Herbicide Oryzalin Research Articles

Effects of chemicals and microbial antagonists on nematodes and fungal pathogens of citrus roots

In pot and field experiments in naturally infested soil, commercial products formulated with microbial antagonists, applied to soil, performed poorly against the nematodes Tylenchulus semipenetrans and Paratrichodorus lobatus, and the root rot fungi Phytophthora nicotianae and Pythium ultimum on citrus, compared with the conventional chemicals aldicarb, cadusafos and metalaxyl. Prosper Nema did not reduce nematode levels even when combined with a sawdust mulch over the soil. Nutri-life 3/20 inhibited citrus growth and caused leaf chlorosis. Tri-D25 did not reduce root rot or isolation frequency of Phytophthora nicotianae and Pythium ultimum. However, a commercial formulation (Actizyme) of Bacillus subtilis stimulated citrus growth, and the herbicide oryzalin both stimulated citrus growth and reduced isolation frequency of Pythium ultimum. Potassium silicate did not reduce isolation frequency of Phytophthora nicotianae and Pythium ultimum or root rot, however, it did reduce levels of T. semipenetrans in soil. Cadusafos and aldicarb were equally effective in controlling T. semipenetrans on roots but cadusafos was more effective in soil and against Paratrichodorus lobatus. Aldicarb stimulated citrus growth, while cadusafos plus metalaxyl was more effective than metalaxyl alone in stimulating citrus growth and preventing leaf chlorosis in soil infected with Phytophthora nicotianae. Results suggested that Phytophthora nicotianae was much more damaging to citrus than Pythium ultimum, and that nematodes (in association with Fusarium solani) were also more damaging than P. ultimum. Relatively low initial combined levels of T. semipenetrans and Paratrichodorus lobatus depressed citrus growth; reproduction rates for P. lobatus exceeded 23-fold the initial level. Cadusafos (3 applications at 3 g/m2 over 6 months) reduced T. semipenetrans to very low levels, but did not eliminate the nematode; mechanical incorporation of nematicide granules improved the level of nematode control after the first, but not succeeding, applications.

Concurrent Patterns of Sorption−Degradation for Oryzalin and Degradates

Sorption and degradation are linked, dynamic processes which largely govern the potential for herbicides and their degradation products to reach groundwater. Patterns of concurrent degradation and sorption of the dinitroaniline herbicide oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) and its degradates were determined on four soils representative of typical use areas. Radiolabeled oryzalin was applied to soil at either 1.64 or 3.14 μg/g and incubated at 25 °C under aerobic conditions for up to 6 months. The time required for 50% and 90% degradation of oryzalin ranged from 24 to 42 and 79 to 140 days, respectively. The radiocarbon was rapidly incorporated into the soil organic matter; up to 57% of the applied radiocarbon was recalcitrant to extraction after 6 months. The degradation pathway deduced is similar to that for the related dinitroaniline herbicide trifluralin. Apparent distribution coefficients were measured separately for the pool of material in the soil solution (Kss, determined from a 5-min desorption) and the total desorbable pool of material (Kd, determined from a 24-h desorption). Sorption coefficients increased by a factor of 3 over 6 months, indicating that the total pool of extractable oryzalin became less available for desorption and degradation. Values of Kss remained constant over time, indicating that material in the soil solution and the desorbable pool were in equilibrium. The amount of oryzalin and degradates in soil solution was a function of the desorption energy from the surface and was not limited by solubility. Similar, though less consistent, trends were observed for oryzalin degradation products. Keywords: Oryzalin; aerobic soil metabolism; sorption; aerobic soil degradation

Inhibition of intracellular Ca 2+ signalling, cytotoxicity and antitumor activity of the herbicide oryzalin and its analogues

Studies were conducted on oryzalin (3,5-dinitro-N,N-di(n-propyl)sulfanilamide), a widely used dinitroaniline sulfonamide herbicide, which was identified from plant extracts as an inhibitor of mitogen- and growth factor-mediated intracellular free Ca2+ ([Ca2+]i) signalling in mammalian cells. Oryzalin inhibited vasopressin, bradykinin and platelet-derived growth factor [Ca2+]i signalling in Swiss 3T3 fibroblasts with IC50 values of 14, 16 and 18 microM, respectively. 45Ca2+ uptake into nonmitochondrial stores of saponin-permeabilized Swiss 3T3 cells was inhibited by oryzalin with an IC50 of 34 microM. Oryzalin inhibited colony formation of HT-29 colon carcinoma cells with an IC50 of 8 microM and inhibited the growth of a number of other cancer cell lines and primary human tumors in vitro with IC50 values in the range 3 to 22 microM. A number of oryzalin analogues were studied and an association was found between the ability to inhibit [Ca2+]i signalling and inhibition of the growth of HT-29 human colon cancer cells (P = 0.001) and of CCRF-CEM human leukemia cells (P = 0.016). Oryzalin at doses up to 600 mg/kg administered orally or subcutaneously daily to mice for 3 to 10 days beginning a day after tumor inoculation inhibited the growth of murine B16 melanoma by 63% but showed no appreciable activity when administered subcutaneously or intraperitoneally to mice beginning a number of days after tumor inoculation against a variety of human tumor xenografts. The peak plasma concentration of oryzalin following repeated subcutaneous administration of oryzalin at 600 mg/kg per day to mice was 37 microM and of its major metabolite N-depropyl oryzalin was 53 microM. It is unlikely that the absence of significant antitumor activity of oryzalin is a result of the inability to achieve adequate plasma concentrations.

Influence of Dinitroanaline Herbicides on Growth, Sporulation, and Infectivity of FourPhytophthoraspp. Pathogenic to Deciduous Fruit Trees

Crown rot of potted Mahaleb cherry seedlings, caused by Phytophthora cryptogea, P. cambivora, and P. megasperma, was virtually prevented by applying the herbicide oryzalin at either of two nonphytotoxic rates (1.12 and 2.24 kglha) to a porous soil mix (1 volume of sandy loam:2 volumes of vermiculite) prior to infestation with the pathogens. In untreated pots, leaf-disk baits exposed during each of five to nine biweekly flooding periods were colonized at frequencies of 96 to 99, 49 to 95, and 13 to 47% by the respective pathogens, but only 0 to 7% of the baits were colonized in pots containing oryzalin-treated soil mix. At 2.24 kg/ha, pendimethalin similarly reduced both the incidence of disease caused by P. cambivora and its frequency of isolation from baits, but pendimethalin had little effect at 1.12 kg/ha. Likewise, pendimethalin had little effect on the incidence of crown rot caused by P. cryptogea when applied at either rate and only modestly reduced the frequency of its baiting. When tested in vitro at 0.06 to 4.0 μg/ml, both herbicides significantly affected pathogen activities. At a concentration approximating that found in solutions of treated field soils (0.25 μg/ml), oryzalin inhibited the formation of sporangia by P. cambivora, P. cryptogea, P. cactorum, and P. mega-sperma by 97, 89, 80, and 65%, respectively, whereas pendimethalin inhibited formation by 93, 49, 54, and 74%, respectively, at this concentration. When added to soil extract containing freshly released zoospores of P. cryptogea, P. cactorum, or P. megasperma, both herbicides significantly reduced the motile period, although pendimethalin generally provided the greater reduction at lower concentrations. Oryzalin was much more inhibitory than pendimethalin to mycelial growth of all four pathogens, although reductions were only modest (≤20% relative to the checks) at concentrations ≤0.25 μg/ml.

Evaluation of Selected Preemergence Herbicides in Field-Grown Landscape Crops in Kentucky

Abstract Research was conducted during 1990 and 1991 at the Horticultural Research Farm in Lexington, Kentucky, to evaluate the efficacy of herbicides available for use on woody landscape plants (simazine and oryzalin), newly labelled herbicides (isoxaben, isoxaben plus oryzalin, metolachlor and metolachlor plus simazine) and those not widely labelled for the nursery industry (oxyfluorfen and dithiopyr). Herbicide phytotoxicity was also evaluated in 10 species of woody nursery crops. Results 6 WAT (weeks after treatment) indicated that the standard of simazine at 1.1 kg ai/ha (1.0 lb/A) plus oryzalin at 3.3 kg ai/ha (3.0 lb/A) provided adequate control of most common broadleaf weeds (98%) and annual grasses (98%) but not yellow nutsedge (31%). Isoxaben plus oryzalin at 4.2 kg ai/ha (4.0 lb/A) (DF formulation) and isoxaben plus trifluralin at 4.2 kg ai/ha (4.0 lb/A) (granular formulation) gave excellent full-season control of nearly all broadleaf and grass weeds with the exception of galinsoga and field bindweed. In addition, yellow nutsedge control was acceptable, ranging from 63 to 96% in these treatments. Isoxaben alone also provided excellent broadleaf control (93%) 6 WAT in 1990 but poorer (<70%) control of giant foxtail, galinsoga and velvetleaf by 12 WAT. Dithiopyr (granular formulation) provided excellent full-season residual control of broadleaf weeds, nutsedge and grasses at the highest rate of 2.2 kg ai/ha (2.0 lb/A). Oxyfluorfen at the higher rate (2.2 kg ai/ha) (2.0 lb/A) also controlled all species except yellow nutsedge. Poor broadleaf control was obtained 12 WAT with 3.3 kg ai/ha (3.0 lb/A) metolachlor or metolachlor plus simazine at rates up to 4.4 kg ai/ha (4.0 lb/A) in both 1990 and 1991. Pronamide at 2.2 kg ai/ha (2.0 lb/A) did not provide adequate control of either broadleaf or grasses at 6 or 12 WAT. No visible phytotoxicity to woody ornamentals was observed in either season up to 8 weeks after application. However, growth reductions were noted in both common lilac and red oak stem or trunk diameter following treatment with isoxaben at 1.1 kg ai/ha (1.0 lb/A).

Re-orientation of cortical F-actin is not necessary for wound-induced microtubule re-orientation and cell polarity establishment

To assess the relative roles of cortical actin and microtubule re-orientation in the establishment of new cell polarity, we have examined the kinetics of cortical actin re-orientation around a wedge-shaped wound in pea roots. Cortical actin re-orients from a transverse alignment to an approximately longitudinal orientation between 5 and 24h after wounding, that is, after the re-alignment of microtubules, which is known to occur before 5h post-wounding. F-actin in root cortical cells does not appear to be necessary for the establishment of new cell polarity around wounds, since normal MT re-alignment, and new planes of cell division are still established around a wound in cytochalasin treated roots. The cytochalasin treatment appeared to totally disrupt cortical and cytoplasmic F-actin in cells of the root cortex. However, in the apparent absence of F-actin in these cells, the rate of wound-induced cell division, but not cell expansion, is slower, and we suggest that an effect on the phragmosomal actin is involved. Finally, we demonstrate that new cell polarity around a wound is not established if microtubules are disrupted by the herbicide oryzalin, but after re-establishment of these arrays following a wash-out of the drug, the typical new planes of cell expansion are observed. We conclude that microtubules play a critical role in establishing and maintaining cell polarity in this system, and that cortical F-actin has a minor and presently unclear function in these processes.

Microtubule organization differs between acid and alkaline bands in internodal cells of Chara but bands can develop in the absence of microtubules

We have studied the relationship between pH banding and the organization of cortical microtubules in the alga Chara corallina Klein ex Willd. Microtubules were visualized by immunofluorescence and also by imunogold-silver enhancement to allow immediate comparison of microtubule arrangement with visible structural cell features. In cells that are nearing growth completion, microtubule number and alignment change between acidic and alkaline bands over a distance of a few micrometres. Thus, it appears that the still unknown mechanisms for microtubule organization respond to the localized differences in membrane properties. Band formation was not prevented when microtubules were depolymerized with the herbicide oryzalin, demonstrating that microtubules are not necessary for pH bands to develop in these cells.

Inhibitors of cell division and protoplasmic streaming fail to cause a detectable effect on intracellular calcium levels in stamen-hair cells of Tradescantia virginiana L.

The herbicides amiprophos-methyl (APM) and oryzalin disrupt mitosis and cytokinesis in plant cells by causing the depolymerization of microtubules. These drugs have also been shown to affect calcium sequestration by mitochondria. Controversy thus exists as to whether microtubule depolymerization occurs as a result of direct interaction between the drug and tubulin, or because of elevated intracellular calcium levels resulting from drug interference with calcium regulation. In order to clarify this issue we have directly measured the effect of these herbicides and other cell-motility-altering drugs on intracellular calcium levels in stamen-hair cells of Tradescantia. The results indicate that low levels (1-3 μM) of APM and oryzalin can act within 3-7 min causing disorganization of mitosis. Studies using the calcium indicator indo-1 injected into stamen-hair cells to monitor internal levels of calcium, show that at drug concentrations where inhibitory effects on mitosis and-or cytokinesis are clearly seen, APM, oryzalin, isopropyl-N-phenyl carbamate, caffeine and cytochalasin D produce no change in intracellular calcium levels. Furthermore, except for cytochalasin D, these drugs do not inhibit cytoplasmic streaming, a calcium-sensitive process. We conclude that the mode of action of these drugs on the cytoskeleton is independent of an effect on intracellular calcium.

Effect of the anti-microtubule drug oryzalin on growth and differentiation of the parasitic protozoan Leishmania mexicana

Abstract The parasitic protozoan Leishmania mexicana differentiates from a non-motile intracellular amastigote in the mammalian macrophage phagolysosome into a motile, extracellular promastigote in the insect vector gut. This development program has been accomplished in vitro, thus providing a useful model for studying changes in the cytoskeleton during cell differentiation. The role of microtubules in leishmania differentiation was demonstrated by using the dinitroaniline herbicide oryzalin, which inhibited both leishmania proliferation and differentiation; 25 μ M oryzalin reduced promastigote division by over 95%. Interestingly, at a sublethal dose (5 μ M), promastigotes became round and multifla-gellated but remained motile. At 50 μ M oryzalin, the number of intracellular amastigotes decreased by 50%. However, leishmania differentiation seemed to be the most drug-sensitive stage: there was a 60% reduction in amastigote-to-promastigote differentiation at 0.5 μ M oryzalin. The specific action of oryzalin on leishmania microtubules was verified by its inhibition of in vitro polymerization of leishmania microtubules, but not control mammalian microtubules (from rat brain). These findings indicate that microtubules play a major role in leishmania proliferation, maintenance of cell shape, and cytodifferentiation.

Weed control among planted and direct-seededEucalyptus, AcaciaandCasuarinawith the herbicides diphenamid, oryzalin, clopyralid and fluazifop-butyl

Summary In a glasshouse pot trial, applications of the pre-emergence herbicide oryzalin at rates equivalent to 4 and 8 kg a.i. ha−1 were toxic to germinating seeds of Eucalyptus maculata, Casuarina glauca and Acacia saligna. The pre-emergence herbicide diphenamid was toxic at rates of 7 and 14 kg a.i. ha−1 to germinating C. glauca and A. saligna, but not to E. maculata. Both oryzalin and diphenamid were selective at these rates when applied over newly-planted seedlings of Eucalyptus melliodora, Casuarina cunninghamiana and Acacia baileyana on a former pasture site. Diphenamid gave greater pre-emergence control of grass weeds, while oryzalin was more effective against the broad-leaved weeds. Overall, the most satisfactory long-term weed control and tree response was achieved with oryzalin. The post-emergence herbicides fluazifop-butyl at 0.6 and 1.2 kg a.e. ha−1 and clopyralid at 0.25 and 0.5 kg a.e. ha−1, were mostly selective to the planted seedlings on the former pasture site, but they gave unsatisfactory weed control, probably because of a combination of poor timing of application and a herbicide-tolerant weed flora.

The microtubule cytoskeleton in developing cysts of the green algaAcetabularia: Involvement in cell wall differentiation

Cysts of the green algaAcetabularia develop a unique lid structure to enable the release of gametes. This lid is separated from the rest of the thick cellulose cell wall by a circular fault line formed within the fibrillar texture of the wall. By immunofluorescence microscopy, we show that, prior to the first division of the single cyst nucleus, the radially symmetrical, perinuclear microtubule system which is a remnant carried over from previous developmental stages of cyst morphogenesis transforms into a circular microtubule band (CMB) around the nucleus. This band consisting of only a few bundled microtubules beneath the plasma membrane encircles the cyst nucleus at a distance of 75 to 100μm. In a previous fine structural study, a lid-forming apparatus (LFA) was described as a circular band of rod-like structures in the plane of the plasma membrane, demarcating the contour of the future lid. Both the CMB and the LFA are superimposed on the rim of the lid. We therefore propose that the microtubule band is a component of the LFA identical with the rod-like structures. Formation of the CMB and, hence, lid formation are blocked by the microtubule-specific herbicide Oryzalin but not by the actin filament-disrupting inhibitor cytochalasin D. Upon recovery from Oryzalin treatment, the nuclei but not the prospective sites of the CMBs serve as nucleation centers, indicating that the CMB is not formed by a pre-existing template in the plasma membrane. This suggests that the dynamic behavior of the microtubules within the perinuclear microtubule cytoskeleton gives rise to the CMB. Since the stage of CMB assembly marks the beginning of cell wall formation, it is proposed that the CMB determines the position of the lid by spatially controlling cell wall deposition. On the basis of current hypotheses, two scenarios for the role of the LFA/CMB in lid formation are discussed.

Reorganization of cortical actin microfilaments and microtubules at preprophase and mitosis in wheat root‐tip cells: A double label immunofluorescence study

AbstractFollowing our recent description [McCurdy et al.: Protoplasma. 147:204–206, 1988] of arrays of transverse cortical microfilaments (MFs) in preprophase roottip cells of wheat (Triticum aestivum L. cv. Kite), we have performed double label immunofluorescence microscopy to correlate the formation of these arrays with the known rearrangement of cortical microtubules (MTs) that occurs during preprophase. At early preprophase, indicated by a broad (i.e., young) preprophase band (PPB) of MTs, actin MFs are transverse only in the central region of the cell cortex. By late preprophase, however, cells that possess a mature (i.e., narrow) PPB of MTs have arrays of transverse MFs that occupy the entire cortical surface of the cell. Thus, apart from the PPB zone, the transverse MFs in these arrays do not colocalize with transverse cortical MTs. Depolymerization of MTs using the herbicide oryzalin does not effect the arrays of cortical MFs; however, experiments using cytochalasin B in combination with oryzalin indicate that cellular MTs are necessary for the formation of the arrays of transverse cortical MFs. The arrays of cortical MFs disintegrate during prophase into short fragments of random, filamentous actin. This situation persists until the completion of cytokinesis. The absence of MFs during mitosis in densely‐cytoplasmic meristematic cells of wheat root tips indicates that filamentous actin may not have a universal function in plant cell division. The possible function of the arrays of cortical MFs in preprophase cells is discussed.

Oryzalin-Induced Microtubule Disassembly and Recovery in Regenerating Protoplasts of the Alga Mougeotia

Summary Cortical microtubules in newly formed protoplasts of the alga Mougeotia undergo rapid organization to form symmetrical arrays centered upon two cortical foci. This process is critical to protoplast regeneration because the orientation of the two foci indirectly establishes the future axis of elongation of the protoplasts. To investigate the extent of cellular control of microtubule organization, we employed the anti-microtubule herbicide oryzalin. Depolymerization and recovery of microtubules in 0–4 h old protoplasts was monitored by immunofluorescence microscopy with anti-tubulin. Data are presented on the effect of varying oryzalin concentration and treatment time, and on the rate of microtubule depolymerization. Organized microtubule arrays, including the cortical foci, were as susceptible to oryzalin as unorganized arrays. During recovery, microtubules repolymerized in clusters in contact with the plasma membrane throughout the cortex. Microtubules assembled into transient, locally-ordered arrays prior to the appearance of arrays indistinguishable from those in untreated protoplasts. The process of microtubule organization proceeded from the stage reached before oryzalin treatment, indicating that the protoplasts retained information about the degree of microtubule organization achieved prior to treatment despite temporary loss of microtubules.

Isolation and characterization of dominant, pleiotropic drug-resistance mutants in Chlamydomonas reinhardtii.

Three independent pleiotropic drug-resistance (pdr) mutants were isolated by selecting for resistance to the anti-microtubule herbicides amiprophos-methyl (APM) and oryzalin (ORY). These three mutants and a previously isolated mutant, ani1 (anisomycin resistance), were semi-dominant in heterozygous diploids, and they displayed varying degrees of resistance to structurally and functionally unrelated inhibitors such as cycloheximide, cryptopleurine, emetine, atrazine, and nonidet P-40. Linkage analysis and genetic mapping suggested that three of the four mutants, including ani1, define a single locus, here named pdr1. The fourth mutant defined a new locus, pdr2, which is located on the left arm of linkage group VI. One pdr1 mutant exhibited unusual genetic interactions, including enhanced ts-lethality and synergistic increases in drug resistance, when combined with pdr2-1 and with herbicide-resistant alleles of three other genes.

Grass Control in Container-grown Ornamentals with Pre- and Postemergence Herbicide Combinations

Abstract Control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] was evaluated with the preemergence herbicides oryzalin (Surflan), oxyfluorfen (Goal), and metolachlor (Dual) and the postemergence herbicides quizalofop (Assure), fenoxaprop-ethyl (Whip), haloxyfop (Verdict), poppenate-methyl (Trophy), fluazifop-P (Fusilade 2000), and sethoxydim (Poast) when applied alone or in combination. Oryzalin combinations provided maximum preemergence control compared to oxyfluorfen or metolachlor combinations. Greatest preemergence and post-emergence control was obtained with oryzalin or metolachlor applied with poppenate-methyl. Antagonism of preemergence or postemergence control occurred with several combinations of preemergence and postemergence herbicides. In some instances, control was enhanced by using other herbicide combinations. Chemical names used: 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); 2-chIoro-1-(3-ethoxy-4-ni-trophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); 2-chloro-N-(2-ethyl-6-methyl-phenyl)-N-(2-methoxy-1-methylethyl) acetamide (metolachlor); ½(±)-2-[4-[(6-chloro-2-quinoxyalinyl)oxy]phenoxy]propanoic acid¼ (quizalofop); (±)-ethyl 2-[4-[(6-chIoro-2-benzoxazolyl) oxy] phenoxy] propanoate (fenoxaprop-ethyl); 2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (haloxyfop); methyl 3-hydroxy-4-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]-pentanoate (poppenate-methyl); (R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (fluazifop-P); and 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one (sethoxydim).

Reorganization of the endoplasmic reticulum in epidermal cells of onion bulb scales after cold stress: Involvement of cytoskeletal elements

In the epidermal cells of onion (Allium cepa L.) bulb scales the endoplasmic reticulum (ER) can be subdivided into three domains: a peripheral tubular network, cisternae, and long tubular strands. The latter are the form in which the ER is moved in onion cells. During cold treatment the arrangement of the three domains changes drastically. The cisternae and long tubular strands disintegrate into short ER tubules which show rapid agitational motion. Long-distance movement is inhibited. The peripheral tubular ER network is presumably retained during cold treatment. Rewarming of previously chilled bulb scales initiates the reorganization of the ER into the three domains. The ER is partly relocated during recovery from cold treatment. Redistribution and reorganization of the ER is not affected by the microtubule-destabilizing herbicides oryzalin and trifluralin (5 μM). Cytochalasin D (2μM), however, inhibits not only the relocation of ER material, as is evident by the absence of long tubular ER strands, but also the movement of other cell organelles. The latter cluster on top of the cisternae in a manner which is characteristic of treatment with the actin-filament inhibitor. The array of actin filaments is similar in unstressed, cold-treated cells, and cells which recover from low temperatures in the presence of oryzalin or tap water alone. In the presence of cytochalasin D the actin filaments are severely fragmented. The results indicate that low temperatures most likely influence either the interaction of the force-generating system, probably myosin, with actin filaments, or the force-generating mechanism of the actomyosin-driven intracellular movement, but do not affect actin-filament integrity.

Interactions of Alfalfa Weevil (Coleoptera: Curculionidae) and Weeds in Reducing Yield and Stand of Alfalfa

Interaction of alfalfa weevil, Hypera postica (Gyllenhal), and weeds in reducing forage production and stand longevity over several years was studied. Insecticide (carbofuran) and herbicides (terbacil and oryzalin) were used to control naturally occurring weevil and weed populations in some plots, in others pesticides were not applied, resulting in four treatment combinations. Seasonal alfalfa yield reductions (as compared with the pest free treatment) averaged 2.0 Mg/ha in the weevil infested treatment, 0.4 Mg/ha in the weed infested treatment, and 3.7 Mg/ha when both pest types occurred. Virtual loss of the alfalfa stand occurred in 2–4 yr due to combined pest infestations, resulting in <10.0 stems/0.1 m2 as compared with 18 stems in the pest-free treatment. Combined effects of H. postica larval feeding damage and weed competition on alfalfa forage yield and stand retention were greater than the sum of the effects of pests occurring individually.

Improved derivatisation method for the gas-liquid chromatographic determination of the herbicide oryzalin

A rapid derivatisation method is described for the determination of the herbicide oryzalin. It involves the use of dimethylsulphinyl anion and methyl iodide or ethyl iodide. Gas-liquid chromatography is used with either an N-P or an electron-capture detector. The method was applied to the residue analysis of fortified sweet potatoes, soils and water. With an electron capture detector, residues as low as 0.01 µg g–1 in sweet potatoes and soils and 0.001 µg g–1 in water may be detected. For an N-P detector the limits of detection are 0.05 µg g–1 in sweet potatoes or soils and 0.005 µg g–1 in water. Recoveries ranged from 80–90% from these matrices at fortification levels of 0.08–0.5 µg g–1. The choice of using either the methyl or the ethyl derivative is an added advantage.