The opportunity cost of herbicide residue effects across crop types (imi trial)

Key Points

• Results are limited by the seasonal conditions and are only indicative of heavy clay soils that have received high rainfall levels (298mm YTD).

• Minimal significant differences in plant numbers were recorded.

• Impacts from the residual chemicals appear to be minimal.

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Aim

To compare the potential yield penalty incurred due to herbicide residues in comparison to the yield penalty inherent in growing a herbicide-resistant variety.

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Background

Herbicides that have long carry over residues can often limit cropping options. Labels are not entirely clear and it can be difficult to know ahead of time if rainfall has been sufficient to limit potential crop damage when planting back into a residue. This topic has been bought up several times by the Liebe R&D committee over the past years. As such a demonstration was proposed to quantify and compare potential yield penalties that may result due to herbicide residues.

Ten residues have been addressed, each being applied in the previous year (2020) in a fallow paddock. This year 7 different crops were sown over the herbicide residues, including both standard and imi tolerant varieties. The aim is to compare the yield penalties associated with herbicide residues and the yield penalties associated with growing an imi resistant variety.

This is a replicated demonstration, however, the applicability of the results is limited by the site and seasonal conditions. The trial has been conducted on a heavy clay soil with a pH >7, and above-average rainfall has fallen at the site this season. Results may differ significantly at sites with lighter, lower pH soils and in seasons with different rainfall patterns.