Getting Group G use right for weed control in summer fallow

A crop field before planting
Group G herbicides have predominantly been used at a relatively low rate, as a knockdown in fallow or ahead of planting. Photo GRDC.

Group G mode of action herbicides have predominantly been used at a relatively low rate – as a spike – in combination with another non-selective herbicide as a knockdown in fallow or ahead of planting.

Group G chemistry inhibits part of the process for making chlorophyll, with plant leaves dying as a result. Herbicide uptake is usually through contact on the leaves of emerged weeds or taken up from the soil as the weed seedlings break through the soil surface.

The choice of partner herbicide for Group G products is commonly a decision between either glyphosate or a paraquat-based chemical.

Fast-acting Group G herbicides destroy cells on contact, so may not always be the ideal mixing partner for glyphosate, which is a systemic herbicide that takes time to enter and translocate throughout the weed.

While this Group G and a glyphosate mix is common and often effective, the biochemical properties of these different herbicides means that this mixture is a compromise and may potentially have adverse effects on weed control, especially grasses where a reduction in efficacy is more apparent.

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