Effects of low concentrations of vapour of the phenoxyalkanoic herbicide 2,4-D-butyl on growth of tomato plants

Tomato plants (5–7 weeks old)were exposed to a range of concentrations of vapour of 2,4-D-butyl (0.12–2.4 ng litre^?;1), for periods of 6 or 24 h, using an air-flow system. Net carbon dioxide exchange of the whole plant was measured for up to 2 days after exposure and was found to decrease in treated plants approximately in proportion to vapour concentration. Six weeks after exposure, shoot dry-weights of plants exposed to herbicide vapour were less than control plants in all cases, by about 20 % or more. All characteristics measured were affected more by a 24-h exposure period than 6 h, at the same vapour concentration. The amount of herbicide vapour, expressed as the product of exposure period and vapour concentration, gave a similar effect at a low range of vapour concentrations (≤1.0 ng litre^?;1)and air-flow rates of about 200 litre min^?;1, but not at higher concentrations at a flow rate of about 120 litre min ^?;1. Better agreement between the experiments carried out at the two concentration ranges was obtained by expressing the herbicide vapour as the total amount to which the plants were exposed (i.e. the product of air-flow rate, vapour concentration and duration of exposure)instead of concentration alone.     

Long- and short-term effects of vapour of the herbicide 2,4-D butyl on the growth of tomato plants

An airflow system has been used to expose tomato plants to a range of concentrations of vapour of the herbicide 2,4-D butyl, from 5 to 50 ng l^?1. Experiments carried out at an air temperature of 20°C indicate that only short periods (less than 2.5 h) are required to produce symptoms of phytotoxicity at concentrations less than 5 ng l^?1, or approximately 2.5% of the saturated vapour pressure of the herbicide. A 5-h period of exposure to approximately 5 ng l^?1 reduced the dry weight and dry matter content of the tomato plants after 7 weeks by 18% and 9%, respectively, compared with the control. Phytotoxicity symptoms were shown by the plants in proportion to the vapour concentration during the period of exposure to herbicide. Rates of photosynthesis of treated plants had begun to decline within an hour of the commencement of exposure, slightly after leaf movement was first observed.     

Differential phytotoxicity of glyphosate in maize seedlings following applications to roots or shoot

The transport and differential phytotoxicity of glyphosate was investigated in maize seedlings following application of the herbicide to either roots or shoots. One-leaf maize seedlings (Zea mays L.) were maintained in graduated cylinders (250 mL) containing nutrient solution. Half of the test plants were placed in cylinders (100 mL) containing different ¹⁴C-glyphosate concentrations; the remainder received foliar appliation of ¹⁴C-glyphosate. After 26 h, the roots and the treated leaves were washed with distilled water, and the plants placed again in cylinders (250 mL) containing fresh nutrient solution for 5 days. Plants were weighed, and split into root, seed, cotyledon, coleoptile, mesocotyl, first leaf and apex. The recovery of ¹⁴C-glyphosate was over 86%. For both application treatments, the shoot apex was the major sink of the mobilized glyphosate (47.9 ± 2.93% for root absorption and 45.8 ± 2.91% for foliar absorption). Expressed on a tissue fresh weight basis, approximately 0.26 μg a.e. g⁻¹ of glyphosate in the apex produced a 50% reduction of plant fresh weight (ED₅₀) when the herbicide was applied to the root. However, the ED₅₀ following foliar absorption was only 0.042 μg a.e. g⁻¹ in the apex, thus maize seedlings were much more sensitive to foliar application of the herbicide.     

Absorption and translocation of 14C-3,6-dichloropicolinic acid in Cirsium arvense (L.) Scop.

Experiments were conducted in a growth cabinet to investigate the absorption and translocation of ¹⁴C-3, 6-dichloropicolinic acid by Cirsium arvense (L.) Scop. (Canada thistle, creeping thistle), a sensitive species. Applications were made, either to the middle four leaves of 12-cm-tall vegetative plants grown under low (40%) and/or high (>95%) relative humidity (r.h.), or to four upper or lower leaves of 30-cm-tall flowering plants grown under low r.h. Following application to vegetative plants, absorption and translocation of ¹⁴C-3,6-dichloropicolinic acid was rapid and was approximately doubled by high r.h. High r.h. increased the amount of radioactivity retained by the treated leaves or translocated to the shoots but did not affect greatly the amount retained in the roots. The herbicide was highly mobile, with over half of that absorbed, translocated out of the treated leaves after two days. The apex accumulated most of the radioactivity, while approximately 8% was recovered from the roots. The absorption and translocation patterns were similar to those reported in the literature for picloram in C. arvense. Absorption of 3,6-dichloropicolinic acid was greater in vegetative than in flowering C. arvense plants, and placement of herbicide on lower leaves tended to decrease the amount of radioactivity recovered from shoot apex and increase the amount recovered from the roots. Approximately 15% of the applied radioactivity could not be recovered from treated plants by 2 days after treatment.     

Phytotoxic activity of root absorbed glyphosate in corn seedlings (Zea mays L.)

Growth chamber experiments were conducted in order to study the absorption, translocation and activity of glyphosate when applied to roots with aqueous solution avoiding any glyphosate–substrate interaction. Corn seedlings at the first leaf stage were set up in individual graduated cylinders containing different solutions of ¹⁴C-glyphosate (0–30 mg ae kg⁻¹). After 26 h of root exposure, plants were transferred to fresh nutrient solution and grown for the next 5 days. After harvest, plants were separated into seed, root, mesocotyle, coleoptile, cotyledon, first leaf and all new leaves (apex), and quantified ¹⁴C radioactivity contained in each part. Glyphosate uptake was only 11% of the theoretical mass flow into the plant. The amount of glyphosate translocated from roots was positively correlated with plant uptake ( P  < 0.01). Total plant fresh weight presented a logistic response to glyphosate amounts, including a growth stimulant effect (hormesis), when plants absorbed less than 0.6 µg. The treated plants presented a normal pattern of glyphosate allocation, with the apex the principal sink, accumulating more than 38% of mobilized glyphosate. When corn plants absorbed more than 0.6 µg they showed a decrease in growth. The relatively high glyphosate quantities allocated in the new leaves showed the relevance of the symplastic pathway in the translocation process for root absorbed glyphosate.     

UNTERSUCHUNGEN ÜBER AUFNAHME UND TRANSLOKATION VON 14C-MARKIERTEN HERBIZIDEN IN AGROSTEMMA GITHAGO L. UND TUSSILAGO FARFARA L.

Studies of the uptake and translocation of ¹⁴C-labelled 2, 4-D, MCPA and aminotriazole in Agrostemma githago L. and Tussilago farfara L. clarified the behaviour of the herbicides in both species. In A. githago, MCPA was more freely mobile than 2,4-D after application to the leaf; it was distributed in the plant more rapidly and in greater quantity. Similarly, following root uptake MCPA was transported in the shoot in greater amounts than was 2,4-D. There is a clear relationship between the susceptibility of A. githago to MCPA and the mobility of the herbicide in the plant. In T. farfara, 2,4-D and aminotriazole applied to the leaves were equally well absorbed and relatively rapidly translocated. During the period up to 72 h the amounts of herbicide in the plant increased to similar levels; after that, ¹⁴C activity in plants treated with 2,4-D fell slightly whereas there was further accumulation of aminotriazole. Following uptake through the roots, translocation and accumulation in the leaves were considerably greater with aminotriazole than with 2,4-D. The lack of accumulation of 2,4-D could be a factor in the resistance of T. farfara to this herbicidie. Recherches sur l'absorption et la migration d'herbicides marqués au ¹⁴ C dans Agrostemma githago L. et Tussilago farfara L.     

Differential translocation of paraquat in paraquat-resistant populations of Hordeum leporinum

Two populations of Hordeum leporinum have evolved resistance to paraquat within a small area in central Tasmania, Australia. One population (THL1) was more than 80-fold resistant to paraquat when treated in winter, compared with a susceptible population (THL4) collected nearby, whereas the other population (THL2) was only 19-fold resistant. Translocation of paraquat was examined in all three populations at warm and cool temperature regimes. Herbicide was applied to a basal section of the second leaf of plants kept in the dark and translocation measured after 16 h of dark and during a subsequent light period. Paraquat absorption into the treated leaf was uniformly high in susceptible and resistant populations, with >93% of the applied herbicide absorbed within 16 h in the dark at both temperatures. Translocation of paraquat out of the treated leaf was low in the dark, with <4% of the herbicide translocated to the remainder of the plant. More herbicide was translocated out of the treated leaves in susceptible plants in the dark, compared with resistant plants at both temperature regimes and more paraquat was translocated at warmer temperatures. Extensive basipetal translocation of paraquat to the rest of the plant occurred in susceptible plants following exposure of the treated plants to light. However, basipetal translocation was much reduced in resistant plants in the light and corresponded to the degree of resistance. Resistance to paraquat in H. leporinum is the result of reduced translocation of paraquat out of the treated leaves.     

Effect of concentration on absorption and translocation of 2,4,5-T in blackberry (Rubus procerus P. J. Muell.)

Radioactive 2,4,5-T was applied to the leaves of small Rubus precerus (P. J. Muell.) plants grown in pots in the glasshouse in amounts ranging from 24 μg to 55.8 μg per leaf. The amount of 2,4,5-T absorbed and translocated was measured 6h and 24h later. The herbicide was translocated throughout the plant within 6h and the concentration in the various plant parts increased between 6h and 24h. More 2,4,5-T was absorbed at high concentrations than at low concentrations although the percentage absorbed in 24h decreased from 13% to 6% as the concentration was increased Translocation of 2,4,5-T-1-14C was variable, although the amount translocated inereased as the amount applied was increased, and was closely correlated to the amount of herbicide absorbed by the leaves.     

Einfluß des Applikationsortes auf die Penetration und Translokation von Diclofop-methyl bei Flughafer (Avena fatua L.)

Effect of the type of application on the penetration and translocation of dictofop-methyl in wild oats (Avena fatua L.) An investigation was curried out with wild oats on the effect of different types of application between the apex and the base of the shoot on the penetration and translocation of ¹⁴C-diclofopmethyl Penetration at the base of the leaf blade is 64% higher in the first leaf and 95% higher in the second than at the lip of the respective leaves Basipetal translocation of ¹⁴C-diclofop-methyl is limited so the nearer to the base of the shoot the herbicide application is made, the higher will be the amount of ¹⁴C-diclofop-methyl at the shoot base which is the principle site of activity Application at the base of the leaf blade gave the optimum distribution of ¹⁴C-diclofop-methyl in the plant. One reason for this is that, with this type of application, the herbicide solution runs down into the leaf sheath giving rise mechanically to basipetal penetration within the sheath into the zone of meristematic tissue at the base of the shoot. These findings lead to a demand for the most accurate possible placing of diclofop-methyl in the zone of the base of the shoots.     

Are pre‐spraying growing conditions a major determinant of herbicide efficacy?

To evaluate the effect of pre‐spraying growing conditions on herbicide efficacy, two years of experimentation were conducted in which Persicaria maculosa plants were exposed to different light intensities for 1–4 days before metribuzin treatment. Specific leaf area, rather than plant growth rate or plant size, was the only parameter that correlated well with herbicide efficacy in both years of experimentation. The negative relationship between the ED₅₀ and the specific leaf area indicates that leaf characteristics might be an important determinant of herbicide efficacy, for instance through an effect on herbicide uptake. In the third year of experimentation this hypothesis was further investigated by raising six cohorts of weed plants at a 1‐week interval and thus exposing them to a range of weather conditions. Clear relationships between uptake and herbicide efficacy were found for a combination of four plant species (Solanum nigrum, Senecio vulgaris, Chenopodium album and Brassica napus) and two herbicides (phenmedipham and bentazone). For phenmedipham, uptake was negatively correlated with global radiation and positively correlated with relative humidity. For the herbicide bentazone the opposite was found. These results were not species‐specific. This study shows the importance of the sensitivity of herbicide × species combinations and indicates that pre‐spraying weather information is relevant for the development of reduced dose rate recommendations.     

The role of waxes in the uptake of metolachlor into sorghum in relation to the protectant CGA 43089

The grass weed herbicide metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxy-1-methylethyl]acetamide) which is especially effective against wild millets, inhibits the formation of epicuticular waxes on sorghum leaves. The metolachlor protectant CGA 43089 [α - (cyanomethoximino) - benzacetonitrile] prevents the depletion of the waxes on the leaves of metolachlor-treated sorghum plants, as demonstrated by scanning electron microscopy. This alteration of the plant surface polymers also changes their permeability to the herbicide. ¹⁴C-metolachlor uptake into isolated coleoptiles and first leaves of sorghum which had been pretreated with the herbicide was increased. Incubation with added protectant reduced the uptake of ¹⁴C-metolachlor. It is postulated that the modifications caused by metolachlor and its protectant to sorghum surface structures influence the action of the herbicide in two ways:

• 1 The selectivity observed against sorghum and millet grasses could occur because of an increased uptake of metolachlor through cuticles which are particularly sensitive to the structural changes caused by the herbicide, since the composition of the plant waxes is very species-specific.
• 2 The loss of cuticular integrity is prevented by the protectant CGA 43089, which greatly reduces penetration of metolachlor.

     

Studies into the differential activity of the hydroxybenzonitrile herbicides: II. Uptake,movement and metabolism in two contrasting species

Uptake, movement, and metabolism of unformulated ioxynil and bromoxynil salts were investigated in Matricaria inodora and Viola arvensis. The morphology of these two species did not give rise to different spray retention and contact angles. After 7 days, uptake of [¹⁴C]ioxynil-Na reached 8.26% of applied ¹⁴C activity in M. inodora and 16.77% of that in V. arvensis compared with 1.54 and 3.83%, respectively, for [¹⁴C]bromoxynil-K. Over 98% of the ¹⁴C activity detected in the plant after 7 days remained in the treated leaves of V. arvensis following [¹⁴C]ioxynil-Na treatment. However, 8.7% of the ¹⁴C activity detected in [¹⁴C]ioxynil-Na-treated M. inodora was recovered from the apex and developing leaves reflecting a greater translocation. [¹⁴C]Bromoxynil-K was more mobile in both species and after 7 days 87.5 and 91.39% were detected in the treated leaves of M. inodora and V. arvensis, respectively. In both species the majority of translocated ¹⁴C activity was recovered from the apex and developing leaves. Up to 20% of the applied [¹⁴C]ioxynil-Na and [¹⁴C]bromoxynil-K was not detected within the treated plant. Extraction of treated plants revealed no detectable metabolic breakdown of ioxynil-Na to halogenated derivatives in either species. However, metabolic breakdown of bromoxynil-K was apparent in V. arvensis. No significant root exudation was detected when [¹⁴C]ioxynil-Na and [¹⁴C]bromoxynil-K were applied to hydroponically grown S. media and V. arvensis. Losses of ¹⁴C activity were due to herbicide volatility or degradation to volatile products on the leaf surface.     

Recovery of non-target plants affected by airborne bromoxynil-octanoate and metribuzin

The present study was conducted to evaluate the recovery potential of non‐target plants affected by two airborne herbicides. Sunflower at the two‐leaf stage was used as a test plant and exposed for 24 h in a wind tunnel to a range of concentrations of airborne bromoxynil‐octanoate and metribuzin. Quantum yield (φ_PSII) of exposed leaves and of the second leaf pair developed after exposure was determined at a particular time up to 16 days following exposure. Maximum depression in quantum yield of exposed leaves from which a complete recovery occurred within 16 days was 63% for bromoxynil‐octanoate and 60% for metribuzin respectively. The corresponding maximum concentrations were 1.310 and 0.390 μg m^?3 respectively. The second leaf pair was also affected and showed a similar recovery potential. From the results it can be concluded that the significance of airborne bromoxynil‐octanoate and metribuzin must not be overestimated, as sunflower and non‐target plants with a similar sensitivity are likely to recover from air concentrations of both herbicides reported under field conditions.     

Auswirkungen des Herbizids Basta® auf die Weinrebe und den Falschen Mehltau

A field experiment was conducted in order to analyse the effects of the herbicide Basta^® with glufosinate-ammonium as the active ingredient (that inhibits specifically the enzyme glutamine-synthetase) on the grapevine plant and the infestation with Plasmopara viticola, the downy mildew pathogen. The herbicide was applied at sublethal concentrations and the toxic effects on leaves and berries based on different quality parameters were estimated. Low concentrations of glufosinate-ammonium (<?0,625?mM) did not affect the chlorophyll and amino acid concentrations in leaves. This was also the case for the content of salicylic acid and phenolic compounds. Furthermore, must parameters such as sugars (glucose and fructose), acids (tartaric acid, malic acid, total acids and volatile acids), and alcohol (ethanol and glycerine) also remained unchanged compared to the fungicide-treated or untreated control, whereas the concentrations of nitrogenous components metabolically available to yeasts increased with increasing concentrations of glufosinate-ammonium. The amount of berries harvested at the end of the experiment depended on the glufosinate-ammonium concentration applied. The harvest was highest when glufosinate-ammonium was applied as a 0.1?mM solution and differed not significantly from the fungicide-treated control, but decreased with increasing herbicide doses. However, the infestation of leaves with P. viticola was significantly reduced by the application of the herbicide, even though not each infection was eradicated due to the non-systemic mode of action of the herbicide. The particular influence of the herbicide onto this host-parasite interaction still remains unclear. Since applications of glufosinate-ammonium at low concentrations seem not to affect grapevine plants negatively, but were able to reduce the infestation with downy mildew, the specific mode of action may reveal new alternatives for the control of fungal pathogens.     

Relation between volatility rating and composition of phenoxy herbicide ester formulations

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T-(iso-octyl) formulation, as complete formulations, and 35-5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut-off area for low-volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high-volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D-ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T-(iso-octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D-(iso-octyl) should not contain more than 11 g litre^?1 2,4–D as methyl ester or 2.0 g litre^?1 2,4–D as ethyl ester. Formulations of 2,4,5–T-(iso-octyl) should not contain more than 26 g litre^?1 2,4–D as methyl ester or 4.7g litre^?1 2,4–D as ethyl ester.     

Some physicochemical factors influencing foliar uptake enhancement of glyphosatemono(isopropylammonium) by polyoxyethylene surfactants

Structure-concentration–foliar uptake enhancement relationships between commercial polyoxyethylene primary aliphatic alcohol (A), nonylphenol (NP), primary aliphatic amine (AM) surfactants and the herbicide glyphosatemono(isopropylammonium) were studied in experiments with wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants growing under controlled-environment conditions. Candidate surfactants had mean molar ethylene oxide (EO) contents ranging from 5 to 20 and were added at concentrations varying from 0·2 to 10 g litre^?-1 to [¹⁴C]glyphosate formulations in acetone–water. Rates and total amounts of herbicide uptake from c. 0·2–μl droplet applications of formulations to leaves were influenced by surfactant EO content, surfactant hydrophobe composition, surfactant concentration, glyphosate concentration and plant species, in a complex manner. Surfactant effects were most pronounced at 0·5 g acid equivalent (a.e.) glyphosate litre^?-1 where, for both target species, surfactants of high EO content (15–20) were most effective at enhancing herbicide uptake: surfactants of lower EO content (5–10) frequently reduced, or failed to improve, glyphosate absorption. Whereas, at optimal EO content, AM surfactants caused greatest uptake enhancement on wheat, A surfactants gave the best overall performance on field bean; NP surfactants were generally the least efficient class of adjuvants on both species. Threshold concentrations of surfactants needed to increase glyphosate uptake were much higher in field bean than wheat (c. 2 g litre^?-1 and < 1 g litre^?-1, respectively); less herbicide was taken up by both species at high AM surfactant concentrations. At 5 and 10 g a.e. glyphosate litre^?-1, there were substantial increases in herbicide absorption and surfactant addition could cause effects on uptake that were different from those observed at lower herbicide doses. In particular, the influence of EO content on glyphosate uptake was now much less marked in both species, especially with AM surfactants. The fundamental importance of glyphosate concentration for its uptake was further emphasised by experiments using formulations with constant a.i./surfactant weight ratios. Any increased foliar penetration resulting from inclusion of surfactants in 0·5 g litre^?-1 [¹⁴C]glyphosate formulations gave concomitant increases in the amounts of radiolabel that were translocated away from the site of application. At these low herbicide doses, translocation of absorbed [¹⁴C]glyphosate in wheat was c. twice that in field bean; surfactant addition to the formulation did not increase the proportion transported in wheat but substantially enhanced it in field bean.     

Effect of different levels of mannitol-induced water stress on the tolerance of cultivated oat (Avena sativa L.) to didofop-methyl

The effect of degree of water stress in Avena sativa on diclofop-methyl efficacy was assessed. Within 24 h of applying stress by adding mannitol to the root medium (0 to 12.5%), the rate of leaf extension of the youngest leaves (leaves 3 and 4) decreased with increasing mannitol concentration. Without water stress, application of diclofop-methyl had little effect on extension rate of leaves 3 and 4 during the first 4 days after spraying. Subsequently, it caused a significant decrease in the extension rate of leaf 4 with more pronounced effects on later leaves. Diclofop-methyl had little effect on leaf extension rate of plants given mannitol. Shoot dry weight at harvest for unsprayed plants decreased with increased mannitol concentration and for sprayed plants it was greater without mannitol than with mannitol (all levels). However, at mannitol concentrations greater than 4%, shoot dry weight for sprayed and unsprayed plants was not significantly different. Sprayed plants exposed to 2–8.5% mannitol produced seed heads but those at zero mannitol did not. When the root medium of all treatments was flushed of mannitol one week after spraying, then main-tained without mannitol, shoot dry weight at harvest for unsprayed plants decreased slightly with increased mannitol concentration applied initially. However, shoot dry weight for sprayed plants increased with increased mannitol concentration. Without mannitol two weeks after spraying, chlorophyll concentrations of leaves 3 and 4 were greater and water saturation deficit (WSD) values were lower for unsprayed plants than sprayed plants but there were no differences at 6.2% mannitol. It is proposed that tolerance to diclofop-methyl by A. sativa as a result of water stress, is primarily due to a decreased rate of leaf expansion resulting in lower demand for membrane synthesis and less strain on membranes damaged by the herbicide.     

The response of resistant and susceptible plants to diclofop-methyl

Wild oat (Avena fatua L.) plants sprayed at the 2-or 3-leaf stages of growth with diclotop-methyl developed chlorosis over the entire leaf blade of all leaves. The leaves became necfrotic ⁷days after spraying Shool growth was inhibited. In wheat (Triticum aesicum L cv.Waldron) discrete chlorotic areas developed only where the herbicide convicted the 2nd or 3rd leaf with no visible injury so new growth uf'ter treutment. Growth inhibition of susceptible oat (Avena sativa L. cv. Garry) was sensitive to placement of diclutop-methyl near the upica and meristematic sites of the plant. Chlorosis and necrosis were independent of herbicide placement. Selective herbicide placement induced chlorosis only or both chlorosis and growth inhibition Root growth in wild oat and barley (Hordeum rulgare L. cv. Dickson) was strongly inhibited by 1–0 μM diclofop-methyl. Wild oat shoots were killed when seedlings were root-treated with 10 μM diclofop-melhyl. The 100 μM rool treatment killed barley shoots but only stunted the growth of wheat shoots by approximately 50%. In root-ireated wheat plants the shoots were turgid and developed a light purple colour, whereas in foliar-treated plants the shoots developed discrete chlorotic areas.     

Uptake of some volatile alkyl methylphosphonofluoridates from the vapour phase by wheat plants

The uptake of cyclohexyl, isopropyl and 1,2,2-trimethylpropyl methylphosphonofluoridates from the vapour phase by growing wheat plants was studied. The compounds were absorbed through the leaves of the plants and were degraded in a manner similar to that following their uptake through the roots from hydroponic culture solution. The levels of the methylphosphonic acid derivatives in the plant extracts were influenced by the vapour concentration of the methylphosphonofluoridate, the period of exposure to the vapour and the state of illumination of the plants, but were not markedly influenced by the chemical nature of the compounds. Likely mechanisms for the uptake are discussed and it is concluded that the main route of absorption involves the stomata. The studies suggest that growing plants can absorb and possibly have a “sink effect” for atmospheric organophosphorus contamination.     

Effect of CGA 123407 as a safener for pretilachlor in rice (Oryza sativa L.). Recordings of elongation rates of single rice leaves

The elongation rates of single attached leaves of rice (Oryza saliva L.) were recorded. The effect of pretilachlor on the elongation rates and the safening effect of CGA 123407 [4, 6-dichloro-2-phenyl-pyrimidine] were evaluated. Both chemicals were applied to the roots in a nutrient solution. Pretilachlor reduced leaf elongation in concentrations as low as 300 μg^?1 (9–6 × 10^?7 M) but. for combination trials with the safener, 3 mg 1^?1 (9–6 × 10^?6 M) was used. in combination with pretilachlor the safener prevented damage in very low concentrations. The ratio of pretilachlor to safener, 30:1, was sufficient when both chemicals were given to roots in nutrient solution, although for field work the ratio of 3:1 is recommended. The safener alone did not influence the elongation rate of rice leaves in the concentrations used. When pretilachlor was given to the roots and CGA 123407 to the shoot, some delay in the herbicidal action was recorded but even with high concentrations of the safener no continuous safening effect was achieved. CGA 123407 was also effective when given previous to the herbicide. This proved true even with a 2-day interval between safener uptake and application of the herbicide. When pretilachlor was given first, the safener effected recovery to various degrees when given 1–4 days after the herbicide application. When pretilachlor was given for a limited period of time only (1–3 days) and was subsequently removed from the nutrient solution, recovery of the plant occurred. It is speculated that the safener either helps this recovery or else competitively prevents the herbicide from occupying the sites of action or from keeping them occupied for a long period of time.