Self-Limitation of Herbicide Mobility by Phytotoxic Action

Abstract

Translocation of phloem-mobile herbicides was inhibited by their phytotoxic action on processes that maintain assimilate translocation. Glyphosate lowered import into developing sink leaves soon after it was applied to exporting sugarbeet leaves. Later, photosynthesis slowed down and starch accumulation stopped, but export of both assimilate and glyphosate continued until it was limited by starch availability at night Experiments with field pennycress and Tartary buckwheat indicated that self-limitation of chlorsulfuron translocation probably occurred and that it resulted from lowered assimilate entry into phloem rather than from inhibition of photosynthesis or carbon allocation. Leakage of chlorsulfuron from the phloem when export was slowed down also may have contributed to its reduced translocation.

Absorption, localisation, translocation and activity of glyphosate in barnyardgrass (Echinochloa crus-galli (L) Beauv): influence of herbicide and surfactant concentration

“…These results appear to support evidence suggesting that glyphosate interferes with the plant processes which maintain phloem transport 6, 19–22. In sugarbeet, a decline in photosynthesis is followed by slowing down of import into sink leaves, apparently reflecting interference with metabolism in the developing leaves 6. This was attributed to a decrease in photosynthesis, resulting in a corresponding decrease in the rate of sucrose synthesis and translocation.…”

“…Phloem movement of glyphosate is presumably controlled by factors which influence assimilate translocation. This is illustrated by the work of Geiger and Bestman6 using sugarbeet leaves. They found that lowering of photosynthesis and starch accumulation on the first day appeared to diminish the duration of glyphosate transport on subsequent days by depriving the plant of some stored carbohydrate that could prolong phloem transport from the treated source leaves.…”

“…Absorption and translocation of [ 14 C]glyphosate has been found to be less in plants at more advanced growth stages or under water stress 5. It has been suggested that mobility of glyphosate is inhibited by its phytotoxic action on processes which maintain assimilate translocation 6. Thus the rate of absorption of glyphosate may influence further uptake and subsequent movement.…”

Balance in the source – sink system: a factor in crop productivity

“…Sensitive and responsive control is needed to regulate the PCR cycle because its metabolite pools are quite small compared to the flux through them (Geiger and Bestman, 1990). A small imbalance between the rate at which a given metabolite is produced and that at which it is used causes a large excursion in the level of the metabolite.…”

In-Season Applications of Glyphosate for Control of Redvine (Brunnichia ovata) in Glyphosate-Resistant Soybean

“…Although glyphosate can result in inhibition of its own translocation to sink tissues (Geiger and Bestman 1990), high rates (e.g., 2.2 kg/ha) have been shown to be as effective against annual weeds as lower recommended rates (Smith et al 1998). Further research should be conducted to determine if multiple applications of glyphosate at rates higher than those recommended for annual weeds used for multiple years significantly reduce redvine populations to a level comparable with expensive preharvest herbicide treatments (e.g., dicamba).…”