THE BIPYRIDYLIUM QUATERNARY SALTS

Summary. In a number of plant species, the biological activity of diquat and paraquat was increased by an increase in environmental humidity. This improved activity resulted from an increase in both uptake and movement.
High humidity was more effective after treatment than before it, and durations of 8 hr or more were required to produce the maximum effect. When periods of low humidity of up to 16 hr were interposed between treatment and high humidity, there was no significant effect on the activity of diquat in darkened tomato or sugar beet.
The increase in activity occurred both in the dark and in the light, and it is therefore concluded that humidity does not exert its effect by modifying the degree of stomatal opening.
Experiments were carried out with wheat using two air humidities combined with different soil moisture contents, ranging from saturated down to only 30% of water-holding capacity. Greatest movement occurred where high air humidity was combined with low soil moisture, and least where low air humidity was combined with high soil moisture. It is concluded that diquat and paraquat would be most effective in the field when sprayed under dry soil conditions in late afternoon or evening when increased humidity (and darkness) can follow soon after treatment.
Les sels quatemaires de bipyridylium
Effet de l'humidité atmosphérique et de l'humidité du sol sur l'absorption et la migration du diquat et du paraquat dans les plantes     

TUBER NECROSIS FOLLOWING THE DESICCATION OF POTATO FOLIAGE WITH DIQUAT

Summary. Necrosis at the stem-end of potato tubers following the application of diquat to the foliage is rare and has occurred mainly in seasons of low rainfall. Damage in the field has been associated with tuber residues of diquat of about ten times the normal level and the extent of damage has shown a linear relationship with the concentration of chemical in the tubers. Normally an increase in the dose of diquat applied causes only a slight increase in amount of chemical in the tubers, but under conditions where damage occurred, tuber residues increased markedly with increase in application rate.
The factors influencing diquat residues in potato tubers were examined in pot experiments. Highest residues were found when plants were subjected to drought and to a period of darkness following spraying at a time when senescence of the foliage had commenced and the tubers were still increasing in fresh weight. Further experiments at a similar stage of growth showed that high residues of diquat caused stem-end rot only when plants were subjected both to a soil moisture stress sufficient to induce wilting before spraying and to reduced light intensity and a high atmospheric humidity after spraying. It is suggested that these conditions promote the rapid downward movement of a high concentration of diquat in the xylem.
In a preliminary experiment with a range of chemical desiccants, only sodium arsenite gave appreciable tuber damage when applied to the foliage.     

Effect of light environment on the activity and behaviour of diquat and paraquat in plants

The importance of controlling the light environment of experiments involving diquat and paraquat is shown in experiments where activity is markedly dependent on the light quality and intensity before treatment and on the time of day of treatment. Activity and uptake are not directly related since treatments after low light intensities give increased activity associated with reduced uptake; following afternoon treatments, reduced activity is associated with increased uptake. Uptake increased when plants were darkened after treatment but the increase was not directly related to its duration, because after a time, uptake decreased. Three possible explanations for this decrease are considered: diquat exudation from the leaves, downward movement into the roots, and the adsorption of diquat in plant tissue. Evidence did not support exudation from leaves or downward movement into the roots.     

THE YIELD AND QUAEITY OF RED BEET SEED AS AFFECTED BY DESICCANT SPRAYS AND HARVEST DATE

Summary. Diquat and sodium monochloroacetate (SMA) were used to desiccate seed crops of red beet in experiments from 1963 to 1965. The seed plants became brown and dry about 7 days after spraying and were then judged suitable for combine harvesting, although this was not done in these experiments. Yields of seed 7 days after spraying were as good as those from the control plants, but were lower than the control yields when harvested 14 days after spraying. In laboratory tests in moist sand at 20° C the percentage of the embryos which germinated was not markedly affected by diquat or SMA treatment. The emergence of seedlings in the field, however, was affected adversely by treatment of the seed crop with 11 and 22 oz/ac of diquat ion in 1963 and by SMA at 20 lb/ac in 1964 and 1965. Diquat at 6·6 oz/ac in 120 gal/ac water in 1964 and 1965 had no serious adverse effects on embryo emergence. Residues of diquat ion in seed varied from 2 to 4 ppm, but the impairment of embryo emergence by diquat was believed to be due to the premature arrest of growth of the seed on the desiccated plants.
It is concluded that when harvesting conditions are poor, desiccants could be valuable.
Influence des traitements dessicants et de la date de récolte sur le rendement et la qualité de la sentence de betterave rouge     

A RE-EXAMINATION OF THE INFLUENCE OF LIGHT AND DARKNESS ON THE LONG-DISTANCE TRANSPORT OF DIQUAT IN LYCOPERSICON ESCULENTUM MILL.

Summary. Using autoradiographic techniques, the long-distance transport of 'ethylene'¹⁴C-labelled diquat dibromide was studied. It was confirmed that a period of darkness after diquat application was necessary for reliable systemic action during a subsequent light exposure. Darkness was necessary in the region where the herbicide was applied, and then only to allow adequate penetration of diquat. This was its only role.
Desiccation following death, with the transfer of free water containing diquat to other leaves are the primary forces of long-distance transport; light is essential only for rapid toxic action and not directly for transport. Orthophosphate-³²P and urea-¹⁴C applied topically with unlabelled diquat were distributed in the same pathway as the herbicide and not in the phloem. These results are discussed.
Nouvelles recherches sur l'influence de la lumière et de l'obscurité sur le transport à longue distance du diquat dans Lycopersicon esculentum Mill .     

The role of soil, seed-potato tuber and haulm in the transmission of Phoma foveata from infected seed to daughter tubers

Infestation of ridge soil by Phoma foveata was examined over 4 years by collecting soil samples at various distances from seed tubers which were either naturally infected or inoculated with a distinctive strain. Samples were taken on four occasions during each growing season. Infestation was greatest immediately around the tuber and was largely confined to a distance of 15 cm until haulm destruction, after which P. foveata was detected more widely in the soil.
The effects of various seed-tuber and haulm treatments on the incidence of daughter-tuber contamination by P. foveata were assessed over 5 years. Removing the infected seed tuber at emergence significantly (P < 0.05) reduced the contamination at haulm destruction of daughter tubers harvested by hand in only 1 out of 4years. In all years, tuber contamination was much less(P < 0.05) when stems were pulled and removed than when they were desiccated by applying diquat dibromide. The incidence of tuber contamination did not increase between haulm destruction and harvest when stems were pulled and removed. In another experiment, tuber contamination increased linearly with the delay in pulling haulms after applying diquat dibromide. Cutting and removal of stems tended to reduce gangrene contamination, relative to the desiccation of stems by applying diquat dibromide, in all years where the seed tuber had been removed, but in only 2 out of 5 years where the tuber was present.     

THE EFFECTS OF SUB-LETHAL DOSES OF MCPA ON THE MORPHOLOGY AND YIELD OF VEGETABLE CROPS

Summary. The effects of sub-lethal doses of MCPA-sodium on the morphology, yield and maturity of French beans, and on the morphology of broad beans, were studied in field and glasshouse experiments. Epinasty in French beans developed at 0.002 lb/ac a.e., but formative effects were not seen at less than 0–1 lb/ac. With doses up to 0.4 lb/ac there was no significant reduction in yield or haulm weight, but at 1.0 lb/ac and above, yield was reduced and some of the plants sprayed at an early stage of growth were killed. There were characteristic modifications of the roots and stems and of those leaves which were at a susceptible stage of development when sprayed. Broad beans were only slightly injured by 0.2 lb/ac but were generally killed by 2.0 lb/ac. Abnormalities were noted in the germination of seed produced by affected plants.
Effets de doses sub-léthales de MCPA sur la morphologic et le rendement des cultures légumières IV. Haricots verts et fèves     

STUDIES ON THE BIOLOGY AND CONTROL OF VAUCHERIA DICHOTOMA FOUND IN FRESHWATERS IN BRITAIN

Summary. Vaucheria plants collected from a ditch near Crowland and from the River Cherwell at Oxford in the first week of October 1970 were identified as V. dichotoma Ag. A nutrient medium is described which allows the growth and the production of organs of sexual reproduction of this alga. Preliminary studies on the control with diquat show that it must be exposed to a concentration of 2 mg/1 for 6 h for the herbicide to be effective. The presence of mud reduces the rate at which chlorophyll disintegrates and hastens the inactivation of diquat.
Etudes sur la biologie et la destruction de Vaucheria dichotoma. Ag. dans les eaux doucei de Grande-Bretagne     

AN INTERNATIONAL EXPERIMENT ON THE EFFECT OF AGE AND STORAGE CONDITIONS ON VIABILITY AND DORMANCY OF AVENA FATUA SEEDS

Summary. Freshly collected ripe seeds of Avena fatua were first kept out of doors on the surface of the soil for 0 to 3 monehs, and then stored dry in the laboratory for 0 to 6 months before testing for dormancy and viability. Results from six European countries agreed well. Only 10% of ripe seeds germinated immediately alter collection and germination rose to 50% by December or January in all countries except Denmark. Viability was scarcely affected by age or storage conditions, except that many seeds died out of doors during winter in Denmark and Germany. The percentage of dormant seeds in December was greater in Denmark than elsewhere, possibly because the seeds were of a different type. Seeds may not behave the same in normal agricultural conditions as they did in this experiment.
Une expérience internationale sur l'influence de l'âge et des conditions de conservation sur la viabilité et la dormance de semences d'Avena fatua     

THE NATURE AND CONSEQUENCE OF INTERFERENCE BY ALOPECURUS MYOSUROIDES HUDS. ON THE GROWTH OF WINTER WHEAT

Summary. In a field experiment with different densities of Alopecurus myosuroides , 10 plants/m² caused no significant reduction in total dry weight of winter wheat at harvest. When autumn- or spring-germinated plants at 100/m² remained until harvest, crop weight was reduced by about 30%. A study of root-zone competition between A. myosuroides and winter wheat in the glasshouse showed that suppression of the weed by the crop was greater at high nitrogen levels; the practical implications of this are discussed.
La nature de l'interférence d' Alopecurus myosuroïdes Huds. sur la croissance du blé d'hiver, et ses conséquences     

Relevance of the deposit structure for the uptake and bio-efficacy of diquat,as monitored by the spatially resolved chlorophyll fluorescence

Aim of our study was to exploit the relation between deposit structure at the microscale and the uptake and biological efficacy of herbicides. For this purpose, we analysed the relevance of the deposit structure of diquat dibromide, as affected by surfactants, on the spatially resolved chlorophyll fluorescence (ChlF) and the desiccation of the leaves. The present study is a sequential work to our studies with the systemic compound glyphosate. On that basis, we hypothesized here that larger deposits of diquat are negatively related to the bio-efficacy of the compound. By using selected ethoxylated rapeseed oil adjuvants (RSO 5, RSO 10, RSO 30, RSO 60) we influenced the deposit properties of diquat dibromide droplet residue on the leaves of easy-to-wet Viola arvensis and the difficult-to-wet Chenopodium album species. With the spatially-resolved pulse amplitude modulated (PAM) ChlF technique we demonstrated the effect of diquat on the physiology of the tissue. As shown, the RSO surfactants did not affect the area of diquat residue on the easy-to-wet leaves of V. arvensis; this trend is similar to those observed for ChlF and the herbicide desiccation potential. In contrary, on C. album, decreased deposit area of diquat droplet was associated with increased effect on ChlF parameters and increased desiccation potential of the herbicide, thus explaining its higher foliar uptake.     

THE EFFECTS OF SOME CHEMICALS ON THE GERMINATION OF A WEED, PSORALEA CORYLIFOLIA L.

Summary. The effects of 2,4-D, 2,4,5-T, IAA and GA on the germination behaviour of one-seeded pods of Psoralea corylifolia L. were studied. For each chemical, inhibition of germination of acid-scarified pods increased with increase in concentration. The inhibition was irreversible and led to death of the seed in the pod. Morality, expressed as percentage of dead pods, was highest for 2,4,5-T and IAA and lowest for GA. Impermeable or 'hard' pods were unaffected by the treatments. Though acid-scarified pods were significantly damaged by an 8 h chemical treatment, weathered pods were unaffected by treatments of less than 30 h duration. After scarification, dry pods were more susceptible than pre-imbibed ones. Rates of water uptake were determined for pods of both categories.
Effets de quelgues produits chimiques sur la germination de Psoralea corylifolia L.     

The effects of desiccation on broad‐leaved dock (Rumex obtusifolius) and curled dock (Rumex crispus) root fragment regeneration

Fresh root fragments of Rumex crispus and Rumex obtusifolius, which initially contain 65–70% moisture, progressively lose moisture when desiccated under conditions matching summer weather in southeast England. The likelihood of shoot emergence and the time it took in glasshouse conditions were both affected by desiccation, with R. crispus the most affected up to 48 hr and R. obtusifolius slower to emerge after 48 hr. These effects converged after longer desiccation periods, and R. crispus entirely failed to emerge after 120 hr. The dry weight of emerged shoots was not significantly different between the species until they were desiccated for 96 hr, after which R. obtusifolius dry weight was significantly reduced. In outdoor trials, desiccation for 24 or 48 hr had a lesser effect on emergence in either species when fragments were planted at the soil surface or at up to a depth of 10 cm, compared to deeper plantings, but emergence was significantly lower in plantings at 15 or 20 cm. Emergence delays were not significantly different between the species until they were planted at 15 or 20 cm, when R. obtusifolius was slower to emerge than R. crispus, an effect exacerbated by increasing desiccation. Similar interactions of increasing soil depth and desiccation were found in reductions in dry weight, number of tillers and leaf area, with R. obtusifolius generally, but not exclusively, better able to withstand more extreme trial conditions. Our findings suggest that control of these highly troublesome weeds can be assisted by appropriate agricultural practices, notably exposing cut fragments to drying conditions followed by deep burial.     

FACTORS AFFECTING PERSISTENCE AND INACTIVATION OF DIQUAT AND PARAQUAT

Summary. The adsorption of diquat cation was found to be 0.3, 2.0–2.5 and 80–100 mg/g on a sandy loam soil, Grade Hydrite 10 Georgia kaolinite and National Standard Bentonite, respectively. Bentonite (113 lb/surface ac) applied to plastic pools previously treated with 1 ppm paraquat reduced the concentration of paraquat to less than 0–05 ppm within 24 hr of application. Only bentonite appeared to hold either diquat or paraquat in a form unavailable to wheat. Appreciable uptake by wheat from soil treated with diquat or paraquat (16 lb/ac pre-emergence) occurred only in soil or sand in which the herbicide leached below the 05 in. zone. A 12 hr dark period following foliage application did not appear to enhance movement of either herbicide in wheat. Loss of radioactivity was observed when diquat or paraquat was exposed to ultraviolet light (2537 Å).
Facteurs agissant sur la persistence et l'inactivation du diquat et du paraquat     

THE HERBICIDAL ACTIVITY OF 2-AMINO-3-CHLORO-1,4-NAPHTHOQUINONE

Summary. An investigation was made of a now herbicide, 2–amino-3–chloio-1,4–naphthociuinone (ACNQ,), which appears to be promising for the control oi Echinochloa crus-galli (L.) Beauv. in transplanted paddy rice [ Oryza sativa L.).
In pot experiments in the glasshouse, seedlings of Echinochloa at different stages of growth were killed by ACNQ, at doses equivalent to 2–4 kg/ha (applied as granules) if they were submerged, but not if the shoots emerged above water. Activity was increased more by raising the level of water in the pot than by increasing the dosage. Emergent rice seedlings were little affected by ACNQ, up to 8 kg/ha, and the observed selectivity is considered to be due mainly to differences in plant height in relation to depth of water.
In laboratory experiments with rice seedlings grown without soil, the activity of ACNQ again increased with the depth of solution. Conversely, at a standard solution depth, there was a reduction in damage with advancing stage of growth, and the chemical had little effect once the leaf tip was above the solution surface.
The rate of leaching of ACNQ. through a sandy soil was slow and, at a dose of 2 kg/ha, persistence was about 15 days.
In evaluating new herbicides for paddy rice it is suggested that screening tests arc necessary on submerged as well as non-submerged plants.
Activité herbicide de la 2–amino-3–chloro-1,'4–naphtoquimne. I. Activité herbicide et profondtur de de l'eau     

PRELIMINARY STUDIES ON THE TRANSLOCATION OF 14C-LABELLED HERBICIDES IN BRACKEN (PTERIDIUM AQUILINUM)

Summary. The translocation of ¹⁴C-labelled herbieides in field bracken has been sludied in some preliminary experiments by means of autoradiography. A detailed account is given of the methods employed. It is shown that when 2,4-D is applied to fronds at different stages of development movement of the tracer into the rhizome is considerably greater from parts of the frond which are still immature. Trasnslocation within the frond is predominantly basipetal at all stages of development; within the rhizome the direction of movement appears to be determined primarily by the nature of the vascular connections with the treated pinna.
In a comparison between the translocation of 2,4-D, 4-CPA and dalapon no difference was apparent after 24 hours, but when the treatment period was extended to 96 hours there was evidence that 4-CPA bad been translocated in a considerably greater amount than either of the other two herbicides.
Rechrches iréliminaires sur la migration des herbieides marqués am ¹⁴ C dans la fougrère algle (Pteridium aquilinum)     

EFFECTS OF DESICCATION AND TEMPERATURE ON SURVIVAL OF CYPERUS ESCULENTUS TUBERS AND CYNODON DACTYLON RHIZOMES

Summary. The effects of all combinations of five desiccation treatments, two temperatures and three durations of desiccation on the survival of Cyperus esculentus tubers and two-node Cynodon dactylon rhizome fragments were examined in laboratory and glasshouse experiments.
Cyperus esculentus tuber survival was greater at 22°C than at 4°C. Duration of desiccation did not influence tuber survival, except at the lower temperature.
Survival of Cynodon dactylon rhizome fragments was greatly influenced by desiccation treatment, duration of desiccation and the interaction of these two factors. No buds survived when rhizomes reached 50% of their original weight, indicating good tolerance of desiccation since the original dry-matter content of rhizomes in this experiment was 41·2%.     

THE EFFECTS OF SUB-LETHAL DOSES OF MCPA ON THE MORPHOLOGY AND YIELD OF VEGETABLE CROPS

Summary. The effects of sub-lethal doses of MCPA-sodium on the morphology, yield and marketability of cabbage, cauliflower and Brussels sprouts were studied in field and glasshouse experiments. The epinastic and formative effects in all three crops were similar. Cauliflower was the most susceptible and cabbage the least, but the marketability of these two crops was adversely affected at lower doses (less than 0.06 lb/ac a.e.) than that of Brussels sprouts (not below 0.1 Ib/ac a.e.), where the damage to the apex had less effect on the economically important portion of the plant. Brussels sprouts also produced lateral shoots on which normal sprouts developed even when the main stem above had been killed. In all three crops, characteristic galls were produced on the stems, and these, together with the effects on the stem apices, the leaves and the roots, are described and contrasted with abnormalities caused by other agencies.
Effets de doses sub-létales de MCPA sur la morphologie et le rendement des cultures tégumières IL Choux, choux-fleurs et choux de Bruxelles     

STUDIES OF THE RESPONSE OF PLANTS TO ROOT-APPLIED HERBICIDES

Summary. Applications of several herbicides -were made to roots and to the bases of shoots of peas, cucumber, mustard and barley grown in soil, sand or water culture.
Localized applications (variation horizontal) of atratone and MCPA to roots of peas and barley in soil produced effects similar to those observed in water euluire, described in Pan I. Airatone killed the plants whether available to the whole or to only a portion of the root system whereas MCPA affected only the roots with which it was in direct contact, and growth continued when a portion of the root system was in herbicide-free environment.
In water culture, MCPA was more effective when applied to the lower (younger) roots with the upper (older) roots kept dry than when twice the concentration was applied evenly to the whole root system in water. When all the roots were kept wet the effect of application to the upper roots was greater than the effect of application to the lower roots. The response of plants to atratone was not appreciably altered whether applications were made to the upper or lower parts of the root system in water culture. Variations in water level had little effect.
Even when the herbicide solution was confined to the stem or hypocotyl, atratone and DNOC were little, if any, less effective than when applied to roots. MCPA, both as ester and sodium salt, was significantly less effective.
Partial replacement of solution in the root zone by sand and air did not reduce the activity of atratone at a given concentration. Similar replacement in the zone of the stem or hypocotyl greatly reduced the effectiveness of all herbicides. When sand of low water content was used, atratone and MCPA-sodium became quite ineffective via the stem, but DNOC and MCPA-ethyl ester remained active.
Études sur les réactions de certaines plantes á des herbicides appliqués aux racines II. Observations nouvelles sur l'effet de l'application localisée.     

Residual effects of triadimefon in soil on powdery mildew and yield of spring barley

Residual triadimefon (or a breakdown product), from a spray application (2 kg/ha) to field soil in 1978, significantly decreased powdery mildew on spring barley throughout two subsequent growing seasons, with consequent yield increases of 42% in 1980 and 18% in 1981.
In other field experiments triadimefon applied to soil at rates >0.06 kg/ha decreased mildew in barley growing in the soil 11 months later. In these experiments triadimefon, but not benomyl, imazalil or prochloraz (all at 0.5 kg/ha) significantly decreased mildew up to harvest and increased yield by 22%.
Triadimefon incorporated into a loam soil and a peat-based compost at rates >0.1 ng/g significantly decreased mildew on barley grown in pots under glasshouse conditions. Plants grown in the treated compost at the same time but in isolated pots supplied with filtered moistened air and capillary watering required more triadimefon (>100 ng/g) in soil for significant mildew control.
Despite strong adsorption of triadimefon to soil (Kd 19.4), an active substance appears to remain available for uptake and translocation by barley plants over long periods. The sensitivity of barley mildew to extremely small residues of triadimefon is discussed in relation to the siting of field experiments on mildew control. The implications for widespread commercial use of formulations containing triadimefon are discussed in relation to disease control practice in cereal growing systems.