Grass Herbicide Efficacy as Influenced by Adjuvant, Spray Solution pH, and Ultraviolet Light

Abstract

Research was conducted at the Brandon Research Centre to determine the effect of spray solution pH or adjuvants on the efficacy of two cyclohexanedione (CHD) herbicides, clethodim and tralkoxydim, and two aryloxyphenoxypropionate (APP) herbicides, fenoxaprop-P and quizalofop, and if ultraviolet light is a factor influencing their activity. CHD herbicide efficacy decreased as spray solution pH increased above 7. APP herbicide efficacy was not affected by spray solution pH, probably due to their formulation as proherbicide esters. The choice of adjuvant affected CHD herbicide efficacy but not APP herbicide efficacy. Amigo®, Canplus-411® plus ammonium sulfate, and Merge® were usually the most effective adjuvants with the two CHD herbicides. Physical removal of ultraviolet light did not improve APP herbicide efficacy but did improve CHD herbicide efficacy.

Degradation of Cyclohexanedione Oxime Herbicides

“…Similar findings were also obtained by Bridges et al [39]. McMullan [40] noted that clethodim efficacy was enhanced as a consequence of the presence of adjuvants in the spray solution. This effect was attributed to an increase of the adsorption rate of the herbicide and thus, a reduction of its photodegradation.…”

Resistance to ACCase‐inhibiting herbicides and isoproturon in UK populations of Lolium multiflorum: mechanisms of resistance and implications for control

“…These herbicides have also been shown to be very active under glasshouse conditions against susceptible Avena sterilis ssp ludoviciana 26. The greater activity of CHD herbicides under glasshouse conditions is probably due to the reduced levels of UV light, and the associated reduction in photodegradation of herbicide 27. However, there is no obvious reason why the greater activity of herbicides should not apply equally to resistant and susceptible populations, so this effect also offers no satisfactory explanation for the very high resistance indices recorded under glasshouse conditions.…”

On the effect of pH on spreading of surfactant solutions on hydrophobic surfaces

“…Whilst alkaline hydrolysis of the pesticides modifies their active ingredients, in an acidic environment hydrolysis of the pesticides is prevented. Thus the protonated form will penetrate more rapidly than the ionised molecule [15]. Therefore, low pH is considered advisable when using pesticides.…”