Matching herbicide application rates with the environmental conditions and growth stages of nodding thistle (Carduus nutans) and hairy buttercup (Ranunculus sardous) in pastures

Glasshouse experiments were conducted to evaluate whether herbicide application rates could be reliably reduced without compromising the efficacy of the herbicide. The seedling, and vegetative and preflowering plants of nodding thistle ( Carduus nutans ) and hairy buttercup ( Ranunculus sardous ) were treated with different rates of glyphosate or a mixture of picloram and triclopyr. Half of the plants were well-watered at all times while the other half was moisture-stressed for 1 week before the herbicide treatments were applied. Hairy buttercup was more susceptible to glyphosate than nodding thistle, while both were equally susceptible to the picloram/triclopyr mixture. Moisture stress significantly reduced the efficacy of both herbicide treatments, regardless of the plant development stage or the herbicide rate applied.