Effects of adjuvants on herbicidal action. I. Effects of a mixture of adjuvants on diclofop-methyl retention and penetration in wheat and ryegrass

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Abstract
A mixture of adjuvants composed of a liquid nitrogenous fertilizer, oil, solvent and surfactant increases diclofop-methyl efficacy against ryegrass (Lolium multiflorum Lam) at application volumes varying from 75 to 500 \.ha-1. The mixture only slightly affects spray retention on ryegrass (whatever the applied volume) and on wheat at 75 \.ha-1, but more than doubles it on wheat at 150, 300 and 500 \.ha-1. Diclofop-methyl penetration is low in wheat (less than 10% in 3 days) as well as through the wettable abaxial surface of ryegrass (less than 5%). By contrast, penetration through the poorly wettable adaxial surface of ryegrass is 29% and 52% at 75 and 500 \.ha-1 respectively. The mixture increases herbicide penetration in both species: 2 to 3 times in ryegrass and 4 to 11 times in wheat, according to application volume. Oil plays a major part in this stimulation. Combined effects on retention and penetration lead to an increase in herbicide entry into the plants, which explains the higher efficacy. The increase is 3 to 4 times greater in wheat than in ryegrass, and this tends to diminish selectivity.

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