Field Application Rates Research Articles

Supplemental Fumigant Placement Improves Root Knot and Fusarium Wilt Management for Tomatoes Produced on a Raised-Bed Plasticulture System in Florida's Myakka Fine Sand.

Fresh-market tomatoes are produced on a raised-bed plasticulture system that relies heavily on soil-applied preplant fumigants for the management of soilborne pathogens, nematodes, and weeds. Since the transition from methyl bromide to alternative fumigants, growers have experienced a resurgence of several soilborne pests and pathogens, including root-knot nematode caused by Meloidogyne spp. and Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici race 3. This resurgence is attributed to the inability of the alternative fumigants to effectively disperse through the soil in the same manner as methyl bromide. Two supplemental fumigation strategies, the application of chloropicrin (PIC) below bed edges (herein "supplemental PIC") and broadcast deep-shank applications of 1,3-dichloropropene (1,3-D), were evaluated in conjunction with standard raised-bed applications of Pic-Clor 60, Pic-Clor 80, and Pic 100 covered with a virtually impermeable film or a totally impermeable film. Large-plot replicated studies were conducted in two separate commercial tomato fields with a history of production losses caused by root-knot nematode and Fusarium wilt. Deep-shank 1,3-D applications significantly reduced the recovery of root-knot and total parasitic nematodes across field sites before the preparation of raised beds. Both supplemental PIC and deep-shank 1,3-D reduced root-knot galling and Fusarium wilt incidence, but the latter supplemental treatment statistically had the greatest impact. Fumigant applied within raised beds or plastic film had no significant effect on root-knot galling or Fusarium wilt. Although both supplemental fumigation strategies had a significant effect on pest and disease pressure, neither statistically improved tomato yields based on small subplot harvests. Controlled laboratory experiments confirmed the fungicidal activity of 1,3-D against F. oxysporum f. sp. lycopersici, with 75, 90, 95, and 99% lethal doses corresponding to estimated field application rates of 56.1, 93.5, 121.6, and 184.7 liters/ha, respectively. The results demonstrate how fumigant placement can improve pest and disease control activity with current fumigant alternatives to methyl bromide and further support the broader pesticidal activity of some chemical fumigants.

N2O and N2 emission characteristics from maize and greenhouse vegetable soils in Northern China

To explore N2O and N2 emissions from upland soils after nitrogen fertilizer application, a 60-day aerobic incubation experiment (25 ℃,80% water-filled pore space) using the 15N tracing method was conducted to quantify the N transformation, N2O and N2 emissions from maize soils from four sites (Harbin, Shenyang, Luancheng and Shouguang) and vegetable soils from two sites (Shen-yang and Shouguang), with urea being applied at 167 mg N·kg-1 to simulate the field application rate of 200 kg N·hm-2. The results showed that for the four sites with maize soils, the cumulative emission of N2O was in the order of Shouguang (20 mg N·kg-1) > Luancheng (14 mg N·kg-1) > Shenyang (5 mg N·kg-1) > Harbin (0.5 mg N·kg-1) and the cumulative N2 emission was in the order of Luancheng (176 mg N·kg-1) > Shenyang (106 mg N·kg-1) > Shouguang (75 mg N·kg-1) > Harbin (12 mg N·kg-1). For vegetable soils, the cumulative N2O emission of Shouguang (21 mg N·kg-1) was 10 times of that of Shenyang (2 mg N·kg-1), but without differences in cumulative N2 emissions (28 and 24 mg N·kg-1, respectively). The N2O/(N2O+N2) of the six soils ranged from 5% to 40%. The N2O/(N2O+N2) of the two soils from Shouguang (30%-40%) was significantly higher than other four soils (1%-10%). Soil bulk N pool contributes to 56% of total N2O emission and 61% of total N2 emission, which was higher than the contribution of fertilizer. The cumulative N2O emission was positively correlated with soil background pH, which indicated that soil background pH might be an important factor regulating N2O and N2 emission from upland soils. In the alkaline soil regions of North China Plain (such as Luancheng and Shouguang), mea-sures to reduce soil pH might have great impact on reducing N gaseous emission.

Environmental and economic trade-offs of using composted or stockpiled manure as partial substitute for synthetic fertilizer.

Manure generated from livestock production could represent an important source of plant nutrients in substitution of synthetic fertilizer. To evaluate the sustainability of partially substituting synthetic fertilizer with soil organic amendments (OAs) in horticulture, an economic and greenhouse gas (GHG) budget was developed. The boundary for analysis included manure processing (stockpiling vs. composting) and transport and spreading of manure and compost (feedlot and chicken) in intensively cultivated horticultural fields. The OA field application rates were calculated based on the nitrogen supplied by OAs. The GHG budget based on directly measured emissions indicates that the application of composted manure, in combination with reduced fertilizer rate, was always superior to stockpiled manures. Compost treatments showed from 9 to 90% less GHG emissions than stockpiled manure treatments. However, higher costs associated with the purchase and transport of composted manure (three times higher) generated a greater economic burden compared with stockpiled manure and synthetic fertilizer application. The plant nutrient replacement value of the OAs was considered only for the first year of application, and if long-term nutrient release from OAs is taken into account, additional savings are possible. Because the income from soil carbon sequestration initiatives in response to OA application is unlikely to bridge this financial gap, particularly in the short term, this study proposes that future policy should develop methodologies for avoided GHG emissions from OA application. The combined income from soil carbon sequestration and potentially avoided GHG initiatives could incentivize farmers to adopt OAs as a substitute for synthetic fertilizers, thereby promoting more sustainable farming practices.

Impact of Oxyfluorfen 23.5% EC on Soil Microorganisms Carbon and Nitrogen Transformations

Oxyfluorfen widely using in paddy field and unknowingly polluting the soil. The present study soil microorganism’s carbon and nitrogen transformation test was conducted in loamy sand soil, the experiment conducted as per Organization for Economic Co-operation and Development (OECD) Guideline 216 and 217. The application of oxyfluorfen 23.5% EC applied dose rates T0-Control, T1-100 g a.i/ha (active ingredient/hectare) and T2-1000g a.i/ha soil dry weight. The test concentrations were one and ten times the recommended field application rate. After application of the soil boxes were incubated at 20°C in dark conditions. The soil samples were collected at 0 (within the 6 hours), 7, 14, and 28 days after imposing the treatment. Carbon transformation (short-term respiration) was determined by amended the glucose to soil samples. Short-term respiration was calculated based on oxygen consumption (BOD) during the experiment. Soil nitrification was determined by measuring the NO3- contents of aqueous soil extracts using calibrated ion-sensitive electrodes and the Orion expandable ion analyzer. The deviation in respiration rates and nitrification compared to controls after applying the test item after 28 days 2.8 % and 7.0 % for the; -3.12% and -7.18% for the respiration rates and nitrification respectively T1 and T2 test concentrations. There was no significant variation between the treatment and control samples.

Can N Fertilizer Addition Affect N2O Isotopocule Signatures for Soil N2O Source Partitioning?

Isotopocule signatures of N2O (δ15Nbulk, δ18O and site preference) are useful for discerning soil N2O source, but sometimes, N fertilizer is needed to ensure that there is enough N2O flux for accurate isotopocule measurements. However, whether fertilizer affects these measurements is unknown. This study evaluated a gradient of NH4NO3 addition on N2O productions and isotopocule values in two acidic subtropical soils. The results showed that N2O production rates obviously amplified with increasing NH4NO3 (p < 0.01), although a lower N2O production rate and an increasing extent appeared in forest soil. The δ15Nbulk of N2O produced in forest soil was progressively enriched when more NH4NO3 was added, while becoming more depleted of agricultural soil. Moreover, the N2O site preference (SP) values collectively elevated with increasing NH4NO3 in both soils, indicating that N2O contributions changed. The increased N2O production in agricultural soil was predominantly due to the added NH4NO3 via autotrophic nitrification and fungal denitrification (beyond 50%), which significantly increased with added NH4NO3, whereas soil organic nitrogen contributed most to N2O production in forest soil, probably via heterotrophic nitrification. Lacking the characteristic SP of heterotrophic nitrification, its N2O contribution change cannot be accurately identified yet. Overall, N fertilizer should be applied strictly according to the field application rate or N deposition amount when using isotopocule signatures to estimate soil N2O processes.

Microbial Ecotoxicity of Biochars in Agricultural Soil and Interactions with Linear Alkylbenzene Sulfonates

Large-scale application of biochar on agricultural land offers the prospect of soil improvement and carbon sequestration for climate-change mitigation. However, negative side-effects on the soil microbial ecosystem are poorly understood, notably in relation to the functions of native microbiomes under realistic routes of biochar exposure. Due to divergent properties, different biochars might interact with soil in complex ways. This might result in decreased or increased ecotoxicity from biochar contaminants, such as heavy metals and polycyclic aromatic hydrocarbons (PAHs). Using five biochars produced from straw and wood under contrasting pyrolysis conditions, we traced their ecotoxicological dose-effect using a bioassay for potential ammonia oxidation (PAO), through microorganisms that are sensitive stress indicators. Assays were made after soil/biochar interaction for up to 3 weeks, where straw biochar with the lowest PAH content (&lt;0.5 mg kg−1) showed the most pronounced dose-effects to PAO, corresponding to a 10% effect concentration (EC10) of 4.6% (dry weight biochar/dry weight soil). In comparison, straw biochar with the highest PAH content was least ecotoxic (EC10, 15.2% after 3 weeks) and wood biochars pyrolysed at high temperature (700–725 °C) showed no ecotoxicity to PAO. Interactions between biochars and anionic surfactants, i.e., linear alkylbenzene sulfonates, which are common soil pollutants, resulted in varying effects on PAO, but the effects were small and of limited ecological importance for soil-amended biochars. In conclusion, the results showed that short-term microbial side-effects of biochar in the soil ecosystem were minor at relevant field application rates (such as &lt;30 Mg ha−1 mixed into a plough layer of 20 cm), and that inherent PAHs in biochar were not a likely source of short-term ecotoxicity. However, there were notable differences in the effects eventually observed at very high biochar rates, stressing that individual biochars need specific ecotoxicological assessment before their safe application at large scale in agricultural soils.

Influence of aqueous film forming foams on the solubility and mobilization of non-aqueous phase liquid contaminants in quartz sands

At sites where aqueous film forming foams (AFFFs) are used for fire suppression or training activities, interactions between dissolved foam constituents and organic liquids could alter contaminant migration in the subsurface. In this study, batch reactor and column experiments were conducted to investigate the potential for AFFF solutions to enhance the solubility and mobility of three representative non-aqueous phase liquid (NAPLs), JP-4 jet fuel, trichloroethene (TCE), and tetrachloroethene (PCE). For AFFF concentrations up to 5% wt. (50,000 mg/L), aqueous solubilities of TCE and PCE increased by less than 50%, indicating the absence of micellar solubilization. However, NAPL-water interfacial tensions were reduced to less than 1.5 mN/m and resulted in accumulation of up to 2.25 mg/m2 of AFFF at the NAPL-water interface. To assess the potential for AFFF to mobilize residual (entrapped) NAPL at a field application rate of 3% wt. (30,000 mg/L), columns were packed with two size fractions of Ottawa sands (20–30 mesh and 60–80 mesh) that yielded residual NAPL saturations ranging from 11.7 to 17.6%. Following injection of 3 pore volumes of the 3% wt. AFFF solution, partial mobilization of residual NAPL was observed for PCE, TCE, and JP-4, with saturation reductions of 0.7 to 2% in 20–30 mesh and 0.3% to 1.3% in 60–80 mesh Ottawa sand. The columns were then flushed with an ultralow-IFT surfactant solution consisting of 4% wt. 1:1 Aerosol AY/OT, which resulted in nearly complete mobilization of the remaining residual NAPL. When NAPL desaturation curves were expressed in terms of the total trapping number (NT), the threshold value of NT required for NAPL mobilization by 3% wt. AFFF was approximately 2 × 10−5, consistent with previous studies. These findings demonstrate that AFFF solutions can lead to partial mobilization of residual NAPL, and that the total trapping number concept can be used to predict such behavior a priori. In addition, the observed IFT reductions are sufficient to alter NAPL accumulation and redistribution behavior in the subsurface through enhanced spreading above the water table (e.g., JP-4) or penetration into lower-permeability media (e.g., TCE, PCE).

Arsenic dynamics in paddy soil under traditional manuring practices in Bangladesh.

Fertilization with organic matter (farm yard manure and/or rice straw) is thought to enhance arsenic (As) mobilization into soil porewaters, with subsequent As assimilation by rice roots leading to enhanced translocation to the grain. Here, interlinked experiments (field manuring and soil batch culture) were conducted to find the effect of organic matter at a field application rate practiced in Bangladesh (5t/ha) on As mobilization in soil for paddies impacted by As contaminated groundwater irrigation, a widespread phenomenon in Bangladesh where the experiments were conducted. Total As concentration in a paddy soil (Sonargaon) ranged from 21.9 to 8.1mg/kg down the soil profile and strongly correlated with TOC content. Arsenic, Fe, Mn, and DOC release into soil solution, and As speciation, are intimately linked to OM amendment, soil depth and temporal variation. Organic matter amendments lead to increased mobilization of As into both soil porewaters and standing surface waters. The As speciation in the porewater was dominated by inorganic As (Asi) (arsenite and arsenate), with traces amounts of methylated species (DMAV and MMAV) only being found with OM amendment. It was noted in field trials that OM fertilization greatly enhanced As mobility to surface waters, which may have major implications for the fate of As in paddy agronomic ecosystems.

Peanut Seed Germination and Radicle Development Response to Direct Exposure of Flumioxazin Across Multiple Temperatures

ABSTRACT Peanut injury in the field can occur from flumioxazin applied PRE, but this is associated with plants that have emerged, or are about to, emerge from soil. The direct effect of flumioxazin on peanut seed germination and radicle development has not been evaluated. Therefore, research was conducted to determine peanut seed radicle development response to flumioxazin at different concentrations (0.0, 0.01, 0.10, 1.0 and 10.0 ppb) when tested at multiple temperatures (20, 23, 26, and 29 C) in laboratory experiments on a thermogradient table. Data analysis indicated that flumioxazin concentration was not different from the nontreated control (0.0 ppb) for 0.01, 0.1, and 1.0 ppb for peanut germination. Flumioxazin at 10.0 ppb was different from all other treatments and the nontreated control. However, comparing linear regression models for each flumioxazin concentration across all temperatures indicated no differences for slope. These data indicate that when there is direct peanut seed exposure to flumioxazin at field application rates, there is no impact on germination and radicle development. Temperature was noted to affect radicle development greater than field application rates of flumioxazin. As temperature decreased, germination and radicle length was inhibited or decreased, respectively. Nomenclature: Flumioxazin, peanut, Arachis hypogaea (L.), radicle, seed germination

Adopting Chip Sealing Performance-Based Approaches to Determine Rational Design Quantities

Abstract Chip seal research advocates for performing rational design computations prior to construction to determine the initial chip and binder application rates. Research indicated that a major concern in chip seal construction industry is the lack of following a formal/documented computational design approach. This study is a result of research that investigated ways to improve chip seal design specifications in Oregon State, focusing on field application rates. The objective of this article is to encourage agencies and contractors to adopt a formal established design approach to determine their aggregates and binder application rates. This is established through identifying the parameters considered in the design while showing straightforward procedures to follow formal design approaches. Chip seal design calls for conducting laboratory and field evaluations and uses the results as input data to estimate the appropriate quantities of materials. Thus, involved parties at the design stage are required to (1) understand the properties of chip seal materials (aggregate and binder), (2) identify the pre-seal road condition, and (3) use said information in the design process. This study uses various roadways located in Klamath Falls, Oregon to verify the importance of using rational design procedures. The roadways were constructed in accordance with Oregon Department of Transportation specifications; however, application rates were based upon the agency’s previous experience rather than using a rational design approach. The study compares roadways’ infield application rates and rationally estimated rates based upon two commonly used methodologies, namely McLeod and New Zealand. Findings shows that roadways constructed using infield application rates close to the rationally estimated rates had better embedment and a longer predicted life span when compared to the rest of roadways that had excessive aggregate amounts and less binder content.

Effectiveness of Aquatain® AMF and Cocobear™ Larvicidal Oil Against Culex quinquefasciatus Larvae and Pupae in an Organically Enhanced Aquatic Habitat.

The efficacy of CocoBear™ Larvicidal Oil and Aquatain® AMF Liquid Mosquito Film against larval and pupal Culex quinquefasciatus was compared (at maximum label field application rates) when applied to concrete troughs treated with composted cow manure. At 1 h posttreatment, CocoBear provided significantly greater reduction of mosquito larvae than Aquatain, but both products were equally effective in producing >97% control at 24 h. Each product provided >98% pupal reduction at 1 h posttreatment, with complete elimination of pupae from troughs at 24 h. CocoBear and Aquatain proved to be equally effective against Cx. quinquefasciatus immatures in organically enriched aquatic habitats.

Residues and dissipation kinetic of abamectin, chlorfenapyr and pyridaben acaricides in green beans (Phaseolus vulgaris L.) under field conditions using QuEChERS method and HPLC

The current study estimated the dissipation rates of abamectin, chlorfenapyr and pyridaben acaricides in pods of green beans (Phaseolus vulgaris L.) under field conditions in Egypt. Pesticides were extracted and cleaned-up by QuEChERS method and were analyzed by HPLC. The dissipation of these acaricides followed the first order kinetics model with half-life (t1/2) values 1.00, 3.50 and 1.50 days for abamectin, chlorfenapyr and pyridaben, respectively. The lowest residues, at different time intervals of field application rate of each pesticide, were observed with abamectin followed by pyridaben and then chlorfenapyr. Pre-harvest intervals (PHIs) were 10.00, 13.50 and 6.00 days for abamectin, chlorfenapyr and pyridaben, respectively and were below the established European maximum residue limits (EU MRLs) 10–14, 14–21 and 7–10 days after application, respectively. If the fresh pods will be consumed after harvest, it is expected that the presence of these pesticides in the food will have a negative impact on human health. Therefore, the elimination of the residues of these harmful pesticides must be carried out.

Lemna minor recovery potential after short-term exposure to sulfonylurea herbicide

We have investigated the effects of the sulfonylurea herbicide Sekator OD 375 on common duckweed (Lemna minor L.) and its potential to recover after the herbicide exposure. The plants were exposed to Sekator OD 375 for a 7-day period at the concentrations ranging from 5 to 100 µL L−1, equivalent to 0.005–0.1 of field application rate. The treated plants were transferred to clean fresh growth medium for a 7-day period to observe the plants recovery. The exposure to herbicide significantly reduced the growth rate and the biomass of common duckweeds (L. minor), lowered the content of photosynthetic pigments and induced membrane lipid peroxidation. After the transfer to fresh, clean growth media, the plants exposed to concentrations higher than 50 µL L−1 of herbicide showed no potential to recover. L. minor exposed to relatively low levels of herbicide (below 50 µL L−1) showed a potential to recover their new fronds production: the relative growth rate in the recovery phase was higher than in the exposure period. However, after the recovery phase, the final biomass of the exposed plants was below initial values. Exposure to the herbicide-induced membrane lipid peroxidation (measured as the concentration of malondialdehyde). Thus, plants failed to recover their membranes during the recovery phase and a further increase in the concentrations of malondialdehyde was observed.

Glyphosate spraying and earthworm Lumbricus terrestris L. activity: Evaluating short-term impact in a glasshouse experiment simulating cereal post-harvest

A glasshouse experiment was conducted to study if glyphosate spraying has immediate short-term effects on the growth, reproduction and residue incorporation of the earthworm species Lumbricus terrestris L. The experiment simulated post-harvest conditions in no-till cereal cultivation, where L. terrestris often abound, and glyphosate is widely used. Pairs of adult, field-collected L. terrestris (median total mass 11.2 g fresh weight) were kept in fine sand-filled cylinders, with chopped wheat straw on the soil surface as feed. The treatment cylinders were sprayed with glyphosate at normal field application rate [Rodeo® XL 3.0 l ha−1, resulting in 1080 g a.i. ha−1 and “Contact” surfactant (0.5 l ha−1)]; the controls were sprayed with water (N = 12 for both). The treatment and control cylinders were maintained for two months at +15 °C, approximate 60% air humidity and 12h:12h light:dark cycle. All individuals survived the experiment. There was no difference in L. terrestris mass change over the experiment, with an average weight change of +0.96% in glyphosate treatment and −0.93% change in the control (p = 0.66). Glyphosate treatment and control did not differ in cocoon production rate (31 vs 28 cocoons cylinder−1 respectively; p = 0.30). The straw incorporation was slightly but not significantly lower in glyphosate-treated soil (decline in surface straw mass 27.5% vs. 30.5%; p = 0.07). The glyphosate treatment applied represents a commonly used practice in spring cereal cultivation, and it did not affect negatively L. terrestris. The varying study results on the effects of glyphosate on earthworms – and on L. terrestris in particular – may partly arise from notable variation in application rates and the formulation-surfactant combinations used in different experiments which needs to be considered in the ecological risk assessment of glyphosate use.

Impact of Pesticides on Microbial Diversity and Enzymes in Soil

Introduction: The presence of pesticides in soils could result in alterations in microbial activities (enzyme activities, microbial populations), soil physical and chemical properties.&#x0D; Research gap/Challenges: Insufficient literatures on extensive monitoring of soil quality through enzyme activity, during pesticides application. Existing literatures concerning analysis of effect of pesticide application on soil enzyme activity are not comprehensive with respect to number of soil enzymes analysed.&#x0D; Aim/Objective: The study was conducted to investigate the effect of carbofuran and paraquat on soil biochemical characteristics on certain soils in the Niger Delta region of Nigeria.&#x0D; Methodology: These pesticides were applied at recommended doses, their effects on soil organic carbon, enzymes activity and microbial populations were assessed using standard methods. The enzymes monitored were amylase, invertase, protease, urease, phosphatase and dehydrogenase. Microbial counts were carried out for total heterotrophic bacteria, fungi, actinomycetes, nitrifying bacteria and phosphate solubilizers using the spread plate method.&#x0D; Results: There were variations in the different enzyme activities in carbofuran – and paraquat - treated soil during this research. Dehydrogenase activity increased in treated soils. Also, urease activity was lower compared to other enzyme activities. As the study progressed, variations in values of soil organic carbon were observed. There was a gradual increase in microbial counts and can be traceable to their ability to temporarily mineralize and use the pesticides as carbon and energy source. The soil organic carbon, enzymes and microbial counts values were significantly different at P=0.05.&#x0D; Conclusion: This research revealed that the pesticides cause temporal impact on microbial populations and enzyme activities, associated with the pesticide type at recommended field application rates. A change in numbers, activity and diversity of soil microorganisms may act as indicators of soil fertility and reflect the soil quality.

The Efficacy of the Bacillus thuringiensis israelensis Larvicide Against Culex tarsalis in Municipal Wastewater and Water from Natural Wetlands.

Water quality is a factor that is likely to interact with the activity of Bacillus thuringiensis israelensis (Bti)-based mosquito larvicides. High rates of adsorption to dense particulate matter and toxin degradation in water may be expected to reduce Bti effectiveness. Therefore, water from wastewater lagoons may serve as a protective habitat for mosquito larvae against Bti larvicides relative to natural wetlands. We conducted a study in which we exposed larvae of Culex tarsalis to various concentrations of Bti in water collected from an urban wetlands and an urban wastewater pond. We used survival analysis and a comparison of life-history characteristics to assess the effects of aquatic media on the relative efficacy of Bti and on fitness indicators. In our study, mosquitoes reared in wastewater and exposed to high (100% of minimum field application rate) and medium (50% of minimum field application rate) concentrations of Bti experienced significantly higher mortality than mosquitoes exposed to corresponding concentrations but reared in water from natural urban wetlands. In addition, females that emerged from wastewater had shorter wings than those that emerged from wetland-collected water. These effects may have been due to higher turbidity and higher ionic concentrations in wastewater than water from natural wetlands.

A study on optimization of pat gene expression cassette for maize transformation.

Phosphinothricin acetyltransferase gene (pat) is an important selectable marker and also a key herbicide trait gene in several commercial products. In maize, the transformation frequency (TF) using pat as a selectable marker is the lowest among the commonly used marker options including epsps, pmi or ppo. Low pat transformation efficiency can become a major bottleneck in our ability to efficiently produce large numbers of events, especially for large molecular stack vectors with multiple trait gene cassettes. The root cause of the lower efficiency of pat in maize is not well understood and it is possible that the causes are multifaceted, including maize genotype, pat marker cassette, trait gene combinations and selection system. In this work we have identified a new variant of pat gene through codon optimization that consistently produced a higher transformation frequency (> 2x) than an old version of the pat gene that has codons optimized for expression in dicot plants. The level of PAT protein in all 16 constructs was also found multifold higher (up to 40 fold) over that of the controls. All of the T0 low copy transgenic plants generated from the 16 different constructs showed excellent tolerance to ammonium glufosinate herbicide spray tests at 4x and 8x recommended field application rates (1x = 595g active ingredient (ai)/hectare of ammonium glufosinate) in the greenhouse.

Coexpression of Methyltransferase Gene dmt50 and Methylene Tetrahydrofolate Reductase Gene Increases Arabidopsis thaliana Dicamba Resistance.

Dicamba, a broad-spectrum and highly efficient herbicide, is an excellent target herbicide for the engineering of herbicide-resistant crops. In this study, a new tetrahydrofolate (THF)-dependent dicamba methyltransferase gene, dmt50, was cloned from the dicamba-degrading strain Rhizorhabdus dicambivorans Ndbn-20. Dmt50 catalyzed the methyl transfer from dicamba to THF, generating the herbicidally inactive product 3,6-dichlorosalicylic acid (3,6-DCSA) and 5-methyl-THF. A dmt50 transgenic Arabidopsis thaliana clearly showed dicamba resistance (560 g/ha, the normal field application rate). However, Dmt50 demethylation activity was inhibited by the product 5-methyl-THF. Mthfr66, encoded by the 5,10-methylene-THF reductase gene mthfr66 could relieve the inhibition by removing 5-methyl-THF in vitro. Compared with expression of dmt50 alone, simultaneous expression of dmt50 and mthfr66 further improved the dicamba resistance (1120 g/ha) of transgenic A. thaliana. This study provides new genes for dicamba detoxification and a strategy for the engineering of dicamba-resistant crops.

Residual toxicity of insecticides used against the Asian citrus psyllid and resistance management strategies with thiamethoxam and abamectin

The Asian citrus psyllid (ACP) is the key pest of citrus due to its role as vector of huanglongbing. ACP control mostly relies on frequent insecticide applications therefore increasing selection for insecticide resistance. Optimization of field application rates and rotation of insecticide modes of action (MoA) would minimize this risk. Baseline toxicity responses of ACP to commonly used insecticides provide a basis for defining application field rates and are thus needed to track potential development of resistance. Residual toxicities of 12 insecticides were evaluated through quantal response bioassays. The development of ACP resistance in response to monthly applications of two insecticides with different MoAs, abamectin and thiamethoxam, applied separately, in rotation or as mixtures was also tested. Highest residual toxicities were found for the abamectin + thiamethoxam mixture. In general, nymphs were more sensitive than adults to residues. Nymphs were 10 and 28 times more sensitive than adults to residues of thiamethoxam and imidacloprid, respectively. We found a wide range among ratios of maximum label field concentrations and estimated LC90s. Highest label rates for malathion and dimethoate were more than 30 times greater than LC90s, in contrast to abamectin, zeta-cypermethrin and fenpyroximate which were 4–7 times lower. Abamectin appeared to synergize the mixture of it with thiamethoxam. We observed resistance to both active ingredients, especially abamectin, after 8 months of sequential applications of both insecticides individually or in mixture. Rapid resistance development of the mixture relative to rotation was attributed to loss of the synergetic effect of abamectin on thiamethoxam.

3.13 Tank mixtures of insecticides and fungicides, adjuvants, additives, fertilizers and their effects on honey bees after contact exposure in a spray chamber

In agriculture honey bees may be exposed to multiple pesticides. In contrast to single applications of plant protection products (PPP), the effects of tank mixtures of two or more PPP on honey bees are not routinely assessed in the risk assessment of plant protection products. However, tank mixes are often common practice by farmers. Mixtures of practically non-toxic substances can lead to synergistic increase of toxic effects on honey bees, observed for the first time in 19921 in combinations of pyrethroids and azole fungicides. 2004 Iwasa et al. already reported that ergosterol-biosynthesis-inhibiting (EBI) fungicides strongly increase the toxicity of neonicotinoids in laboratory for the contact exposure route. Furthermore, in agricultural practice additives, adjuvants and fertilizers may be added to the spray solution. For these additives usually no informations on potential side effects on bees are available when mixed with plant protection products. Therefore, it is considered necessary to investigate possible additive or synergistic impacts and evaluate potentially critical combinations to ensure protection of bees. Here, we investigated the effects on bees of combinations of insecticides, fungicides and fertilizers under controlled laboratory conditions. A spray chamber was used to evaluate effects following contact exposure by typical field application rates. Subsequently, mortality and behaviour of bees were monitored for at least 48 h following the OECD acute contact toxicity test 2143. Dependencies of synergistic effects and the time intervals between the applications of the mixing partners were evaluated.