皖江圩区春玉米田杂草发生规律及化学除草技术研究

研究了皖江圩区春玉米田杂草的主要种类、群落组成、发生规律和化学除草技术.在19科57种杂草中,主要杂草有10种,其中马唐、牛筋草、旱稗、香附子、铁苋菜构成优势种;主要杂草群落有6种.玉米在生育期内有2个出草高峰,分别出现在播后55和95天.研究表明,乙草胺、草杀胺、莠去津均具有良好的除草效果,是该区适宜的玉米田除草剂品种.最后对该区春玉米田杂草防除提出了建议.     

Effect of certain herbicides on growth and pathogenicity of take-all fungus on wheat (Triticum aestivum L.)

Summary The effects of Spray Seed (diquat + paraquat), Roundup (glyphosate), Banvel-D (dicamba), Treflan (trifluralin), Glean (chlorsulfuron) and Dacthal (chlorthal dimethyl) at concentrations of 0–500 ppm product on the vegetative growth, vigour and pathogenicity of Gaeumannomyces graminis var. tritici (Ggt) on wheat were examined. All herbicides with the exception of dicamba and chlorsulfuron inhibited fungal growth on potato dextrose agar (PDA) at concentrations 10–500-fold of rates recommended for use in the field. The vegetative growth of the pathogen growing out of straw colonized on PDA supplemented with 100 ppm diquat + paraquat or glyphosate was reduced by 47.4% and 42.4%, respectively. When portions of these colonies were subcultured onto unamended PDA, their growth and the pathogenicity of straw pieces colonized by these subcultures were found to be unaltered. Straw colonized by Ggt on agar amended with concentrations of diquat + paraquat or at all concentrations of glyphosate produced less root disease in wheat seedlings in comparison to those colonized on unamended agar. It is proposed that the reduced pathogenicity of inocula prepared on agar amended with these two herbicides is due to poor colonization by the pathogen of straw on these media, and that a similar effect on saprophytic colonization in the field could lead to a reduction in the field inocula of the pathogen.     

The costs of alternative methods of managing ‘set-aside’ land within the European Community

With low annual income from compensatory payments in the European Community set-aside scheme, the cost of managing such land is critical. The scheme was designed to temporarily remove land from production of arable crops that are in surplus. Based upon field experiments in the UK, over 2 years and 5 years, respectively, cultivations and herbicides are shown to be more expensive than mowing for vegetation control on set-aside land. They are highly effective but until recently have been discouraged by The Ministry of Agriculture, Fisheries and Food on environmental grounds. Mowing has been shown to cost less even when a final application of herbicide is included. In the 5 year set-aside scheme mowing does not produce serious agronomic problems for future crops. It is therefore recommended as the most appropriate management method. Hay-making on set-aside land is unlikely to be economically viable.     

Interaction of a Foliar Application of Iron HEDTA and Three Postemergence Broadleaf Herbicides with Soybeans Stressed from Chlorosis

Abstract

Soybeans stressed from chlorosis are often treated with postemergence herbicides to coincide with susceptibility of control of weed seedlings. Three postemergence herbicides, acifluorfen, imazamox, and lactofen were applied to chlorosis stressed soybeans with and without iron HEDTA. At one location, iron amendment resulted in lower yields with acifluorfen and lactofen. Yields were higher with iron amendment in the imazamox treatment, but lower crop injury and poorer weed control was also observed, suggesting that iron amendment antagonized imazamox. Iron amendment did not reduce visual symptoms of chlorosis, herbicide injury, nor did it result in yield increase at any location. Application of iron HEDTA with these herbicides would not be recommended for chlorosis relief.     

Mineralization of C-atrazine in an entic haplustoll as affected by selected winter weed control strategies

The effect of winter weed control (WWC) management on ¹⁴C-atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine) mineralization was investigated in an Entic Haplustoll in Argentina. Three WWC managements were selected: Chemical Fallow (CF) and Cereal Cover Crop (CCC), both under no-tillage, and Reduced Tillage (RT) with chisel and moldboard plow. Soil was sampled at two depths: 0–5 and 5–10 cm, to evaluate the soil stratification induced by the tillage system. To distinguish differences in atrazine degradation in soils with and without previous history of atrazine application two crop sequences were selected: continuous soybean [Glycine max L., Merr.] (CS) without previous atrazine exposure, and soybean–maize (Zea mays L.) rotation (SM) with atrazine application every winter and in alternate springs. The release of ¹⁴C-CO₂ during laboratory incubations of soils treated with ring labelled ¹⁴C-atrazine was determined. Soil organic matter (SOM) distribution was determined with depth and among three soil size fractions: 200–2000 μm, 50–200 μm and <50 μm. Previous atrazine application enhanced atrazine degrading microorganims. Atrazine mineralization was influenced by both WWC management and the tillage system. Chemical fallow showed the highest atrazine mineralization in the two crop sequences. Depth stratification in atrazine degradation was observed in the two WWC treatments under the no-tillage. Depth stratification in the content of soil organic C and relative accumulation of organic C in coarsest fractions (200–2000 and 50–200 μm) were observed mainly in no-till systems. Depth stratification of atrazine degrading activity was mainly correlated to the stratification of fresh organic matter associated with the coarsest fractions (200–2000 μm). Atrazine persistence in soil is strongly affected by soil use and management, which can lead to safe atrazine use through selection of appropriate agricultural practices.     

几种除草剂在直播芹菜田的应用技术研究

为筛选适合芹菜直播田使用的除草剂,进行了3种除草剂在直播芹菜上的田间药效试验。试验结果表明．播种当天施药,各药剂的株防效均较好,但对芹菜成苗影响较大;播前3d施药,48％氟乐灵乳油表现出较好的安全性和除草效果,其中,120mL／667m2处理的成苗率接达96．42％,僵苗率仅0．04％,对禾本科杂草的株防效高达98．51％,对双子叶杂草的株防效接近70％;播前7d施药,3种药剂均表现出良好的安全性和除草效果,仅96％精一异丙甲草胺乳油各处理的安全性相对稍差。因此,直播芹菜田应用除草剂时,在播前3—7d用药较为合适。     

Using earthworm avoidance behaviour to assess the toxicity of formulated herbicides and their active ingredients on natural soils

Background, aim, and scope

Soil quality has been threatened by intensive agricultural practises, namely those relying on the application of pesticides, such as herbicides. Among the non-target terrestrial organisms exposed to such scenarios, earthworms are key ecological receptors widely used in ecotoxicological studies. As such, this work aims to assess the effects of two herbicide active ingredients (a.i.)—sulcotrione and penoxsulam—and their respective commercial formulations—MIKADO® and VIPER® (referred as Mikado and Viper)—on the avoidance behaviour of Eisenia andrei. In an attempt to enhance the ecological relevance of the generated toxicity data, the avoidance tests were run with standard (LUFA 2.2; L) and natural soils (from corn and rice fields), as long as their habitat function did not constrain the earthworm behaviour.

Methodology

Earthworms were bred in the lab before test conductance. The natural soils used as substrates were collected before the cropping season on corn (C) and rice (R) fields, which are integrated in a wide area exploited for agriculture. Their physico-chemical characterization evolved the determination of pH (H₂O, KCl), conductivity, organic matter (OM) and clay/silt contents, and water-holding capacity (WHC). The avoidance tests intended to ascertain (1) the random distribution of earthworms in the natural soils C and R (dual-control tests), (2) the habitat function of natural soils against each other and against L soil, (3) the effect of active ingredients and formulated herbicides on E. andrei behaviour. Avoidance tests with the a.i.s were only performed in L soil. Data evaluation followed ISO (2005) guidelines.

Results

C and R soils presented higher OM (5.1% and 4.5%, respectively) and clay/silt (53.3 and 43.1, respectively) contents and WHC (107.2 and 109.9%, respectively) than L soil (4.1, 21.4 and 48.0%, correspondingly). Earthworms distributed randomly in dual-control tests, but preferred R soil significantly, relative to L or C soils. The LOEC and EC₅₀ values calculated for sulcotrione (>1,000.0 and 1,263.3 mg a.i. kg^-1, respectively) and Mikado (1,012.8 and 1,301.3 mg a.i. kg^-1, respectively) were much higher than those calculated for penoxsulam (100 and 80.6 mg a.i. kg^-1, respectively) or Viper (52.7 and 51.5 mg a.i. kg^-1, respectively), when L soil was used as substrate. Moreover, the habitat function of L soil contaminated with the formulated herbicide Viper was more constrained relative to that of the a.i. penoxsulam. Viper induced higher % avoidance on E. andrei exposed to the contaminated L soil compared to that under the R soil.

Discussion

The response of earthworms to R (attraction) and C (avoidance) soils could be related, not only to the quantity of OM content, but also to the quality of organic and inorganic fractions of soil, beyond other intrinsic properties of soils. Both Mikado and sulcotrione impacted the behaviour of E. andrei only slightly. This endpoint was more affected under penoxsulam or Viper exposures on L soil, being the latter-formulated product even more repellent for E. andrei than the a.i. The effect of adjuvants added to the commercial formulation of Viper, may have increased the toxicity of the a.i. Thereby, our results reinforce the need for a careful assessment of the impacts of formulated products. Furthermore, since there was a reduction in earthworm % avoidance under Viper exposures on the natural soil R, it was possible that pesticide bioavailability had been reduced by its sorption to OM and clay mineral sorption sites.

Conclusions

Though the standard L soil should be used for reproducibility and comparison means, other natural soils should be added to the assessment of chemicals, for sake of ecological relevance. Both herbicides induced avoidance behaviour on E. andrei, albeit stronger effects were denoted by penoxsulam and its respective formulated product, Viper. Overall, avoidance tests provided a sensitive, valuable and feasible response either to compare the habitat function of different standard and agricultural natural soils or to test the effect of herbicides.

Recommendations and perspectives

An effort should be made to enlarge the terrestrial ecotoxicological database as a way to fulfil the huge lack of information available for this ecosystem. In this context, additional research congregating a potential linkage between physiological activities sustaining the regular metabolism of earthworms and their avoidance behaviour or even their reproductive effects would be welcomed, especially in what regards formulated pesticides. Such approach would provide a robust and comprehensive understanding of chemical effects. Furthermore, it is encouraged that natural soils should be used to improve the reliability of chemical testing.     

Effect of Select Surfactants on Activities of Soil Enzymes Involved in Nutrient Cycling

Experiments were conducted to investigate the impact of commonly used herbicides and surfactants on the activity of acid phosphatase, β-glucosidase, arylsulfatase, β-glucosaminidase, and dehydrogenase, using two soils (silt loam and silty clay loam) from Mid-Missouri, USA. The surfactants used in this study were alkylphenol ethoxylate + alcohol ethoxylate (ACTIVATOR 90), polyethoxylate (Agri-Dex®) and a blend of ammonium sulfate, drift reduction/deposition polymers, and an antifoam agent (THRUST®). The herbicides were glyphosate, atrazine, and bentazon. Surfactants and herbicides were applied to soils at the label rate, either alone or combined. In general, enzyme activity was enhanced more in silt loam soil than in silty clay loam soil. Acid phosphatase displayed the greatest amount of enzymatic activity within soils; dehydrogenase displayed the most inhibition, whilst β-glucosidase and β-glucosaminidase fluctuated based on treatment. ACTIVATOR 90 appeared to have the most inhibitory effect on enzymatic activity within soils compared to the control.     

Differential influence of herbicide treatments on activity and kinetic parameters of C4 photosynthetic enzymes from Zea mays

The recommended field dose of rimsulfuron, imazethapyr, alachlor, atrazine or fluometuron differentially reduced shoot fresh and dry weight of 10-day-old maize seedlings as well as leaf protein content during the following 12 days. These reductions seemed consistent during the whole period with fluometuron, atrazine and alachlor but appeared to be nullified by the 5th day of treatment with rimsulfuron and imazethapyr. On the other hand, all herbicides mostly provoked significant inhibitions in specific activities of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), malate dehydrogenase (MDH, EC 1.1.1.82), pyruvate phosphate dikinase (PPDK, EC 2.7.9.1) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in leaves during the first 2 days. Thereafter, the inhibition was recovered in samples treated with rimsulfuron and imazethapyr, leveled off with alachlor but consistently augmented with atrazine and fluometuron. The kinetic characterization showed that rimsulfuron or imazethapyr unchanged V_max of all enzymes in vitro, however, V_max of PEPC, PPDK and Rubisco were decreased in vivo. Nevertheless, atrazine or fluometuron substantially reduced V_max of all enzymes while alachlor showed a reduction in this value of PEPC, MDH and Rubisco. Thus atrazine, fluometuron and, to a lower extent, alachlor reduced concentrations of all enzymes as well as rimsulfuron and imazethapyr for only Rubisco. On the contrary, K_m values of all enzymes were progressively increased by all herbicides indicating that the different herbicides altered the structural integrity of all enzymes. These findings conclude that rimsulfuron or imazethapyr competitively inhibited MDH but revealed mixed inhibition to PEPC, PPDK and Rubisco. Atrazine or fluometuron revealed mixed inhibitions to all enzymes whereas alachlor seemed to be either a competitive inhibitor to PPDK or a mixed inhibitor to PEPC, MDH and Rubisco.