WITH northern region cropping operations entering the all-important summer fallow weed control period, an urgent appeal has gone out for growers to use glyphosate wisely.
James Clark, Grains Research and Development Corporation (GRDC) northern panel chair, said that glyphosate resistance is shaping up as the single biggest threat to Australia's sustainable farming system.
Mr Clark said growers could face production falls of 20 per cent if glyphosate resistance reaches a level where tillage becomes a regular part of the farming system once more.
"GRDC has funded a major new five-year research project on integrated weed management (IWM) for northern region weeds to follow-on from the current projects on herbicide resistance, fleabane control and delivering applied solutions in central Queensland," Mr Clark said.
"The new IWM project will have key researchers based in Toowoomba and Tamworth who are responsible for delivering IWM outcomes across the whole northern region."
Current GRDC research shows moisture stress and glyphosate resistance are the two big issues in the fight against barnyard grass.
Dr Steve Walker, Department of Employment, Economic Development and Innovation (DEEDI) weed researcher, said spray failures in summer fallows are often a result of plant moisture stress at the time of herbicide application.
"This can be confounded by the presence of glyphosate resistance," he said.
"Fortunately, last summer was rather wet, limiting the number of glyphosate applications to stressed weeds.
"This would have been an ideal time to inspect for potential glyphosate resistant barnyard grass as moisture stress was unlikely."
Dr Walker says there is still some belief in the industry that glyphosate resistance in barnyard grass is essentially poor control due to moisture stress, and not due to selection pressure of a specific plant type.
"Moisture stress will lead to unsatisfactory control, however poor control is also caused by glyphosate resistant populations," he said.
A glasshouse-based experiment examined if an interaction exists between moisture stress, glyphosate resistance status and herbicide rate.
It showed that survival is a complex combination of factors including resistance status, herbicide rate and moisture stress.
Dr Walker says growers must ensure herbicide are applied to actively-growing barnyard grass plants.
"This is best achieved by controlling plants within a seven to 14-day period after good rain.
"Plants are likely to be small, less likely to be stressed and can also be controlled with Group L herbicides."
He said growers needed to undertake resistance testing to confirm the presence or absence of glyphosate resistance.
An excellent time to monitor for glyphosate resistance is after plants have been treated with glyphosate under ideal conditions as this is a time when a large majority of susceptible plants will die and any resistant individuals are more obvious, he said.
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