Controlling Annual Ryegrass Through Canola Pre-Windrowing Desiccation

With the weather gradually warming up and harvest season fast approaching, growers and agronomists alike are thinking ahead and considering options for controlling annual ryegrass in canola crops prior to harvest. Desiccation of canola pre-windrowing is an effective control method that can greatly reduce ryegrass numbers for the following years crop. The earlier season ripening that canola offers, allows us to target and stop ryegrass seed set through use of glyphosate. Other weeds such as wild radish and sow thistle can also be targeted under this method of control. This technique is particularly beneficial, especially for those growers who do not implement harvest weed seed techniques such as chaff lining, seed destructing or having trouble with windrow burning. The method is also effective in controlling any ryegrass that may have escaped selective spraying during the early stages of canola maturity.

Optimum timing for desiccation spraying

Timing is critical when it comes to desiccation. Apply glyphosate to a standing crop at early senescence. This is when approximately 20% of seeds in elongated pods have changed colour (green to brown or black). Check several of pods and collect a random sample from various heights on the main stem to determine the average senescence of the crop. If we spray top prior to 20%, yield reductions may occur. Desiccation of canola needs to occur prior to full senescence to prevent shatter losses from ground boom application and to ensure ryegrass seed heads are successfully sterilised. Desiccation also aids in the harvestability of canola when direct heading, allowing the crop to ripen evenly and not be left waiting for ‘green patches’ to dry out sufficiently. See the below image for a reference point on what is considered to be 20% seed colour change.

Photo 1. Canola 20% seed colour change; note colour change from green to dark brown or black which represents optimal timing for ryegrass control and no impact on yield.

 

Desiccation for harvest aid and weed control applies to triazine tolerant (TT), Clearfield (Cl), Roundup Ready and conventional canola varieties. Crop safety trials proved that this use pattern has no negative effects on yield or oil content in canola, however It is important to note that any crops that are desiccated are unable to be kept as seed for the following seasons as germination and vigour is negatively affected.

 

Products registered for desiccation spraying

Weedmaster DST and Roundup UltraMAX are two herbicide options used for desiccating canola. Chemical rates for crop topping can vary, depending on both ryegrass size and numbers. Rates from 2.0-3.0L/ha are commonly seen throughout the Wimmera and Western Districts (Contact your agronomist for a specific rate unique to your crops). The cost of desiccation is approximately $15-25/ha, but this can vary with chemical rates and application method.

 

Nufarm have rigorously tested the use of glyphosate in trials pre harvest and have shown no MRL issues with residue levels well below maximum for all canola systems with no impact on product export suitability when applied at the recommended timing.

 

For an effective desiccation, growers should use high rates of water. A minimum of 80L/ha is recommended, in combination with a course droplet size. This allows the herbicide to penetrate the pod layer and contact the ryegrass plant. Windrowing can begin immediately after application is complete, however there is a 5 day harvest withhold after the application to the standing crop.

 

To discuss the option of desiccating your canola crop for annual weed control this harvest please consult with your local Western AG agronomist today.

Article produced by - Jaron Dunstan, Western Ag - Derrinallum

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