Effect of phosphine dose on sorption in wheat

BACKGROUND: In spite of the extensive use of phosphine fumigation around the world to control insects in stored grain, and the knowledge that grain sorbs phosphine, the effect of concentration on sorption has not been quantified. A laboratory study was undertaken, therefore, to investigate the effect of phosphine dose on sorption in wheat. Wheat was added to glass flasks to achieve filling ratios of 0.25-0.95, and the flasks were sealed and injected with phosphine at 0.1-1.5 mg L(-1) based on flask volume. Phosphine concentration was monitored for 8 days at 25 degrees C and 55% RH. RESULTS: When sorption occurred, phosphine concentration declined with time and was approximately first order, i.e. the data fitted an exponential decay equation. Percentage sorption per day was directly proportional to filling ratio, and was negatively correlated with dose for any given filling ratio. Based on the results, a tenfold increase in dose would result in a halving of the sorption constant and the percentage daily loss. Wheat was less sorptive if it was fumigated for a second time. CONCLUSIONS: The results have implications for the use of phosphine for control of insects in stored wheat. This study shows that dose is a factor that must be considered when trying to understand the impact of sorption on phosphine concentration, and that there appears to be a limit to the capacity of wheat to sorb phosphine.     

Changes in phosphine sorption in wheat after storage at two temperatures

BACKGROUND: Wheat can be stored for many months before being fumigated with phosphine to kill insects, so a study was undertaken to investigate whether the sorptive capacity of wheat changes as it ages. Wheat was stored at 15 or 25 °C and 55% RH for up to 5.5 months, and samples were fumigated at intervals to determine sorption. Sealed glass flasks (95% full) were injected with 1.5 mg L^?1 of phosphine based on flask volume. Concentrations were monitored for 11 days beginning 2 h after injection. Some wheat samples were refumigated after a period of ventilation. Several fumigations of wheat were conducted to determine the pattern of sorption during the first 24 h. RESULTS: Phosphine concentration declined exponentially with time from 2 h after injection. Rate of sorption decreased with time spent in storage at either 15 or 25 °C and 55% RH. Rate of sorption tended to be lower when wheat was refumigated, but this could be explained by time in storage rather than by refumigation per se. The data from the 24 h fumigations did not fit a simple exponential decay equation. Instead, there was a rapid decline in the first hour, with phosphine concentration falling much more slowly thereafter. CONCLUSIONS: The results have implications for phosphine fumigation of insects in stored wheat. Both the time wheat has spent in storage and the temperature at which it has been stored are factors that must be considered when trying to understand the impact of sorption on phosphine concentrations in commercial fumigations. Copyright © The state of Queensland (through the Department of Employment, Economic Development and Innovation) 2009. Published by John Wiley and Sons, Ltd.     

Establishing targeted control of creeping perennial weeds with soil‐active chemical injections: Assessment of subterranean bud responses in contact

Increased infestation of aggressive creeping perennial weeds is a significant problem in urban vegetation management programs. These weeds produce vigorous biomass and extensive underground networks of either rhizomes or creeping roots that easily regrow from numerous buds. Foliar application of proper systemic herbicides has been a most effective way to suppress regrowth from underground creeping organs; however, killing the mature plants has disadvantages from aesthetic, economic, and ecological viewpoints. Therefore, we intended to test the possibility of soil‐injection of soil‐active herbicides for effective control of the perennial weeds which develop underground network systems. A pot experiment using combinations of seven species (seven rhizomatous and two having creeping roots) and five chemicals (four herbicides and a plant growth regulator) was conducted to assess whether and how chemicals diffused in soil affect the sprout and growth of buds on creeping organs. All the tested herbicides completely inhibited bud sprouting in one and more species when applied at median or high rates, while most of the flurprimidol‐applied segments sprouted but shoot elongation was significantly reduced. Characteristics of each herbicide were also reflected in the selectivity and features of new outgrowth. The results indicated that chemicals existing in soil were undoubtedly absorbed and affected bud activities. It is concluded that soil injection that delivers the probable soil‐active chemicals to subterranean creeping systems could be a promising technology for controlling noxious creeping perennials.     

小麦玉米轮作区不同用药方式防治灰飞虱及玉米粗缩病的研究

通过小麦用药、小麦和玉米均用药、玉米用药 3种不同用药方式防治灰飞虱和玉米粗缩病的试验 (各用药方式之间差异达极显著水平 )表明 ,在小麦玉米轮作区 ,小麦和玉米田均用药是最佳的防治措施。     

Integrated Control of Heterodera avenae1

Cereal cyst nematode is a major pathogen in southern Australia costing $40 to $80 million in lost production each year. Our research has shown that three chemicals applied with the seed in the drill row, viz. Counter (terbufos) granules, Vydate (oxamyl) as a seed dressing and Nemadi (ethylene dibromide), reduced Heterodera avenae damage and gave yield increases which are economical in the Australian wheat farming system. A plant assay of soil has been developed to assess potential damage by H. avenae before employing chemical control. Wheat yields 2 years after growing H. avenae-resistant Festiguay wheat were 0.4 to 1 t/ha higher than after other cultivars. Rotations with legumes alternating with wheat reduced damage from H. avenae. Wheat sown without cultivation (minimum tillage) resulted in less root damage from H. avenae and higher yields than when sown into cultivated soil.     

Identification of a Chlorosis-Inducing Toxin from Pyrenophora tritici-repentis and the Chromosomal Location of an Insensitivity Locus in Wheat

ABSTRACT Culture filtrate from Pyrenophora tritici-repentis race 1 isolate 78-62 contained a genotype-specific toxin which elicited extensive chlorosis on sensitive wheat genotypes. This toxin was partially purified using gel filtration, ion exchange, and reversed-phase chromatography. The chlorosis toxin was found to be a polar, nonionic, low-molecular-weight molecule. Wheat genotypes infiltrated with crude culture filtrate and partially purified chlorosis toxin exhibited the same chlorotic symptoms seen with conidial inoculations of isolate 78-62. All tested wheat genotypes that exhibited extensive chlorosis to the toxin also exhibited extensive chlorosis to conidial inoculations, and all wheat genotypes insensitive to the toxin did not exhibit extensive chlorosis to conidial inoculations. The recombinant inbred population derived from the cross W-7984 x Opata 85 segregated for chlorosis induction from infiltration with partially purified chlorosis toxin from isolate 78-62. The locus identified by the marker XGli1, associated with resistance to conidial inoculations from race 1 isolates Pti2 and 78-62 and race 3 isolate D308, also was associated with insensitivity to infiltration of crude culture filtrate and partially purified chlorosis toxin. The marker XGli1, located on the short arm of chromosome 1A, is linked to the insensitivity locus within 5.7 cM. We propose that this chlorosis toxin be designated Ptr ToxC.     

烯丙异噻唑对水稻叶片中NAA、ABA含量的影响与稻瘟病抗性的关系

经过１０余年小麦白粉病综合治理系统研究,摸清了东北春麦区小麦白粉病初菌源来源及侵染循环规律,建立了准确度达８６％以上的预测小麦白粉病发生与流行的预测式,明确了东北春麦区小麦白粉病菌的小种种群构成及毒力频率。     

The effect of soil moisture content on the sorption of five sterol biosynthesis inhibiting fungicides as a function of their physicochemical properties

We investigated the sorption of five widely used sterol biosynthesis inhibitor fungicides (SBIs: flusilazole, propiconazole, epoxiconazole, fenpropimorph and prochloraz) on a loam soil to assess availability of the SBI residues that are usually left in soil after crop treatments. We focused particularly on the soil moisture content effect, which is poorly documented and is difficult to investigate under realistic conditions. SBI sorption was determined (using diuron as a reference) at two soil moisture contents (26.1% and 46.6% w/w) over a period of 3 weeks using a direct soil solution sampling method. After 24 h of contact, <1% of each applied fungicide was recovered in the soil solution. Despite their low availability in the liquid phase, long‐term sorption was observed for all the compounds, reducing concentrations in the soil solution and doubling the value of the partition coefficient. Significant effects of soil moisture on long‐term sorption were observed, depending on the properties of the chemicals and the sorption mechanisms. Wershaw's humus model (humic substances have a membrane‐like structure) was adapted to fit our observations. Low soil moisture content is assumed to modify the structure of humic substances and to generate hydrophobic surfaces, which favour sorption of hydrophobic fungicides (flusilazole, propiconazole and epoxiconazole). This effect is likely to decrease with the increase in the hydrophobic character of non‐ionic pesticides. It becomes adverse for the more hydrophilic compounds (diuron), which are more sorbed at high soil moisture content due to their higher affinity for hydrophilic regions of humus and to diffusion. Soil moisture effects are more complex when compounds are likely to be protonated in soil. Weakly basic compounds (prochloraz) may partition rapidly into the liquid‐like interior of humus at low soil moisture content but increased diffusion at high soil moisture content may cause additional sorption by ion exchange at colloid surfaces. Strongly basic compounds (fenpropimorph) may essentially adsorb due to ionic interactions with colloids, and their sorption is enhanced at high soil moisture content due to diffusion. Consequences for environmental fate and biological activity of pesticides are briefly discussed. © 2000 Society of Chemical Industry     

The pesticide module of the Root Zone Water Quality Model (RZWQM): testing and sensitivity analysis of selected algorithms for pesticide fate and surface runoff

The Root Zone Water Quality Model (RZWQM) is a one-dimensional, numerical model for simulating water movement and chemical transport under a variety of management and weather scenarios at the field scale. The pesticide module of RZWQM includes detailed algorithms that describe the complex interactions between pesticides and the environment. We have simulated a range of situations with RZWQM, including foliar interception and washoff of a multiply applied insecticide (chlorpyrifos) to growing corn, and herbicides (alachlor, atrazine, flumetsulam) with pH-dependent soil sorption, to examine whether the model appears to generate reasonable results. The model was also tested using chlorpyrifos and flumetsulam for the sensitivity of its predictions of chemical fate and water and pesticide runoff to various input parameters. The model appears to generate reasonable representations of the fate and partitioning of surface- and foliar-applied chemicals, and the sorption of weakly acidic or basic pesticides, processes that are becoming increasingly important for describing adequately the environmental behavior of newer pesticides. However, the kinetic sorption algorithms for charged pesticides appear to be faulty. Of the 29 parameters and variables analyzed, chlorpyrifos half-life, the Freundlich adsorption exponent, the fraction of kinetic sorption sites, air temperature, soil bulk density, soil-water content at 33 kPa suction head and rainfall were most sensitive for predictions of chlorpyrifos residues in soil. The latter three inputs and the saturated hydraulic conductivity of the soil and surface crusts were most sensitive for predictions of surface water runoff and water-phase loss of chlorpyrifos. In addition, predictions of flumetsulam (a weak acid) runoff and dynamics in soil were sensitive to the Freundlich equilibrium adsorption constant, soil pH and its dissociation coefficient.     

2%三唑醇·戊唑醇种衣剂对小麦纹枯病菌麦角甾醇含量的影响

分别用三唑醇原粉、戊唑醇原粉和2%三·戊种衣剂(1.2%三唑醇＋0.8%戊唑醇,质量分数)处理小麦纹枯病菌Rhizoctonia cerealis后,采用皂化处理样品法提取并用高效液相色谱法测定其体内的麦角甾醇含量。结果表明,随着药剂浓度升高,麦角甾醇的含量逐渐降低,说明药剂浓度越高抑制作用越强。当药剂有效成分浓度为5.0 μg/mL时,7 d后对病菌的抑制率分别为60.4％、63.8％、63.8%。药剂处理浓度相同时,菌丝麦角甾醇的含量高低顺序为:三唑醇处理＞三·戊种衣剂处理＞戊唑醇处理。说明药剂处理菌丝后其体内麦角甾醇的合成受到抑制,从而导致其含量显著降低。     

Adsorption of glyphosate by soils

The adsorption of glyphosate in a slurry system by 9 soils was correlated with an arbitrary single point inorganic phosphate sorption index which gave a measure of unoccupied phosphate sorption capacity, but not with total phosphate sorption capacity at pH 2.6, the level of iron and aluminium soluble in Tamm's acid oxalate or with clay content, organic matter content or pH. It is concluded that inorganic phosphate excludes glyphosate from sorption sites. The extent of adsorption was higher than, though of the same order as, that of diuron though the two are not related. From consideration of the results of previous experiments with plants grown in culture solution it is suggested that the low phytotoxicity of glyphosate applied to the soil is not due simply to high adsorption. Rather it is the result of a combination of moderate adsorption and the low intrinsic activity of this compound when made available to the root system.     

Effects of nonionic surfactants on cuticular sorption and penetration of 2, 4-dichlorophenoxy acetic acid

Surfactants increase the uptake of some foliar-applied chemicals to a greater extent than would be expected from their effects on surface tension and spray coverage. This study of the uptake of 2, 4-D [(2, 4-dichlorophenoxy)acetic acid] evaluated the effect of surfactants on penetration through and sorption by isolated cuticles of apple leaves. [¹⁴C]2, 4-D was placed in glass chambers affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been treated with various surfactants. The same surfactant pretreatments were included in sorption studies in which cuticle segments were immersed in [¹⁴C]2, 4-D for 96 h. Quantities of 2, 4-D passing through or sorbed by the cuticle were determined. Similar experiments were conducted with unaltered cuticles and cuticles dewaxed with chloroform. The hydrophile-lipophile balance (HLB) of polyethylene-glycol-based surfactants was inversely related to the sorption of those surfactants by the cuticles and penetration of 2, 4-D. Sorption of 2, 4-D by apple leaf cuticles was unaffected by surfactant pretreatment. Dewaxed cuticle membranes showed a similar response to 2, 4-D penetration and sorption following the surfactant pretreatment.     

Sorption of sulfuryl fluoride by food commodities

BACKGROUND: The use of sulfuryl fluoride, a structural fumigant for termite and woodborer control, has recently been expanded to treating stored food commodities and food facilities. There is, however, a lack of data on the sorption of sulfuryl fluoride by food commodities. Knowledge about sorption is important in the context of effective treatment and residues.RESULTS: When sulfuryl fluoride was applied at a dose of 50 g m(-3) to various food commodities (total 68) with 300 g per replicate in 0.75 L gas wash bottles (fumigation chambers) at 25 +/- 1 degrees C, in most cases (81%) the gas concentrations in the free space of the commodities exceeded 50 g m(-3) (range 51-80 g m(-3)) at the end of 24 h exposure. In chambers without the substrate, an average concentration of 49.7 g m(-3) was recorded. About 54% of the commodities showed low-level ( < or = 25%) sorption of sulfuryl fluoride, 34% showed medium-level (26-50%) sorption and only 12% were highly sorptive (>50%). The latter include white oats (terminal gas concentration 17.8 g m(-3)), some of the decorticated split pulses (24.0-29.3 g m(-3)), chickpea flour (26.3 g m(-3)), dried ginger (29.0 g m(-3)), refined wheat flour (30.3 g m(-3)) and coriander powder (40.5 g m(-3)). In unfumigated control commodities, owing to interfering volatiles, Fumiscope readings in the range 0-13 were noted.CONCLUSION: Sulfuryl fluoride has the advantage of a low or moderate level of sorption with the majority of the food commodities.     

Modelling the kinetics of ethyl formate sorption by wheat using batch experiments

BACKGROUND: Ethyl formate formulations are being considered to replace methyl bromide for fast grain disinfestation. Grain adsorbs ethyl formate rapidly, which can result in inadequate fumigation concentrations and unacceptable grain residues. A model of ethyl formate sorption kinetics will enable fumigation approaches to be determined that meet disinfestation and food safety requirements. RESULTS: This paper identifies all mass transport processes involved in ethyl formate sorption by wheat from published and experimental evidence. The model accounts for reaction losses of ethyl formate in air and grain using first‐order kinetics, transport in the gas and solid phases with linear mass transfer coefficients and uses a linear partition relationship representation of sorption equilibrium. Batch experimental data were measured to determine model coefficients. Novel gaseous breakdown data for ethyl formate in air were measured, and first‐order kinetics was demonstrated, although the specific reactions involved were not identified. CONCLUSION: The model predicts air and grain fumigant concentrations relevant for grain disinfestation and food residue contamination successfully. The form of the model should be applicable to all fumigant–grain systems, as it accounts for the diffusion and reaction influences known to occur with all modern fumigants under concentration and exposure conditions relevant to industry. Copyright © 2009 CSIRO, Australia. Published by John Wiley & Sons, Ltd.     

水稻纹枯病的"后效应"观察

通过单独或混合施用不同浓度的两种药剂,造成水稻纹枯病不同发生程度,继而观察接茬小麦纹枯病病情,结果进一步证明,水稻纹枯病与接茬小麦纹枯病极显著正相关,其后效应明显。指出在实行水稻—小麦种植方式地区,要注意水稻与小麦纹枯病的交叉感染。     

Adsorption-desorption of metalaxyl as affecting dissipation and leaching in soils: role of mineral and organic components

Adsorption-desorption studies of metalaxyl in fifteen agricultural soil samples from Southern Portugal and Spain were performed following a batch equilibration method. Very high sorption was observed on a clay soil of high content in altered illite, but, when this soil was excluded from regression analysis, organic matter (OM) was the most important single soil property affecting sorption at low concentrations of metalaxyl. At higher concentrations, no correlation was observed with any soil property. The relevance of OM on sorption was also corroborated by the increase in sorption coefficients when soil OM was increased artificially by the addition of an organic amendment. Sorption studies with the colloidal fraction of selected soils also revealed the importance of mineral surfaces in metalaxyl sorption. Sorption of metalaxyl in most of the soil samples was hysteretic. Selected soil samples were incubated in the dark, sampled periodically and extracted for their fungicide content. Metalaxyl half-lives increased with sorption and OM content of the soil, and were specially high in the amended soil. Leaching studies in hand-packed columns under saturated/unsaturated flow conditions showed an inverse relation between leaching and sorption. Recoveries from the soil columns were close to 80% of the metalaxyl applied, except for the soil which OM was artificially increased, in which recovery was lower and this has been attributed to the much higher irreversibility of metalaxyl sorption in the amended soil.     

Sorption of aged dicamba residues in soil

The effect of aging (residence time in soil) on dicamba (3,6-dichloro-2-methoxybenzoic acid) and a major metabolite, 3,6-dichlorosalicylic acid (3,6-DCSA) sorption was determined in an unamended and a carbon-amended sandy loam and in a silt loam soil. During the incubation, sequential solvent extraction with 0.01 M calcium chloride solution and aqueous acetonitrile + hydrochloric acid was used to determine the solution and sorbed concentrations of dicamba and 3,6-DSCA, and sorption coefficients were calculated. Dicamba was weakly sorbed to soil (Kd < 0.7). In contrast to some other classes of pesticides, sorption of dicamba did not significantly increase with aging, at least not until < 15% of the applied dicamba remained. 3,6-DSCA was strongly sorbed to soil (Kd > 8) and the Kd-a value increased by a factor of 2-6 during a 28-day aging period. Addition of a carbon source to the soil had minimal effect on the strength of sorption of aged dicamba. However, it did appear to decrease 3,6-DSCA availability to soil micro-organisms; once formed 3,6-DSCA was not further mineralized. While it appears that sorption can be well characterized for weakly sorbed pesticides using the batch equilibration method with freshly treated soils, this procedure may not be adequate for more strongly sorbed pesticides and their degradates.     

湖北省小麦条锈菌越夏的初步研究

 调查试验结果表明,在湖北省西北部包括郧阳和神农架两地区,在海拨1700-2050公尺的高山地带,七、八月份最热一旬平均气温,18.7~19.7℃,虽条锈菌可越夏,但很困难.广泛调查残余的绿色小麦、黑麦植株和自生麦苗都没有发现条锈病,不能为本省广大冬麦秋苗提供越夏菌源。调查了十多种禾本科杂草,其中仅在甜茅(Glyceria sp.)上发现很少条锈病夏孢子堆,室内接种可侵染小麦,但在条锈病流行中没有发现其作用.     

Sorption/desorption behaviour of sulfonylurea herbicides as affected by the addition of fresh and composted olive cake to soil

The olive industry generates residues which can be applied as amendments to soils in their original form (olive cake) or after composting or vermicomposting processes. The addition, fresh or incubated, of these amendments to soil and of their different organic fractions was studied in relation to the sorption/desorption of three sulfonylurea herbicides, bensulfuron‐methyl, chlorsulfuron and prosulfuron. Herbicide sorption was low or very low, slightly promoted by the addition of the agricultural by‐products, especially olive cake, and mainly affected by pH of the soil solution, with the organic carbon content having no significant effect on herbicide retention. Desorption was only reduced when fresh olive cake was added. The incubation of soil and amendments for 3 months did not modify herbicide sorption, but made desorption reversible except for olive cake. The transformation of the organic matter of the amendments due to humification and maturity processes are likely to be responsible for this behaviour. Different organic fractions were removed to assess the influence of each fraction on sulfonylurea sorption. Only the removal of all studied organic fractions increased herbicide sorption, revealing the role of humin and mineral fractions in this process. Therefore, the use of organic amendments is not useful for reducing the risk of movement of ionisable molecules in soil.     

Measured and simulated behaviour of aldicarb and its oxidation products in fallow soils

Aldicarb and its oxidation product aldoxycarb (aldicarb sulphone) were applied separately to columns of fallow, sandy loam soils under field conditions. The breakdown and movement of these compounds were monitored, as was the behaviour of aldicarb sulphoxide and aldoxycarb formed by oxidation of the applied aldicarb. The behaviour of these compounds was simulated by a computer model using laboratory data for adsorption and rates of degradation in soil. The model simulated the observed behaviour reasonably well, although redistribution of chemicals was often more rapid than predicted. Production of aldoxycarb from the sulphoxide was less in the field than was expected from the laboratory incubations. Accumulation of chemicals near the soil surface in dry periods was overestimated, indicating that the processes occurring under these conditions are not well described by the model. About 4 months after application, only aldoxycarb, in small amounts, remained in the soils.