Synergistic effects of the entomopathogenic fungus Isaria javanica and low doses of dinotefuran on the efficient control of the rice pest Sogatella furcifera

The rice planthopper,Sogatella furcifera,is a piercing-sucking insect pest of rice,Oryza sativa.It is responsible for significant crop yield losses,and has developed moderate to high resistance to several commonly used chemical insecticides.We investigated the effects of the insect fungal pathogen Isaria javanica,alone and in combination with the chemical insecticide dinotefuran,on S.furcifera under both laboratory and field conditions.Our results show that I.javanica displays high infection efficiency and mortality for different stages of S.furcifera,reducing adult survival,female oviposition and ovary development.Laboratory bioassays showed that the combined use of I.javanica with a low dose(4-16 mg L^(-1))of dinotefuran resulted in higher mortality in S.furcifera than the use of I.javanica or dinotefuran alone.The combined treatment also had more significant effects on several host enzymes,including superoxide dismutase,catalase,peroxidase,and prophenol oxidase activities.In field trials,I.javanica effectively suppressed populations of rice planthoppers to low levels(22-64%of the level in untreated plots).Additional field experiments showed synergistic effects,i.e.,enhanced efficiency,for the control of S.furcifera populations using the combination of a low dose of I.javanica(1×10^(4) conidia mL^(-1))and a low dose of dinotefuran(~4.8-19.2%of normal field use levels),with control effects of>90%and a population level under 50 insects per 100 hills at 3-14 days post-treatment.Our findings indicate that the entomogenous fungus I.javanica offers an attractive biological control addition as part of the integrated pest management(IPM)practices for the control of rice plant pests.

Spatial and temporal variation of nitrogen exported by runoff from sandy agricultural soils

The eutrophication problem has drawn attention to nutrient leaching from agricultural soils, and an understanding of spatial and temporal variability is needed to develop decision-making tools. Thus, eleven sites were selected to monitor, over a two-year period, spatial and temporal variation of runoff discharge and various forms of N in surface runoff in sandy agricultural soils. Factors influencing the variation of runoff discharge and various forms of N in surface runoff were analyzed. Variation of annual rainfall was small among 11 sites, especially between 2001 and 2002. However, variation of annual discharge was significant among the sites. The results suggest that rainfall patterns and land use had significant effect on discharge. The concentrations of total N, total kjeldahl N （TKN）, organic matter-associated N （OM-N）, NO3- -N, and NHn＋-N in the runoff ranged widely from 0.25 to 54.1, 0.15 to 20.3, 0.00 to 14.6, 0.00 to 45.3, and 0.00 to 19.7 mg/L, respectively. Spatial and temporal variations in the N concentration and runoff discharge were noted among the different sites. Annual loads of N in the runoff varied widely among monitoring sites and depend mainly on runoff discharge. High loads of total N, OM-N, NO3--N, and NHn＋-N in the runoff either in citrus groves or on vegetable farms occurred from June to October for each year, which coincided with the rainy season in the region. This study found that N in surface runoff was related to rainfall intensity, soil N level, and fertilizer use.

Review:Assessing potential dietary toxicity of heavy metals in selected vegetables and food crops

Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmosphere, soil and water, even in traces can cause serious problems to all organisms, and heavy metal bioaccumulation in the food chain especially can be highly dangerous to human health. Heavy metals enter the human body mainly through two routes namely: inhalation and ingestion, ingestion being the main route of exposure to these elements in human population. Heavy metals intake by human populations through food chain has been reported in many countries. Soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cumulative loading limits. For soil-plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bioavailable concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops does not exceed food hygiene standards. Factors affecting the thresholds of dietary toxicity of heavy metal in soil-crop system include: soil type which includes soil pH, organic matter content, clay mineral and other soil chemical and biochemical properties; and crop species or cultivars regulated by genetic basis for heavy metal transport and accumulation in plants. In addition, the interactions of soil-plant root-microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops. Agronomic practices such as fertilizer and water managements as well as crop rotation system can affect bioavailability and crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. This paper reviews the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assesses soil heavy metal thresholds for potential dietary toxicity.

Ammonia Volatilization and Nitrogen Utilization Efficiency in Response to Urea Application in Rice Fields of the Taihu Lake Region,China

Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 （control）, 100, 200, 300, or 350 kg N ha^-1. After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate, and the two higher N application rates （300 and 350 kg N ha^-1） showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surplus N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields. Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha^-1 for the type of paddy soil in the Taihu Lake region. However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.

Phytoremediation of heavy metal polluted soils and water:Progresses and perspectives

Environmental pollution affects the quality of pedosphere,hydrosphere,atmosphere,lithosphere and biosphere.Great efforts have been made in the last two decades to reduce pollution sources and remedy the polluted soil and water resources.Phytoremediation,being more cost-effective and fewer side effects than physical and chemical approaches,has gained increasing popularity in both academic and practical circles.More than 400 plant species have been identified to have potential for soil and water remediation.Among them,Thlaspi,Brassica,Sedum alfredii H.,and Arabidopsis species have been mostly studied.It is also expected that recent advances in biotechnology will play a promising role in the development of new hyperaccumulators by transferring metal hyperaccumulating genes from low biomass wild species to the higher biomass producing cultivated species in the times to come.This paper attempted to provide a brief review on recent progresses in research and practical applications of phytoremediation for soil and water resources.

Extractability and Mobility of Copper and Zinc Accumulated in Sandy Soils

Extractability and mobility of Cu and Zn and their relationships with 1) accumulation of Cu and Zn and 2) soil pH were studied in three sandy soils (Wabasso, Ankona, and Winder) from commercial citrus groves in Florida, USA. The soils, with a broad range of Cu and Zn concentrations, were fractionated by a modified procedure of Amacher, while Cu and Zn mobility were evaluated using column leaching. The extractability of Cu and Zn increased with decreasing soil pH. Also with increasing total soil Cu and Zn for extractable Cu in the Wabasso sand a threshold level, where the metal extraction rate increased, was noted at 100 mg kg-1, whereas for extractable Zn in the Wabasso sand the threshold level was found at 60 mg kg-1 and in the Ankona sand at 120 mg kg-1. These results suggested that the release potential of Cu and Zn was greater in the Wabasso sand than in the Ankona sand. The column leaching experiment showed that at total soil Cu or Zn concentrations < 100 mg kg-1 all leachates had low Cu and Zn concentrations. However at total concentrations > 200 mg kg-1 for Cu and > 150 mg kg-1 for Zn with decreasing soil pH, the concentrations of both Cu and Zn in the leachates increased exponentially. Also in these sandy soils soluble Cu and Zn mainly originated from the exchangeable fractions, and pH was a key factor controlling Cu and Zn extractability and mobility.

Reprogramming of a defense signaling pathway in rough lemon and sweet orange is a critical element of the early response to‘Candidatus Liberibacter asiaticus’

Huanglongbing(HLB)in citrus infected by Candidatus Liberibacter asiaticus(CLas)has caused tremendous losses to the citrus industry.No resistant genotypes have been identified in citrus species or close relatives.Among citrus varieties,rough lemon(Citrus jambhiri)has been considered tolerant due to its ability to produce a healthy flush of new growth after infection.The difference between tolerance and susceptibility is often defined by the speed and intensity of a plant’s response to a pathogen,especially early defense responses.RNA-seq data were collected from three biological replicates of CLas-and mock-inoculated rough lemon and sweet orange at week 0 and 7 following infection.Functional analysis of the differentially expressed genes(DEGs)indicated that genes involved in the mitogen activated protein kinase(MAPK)signaling pathway were highly upregulated in rough lemon.MAPK induces the transcription of WRKY and other transcription factors which potentially turn on multiple defense-related genes.A Subnetwork Enrichment Analysis further revealed different patterns of regulation of several functional categories,suggesting DEGs with different functions were subjected to reprogramming.In general,the amplitude of the expression of defense-related genes is much greater in rough lemon than in sweet orange.A quantitative disease resistance response may contribute to the durable tolerance level to HLB observed in rough lemon.

Study on Agrobacterium-Mediated Transformation of Pepper with Barnase and Cre Gene

This study was designed to control plant fertility by cell lethal gene Barnase expressing at specific developmental stage and in specific tissue of male organ under the control of Cre/lox system, for heterosis breeding of chili pepper （Capsicum annuum L.）. Chili pepper inbred lines （A, D, E, and I） were transformed with Cre gene and Barnase gene situated between loxp, separately, by means of Agrobacterium co-culture. In this study, we had established a high transformation system by extensive study of affecting factors including genotype, selection of marker, and lethal dose. Cotyledon with petiole from 9-11-day-old seeding was pre-cultured on media MR[MB（MS mineral＋vitamine B5）＋BA（6-Benzyladenine） 5.0 mg·L^-1 ＋IAA（indoleacetic acid） 1.0 mg·L^-1＋GA3（gibberellic acid） 1.0mg·L^-1＋sucrose 3%＋agar 6.5g·L^-1] for 2d. The explants were infected by Agrobacterium tumefaciens when their OD600（optical density at 600 nm）reached 0.6-0.9. After co-cultured for 4-5 d on media MC [MB＋BA5.0 mg·L^-1＋IAA 1.0 mg·L^-1 ＋GA3 1.0 mg·L^-1＋sucrose 3% ＋agar 6.5 g·L^-1＋AS （acetosyringone） 200μmol·L^-1, these cotyledons with petiole were cultured on selective differentiation medium in the media MT[MB medium supplemented with BA [5.0 mg·L^-1＋ IAA 1.0 mg·L^-1＋ GA3 1.0 mg·L^-1＋ AgNO3 5.0 mg·L^-1＋ CW （coconut water） 5% ＋ Km （kanamycin） 65 mg·L^-1＋ Cb （carbenicillin） 500 mg·L^-1＋ 3% sucrose ＋ agar 6.5 g·L^-1].The Kmr （kanamycin resistant） bud rosettes were elongated on selective elongation medium and rooted on rooting medium. PCR and Southern blotting analysis of Kmr plantlet indicated that the foreign genes had been integrated into the genome of pepper. The transgenic plants with Cre gene developed well, blossomed out, and set fruit normally. The transgenic plants with Barnase gene grew well with normal appearance of flower, but they showed different fertility from complete sterility, partial sterility to complete fertility, and similar results were obtained from in vitro pollen germination experiments.

Construction of citrus gene coexpression networks from microarray data using random matrix theory

After the sequencing of citrus genomes,gene function annotation is becoming a new challenge.Gene coexpression analysis can be employed for function annotation using publicly available microarray data sets.In this study,230 sweet orange(Citrus sinensis)microarrays were used to construct seven coexpression networks,including one condition-independent and six condition-dependent(Citrus canker,Huanglongbing,leaves,flavedo,albedo,and flesh)networks.In total,these networks contain 37633 edges among 6256 nodes(genes),which accounts for 52.11%measurable genes of the citrus microarray.Then,these networks were partitioned into functional modules using the Markov Cluster Algorithm.Significantly enriched Gene Ontology biological process terms and KEGG pathway terms were detected for 343 and 60 modules,respectively.Finally,independent verification of these networks was performed using another expression data of 371 genes.This study provides new targets for further functional analyses in citrus.

Fate of Nutrients, Trace Metals, Bacteria, and Pesticides in Nursery Recycled Water

Faced with rapid population growth and fresh water scarcity, reuse of reclaimed water is growing worldwide and becoming an integral part of water resource management. Our objective was to determine the fate of nutrients, trace metals, bacteria, and legacy organic compounds (organochlorine pesticides) in the recycled water from five commercial nursery ponds in Florida. The pH of recycled water at all sites was 8.1 - 9.3, except one site (6.5), while the electrical conductivity (EC) was 0.31 - 0.36 dS/m. Concentrations of trace metals in recycled water were low: Fe (0.125 - 0.367 mg/L), Al (0.126 - 0.169 mg/L), B (0.104 - 0.153 mg/L), Zn (0.123 - 0.211 mg/L), and Mn (<0.111 mg/L). Total phosphorus (P) and total nitrogen (N) in the recycled water were 0.35 - 1.00 mg/L and 1.56 - 2.30 mg/L, respectively. Among organochlorine pesticides, endrin aldehyde was the only pesticide detected in all nursery recycled water ponds, with concentrations from 0.04 to 0.10 μg/L at four sites and 1.62 μg/L at one site. Other detected pesticides in recycled water were methoxychlor, endosulfan sulfate, dichlorodiphenyldichloroethylene (DDE) and α-chlorodane, with concentrations < 0.20 μg/L. Total coliforms and Escherichia coli (E. coli) in recycled water were 20 - 50 colony forming units (CFU)/100 mL. We conclude that the concentrations of various inorganic and organic compounds in recycled water are very low and do not appear to be problematic for irrigation purposes in Florida’s nursery recycled water ponds.

Agronomic, Water Productivity and Economic Analysis of Irrigated Rice under Different Nitrogen and Water Management Methods

The most limiting factors for irrigated rice farming are water and nitrogen. Efficient water and nitrogen management has remained critical for sustainable rice production in irrigated rice farming system. Due to rapid global population growth and climate change, future rice production will depend heavily on developing strategies and practices that use water and nitrogen efficiently. The study therefore set to evaluate agronomic, water productivity and economic analysis of irrigated rice under various nitrogen and water management methods. To achieve the set objectives, field and pot experiments were carried out at the Soil and Irrigation Research Centre, University of Ghana, Kpong in 2015 and 2016 cropping season. The field experiment was laid in a split plot design with water management treatments as main plots and N fertilizer as subplot treatment. The pot experiment was carried out in a randomized complete block design with five replications. The water management treatments were;continuous submergence (SC), alternate wet and dry soil condition (AWD) and moist soil condition (MC). Nitrogen fertilizer rates were;no N fertilizer (N0), 60 kg N/ha (N1) and 90 kg N/ha (N2). Data such as yield and yield parameters of rice, water use, water productivity, costs and returns were recorded. Results obtained from both pot and field experiments revealed that rice yields were at par in AWD and SC but yields were lower in MC treatment. With N fertilizer, higher yields were observed with 90 kg N/ha. The interaction effect of submerged with 90 kg N/ha gave the highest grain yield. N fertilizer effect on water use and water productivity was ranked as N2 > N1 > N0 while water management effect on water use and water productivity was ranked in this order: SC > AWD > MC and MC > AWD > SC respectively.

<i>Agrobacterium</i>-Mediated Transformation of Mexican Lime (<i>Citrus aurantifolia</i>Swingle) Using Optimized Systems for Epicotyls and Cotyledons

Transgenic Mexican lime (Citrus aurantifolia Swingle) was produced through two explant sources, each using systems previously optimized for each source. One used epicotyls segments, which was the predominant explant for transgenic Citrus production following co-cultivation with Agrobacterium, and has a well-established protocol. The other procedure used embryo cotyledons from mature seeds, which was developed in our lab as an alternative for stable Citrus transformation. Cotyledon transformation and regeneration protocols were optimized by comparing variables in culture medium composition on shoot regeneration and four parameters in transient transformation. The optimized protocols were compared, and frequency of regeneration, frequency of transgenic plant-recovery and stable transformation efficiency indicated the superiority of the cotyledon protocol for Agrobacterium-mediated genetic transformation in Mexican lime. The tissue choice resulted in marked improvement in shoot regeneration (14.1% of explants producing shoots in epicotyls;55.8% in cotyledons), stable transformation frequency (11.4% of epicotyls explants;40.2% in cotyledons), and frequency of transgenic plant-recovery (37.9% in epicotyl explants;92.6% in cotyledons). Thus, easy availability of explants using embryo cotyledons from mature seeds, technical simplicity, shortening of transformation time-course, and higher transformation and regeneration frequencies makes this new system an attractive alternative over the previously published Citrus transformation protocols. In the course of this project, we generated Mexican lime with a Recombinase Mediated Exchange Cassette landing pad, which was designed for stacking transgenes.

Trials for Gathering Information on an Unknown Peak in the GC-MS Spectra of Horse and Pony Hair Extracts

The volatile compounds from horse and pony hairs and skin were analyzed to determine bioactive molecules that are kairomones used for host location by blood-feeding diptera. In this study, horse and pony hair samples were extracted with organic solvents (pentane or hexane) and analyzed by gas chromatography-mass spectrometry analysis (GC-MS) with closed electron ionization (CEI). Using the GC-MS analysis, we observed a compound peak, which could not be identified by comparison to mass spectra in the mass spectral library. This unknown compound was often the largest peak in the chromatogram and had a retention index and mass spectral fragmentation similar to nonanal. However, there were several differences in the fragmentation pattern. When compared to a nonanal reference standard, it was evident that this was a different compound. Hydrodistillation of pony hair was another extraction method to obtain the unknown component in higher concentrations. Analysis of this extract with GC-flame ionization detector (FID) with GC-MS confirmed the same unknown peak. Further experiments and analysis with the various mass spectroscopy tools gave the possible molecular ion with mass-to-charge ratio (m/z) 142, corresponding to the unknown component.

Biological Synthesis of Nanoparticles and Their Applications in Sustainable Agriculture Production

Nanotechnology is a developing field in biotechnology. The synthesis of nanoparticles is an important step in the field of nanotechnology. Overcoming the limitations of traditional methods, a green scheme for synthesizing nanoparticles has emerged. Plants and microorganisms are mainly used for the green synthesis of metal nanoparticles. Some of the nanoparticles showed strong antimicrobial effects against different plant pathogens. Compared with microorganisms, the use of plants to synthesize nanoparticles is on the rise, and has advantages compared with microorganisms, because plants have a wide range of bio-molecular variability, which can act as blocking/stabilizing agents and reducing agents, thereby increasing reduction rate and stability of synthetic nanoparticles. Of all living things, plants seem to have the best potential for nanoparticle biosynthesis and are suitable for large-scale biosynthesis. Compared with microorganisms, the synthesis of plant-derived nanoparticles is faster and more stable. Therefore, this review focuses on the use of microbial and plant sources to synthesize nanoparticles and their applications in agriculture.

Soil Carbon Pool as Influenced by Soil Microbial Activity—An Overview

Soil is a significant carbon reservoir with the capacity to store carbon twice as much as the atmosphere or plants. Given the significant potential of soil to capture and store atmospheric CO2, it presents a viable solution for mitigating the present and future impacts of climate change. However, due to its high susceptibility to global environmental issues like land degradation, loss of biodiversity, and climate change, monitoring and protecting soil carbon pools is a complex challenge. Intensive agricultural operations have detrimental effects on the soil, including the rapid breakdown of soil organic carbon, which releases excess carbon into the air, causing increased atmospheric CO2 levels and a depletion of the soil carbon reserves. The diversity and abundance of soil microbial communities play a crucial role in controlling essential ecosystem processes, including the decomposition of organic matter and nutrient cycling, including carbon. Heterotrophic soil microorganisms facilitate the soil organic matter turnover to obtain the nutrients and energy required for their growth and maintenance. Therefore, the microbial residues and exudates have up to 80% carbon in the stable soil organic matter fractions. This overview attempts to summarize the information on various carbon pools, soil carbon interaction with microbes, impacts on environmental changes, and strategies to enhance the storage of belowground carbon.

Microbial activity and community diversity in a variable charge soil as affected by cadmium exposure levels and time

Effects of cadmium （Cd） on microbial biomass, variable charge soil （Typic Aquult） using an incubation study activity and community diversity were assessed in a representative Cadmium was added as CdCNO3）2 to reach a concentration range of 0-16 mg Cd/kg soil. Soil extractable Cd generally increased with Cd loading rate, but decreased with incubation time. Soil microbial biomass was enhanced at low Cd levels （0.5-1 mg/kg）, but was inhibited consistently with increasing Cd rate. The ratio of microbial biomass C/N varied with Cd treatment levels, decreasing at low Cd rate （〈0.7 mg/kg available Cd）, but increasing progressively with Cd loading. Soil respiration was restrained at low Cd loading （〈1 mg/kg）, and enhanced at higher Cd levels. Soil microbial metabolic quotient （MMQ） was generally greater at high Cd loading （1-16 mg/kg）. However, the MMQ is also affected by other factors. Cd contamination reduces species diversity of soil microbial communities and their ability to metabolize different C substrates. Soils with higher levels of Cd contamination showed decreases in indicator phospholipids fatty acids （PLFAs） for Gram-negative bacteria and actinomycetes, while the indicator PLFAs for Gram-positive bacteria and fungi increased with increasing levels of Cd contamination.

Strawberry sweetness and consumer preference are enhanced by specific volatile compounds

Breeding crops for improved flavor is challenging due to the high cost of sensory evaluation and the difficulty of connecting sensory experience to chemical composition.The main goal of this study was to identify the chemical drivers of sweetness and consumer liking for fresh strawberries(Fragaria×ananassa).Fruit of 148 strawberry samples from cultivars and breeding selections were grown and harvested over seven years and were subjected to both sensory and chemical analyses.Each panel consisted of at least 100 consumers,resulting in more than 15,000 sensory data points per descriptor.Three sugars,two acids and 113 volatile compounds were quantified.Consumer liking was highly associated with sweetness intensity,texture liking,and flavor intensity,but not sourness intensity.Partial least square analyses revealed 20 volatile compounds that increased sweetness perception independently of sugars;18 volatiles that increased liking independently of sugars;and 15 volatile compounds that had positive effects on both.Machine learning-based predictive models including sugars,acids,and volatiles explained at least 25%more variation in sweetness and liking than models accounting for sugars and acids only.Volatile compounds such asγ-dodecalactone;5-hepten-2-one,6-methyl;and multiple medium-chain fatty acid esters may serve as targets for breeding or quality control attributes for strawberry products.A genetic association study identified two loci controlling ester production,both on linkage group 6 A.Co-segregating makers in these regions can be used for increasing multiple esters simultaneously.This study demonstrates a paradigm for improvement of fruit sweetness and flavor in which consumers drive the identification of the most important chemical targets,which in turn drives the discovery of genetic targets for marker-assisted breeding.

Novel assembly strategy cracks open the mysteries of walnut genome evolution

High quality chromosome-scale assemblies from an interspecific hybrid between walnut and a wild relative reveal the persistence of asymmetric fractionation between the sub-genomes and suggest a late-Miocene origin for the genus Juglans.

Development of a Procedure to Maximize Production of Hardy Rootstocks of Citrus Using Stem Cuttings

Shoots of Citrus sp. Kuharske were used to develop protocols for rooting reportedly HLB resistance rootstocks under intermittent mist. Investigated were shoot maturity, nodes per cutting, leaves per cutting, effects of buds, auxin concentrations and auxin solvent. Shoot maturity was most influential for success, with cuttings taken below the first 30 cm of active terminal growth producing greater root generation. Use of a thickening agent (Natrosal) to dilute the commercial auxin was second most in importance for rooting success. Root mass increased with increasing number of leaves. Cutting stems between nodes or below the lowest bud were inconsequential. To produce maximum number of viable cuttings, single node-single leaf cuttings were preferred. Single bud cuttings produced one shoot after rooting. This was adventitious since multi-node cuttings usually sprouted new shoots that would need to be removed before budded. Evaluation of the best combination of auxin and cutting-related attributes were evaluated with four additional common rootstocks in June 2016. Rooting was 100% successful. A quick dip (0.5 s) in a 7500 ppm solution of Dip&Gro produced the most root generation in six weeks for all rootstocks. Root quantity varied by rootstock.

Weed Control Efficacy and Citrus Response to Flazasulfuron Applied Alone or in Combination with Other Herbicides

Field experiments were conducted to evaluate the phytotoxicity of flazasulfuron on citrus species and efficacy on weeds when applied alone or in combination with other herbicides. Grapefruit was the most sensitive and tangerine was the least sensitive to flazasulfuron. Injury to grapefruit was 70% with the application of flazasulfuron at 0.20 kg a.i. ha–1 at 60 DAT and was reduced (5%) when flazasulfuron at 0.05 kg a.i. ha–1 was tank mixed with glyphosate at 0.84 kg·a.i.· ha–1. Flazasulfuron alone at all rates did not control grass weeds and common ragweed. Florida/Brazil pusley was moderately controlled with high rates of flazasulfuron from 30 to 45 DAT;however, control did not exceed 75%. There was good control of Spanishneedles (78% - 85%) and horseweed (73% - 81%) with flazasulfuron at all rates at 30 DAT but control declined later in the season. Tank mix of flazasulfuron with glyphosate improved flazasulfuron efficacy on grass and broadleaf weeds. Flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1 was more effective in controlling grass weeds (83%) at 60 DAT and provided the highest control (79%) of Florida/Brazil pusley at 45 DAT. There was excellent control (75% to 94%) of Spanishneedles and adequate control of eastern black nightshade and common ragweed with flazasulfuron tank mixed with glyphosate or diuron. This study showed that flazasulfuron alone does not adequately control grasses and some broadleaf weeds in citrus and tank mixing it with glyphosate or diuron improved flazasulfuron’s efficacy. However, injury to grapefruit was observed at rates which effectively controlled weeds. Further studies are needed to determine the most suitable flazasulfuron rate that could be used to manage weeds in grapefruit.