Further studies with additives: Effects of phosphate esters and ammonium salts on the activity of leaf-applied herbicides

The phytotoxicity of glyphosate applied to the leaves of dwarf bean (Phaseolus vulgaris L.) and several woody species was enhanced by mixed butyl acid phosphates (BAP, a technical mixture of dibutyl hydrogen and butyl dihydrogen phosphates) or ammonium sulphate. Tributyl phosphate, or the mixed sodium salts of BAP, similarly increased the activity of aminotriazole. This type of effect did not occur with mixtures of this herbicide and inorganic ammonium salts or the ammonium salts of BAP. Neither phosphate esters nor ammonium salts enhanced the activity of paraquat. Ammonium BAP was more effective than sodium BAP as an activator for leaf-applied picloram or MCPA salts. While phosphate esters and ammonium salts probably have separate modes of action they have similar effects in mixture with many water-soluble herbicides and for many purposes may be regarded as alternative activators. Ammonium salts, particularly ammonium sulphate, have obvious advantages because of their cheapness and low mammalian toxicity.     

Antagonistic effects of 2,4-D amine and bentazone on control of Avena fatua with tralkoxydim

Control of Avena fatua with tralkoxydim was significantly reduced in glasshouse experiments when the herbicide was tank-mixed with either 2,4-D amine or bentazone. Antagonism increased with increasing rates of these broadleaf herbicides in the tank-mixture and it could, in turn, be decreased by increasing rates of tralkoxydim. When herbicide solutions were applied to single leaves with a micropipette applicator, bentazone was antagonistic only when mixed in the same droplet with tralkoxydim and not when the two herbicides were applied adjacently in separate droplets. In contrast, both separate and combined applications of 2,4-D amine and tralkoxydim were antagonistic. There was no antagonism when mixtures with either 2,4-D amine or bentazone were applied between the leaf sheath and culm. Antagonism could be circumvented by sequential applications of the herbicides. When tral-oxydim was applied first, there was no loss of A. fatua control if bentazone application was delayed 0.5 h or if 2,4-D amine was delayed 24 h. Results suggest that bentazone affects only cuticular penetration of tralkoxydim, whereas 2,4-D amine also influences subsequent translocation.     

助剂在除草剂应用中的作用及发展前景

对助剂在除草剂中的应用历史、国外现状、发展趋势进行了综述。主要内容有助剂在除草剂中的作用,如抗飘移、兼容、沉积、去泡、水质调节等及相应的助剂品种;按来源和化学结构,助剂的类型有表面活性剂类、油类、无机盐类等,这些助剂对除草剂活性提高都有促进作用。文中指出了生物源、环境相容性、低水生生物毒性、易降解、对作物没有毒害的高效新型助剂是助剂开发的方向,并介绍了部分国外新品种;作者还对我国应采取的对策提出了建议。     

CONTROL OF SONCHUS ARVENSIS (L.) WITH CHEMICALS

Summary. Pot experiments concerning the control of Sonchus arvensis with chemicals showed that the time of application of MCPA or 2,4-D has a dominant influence on the results obtained. Foliage applications at late rosette to early bud stage gave considerably better effects than did earlier or later applications as assessed by the. weight of roots, this assessment being considered the most reliable for final effects. Increasing the rates from 1 to 3 kg/ha was of less significance than the time of application. A good wetting ability of the spray solution is also essential for an effective control of this weed, which has very waxy leaves. The addition of a wetting agent to aqueous solutions of various salts of 2,4-D had a great and significant influence on the effects. This was not the case with 2,4-D acid in Carbowax. When wetter was added, there was no difference in the effects of the sodium, ammonium and triethanolamine salts. The latter were also slightly more effective than MCPA. 2,4-D-ester was much more effective than MCPA by foliage application. When the chemicals were applied to the roots through sub-irrigation pipes, however, MCPA was at least as effective as 2,4-D-ester. The maximum effect by this method of application was obtained at a somewhat later stage of development than by foliage application. By foliage application of MCPA and dinoseb or DNOC at various rates used alone or in mixture, an antagonism between the growth regulator and the contact herbicides was demonstrated as regards the reduction in root weight of S. arvensis . The scorching effects of dinitro compounds were, on the contrary, increased when applied in combination with MCPA. Amitrole at rates of 5, 7.5 and 10 kg/ha applied at late rosette stage gave a complete kill of S. arvensis.
La destruction du Sonchus arvensis L. à l'aide de produits chimiques     

Improved control of Stellaria media (L.) Vill in leys with Trifolium repens, using bentazone and benazolin with additives

In pot experiments, mixtures of ammonium sulphate with surfactants or oil additives increased the phytotoxicity of commercially formulated bentazone (‘Basagran’) to Stellaria media (chickweed). Ammonium sulphate with a proprietary oil adjuvant Actipron had similar effects with benazolin potassium salt, but not with an ethyl ester formulation of benazolin. The phytotoxicity of bentazone and benazolin salts to Trifolium repens (white clover) and Lolium perenne (perennial ryegrass) was almost unaffected by these additives. In a field experiment, a mixture of ammonium sulphate with Actipron improved the control of S. media by bentazone and benazolin salts. Oils and surfactants markedly increased rates of entry of ¹⁴C bentazone into leaves of S. media, white clover and Chrysanthemum segetum. Ammonium sulphate sometimes had similar effects but on other occasions reduced uptake. In some circumstances the additives apparently interacted synergistically, to increase uptake of labelled herbicide into the leaf or to enhance its transport within the plant. In these test species, differential absorption of bentazone could not explain differences in species susceptibility, suggesting that the main cause of resistance was the ability of plants to degrade the herbicide.     

Study of the enhancement of herbicide activity and rainfastness by an organosilicone adjuvant utilizing radiolabelled herbicide and adjuvant

‘Sylgard® 309’ organosilicone surfactant is a very effective adjuvant for broadleaf weed control with a number of herbicides. It is also effective in providing rainfastness lo these post-emergence herbicide applications. To elucidate the basis for herbicide activity enhancement and rainfastness, the absorption of [¹⁴C]acifluorfen, [¹⁴C]bentazone and [¹⁴C]‘Sylgard 309’ were studied. Non-ionic surfactants and crop oil concentrates were used as adjuvants with [¹⁴C]acifluorfen and [¹⁴C]bentazone, respectively, for purposes of comparison. Maximum absorption of [¹⁴C]acifluorfen and [¹⁴C]bentazone was obtained within 15 min after herbicide application with the organosilicone, versus ≥ 24 h with the convenlional adjuvants. [¹⁴C]-Organosilicone absorption closely paralleled that of the [¹⁴C]-herbicides. The organosilicone appears to exert its action by increasing greatly herbicide absorption. The enhancement effect did not appear to be a function of reduced surface tension. Rainfastness appeared to be a result of greatly accelerated herbicide penetration through the leaf cuticle in the presence of the organosilicone.     

Effect of adjuvants on the rainfastness and performance of tribenuron‐methyl on broad‐leaved weeds

The influence of a non‐ionic surfactant (20% isodecyl alcohol ethoxylate plus 0.7% silicone surfactants), an anionic surfactant (25.5% alkylethersulfate sodium salt), and a vegetable oil (95% natural rapeseed oil with 5% compound emulsifiers) on the performance and rainfastness of a new commercial formulation of tribenuron‐methyl was assessed on four broad‐leaved weeds: wild mustard (Sinapis arvensis), scentless mayweed (Tripleurospermum inodorum), common poppy (Papaver rhoeas), and common lambsquarters (Chenopodium album). In one experiment, six doses of tribenuron‐methyl alone or in a mixture with each of the three adjuvants were applied to each weed species at two different leaf stages. In another experiment, the plants of T. inodorum were sprayed and subsequently subjected to 3 mm of rain at 1, 2, and 4 h after treatment (HAT). The activity of tribenuron‐methyl was significantly enhanced by all the adjuvants on all the weed species and only minor differences were observed among the tested adjuvants. The impact of the adjuvants varied among the weed species and growth stages. The highest response to the inclusion of adjuvants in the spray liquid was found at the late growth stage and on C. album, followed by P. rhoeas and T. inodorum, while S. arvensis was less responsive to the adjuvants. All the adjuvants significantly improved the rainfastness of tribenuron‐methyl on T. inodorum, with differences among the adjuvants being more pronounced when rain occurred shortly after herbicide application. The effect of the vegetable oil on tribenuron‐methyl's rainfastness was significantly lower than that of the surfactants with rain at 1 HAT, while no significant differences among the three adjuvants were observed when rain occurred at 2 and 4 HAT.     

Effect of ammonium sulphate and other additives upon the phytotoxicity of glyphosate to Agropyron repens (L.) Beauv

In several pot and field experiments additions of 1–10% w/v ammonium sulphate and/or 0.1–2.5% w/v surfactant increased the phytotoxicity to A. repens of sprays containing 0.2–0.5 kg/ha glyphosate. There were similar results with technical glyphosate-isopropylamine salt and formulated ‘Roundup’. Higher ammonium sulphate concentrations were sometimes antagonistic. Additions of ammonium sulphate without surfactant generally had less effect on phytotoxicity. While several surfactants increased glyphosate activity the order of effectiveness of these products varied according to whether or not ammonium sulphate was also present. When used alone, relatively hydrophilic non-ionic or cationic products had more effect. In mixtures with ammonium sulphate, however more lipophilic surfactants gave superior results. Ammonium sulphate (5%) with a lipophilic cationic surfactant (0.5% Ethomeen C12) enhanced the effects of very low volume controlled-drop applications as well as conventional medium volume sprays. In a field trial 0.25 kg/ha glyphosate applied with those additives in 20 l/ha of spray had as much effect on bud viability as l kg/ha applied conventionally.     

Pesticides and the Honey Bee

Abstract

In wheat fields, irrigated with treated sewage water, the performance of six herbicides: bromoxynil/MCPA; bentazon/ dichlorprop; diclofop‐methyl; tralkoxydim; pendimethalin and bromophenoxim; and some their combinations were assessed at two different locations around the city of Riyadh. The common weeds include: Lolium spp.; Phalaris spp.; Avena spp.; Malva spp.; Chenopodium spp. and others. The best weed control treatments were: bentazon/dichlorprop followed by bromoxynil/MCPA for the broad‐leaved, and diclofop‐methyl followed by tralkoxydim for the grassy weeds. The combinations of bromoxynil/MCPA with either pendimethalin or tralkoxydim were far more effective against the broad‐leaved weeds, and significantly improved the wheat growth and yield, compared with the single treatments. However, bromoxynil/MCPA combination with diclofop‐methyl was less effective against the grassy and broad‐leaved weeds than each of them. Bromophenoxim showed an effective control of the whole weeds, with appreciable improvement in the wheat growth and yield.     

Effect of ammonium sulphate and related salts on the phytotoxicity of dichlorprop and other herbicides used for broadleaved weed control in cereals

In glasshouse experiments, additions of 10–100 g 1^?1 ammonium sulphate enhanced the phytotoxicity to broadleaved weeds and cereals of several water-soluble herbicides applied post-emergence in 75–300 1 ha^?1 with hydraulic nozzles. Studies with dichlorprop potassium salt and chickweed Stellaria media (L.) Vill. examined interactions between ammonium sulphate and environmental, application and formulation factors. Simulated rainfall immediately after spraying greatly reduced dichlorprop activity, whether or not ammonium sulphate was present. However, when there was an interval of 2–24 h between spraying and rainfall, the additive increased phytotoxicity. Surfactants tended to reduce dichlorprop phytotoxicity to Stellaria media, both in the presence and absence of ammonium sulphate. Certain other inorganic salts including sodium sulphate also enhanced phytotoxicity. Applications by rotary atomizer in very low spray volume (15 1 ha^?1, 250–280 μm drops) were less effective than conventional 150 1 ha^?1 applications. When very low volume application was used, addition of ammonium sulphate or nitrate tended to reduce activity further. In the field, ammonium sulphate significantly increased the effects against weeds of a commercial dichlorprop potassium salt formulation applied conventionally in 200 1 ha^?1 spray volume. Neutralized phosphoric acid had a similar effect but a mixture of this additive and ammonium sulphate reduced phytotoxicity. Both additives slightly increased dichlorprop injury to barley.     

Effect of ammonium carbonate and sodium bicarbonate on anthracnose of papaya

Colletotrichum gloeosporioides is the causal organism of anthracnose inCarica papaya L. (papaya, papaw). The effect of ammonium carbonate (3%) or sodium bicarbonate (2%) in aqueous solution or when incorporated into a wax formulation on anthracnose severity in inoculated or naturally infected fruits was examined. Both salts had significant effects, but that of ammonium carbonate was greater than that of sodium bicarbonate in controlling anthracnose. Ammonium carbonate (3%) incorporated into the wax formulation effectively reduced anthracnose incidence by 70% in naturally infected papaya and extended the storage life by maintaining the firmness, color and overall quality of the fruit in low temperature storage (13.5°C) and 95% r.h. for 21 days followed by 2 days under marketing conditions. The mode of action of ammonium carbonate on the control of anthroacnose appears to bevia complete inhibition of radial mycelial growth and conidia germination. http://www.phytoparasitica.org posting Aug. 14, 2002.     

降雨及助剂对咪唑乙烟酸药效的影响

以苘麻Abutilon theophrasti为测试植物,研究了施药后降雨和助剂对咪唑乙烟酸除草活性的影响。结果表明,咪唑乙烟酸有较好的耐雨性,药后2 h内无降雨,可保持相当的防效,药后4~8 h内无降雨,与无降雨的没有显著差异。添加非离子表面活性剂能明显提高咪唑乙烟酸的除草活性。其中增效作用从大到小依次为:AM-100＞PPJ-15＞OP-10＞SDP,咪唑乙烟酸的IC50值分别比未加助剂处理的下降了33.6%、35.4%、29.5%和17.1%。咪唑乙烟酸的用量越低,助剂的增效作用越明显。     

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.     

Effect of MCPA on the phytotoxicity of imazamethabenz-methyl applied to wild oats (Avena fatua L.)

Greenhouse studies were conducted to determine the effect of both ester and amine formulations of MCPA on the phytotoxicity of imazamethabenz applied to wild oats (Avena fatua). The MCPA ester antagonized activity of the liquid concentrate (LC) formulation of imazamethabenz but not the suspension concentrate (SC) formulation of imazamethabenz when the combination was applied to wild oats at two-to three-leaf stage without tiller. The MCPA amine antagonized the efficacy of both formulations of imazamethabenz on wild oats at the two-to three-leaf stage. When the herbicides were applied at the three- to four-leaf stage with one or two tillers, the antagonism was found only with MCPA amine and imazamethabenz-LC. In general, antagonism is most likely to occur at an early stage of wild oats. MCPA amine was more antagonistic than MCPA ester on the phytotoxicity of imazamethabenz. Imazamethabenz-SC can be tank mixed with MCPA ester but should not be tank mixed with MCPA amine. Imazamethabenz-LC should not be tank mixed with either ester or amine of MCPA because of antagonism, especially when herbicides are applied at early stage. When MCPA was applied at intervals of from 2 to 24 h following applications of imazamethabenz-LC, there was no antagonistic effect of MCPA and the same level of phytotoxicity was produced as with imazamethabenz-LC alone. In the reverse sequence of MCPA followed by imazamethabenz-LC, the greatest antagonism of phytotoxicity of imazamethabenz-LC occurred when 2 h separated the two applications. This effect was lessened when the elapsed time increased. Effet du MCPA sur I'efficacitée de l'imazaméthabenz-méthyle sur la folle avoine (Avena fatua L.) Des études en serres ont étéé réalisées pour déterminer I'effet de formulations ester et amine du MCPA sur l'efficacité de l'imazaméthabenz contre la folle avoine (Avena fatua L.). Lorsque le mélange était appliqué sur des folles avoines au stade 2–3 feuilles sans talle, l'ester de MCPA était antagoniste de la formulation de l'imazaméthabenz en concentré liquide (LC) mais pas de la formulation en suspension concentrée (SC). Le MCPA amine était antagoniste des deux formulations d'imazaméthabenz. Quand les herbicides étaient appliqués au stade 3–4 feuiles avec 1–2 talles, l'antagonisme ne s'observait qu'avec le MCPA amine et l'imazaméthabenz- LC. En général, l'antagonisme se produisait surtout aux stades précoces de la folle avoine. Le MCPA amine était plus antagoniste de l'activité de l'imazaméthabenz que le MCPA ester. L'imazaméthabenz-SC peut étre mélangé au moment du traitement avec le MCPA ester mais pas avec le MCPA amine. L'imazaméthabenz- LC ne doit pas étre mélangé au moment du traitement avec le MCPA, qu'il soit sous forme ester ou amine, surtout quand les herbicides sont appliqués è un stade précoce. Quand le MCPA était appliquéè des intervalles de 2 è 24 h après l'imazaméthabenz-LC, il n'y avait pas d'antagonisme du MCPA. Si l'ordre des applications était inversé, l'antagonisme était le plus important lorsque 2 h les séparaient et il diminuait lorsque l'intervalle augmentail. Beinflussung der Phytotoxizität von Imazamethabenz-methyl auf Avena fatua L. durch MCPA In Gewächshausversuchen setzte MCPA-Ester die Wirkurlg der Flüssig-Formulierung von Imazamethabenz-methyl auf Avena fatua L. im 2- bis 3-Blatt-Stadium herab, aber nicht die der Suspensions-Formulierung. MCPA-Amin war gegenüber beiden Formulierungen antagonistisch. Im 3- bis 4-Blatt-Stadium bei 1 bis 2 Bestockungstrieben trat die Wirkungsminderung durch MCPA-Amin nur bei der Flüssig- Formulierung ein. Also scheint der Wirkungsantagonismus in frühen Avena-fatua- Entwicklungsstadien und für MCPA-Amin am stärksten zu sein, so daé es von Tankmischungen mit der Suspensions-Formulierung ausgenommen werden sollte. Die Flüssig-Formulierung sollte weder mit MCPA-Amin noch -Ester gemischt werden. Bei Applikation von MCPA 2 bis 12 h nach Imazamethabenz-methyl in der Flüssig-Formulierung wurde die Wirkung nicht beeinträchtigt. Umgekehrt ergab sich bei Anwendung der Flüssig-Formulierung 2 h nach einer MCPA-Ausbringung der gröte Antagonismus, der sich mit längerem Abstand zwischen den Anwendungen verringerte.     

A scanning electron microscope study of glyphosate deposits in relation to foliar uptake

The effects of several formulations on foliar uptake of glyphosate, and on the morphology of glyphosate deposits on leaves, were examined in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.). [¹⁴C]glyphosate, in the form of the free acid or the isopropylamine salt (IPAS), was applied to foliage alone or with various adjuvants. Uptake of all glyphosate IPAS formulations was greater than that of the corresponding acid formulation. Addition of ‘Tween 20’ enhanced the uptake of glyphosate IPAS compared to glyphosate alone, but had no effect on the uptake of glyphosate acid. Ammonium sulfate and the ‘Roundup’ formulation blank increased the uptake of glyphosate acid and IPAS to 2-3 times that of herbicide alone. Surface deposits, as observed by scanning electron microscopy, varied with the formulation of the herbicide, although there were no differences between the acid and IPAS formulations. Glyphosate alone initially formed a deposit with both crystalline and smooth, amorphous areas. Later in the treatment period (48 and 72 h after application), the deposit was almost entirely crystalline. The addition of ‘Tween 20’ or of formulation blank resulted in the formation of a more amorphous, non-crystalline deposit. Herbicide solutions containing ammonium sulfate dried to form a highly crystalline deposit. However, crystals similar to those of glyphosate alone were not visible in these deposits. The ability of these adjuvants to prevent or delay crystal formation may play a role in their enhancement of herbicide uptake.     

The plasma membrane as a barrier to herbicide penetration and site for adjuvant action

Adjuvants are traditionally thought to exert their main effect on the cuticle or spray droplet to enhance foliar-applied herbicide penetration. However, considerable evidence exists indicating that the plasma membrane is a barrier to intracellular penetration of herbicides and a site of action for adjuvants. Surfactants may penetrate through the cuticle and into the region of the plasma membrane. Insertion into the membrane causes a general “ loosening” to provide greater penetration by highly polar herbicides such as glyphosate. Weak acid herbicides typically have a lipophilic moiety and, therefore, can move more easily through the membrane but the rate and accumulation is dependent on pH conditions across the membrane. Ammonium salts have been shown to affect the pH of the apoplast in a manner which allows faster penetration and greater accumulation of weak acid herbicides. Examination and understanding of the plasma membrane as a barrier to herbicide penetration will aid in defining the mechanisms of adjuvant action and improve the efficiency of agrochemical use.     

Response of winter wheat (Triticum aestivum L.) and weeds to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl

Field and greenhouse experiments were conducted in 2004 and 2005 to study weed control and the response of winter wheat to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl. The field experiments were conducted at Yazd and Oroumieh, Iran, with factorial combinations of 2,4-D plus MCPA at 0, 975, and 1300 g ai ha⁻¹ and with clodinafop propargyl at 0, 64, 80, 96, and 112 g ai ha⁻¹ in four replications. The greenhouse experiments further evaluated the effect of these tank mixtures on weed control, where each herbicide mixture was considered as one treatment and the experiment was established in a randomized complete block design with four replications. In the field experiments, the herbicides were applied at wheat tillering, while in the greenhouse experiments they were applied at the beginning of the tillering stage and at the four-leaf stage of the grass and broadleaf weeds, respectively. The results indicated antagonistic effects between 2,4-D plus MCPA and clodinafop propargyl. The best tank mixture with regard to weed control efficacy was 2,4-D plus MCPA at 975 g ai ha⁻¹ with clodinafop propargyl at 96 g ai ha⁻¹. The wheat grain yield was also increased by the tank mixture of clodinafop propargyl with 2,4-D plus MCPA. Generally, to inhibit clodinafop propargyl efficacy reduction due to tank-mixing with 2,4-D plus MCPA, it is recommended that the application dose of 64 g ai ha⁻¹ should be increased to 96 g ai ha⁻¹.     

Leaf surface characteristics of apple seedlings, bean seedlings and kohlrabi plants and their impact on the retention and rainfastness of mancozeb

A study was made of the influence of the upper leaf surface characteristics on the retention and rainfastness of the contact fungicide mancozeb with and without tank-mix adjuvants (RSO 5 and RSO 60) on apple seedlings, bean seedlings and kohlrabi plants. Large differences in roughness, in the amount and composition of surface waxes and in the retention and rainfastness of mancozeb were found among species. Strong correlations between roughness and total amount of surface waxes and mass of C29 alkane in the wax mass were also found. Fungicide retention was strongly, negatively correlated with surface roughness, total epicuticular wax, amount of C29 alkane and the total mass of alkanes. Rainfastness correlated strongly or very strongly with the amount of C28 alcohol and C33 alkane. The addition of a more hydrophobic (RSO 5) or a more hydrophilic (RSO 60) adjuvant to the spray solution influenced retention and rainfastness, and also altered the correlation coefficients. The present results support earlier observations which show that the success of adjuvants in enhancing the retention and rainfastness of agrochemicals depends on the characteristics of the leaf surface.     

The effect of nitrogenous compounds on in vitro germination of Orobanche crenata Forsk.

The effect of nitrogen (ammonium, urea and nitrate), applied during a conditioning or germination phase, on germination of Orobanche crenata Forsk, seeds was investigated in vitro. Ammonium sulphate (8 mM) applied during conditioning in combination with the nitrification inhibitor nitrapyrin, reduced germination of seeds from 46% to 26%. A lower concentration of 4 mM ammonium sulphate or supplying nitrogen as 8 mM urea or 16 mM nitrate did not inhibit germination. Applied after conditioning during the germination phase, 4 mM ammonium sulphate strongly inhibited germination, especially in combination with a nitrification inhibitor: germination was reduced to less than 5%. Urea (8 mM) reduced germination to only a limited extent (from 58% to 40%). When a urease inhibitor (carbon disulfide) was additionally applied, germination percentage was not affected. Nitrate had no effect. It is hypothesized that the inhibition by ammonium of O. crenata germination is connected with a reduced ability to detoxify ammonium, owing to the reduced activities of the enzymes GS and GOGAT. The inhibitory effect of urea may be indirect, occurring through conversion to ammonium. The effect of a short-term exposure to ammonium was largely reversible and no increase in mortality could be detected. The presence of 6 mM phosphate, Hepes or Mops buffer was found to intervene with the inhibition by ammonium.     

Interaction between benzoylprop ethyl, flamprop methyl or flamprop isopropyl and herbicides used for broadleaved weed control

A marked antagonism of A. fatua control was found when 2,4-D, dicamba, 2,4-D-dicamba-mecoprop or bromoxynil were added to benzoylprop ethyl, flamprop methyl or flamprop isopropyl. Because of the much poorer control of A. fatua by these mixtures obtaining broad spectrum weed control with them in one spray operation would not be possible. The A. fatua herbicides did not affect the activity of the added herbicides on Fagopyrum lataricum. In eight out of nine mixtures tested there was no significant antagonism in the field conditions when MCPA or bromoxynil-MCPA was added to the A. fatua herbicides. There were significant antagonistic effects, however, in six out of nine such mixtures in glasshouse experiments. This suggests that under farm use conditions benzoylprop ethyl, flamprop methyl or fiamprop isopropyl can be mixed with MCPA amine or ester or with bromoxynil-MCPA to obtain broad spectrum weed control from one spray operation, though slightly poorer A. fatua control may be expected with these mixtures.