Translocation, glyphosate

Sprankle, P., Meggitt, W.F., and Penner, D. Absorption action and translocation of glyphosate, Weed Sci., 23 235-240, 1975. Sprankle, P., Meggitt, W.F., and Penner, D. Absorption, mobility, and microbial degradation of glyphosate in soil, Weed Sci., 23 229-234, 1975a. 

Feng, P.C.C., M. Tran, T. Chiu, R.D. Sammons, G.R. Heck, and C.A. CaJacob (2004). Investigations into glyphosate-resistant horseweed (Conyzja canadensis) Retention, uptake, translocation, and metabolism. Weed Sci., 52 498-505. 

Monquero, P.A., P.J. Christoffoleti, M.D. Osuna, R. De Prado Amian, A.J. Matas, and A. Heredia. (2004). Absorption, translocation, and metabolism of 14C-glyphosate and leaf surface and wax analysis. 4th International Weed Science Congress, p. 60, S15MT08P00. 

Ahmadi, M.S., L.C. Haderlie, and G.A. Wicks (1980). Effect of growth stage and water stress on bamyardgrass (Echinochloa crus-galli) control and on glyphosate absorption and translocation. Weed Sci., 28 277-282. 

The phytotoxic effect of glyphosate can be increased by additives enhancing absorption and translocation. According to the investigations of Wills (1973) the addition of various salts and surfactants to glyphosate does not increase its initial phytotoxicity, but increases the duration of effectiveness from 2 to 8 months. Of the cations K, of the anions POJ had the best effect. 

Absorption and Translocation. Absorption and translocation of glyphosate is summarized and discussed in depth elsewhere... 

Glyphosate is a popular herbicide commercially called Round-Up. It kills plants by translocation to roots, where it has lethal effects. Glyphosate is then harmlessly decomposed in the soil. GMO crops incorporate a gene that allows than to produce a modified enzyme that makes them tolerant of glyphosate. Thus, fields can be sprayed with this habicide, and the only plants to die are the weeds. 

With the track sprayer method, systemic translocation of absorbed glyphosate among commercial formulations was measured in roots that were shielded from the spray in velvetleaf plants. Formulation A, which showed the highest absorption (28%, Fig. 6.2.2), showed 6% translocation to roots at 24 HAT (Fig. 6.2.3) [10]. Root translocation was proportional to foliar absorption and followed the ranking of formulation A > C > B, which is also the ranking of overall plant efficacy. These results showed that, even with efficient absorption, only about one-third of the applied dose was absorbed, and only a fraction of that was translocated to the roots at 24 HAT. Since the amount translocated was proportional to that absorbed, increasing absorption would increase overall efficacy as long as translocation is not hindered in the process. 

Fig. 6.2.3. Comparison of root translocation of C-glyphosate with time (hours after treatment, HAT) in commercial formulations A, B, and C following over-the-top spray application in young velvetleaf plants.

Glyphosate, a herbicide, is one example of a water-soluble amine salt of an AI acid that is usually delivered as a solution. Stabilizers and surfactants are combined in the formulation for effective application. The surfactant of choice, in fact critical for activity, is a tallow amine ethoxylate. This surfactant appears to be involved with translocation of the glyphosate across the leaf cuticle so the AI can be moved through the plant to the roots [7]. Example aqueous solution formulations are shown in Table 12.1. 

Translocated herbicides are those which can move through the plant before acting on one or more of the growth processes. Some of these herbicides can be very effective at controlling perennial weeds, e.g. the control of couch by glyphosate. Good spray cover is not so important with this type of herbicide. 

Glyphosate horseweed from Delaware has previously been examined to elucidate the resistance mechanism (20). Initial indications are that glyphosate uptake into the plant and subsequent translocation to the active site were not responsible for the observed resistance. However, enhanced glyphosate metabolism was also not implicated in this preliminary report. A hypothesis of this research group (20) was that an altered form of the EPSPS enzyme was present in glyphosate-resistant horseweed, although the plants retained some susceptible isoforms of the same enzyme. 

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