Selectivity and mode of action of flamprop‐isopropyl, isopropyl (±)‐2‐[N‐(3‐chloro‐4‐fluorophenyl)benzamido]propionate, in the control of Avena fatua in barley

Abstract

The post‐emergence herbicide isopropyl (±)‐2‐[N‐(3‐chloro‐4‐fluorophenyl)benzamido]propionate (flamprop‐isopropyl) showed good activity against wild oat with selectivity in barley. The basis for activity and selectivity was similar to that previously established for benzoylprop‐ethyl, and found to be dependent on its rate of degradation to the biologically active acid flamprop. Flamprop stunted the growth of the oat by inhibiting cell elongation and showed a relatively high rate of movement in the phloem, approximately five times that of benzoylprop. Selectivity of flamprop‐isopropyl was dependent on its relative rate of hydrolysis and the subsequent detoxication of the acid to inactive conjugates. However, although the relative rate of de‐esterification of flamprop‐isopropyl was lower than that of benzoylprop‐ethyl similar quantities of the parent ester gave comparable effects on oat. The inherent activity of flamprop is approximately twice that of benzoylprop. The effect of flamprop‐isopropyl was best seen when the compound was applied during growth stages when the crop could offer the most effective competition to the wild oat. Throughout a range of growth stages the rate of hydrolysis of flamprop‐isopropyl was higher in oat than in barley. The metabolism of the compound was not markedly affected when the plants were under stress.

The influence of growth stage and foliage or soil application on the activity of AC 222,293 against Alopecurus myosuroides and Arena fatua

“…fatua L., A. myosuroides and Brassica species with different extents and patterns of metabolism between the species (Shaner et al, 19826). These authors suggested that the mechanism of activity and selectivity of the herbicide is due to the formation of higher levels of the biologically active acid in susceptible as compared to resistant species, in a similar fashion to that shown by some other wild oat herbicides such as diclofop-methyl (Shimabukuro, Walsh & Hoerauf, 1979) and flamprop-isopropyl (Jeffcoat & Harries, 1975).…”

Reinvestigating adjuvants for the wild oat herbicide, flamprop‐M‐isopropyl. I: Glasshouse trials

“…The physiological mode of action of this group of herbicides, via their phloem-translocated active acid moieties rather than their applied esters,' '. 16 is to inhibit cell development and elongation at meristematic regions. Selectivity occurs through differential metabolism, especially at the de-esterification step to the active acid moiety.…”

Carboxylesterase activities toward pesticide esters in crops and weeds

“…In recent years, a wide range of plants have been surveyed for their content of detoxifying glutathione transferases (Pflugmacher et al, 2000) and glucosyltransferases (Pflugmacher and Sandermann, 1998). Using a selection of major crops and weeds, we have examined the biodiversity of xenobiotic-hydrolysing esterase activities which are known to regulate the biological activity of both pesticides (Jeffcoat and Harries, 1975;Nandula and Messersmith, 2000) and pollutants (Krell and Sandermann, 1984) in plants. The available evidence suggests that unlike glutathione transferases and glucosyltransferases, carboxylesterases have evolved in parallel from several distinct protein families rather than divergently from single progenitors.…”

“…In the monocots assayed, activities toward the AOPP esters were of a similar order of magnitude in crops and weeds. This in contrast to the studies with temperate cereals and grass weeds, where much higher levels of AOPP-hydrolysing activities were determined in black-grass and wild oat as compared with wheat and barley (Cummins et al, 2001;Jeffcoat and Harries, 1975). …”

“…Thus, whereas wild oats (Avena fatua L.) rapidly hydrolyse flamprop-isopropyl to the phytotoxic flamprop acid, this reaction is much slower in barley (Hordeum vulgare L.), allowing the crop to safely detoxify the herbicide (Jeffcoat and Harries, 1975). In contrast, the rapid build up of active flamprop in wild oats leads to toxicity, with this bioactivation contributing to the selective graminicidal action of this herbicide.…”