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RIM analysis – Michael and Marnie Fels, WA

This case study was updated in March 2023.

The RIM analysis below was conducted on a crop rotation that the Fels no longer use on their farm at Wittenoom, WA. Although the model suggested that the double stacked rotation was effective in conjunction with HWSC, Mic found that weeds did build up and he altered their rotation.

How many consecutive cereal crops can you safely grow?

Mic’s farming system has been tested using the RIM (Ryegrass Integrated Management) analysis tool. The scenario tested was a double stacked canola rotation to control ryegrass and then growing four consecutive cereal crops (2 wheat then 2 barley) before rotating back to canola. The question being considered was ‘is this crop rotation plus herbicides sufficient to control annual ryegrass?’.

This RIM analysis result, and a similar one done in a low rainfall cropping environment, indicates that a grower can choose the crop rotation that best suits their farm, provided sufficient weed control measures are in place to prevent a blow out in ryegrass numbers. In these analyses, using harvest weed seed control every year was enough to beat ryegrass and keep the rotation going.

Peter Newman, Communication Lead at the Australian Herbicide Resistance Initiative says even on a farm where there is no weed resistance to glyphosate or pre-emergent herbicides, and using the best herbicides available, a blow out in ryegrass numbers would be expected in the fourth wheat crop following two consecutive canola crops if there is no harvest weed seed control.

“If the grower adds harvest weed seed control to their management every year then it is possible to grow at least four consecutive cereal crops while also maintaining ryegrass numbers at or near zero,” he says. “Returning to the two seasons of canola with ryegrass numbers still low is the ideal outcome for managing weeds and herbicide resistance risk.”

“It doesn’t matter what harvest weed seed control system you use, all that matters is that it happens every year. With all the weed control measures that Mic has in place, the system even works in the face of Group A and glyphosate resistance.”

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