Interaction between diclofop-methyl and 2,4-D in wild oat (Avena fatua L.) and cultivated oat (Avena sativa L.), and fate of diclofop-methyl in cultivated oat

Influence of 2,4-D on toxicity of diclofop-methyl to Avena sativa (cv. Selma) and Arena fatua at 2·5 leaf stage has been evaluated under controlled conditions. Effects of 2,4-D on the fate of diclofop-methyl in cultivated oat have also been studied. Mixture with 2,4-D reduced the toxicity of diclofop-methyl to both species. When applied immediately after diclofop-methyl treatment, 2,4-D still reduced herbicide toxicity to wild oat. This reduction was smaller in cultivated oat. and was only observed at higher phytotoxicity. No interaction was observed when a 10-day period separated the two applications. In mixture, 2,4-D enhanced diclofop-methyl penetration and diclofop acid conjugation in cultivated oat, and it slightly increased conjugation when applied separately. None of these effects clearly explain the reduction of diclofop-methyl toxicity by 2, 4-D in cultivated oat. Other processes are possibly involved and could be connected with the site of action of diclofop-methyl.     

Control of Avena fatua and Fagopyrum tataricum with tank mixtures of linuron or linuron + MCPA and sequential applications of linuron, and post-emergence A. fatua herbicides

Linuron (0.21 and 0.28 kg/ha) and linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture with field rates of barban, difenzoquat and flamprop-methyl reduced the phytotoxicity of these herbicides to Avena fatua. When linuron was applied immediately following or 6 days after the A. fatua herbicides no reduction in phytotoxicity to A. fatua occurred, suggesting that the antagonism may be occurring as a result of physical or chemical incompatability when the herbicides are mixed together. The possibility of obtaining broad-spectrum weed control with one trip over the field by applying linuron and one of these wild oat herbicides separately but at the same time using a double-boom, double-tank system deserves evaluation. When linuron was applied in a tank mixture (0.21 and 0.28 kg/ha), immediately after, or 6 days after diclofop-methyl (0.70 kg/ha), there was no reduction of A. fatua control, and wheat tolerance to the tank mixture was good. This tank mixture offers potential for control under field conditions of A. fatua and some broad-leaved weeds in one spray operation. Linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture severely reduced A. fatua control with diclofop-methyl. No loss of phytotoxicity to Fagopyrum tataricum occurred when the A. fatua herbicides tested were tank mixed with linuron or linuron + MCPA. Lutte contre Avena fatua et Fagopyrum tataricum avec des mélanges extemporanés de linuron ou de linuron + MCPA et des applications successives de linuron et d'herbicides de postlevée actifs contre A. fatua     

Persistence studies with [14C] 2,4-D in soils previously treated with herbicides and pesticides

The persistence of [¹⁴C] 2,4-D at a rate equivalent to 1 kg/ha was compared under laboratory conditions in samples of heavy clay, sandy loam, and clay loam at 85% of field capacity moisture and 20 ± 1°C which had either received no pre-treatment, or had been pre-treated for 7 days at the 2 μg/g level with the herbicides benzoylprop-ethyl, diclofop-methyl, dinitramine, flamprop-methyl, nitrofen, picloram, tri-allate, trifluralin, and a combination of tri-allate and trifluralin. The breakdown of [¹⁴C] 2,4-D was also studied in the same soils that had similarly received pre-treatments of 2 μg/g of the cereal seed dressing Vitaflo-DB, the insecticide, malathion, and a combination of Vitaflo-DB and malathion. In each soil type, the half-life of the 2,4-D was similar regardless of whether the soil had, or had not, received any pre-treatment, indicating that none of the chemicals investigated adversely affected the soil degradation of 2,4-D.     

Alternatives to hexazinone and terbuthylazine for chemical control of Cytisus scoparius in Pinus radiata plantations in New Zealand

Two herbicides used for post‐plant weed control in commercial forests in New Zealand, terbuthylazine and hexazinone, are not endorsed for use on land certified by the Forest Stewardship Council (FSC). These herbicides are effective for controlling competitive woody weeds, such as Cytisus scoparius (broom). To investigate the potential of non‐residual, alternative herbicides for the control of C. scoparius after planting, a range of treatments were implemented at two trials. The trials were established in newly planted Pinus radiata plantations where C. scoparius dominated. The objectives were to (i) optimise application rates of alternative herbicides and compare their efficacy to current practice and (ii) identify if treatment efficacy varied across sites. Treatments at each site included weedy and weed‐free controls, current practice using terbuthylazine and hexazinone, applied as both spot treatment and broadcast application, and a range of new treatments consisting of different dosage combinations of clopyralid, triclopyr and picloram. Broadcast application of the clopyralid, triclopyr and picloram mixture showed increasing weed‐control efficacy against C. scoparius with increasing dose rate, resulting in increased tree volume. Broadcast application of the clopyralid, triclopyr and picloram mixture at 75% or 100% of a typical industry use rate (100% industry rate includes clopyralid 1.5 kg a.i. ha^?1, triclopyr 0.15 kg a.i. ha^?1 and picloram 0.05 kg a.i. ha^?1) achieved greatest tree volume by year four with tree volumes exceeding that obtained using the operational spot treatment with terbuthylazine and hexazinone. Treatment rankings were similar between locations. The result supports the use of clopyralid, triclopyr and picloram to control C. scoparius during the first year of P. radiata establishment.     

Optimizing the performance of diclofop-methyl, cycloxydim, and clodinafop-propargyl on littleseed canarygrass (Phalaris minor) and wild oat (Avena ludoviciana) control with adjuvants

Optimizing the herbicide dose by the addition of adjuvants is an acceptable way to reduce the risk of side-effects from herbicides. Therefore, to detect a suitable adjuvant for diclofop-methyl, cycloxydim, and clodinafop-propargyl against littleseed canarygrass ( Phalaris minor ) and wild oat ( Avena ludoviciana ), six dose–response experiments were conducted. The treatments consisted of diclofop-methyl at 0, 112, 225, 450, 675, and 900 g ai ha⁻¹, cycloxydim at 0, 15, 30, 60, 90, and 120 g ai ha⁻¹, and clodinafop-propargyl at 0, 8, 16, 32, 48, and 64 g ai ha⁻¹ with and without the adjuvants of Frigate, olive oil, and castor oil at 0.2% (v/v) in order to control both littleseed canarygrass and wild oat. Tested herbicides performance was enhanced by all adjuvants against littleseed canarygrass and wild oat. The addition of Frigate and the vegetable oils had the lowest and the highest effect on the performance of all of the herbicides on both littleseed canarygrass and wild oat, respectively, which confirms the solubilizing nature of the cuticular waxes by vegetable oils. A comparison between the two vegetable oils revealed that olive oil exerted a greater control of littleseed canarygrass than did the castor oil. In contrast, castor oil exerted a greater control of wild oat than did the olive oil, which can be related to differences in the leaf surface micromorphology of the weeds.     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Penetration of clopyralid and related weak acid herbicides into and through isolated cuticular membranes of Euonymus fortunei

A model system consisting of chemically isolated cuticular membranes placed on agar was used to study the penetration of various formulations of ¹⁴C-labelled clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D into and through cuticular membranes. Clopyralid, commercially formulated as the acid, or 1-decyl ester was rapidly absorbed after 12 h by isolated cuticles of Euonymus fortunei. There was less absorption of the monoethanolamine and potassium salt formulations when compared to the acid and 1-decyl ester. However, in terms of the absorbed ¹⁴C-activity that partitioned into the agar, there was no difference between the acid and salt formulations with approximately 90% being partitioned after 48 h. Conversely, the 1-decyl ester formulation of clopyralid was retained in the cuticle; less than 5% of the absorbed fraction was recovered in the agar after 48 h. When the acid forms of clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D were compared, there was little or no difference in absorption among the herbicides. However, the ¹⁴C-activity from clopyralid partitioned the most (90%) and triclopyr the least (50%) into the agar. When ester formulations of clopyralid, fluroxypyr, and triclopyr were compared, at least 95% of the ¹⁴C-activity was absorbed 24 h after application. However, of the amount absorbed, significantly more of the butoxyethyl ester of triclopyr (36%) partitioned into the agar than did the 1-decyl ester of clopyralid (6%) or the 1-methylheptyl ester of fluroxypyr (5%). Differential retention of various herbicide formulations in this model system may explain, in part, the differences in absorption and translocation among radiolabelled clopyralid formulations observed in previous research (Kloppenburg & Hall, 1990).     

The control of Achillea millefolium in the Snowy Mountains of Australia

The response of Achillea millefolium L. to herbicides was measured to determine the effectiveness of the current recommendations and to test alternative herbicides. Five plots at each of the three replicate sites were selected and randomly treated with one of the four herbicides: dicamba/2,4‐D, glyphosate, metsulfuron‐methyl and triclopyr/picloram. After 12 months, the recommended treatment, dicamba/2,4‐D, did not cause a significant reduction in aerial biomass compared with untreated controls and the number of flowering stems was significantly increased in treated plots. Metsulfuron‐methyl and triclopyr/picloram caused a significant reduction in A. millefolium aerial biomass but did not affect the number of flowering stems. Glyphosate produced a significant reduction in aerial biomass and was less effective. These results suggest that the current recommendation for A. millefolium might be improved. Site‐specific effects such as aspect may also influence the effectiveness of herbicides on this species.     

Degradation of the herbicide flamprop-methyl in soil

The degradation of the wild oat herbicide flamprop-methyl [methyl DL -N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate] in four soils has been studied under laboratory conditions using ¹⁴C-1abelled samples. The flamprop-methyl underwent degradation more rapidly than its analogue flamprop-isopropyl. However, similar degradation products were formed, namely the corresponding carboxylic acid and 3-chloro-4-fluoroaniline. The latter compound occurred mainly as ‘bound’ forms although evidence was obtained of limited ring-opening to give [¹⁴C]carbon dioxide. The time for depletion of 50% of the applied herbicide was approximately 1-2 weeks in sandy loam, clay and medium loam soils and 2-3 weeks in a peat soil.     

Response of wheat and oat seedlings to root-applied diclofop-methyl and 2,4-dichlorophenoxyacetic acid

Roots of wheat and oat seedlings were treated with diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) in a specially designed Plexiglas treatment apparatus. Diclofopmethyl severely inhibited the root growth of susceptible oat seedlings but roots of resistant wheat seedlings were unaffected. Diclofop-methyl at 0.3 μM reduced the growth of oat roots to 50% of the control. Direct contact between diclofop-methyl and the inhibited root zone was necessary for growth inhibition since other parts of the seedling (roots and shoots) isolated from contact with diclofop-methyl solution by a physical barrier were unaffected. Diclofop (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid), the free acid metabolite of diclofop-methyl, was somewhat more phytotoxic than the parent compound. The herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), which engenders auxin responses, slightly enhanced the inhibition of oat root growth by diclofop-methyl. The primary wheat metabolite, ring-hydroxylated diclofop, was nonphytotoxic to oat root growth, whereas the acetylated derivative of the primary water-soluble oat metabolite (neutral glucose ester of diclofop) inhibited oat root growth to the same extent as diclofop-methyl. These results support the hypothesis that the basis for selectivity between resistant wheat and susceptible oat is the metabolism of diclofop-methyl by aryl hydroxylation and conjugation but not glucose ester conjugation. Translocation is also not an important factor in the phytotoxic activity of diclofop-methyl.     

Effect of chlorsulfuron on four graminicides for weed control and wheat yield

In field experiments with spring wheat (Triticum aestivum L., cv. Neepawa), the low rate (0·02 kg ha^-1) of chlorsulfuron significantly reduced wild oat control from individual applications of only barban and diclofop-methyl. The high rate (008 kg ha^-1) affected wild oat control by all four graminicides, including difenzoquat and flam-prop-methyl. In most cases, the graminicides did not affect the broad-leaved weed control of chlorsulfuran. Overall, a low rate of chlorsulfuron in mixture with graminicides did not reduce wheat yield, whereas a high rate of chlorsulfuron in the mixtures gave a significant yield reduction compared with individual graminicides applied alone. All herbicide treatments increased wheat yield over the control. In the glasshouse, reduction in wild oat control by diclofop-methyl was directly related to the rate of chlorsulfuron added to diclofop-methyl. The effect of 0·02 kg ha^-1 chlorsulfuron on control of wild oat was decreased when the rate of diclofop-methyl increased from 0·5 to 0·9 kg ha^-1 and was completely eliminated when diclofop-methyl reached 1·1 kg ha^-1. Conversely, diclofop-methyl (0·7 and 1·1 kg ha^-1) gave some reduction of wild mustard (Sinapis arvensis L.) and redroot pigweed (Amaranthus retrofiexus L.) control by chlorsulfuron (0·01 and 0·02 kg ha^-1), even though in some cases diclofop-methyl/chlorsul-furon gave better control of these broad-leaved weeds. In the laboratory, the absorption and translocation of [¹⁴C]-diclofop-nieihyl in wild oat seedlings were significantly reduced when chlorsulfuron was added, compared with [¹⁴C]-diclo-fop-methyl applied alone. Effet du chlorsulfuron sur l'efficacité et l'effet sur le rendement de quatre graminicides Dans des essais de plein champ sur blé de printemps (Triticuni aestivum L., cv. Neepawa), la faible dose (0, 02 kg ha^-1) de chlorsulfuron a réduit significativement l'efficacité d'une application séparée de barbane et de diclofop-methyl. La forte dose (0, 08 kg ha^-1) a contrarié la destruction de la folle avoine pour les quatre graminicides dont le difenzoquat et le flamprop-methyl. Dans la plupart des cas, les graminicides n'ont pas eu d'incidence sur la destruction des dicotylédones par le chlorsulfuron. Par ailleurs. une faible dose de chlorsulfuron en mélange avec les graminicides n'a pas réduit le rendement en blé, en revanche, une forte dose de chlorsulfuron en mélange a entrainé une baisse significative de rendement en comparaison des graminicides appliqués seuls. Tous les traitements herbicides ont entrainé un gain de rendement par rapport au témoin non traité. En serre, la réduction d'efficacité sur folle avoine du diclofop-methyl était directement correlée à la dose de chlorsulfuron ajouté. Les effets de 0, 02 kg ha^-1 sur la destruction de la folle avoine baissaient quand le niveau de diclofop-methyl augmentait de 0,5 à 0,9 kg ha^-1 et étaient complètement éliminés quand la dose de diclofop-methyl atteignait 1, 1 kg ha^-1. Par ailleurs, le diclofop-méthyl (0,7 et 1,1 kg ha^-1) a réduit l'efficacité du chlorsulfuron (0,01 et 0,02 kg ha^-1) sur la sanve (Sinapis arvensis L.) et l'amaranthe réflechie (Amaranthus retroflexus L.) même si dans certains cas l'association diclofop-mélhyl-chtorsulfuron a eu une meilleure efficacité sur ces mauvaises herbes. Au laboratoire, l'ab sorption et la translocation du diclofop-methyl C¹⁴ dans les plantules de folle avoine ont été réduites significativement par l'addition de chlor-sulfuron en comparaison du diciofop-méthyl C¹⁴ appliqué seul. Wirkung von Chlorsulfuron zusammen mil Vier Graminiziden auf die Unkrautbekämpfung und den Ertrag von Weizen In Freilandversuehen mit Sommerweizen (Triticum aesttotm L. ‘Neepawa’) verminderie Chlorsulfuron in niedriger Aufwandmenge (0,02 kg ha^-1) den Bekämpfungserfolg gegen Flug-Hafer nur bei Barban und Diclofop-menthyl. Die hohe Aufwandmenge (0,08 kg ha^-1)beeinträchtigte die Wirkung aller 4 Graminizide, einschliesslich Difenzoquat und Flamprop-methyl. Die Graminizide beeinfiussten die Wirkung von Chlorsulfuron gegen zweikeimblättrige Arten meistens nicht, Der Weizenertrag blieb bei der Mischung der niedrigen Aufwandmenge von Chlorsulfuron mit den Graminiziden unverändert, die hohe Aufwandmenge führte aber in den Mischungen zu einem signifikaten Abfall des Ertrags, vergli-chen mit dem bei Anwendung der Graminizide allein. Mit allen Herbizidbehandlungen wurden gegenüber Unbehandelt höhere Erträge erzielt. Im Gewächshaus war die Wirkung von Diclofopmethyl gegen Flug-Hafer direkt von der zugefügten Menge an Chlorsulfuron abhängig. Der Einfluss von 0,02 kg ha^-1 Chlorsulfuron aif die Bekämpfung von Fiug-Hafer nahm ab. wenn die Aufwundmenge von Diclofop-methyl von 0,5 auf 0,9 kg ha^-1 gesteigert wurde; bei 1, 1 kg ha^-1 Diclofop-methyl war er aufgehoben. Andererseits trat bei 0,7 und 1,1 kg ha^-1 Diclofop-methyl eine Minderung der Wirkung von Chlosulfuron (0,01 und 0,02 kg ha^-1) gegen Acker-Senf (Sina-psis arvensis L.) und Zurückgekrümmten Fuchsschwanz (Amarenthus retroflexus L.) ein, wenn auch dise Mischung in einigen Fällen gegen dise Arten starker wirkte. Im Labor wurde einc signifikant geringere Absorption und Trans-lokation von ¹⁴C-Diclofop-methyl in Keimpflan-zen des Flug-Hafers beobachtet, wenn Chlorsulfuron zugefügt worden war.     

Diclofop-methyl tolerance in cultivated oats (Avena sativa L.)

The feasibility of achieving selective wild oat (Avena fatua L.) control in a stand of the Australian oat (Avena sativa L.) cv. Savena I was examined. Diclofop-methyl was applied at rates of 0·4–0·7 kg a.i. ha^?1 at the three- and five-leaf stages of A. fatua (84–132 culms m²). Although all rates of diclofop-methyl caused initial chlorosis and necrosis to the crop, the subsequent control of A. fatua permitted increased crop tillering. Avena fatua control and crop yield response were maximized when diclofop-methyl was applied at the three-leaf stage. Crop grain yield was increased by as much as 32% and 22% during 1984 and 1985, respectively. In the absence of A. fatua competition, crop shoot dry weight at ear emergence was reduced only where diclofop-methyl was applied at 0·6 or 0·7 kg ha^?1. However, final grain yield was not reduced by any treatment. Only 11 of 240 cultivars or lines tolerated diclofop-methyl, and none reached the level attained by Savena I and a closely related Australian line [(Irwin × (West × New Zealand Cape/42)) × West]/24. The nature of the inheritance of diclofop-methyl tolerance was examined (1983–1985) by crossing and backcrossing (BC) Savena I with four diclofop-methyl susceptible, but agronomically superior, lines. Inheritance of diclofop-methyl tolerance appeared to be controlled by two genes, with susceptibility being dominant to tolerance in F₃, BCIF₂ and BCIF₃ lines.     

Factors favouring the choice of flamprop-methyl,methyl (±)-2-[N-(3-chloro-4-fluorophenyl)benzamido] propionate for the control of avena species in wheat

The post-emergence herbicide, methyl (±)-2-[N-(3-chloro-4-fluorophenyl)benzamido]-propionate, flamprop-methyl, showed good activity against oat with selectivity in wheat. It was superior in performance to flamprop-isopropyl and benzoylprop-ethyl already being marketed for wild oat control. It gave even more effective control of seed set in the oat than did the other compounds, prevented tiller growth and as a result of its higher activity was less dependent on crop competition. Selectivity of flamprop-methyl, however, was similar to that previously reported for related compounds, i.e. it was dependent on its rate of degradation and the subsequent detoxication of the biologically active acid to inactive conjugates. The rate of degradation of flamprop-methyl is comparable to that of benzoylprop-ethyl but the more active acid produced accounts for the improved performance of the former. The corresponding ethyl ester showed the highest rate of degradation and although generally comparable in performance to the methyl ester there was a tendency for the inhibition on the oat to last for a shorter period. Performance of flamprop-methyl is influenced by environmental factors such as temperature or water stress. These factors had an effect during the first 2 weeks after compound application, reducing the translocation of the active metabolite to its site of action and having a small but detectable effect on the amount of acid produced.     

Mixtures of picloram and 2,4,5-T for the control of blackberry (Rubus fruticosus L. agg.)

The effectiveness of‘Tordon 50-d’(5% a.i. picloram plus 20% a.i. 2,4-D both as the triisopropanolamine salts) and various mixtures of 2,4,5-T and picloram were tested for the control of blackberry (Rubus fruticosus L. agg.) in Victoria, Australia. A high correlation was obtained between the % reduction in live canes and the % kill of crowns 13 months after Rubus procerus P.J. Muell. thickets were sprayed with 2,4,5-T or‘Tordon 50-d'. Counting the number of live canes is, therefore, a convenient method of comparing the efficacy of these herbicides for the control of blackberry. ‘Tordon 50-d’was generally more effective than 2,4,5-T but stimulation of suckering from roots was recorded at one site when low rates of‘Tordon 50-d’were used. It was necessary to add high dose rates of‘Tordon 50-d’to 2,4,5-T before there were worthwhile improvements in weed control.‘Tordon 5–20’(5% a.i. picloram as triisopropanolamine salt plus 20% 2,4,5-T as the ethyl hexyl ester) was only slightly more effective in controlling blackberry than‘Tordon 50-d'. The cost and soil residue problems associated with picloram should limit its use as an additive to 2,4,5-T for the control of blackberry in Australia.     

Interactions between barban and benzoylprop etbyl, flamprop metbyl or flamprop isopropyl applied at two growtb stages for wild oat control in cereals

Barban was combined with benzoylprop ethyl, flamprop methyl, or flamprop isopropyl, and the eflects of the combinations on wild oat control and crop yield were assessed, tn greenhouse experiments, the interaction in all three combinations was synergistic, following application at the 2- or 4-leaf stage of wild oats. Under field conditions, combinations of barban + benzoylprop ethyl applied at the 2- or 4-leaf stage of wild oats were as eflective for wild oat control and wheat yield response as barban at 028 kg/ha applied at the 2-leaf or benzoylprop ethyl at 14 kg/ha applied at the 4-leaf stage of wild oats. Mixtures of barban + flamprop methyl applied at the 2- or 4-leaf stage of wild oats provided excellent wild oat control and wheat yield increases. Mixtures of barban + flamprop isopropyl applied at the 2- or 4-leaf stage of wild oats provided comparable wild oat control and barley yield increases to barban (028 kg/ha) applied at the 2-leaf or flamprop isopropyl (14 kg/ha) applied at the 4-leaf stage of wild oats.     

Control of the invasive liana, Hiptage benghalensis

The liana, hiptage ( Hiptage benghalensis ), is currently invading the wet tropics of northern Queensland and remnant bushland in south-eastern Queensland, Australia. Trials using seven herbicides and three application methods (foliar, basal bark, and cut stump) were undertaken at a site in north Queensland (158 700 hiptage plants ha⁻¹). The foliar-applied herbicides were only effective in controlling the hiptage seedlings. Of the foliar herbicides trialed, dicamba, fluroxypyr, and triclopyr/picloram controlled >75% of the treated seedlings. On the larger plants, the cut stump applications were more effective than the basal bark treatments. Kills of >95% were obtained when the plants were cut close to ground level (5 cm) and treated with herbicides that were mixed with diesel (fluroxypyr and triclopyr/picloram), with water (glyphosate), or were applied neat (picloram). The costings for the cut stump treatment of a hiptage infestation (85 000 plants ha⁻¹), excluding labor, would be $A14 324 ha⁻¹ using picloram and $A5294 ha⁻¹ and $A2676 ha⁻¹, respectively, using glyphosate and fluroxypyr. Foliar application using dicamba for seedling control would cost $A1830 ha⁻¹. The costs range from 2–17 cents per plant depending on the treatment. A lack of hiptage seeds below the soil surface, a high germinability (>98%) of the viable seeds, a low viability (0%) of 2 year old, laboratory-stored fruit, and a seedling density of 0.1 seedlings m⁻² 12 months after a control program indicate that hiptage might have a short-term seed bank. Protracted recolonization from the seed bank would therefore be unlikely after established seed-producing plants have been controlled.     

Soil persistence studies with bromoxynil, propanil and [14C]dicamba in herbicidal mixtures

The persistence of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), [¹⁴C]dicamba (3,6-dichloro-2-methoxybenzoic-7-¹⁴C acid) and propanil [N-(3,4-dichlorophenyl)propionamide] at rates equivalent to 1 kg ha^?1, were studied under laboratory conditions in a clay loam, a heavy clay and a sandy loam at 85% of field capacity and at 20±1°C, both singly and in the presence of herbicides normally applied with these chemicals as tank-mix or split-mix components. The degradation of bromoxynil was rapid with over 90% breakdown occurring within a week in the heavy clay and sandy-loam soils, while in the clay-loam approximately 80% of the bromoxynil had broken down after 7 days. In all three soils degradation was unaffected by the presence of asulam, diclofop-methyl, flamprop-methyl, MCPA, metribuzin or propanil. Propanil underwent rapid degradation in all soil treatments, with over 95% of the applied propanil being dissipated within 7 days. There were no noticeable effects on propanil degradation resulting from applications of asulam, barban, bromoxynil, dicamba, MCPA, MCPB, metribuzin or 2,4-D. The breakdown of [¹⁴C]dicamba in a particular soil was unaffected by being applied alone or in the presence of diclofop-methyl, flampropmethyl, MCPA, metribuzin, propanil or 2,4-D. The times for 50% of the applied dicamba to be degraded were approximately 16 days in both the clay loam and sandy loam, and about 50 days in the heavy clay.     

Detection of triazine and urea herbicide residues by various characteristics of oat seedlings in bioassays

Atrazine, simazine, diuron, and linuron applied to soil increased the percentage moisture of oat (Avena sativa L.) shoots in bioassays at the lowest dose tested of 0·25 ppm. Further increases occurred up to 2 ppm but at higher concentrations the percentage moisture decreased. At all doses of each herbicide, shoot dry weight was decreased. In oats grown on soil collected from a peach orchard which had received repeated annual applications of these herbicides, the percentage moisture of the oat shoots was higher than the control value whenever the oat dry weight was decreased and provided a method of residue detection as sensitive as dry weight measurements. Treatment of oats by soil application of the above herbicides in bioassays also caused increases in the electrical conductivity of an aqueous extract of the oat shoots per mg of dry weight and this characteristic was slightly more sensitive than dry weight in detecting herbicides in orchard soil. The conductivity of the extract per mg of water in the shoots, however, only increased as percentage moisture decreased. The weight of neutral water-soluble material in oat shoots decreased much more rapidly than dry weight in bioassays with standard herbicide concentrations. Determination of the weight of neutral water-soluble material in oat plants grown on orchard soil samples indicated the presence of herbicide residues in 50% of the cases in which residues were not detectable by dry weight. The weight of neutral material as a percentage of dry weight was almost as sensitive. Chemical analysis of soil in which oat plants had a decreased level of neutral water-soluble compounds indicated that this characteristic had a lower limit of detection for herbicide residues of approximately 0.10 ppm.     

Interaction between glyphosate and various herbicides for broadleaved weed control

The effects of several herbicides for broadleaved weed control on glyphosate (n-phosphonomethyl glycine) phytotoxicity to wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and wild oats (Avena fatua L.) were studied in the greenhouse. In tank mixtures, dicamba (3,6-dichloro-o-anisic acid), 2,4-D (2,4-dichlorophenoxy-acetic acid) and bromoxynil (3,5-dibromo-4-hydroxy benzonitrile) reduced the phytotoxicity of threshold rates of glyphosate on all three species. With increasing rates of the herbicides for broadleaved weed control relative to a fixed rate of glyphosate, there was a general trend towards increased antagonism. Increasing glyphosate rates above the threshold level in mixtures containing a fixed rate of herbicides for broadleaved weed control overcame the antagonism. Both the inert and active ingredients of 2,4-D amine and ester appeared to be involved in the antagonism. There was no reduction in glyphosate phytotoxicity on the annual grasses when 2,4-D or bromoxynil were sprayed sequentially at various times in relation to glyphosate. When droplets of bromoxynil and glyphosate were placed side by side on a leaf, glyphosate phytotoxicity was not reduced, whereas when the two herbicides were mixed and applied as one droplet, considerable reduction in glyphosate phytotoxicity occurred. These results suggest that the reduction in glyphosate phytotoxicity caused by tank mixing with herbicides such as 2,4-D, bromoxynil and dicamba may be due to a physical or chemical incompatability within the tank mixture rather than to a biological interaction in the plant.     

Increased foliar activity of clodinafop‐propargyl and/or tribenuron‐methyl by surfactants and their synergistic action on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis)

Surfactants can improve postemergence herbicide efficacy and reduce the amount of herbicide required to obtain weed control. The effect of surfactants on the efficacy of herbicides is complicated and depends on the interaction among the plant, surfactant, and herbicide. The effects of surfactants on the efficacy of clodinafop‐propargyl and/or tribenuron‐methyl on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis) under greenhouse conditions were investigated. In addition, the surface tension of aqueous solutions of the surfactants and surfactants + herbicides was determined. Significantly lower surface tension values were obtained with the aqueous solutions of citofrigate (Citogate plus Frigate) alone and with the herbicides used in this study. The citofrigate surfactant lead to the greatest enhancement of clodinafop‐propargyl and/or tribenuron‐methyl efficacy and the effect was species‐dependent. The efficacy of clodinafop‐propargyl and/or tribenuron‐methyl in the presence of surfactants in controlling wild oat was higher than for wild mustard. The foliar activity of the tested herbicides rose with increasing surfactant concentrations. The tank mixture of clodinafop‐propargyl and tribenuron‐methyl showed a synergistic effect in controlling wild oat and wild mustard. The synergistic effect in controlling wild mustard was greater than for wild oat.