozzles are even better. The main thing is to strike a balance between an acceptable amount of drift, and good coverage of the target plant. For this reason I avoid true Air Induction nozzles.
Contact graminicides such as Fusilade (fluazifop) and Select (clethodim) do provide very good suppression, so including crops such as Peas and Canola in the rotation can be very beneficial. For really bad localised patches of Cynodon grass, rotavating or ripping with a Chisel in before planting season or during fallow season can help; the dry weather will dry out and desiccate the Rhizomes.
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.