Citrus Groves Research Articles

Cost-effective control of plant disease when epidemiological knowledge is incomplete: modelling Bahia bark scaling of citrus.

A spatially-explicit, stochastic model is developed for Bahia bark scaling, a threat to citrus production in north-eastern Brazil, and is used to assess epidemiological principles underlying the cost-effectiveness of disease control strategies. The model is fitted via Markov chain Monte Carlo with data augmentation to snapshots of disease spread derived from a previously-reported multi-year experiment. Goodness-of-fit tests strongly supported the fit of the model, even though the detailed etiology of the disease is unknown and was not explicitly included in the model. Key epidemiological parameters including the infection rate, incubation period and scale of dispersal are estimated from the spread data. This allows us to scale-up the experimental results to predict the effect of the level of initial inoculum on disease progression in a typically-sized citrus grove. The efficacies of two cultural control measures are assessed: altering the spacing of host plants, and roguing symptomatic trees. Reducing planting density can slow disease spread significantly if the distance between hosts is sufficiently large. However, low density groves have fewer plants per hectare. The optimum density of productive plants is therefore recovered at an intermediate host spacing. Roguing, even when detection of symptomatic plants is imperfect, can lead to very effective control. However, scouting for disease symptoms incurs a cost. We use the model to balance the cost of scouting against the number of plants lost to disease, and show how to determine a roguing schedule that optimises profit. The trade-offs underlying the two optima we identify—the optimal host spacing and the optimal roguing schedule—are applicable to many pathosystems. Our work demonstrates how a carefully parameterised mathematical model can be used to find these optima. It also illustrates how mathematical models can be used in even this most challenging of situations in which the underlying epidemiology is ill-understood.

Characterization of sensitivity of grove and packing house isolates of Penicillium digitatum to pyrimethanil

In most northeast Argentinean citrus packing houses, postharvest fungicide treatments are based on the use of thiabendazole and imazalil. However, these fungicides have been used in a manner highly conducive to the selection and proliferation of resistant biotypes of Penicillium digitatum, the main fruit decay fungus in the area. Recently, a new fungicide, pyrimethanil (PYR), was introduced to control molds. Aims of this study were to determine the baseline sensitivities for PYR against isolates of P. digitatum considering its use in the region is not yet widespread and to evaluate the control of the fungus in vivo. One hundred and nine (109) P. digitatum isolates were collected from diseased fruit within citrus groves (43 isolates) and packing houses (66 isolates). EC50 was determined for each isolate by measuring colony diameters on different agar dilutions of the fungicide. The mean EC50 value of the green mold isolates collected from the groves was 0.14±0.03mgL−1 while the mean EC50 of those collected from packing houses was 0.13±0.05mgL−1. No resistant isolates were found in the field where the fungicide is not used, while one isolate originated from a packing house showed an EC50 of 3.40mgL−1, 26-fold higher than the mean level. This isolate was collected from lemons stored in cool rooms of a packing house where PYR had not been used. Fruit decay by sensitive isolates was reduced approximately 80% by PYR applied at 500–600mgL−1 by immersion for 60s at room temperature to inoculated oranges and mandarins. In contrast, the resistant isolate was not controlled by PYR applied at 1000mgL−1. Thus, the introduction of PYR applied into packing houses should be done carefully and control strategies should be implemented in order to minimize the development of resistant isolates.

First Report of Citrus Aleurocanthus woglumi Ashby (Hemiptera: Aleyrodidae) in the State of Paraná, Brazil

The citrus blackfly Aleroucanthus woglumi Ashby, (Hemiptera Aleyrodidae) is an important pest that occurs in citrus groves, native to south-east Asia. In Brazil, according to the Ministry of Agriculture, this is a quarantine pest (A2) under official control IN 52, 2007 (MAPA) and is not widespread in the country. The insect can infest more than 300 host plants, including cultivated plants, ornamentals and weeds, but mostly occurs in the plants of the genus citrus. This paper is the first report of citrus blackfly in the State of Parana.

Water Use in Drip- and Microsprinkler-Irrigated Citrus Trees

Advanced citrus production systems (ACPS) are being evaluated in Florida citrus groves for sustainable, profitable citrus production. The ACPS practices provide tight control over water and nutrient-mediated plant growth and development using irrigation to train the root system into a limited area and fertigate with daily nutrient requirements. Thus, a study was undertaken to (i) compare daily water use using the stem heat balance method on ≤5-yr-old citrus trees using two ACPS irrigation methods (using daily drip and microsprinkler irrigation) and conventional irrigation on two Florida sandy soils; (ii) determine relationships between hourly sap flow and time of day, and daily water use vs. total available soil water in the irrigated zone; and (iii) evaluate the effect of Huanglongbing (HLB) disease on water uptake. The sap flow data suggest that intensive drip and microsprinkler irrigation systems resulted in similar or higher water use than conventional irrigation. Water use was greater (P ≤ 0.01) with ACPS than conventional microsprinkler practice irrigation in summer 2010, spring 2011, and late summer 2011 at the Entisol site. Water use was 29 to 38% greater using ACPS than conventional irrigation in June 2011 at the Spodosol site, albeit, not significantly different. All irrigation systems showed water contents close to field capacity at both sites, indicating that water was nonlimiting in each irrigation system despite having different irrigation schedules. The high water uptake using intensive irrigation systems is ascribed to frequent irrigation and improved water distribution in the irrigated zone.

Effects of Short-term Drought Stress and Mechanical Harvesting on Sweet Orange Tree Health, Water Uptake, and Yield

One of the primary reasons for the slow adoption of mechanical harvesting by Florida citrus growers is the physical injuries associated with it, including loss of leaves, twigs, flowers, and young fruits, limb breakage, and injuries to the bark and root. However, it has been shown that well-managed trees are capable of tolerating defoliation, limb loss, and root and bark injury caused by mechanical harvesting. Irrigation management is one of the most crucial factors that influence citrus tree health. A multiple-year field study was conducted on ‘Valencia’ sweet orange trees in a commercial citrus grove near Immokalee, FL, to determine the effect of initial tree canopy density and short-term drought stress on tree health, water uptake, and productivity of mechanically harvested trees. Three blocks were based on canopy density and overall appearance and indicated as low, moderate, and high canopy density. The experiment was laid in a split-plot design with four replications of six-tree plots of hand-harvested or mechanically harvested trees, taking drought stress or full irrigation as main treatments. The experimental design was repeated with trees in each plot of one of the three canopy density categories. After harvest, each six-tree plot was split into two three-tree subplots, where one subplot was drought-stressed and the other was fully irrigated. Harvesting was conducted in the Spring of 2010, 2011, and 2012 with the same experimental design and data collection procedures. The effects of short-term drought on water use and stem water potential were masked by heavy rains in Spring 2010 and thus no differences in the irrigation treatments were observed. In 2011 and 2012, stem water potential was unaffected by harvesting method. Water use was unaffected by harvesting method across the 3 years. Drought stress significantly increased pull force required to remove fruit and stem water potential after harvest. Although mechanically harvested trees lost leaf mass, with no rain before harvest, results from Spring 2011 and 2012 indicated that short-term drought stress had no effect on citrus leaf area irrespective of harvest method. Drought stress significantly increased fruit detachment force in low and moderate density but not in high-density trees resulting in increased force required to remove fruit from trees with moderate- to low-density canopies. Yield increased from 2010 to 2011 for mechanically harvested trees compared with hand-harvested for low-canopy density trees by 17% and moderate-canopy density trees by 8%, whereas high-density plots indicated similar yield after mechanical harvesting. Comparatively, yield in 2012 decreased in the low and moderate densities compared with yield in 2011 but increased in the high density by 14% and 53% in hand- and machine-harvested trees, respectively. Despite finding 2- to 3-fold more debris in the mechanically harvested trees than the hand-harvested trees, yields and other measured parameters were unaffected suggesting that mechanical harvesting of citrus trees did not have an adverse effect on growth and production of well-watered citrus trees.

Molecular characterization of Citrus yellow mosaic badnavirus (CMBV) isolates revealed the presence of two distinct strains infecting citrus in India

Citrus yellow mosaic badnavirus (CMBV) is a non-enveloped, bacilliform DNA virus and the etiologic agent of yellow mosaic disease of citrus in India. The disease was initially reported from the southern parts of India and has now spread to other parts of the country. It is a serious disease of sweet orange (Citrus sinensis) in southern India, where it causes significant yield losses. During a recent survey of citrus groves in the Nagpur region, central India, characteristic mosaic symptoms were observed in mandarin orange (Citrus reticulata) and sweet orange. Virus transmission studies, electron microscopy, PCR amplification and sequencing of cloned PCR products from samples showing mosaic symptoms confirmed the presence of a badnavirus. The CMBV–Nagpur isolate could be transmitted to the Rangpur lime (C. limonia) and acid lime (Citrus aurantifolia) by graft inoculation. Sequence analysis of a segment of ORF-III region and intergenic region (IR) of the viral genome revealed that CMBV–Nagpur isolate formed a distinct clade along with some previously reported isolates that are known to infect acid lime and Rangpur lime. CMBV isolates that infect citrus species other than the acid lime and Rangpur lime formed a second clade. Based on the transmission studies and phylogenetic analyses, it was concluded that at least two strains of CMBV exist in India currently.

Occurrence of ‘Candidatus Phytoplasma asteris’ in citrus showing Huanglongbing symptoms in Mexico

Huanglongbing (HLB), one of the most devastating citrus diseases in the world, was detected in Mexico in 2009. Currently, HLB is associated with the bacteria Candidatus Liberibacter spp., although several phytoplasmas have been found from trees showing HLB-like symptoms in Brazil and China. The aim of this study was thus to determine if, in addition to ‘Ca. L. asiaticus’ (CLas), phytoplasma species are also associated with HLB-like symptoms in citrus groves of Mexico. Citrus plants exhibiting symptoms such as diffuse chlorosis, blotchy mottle and vein yellowing were collected in the Mexican States of Nayarit, Colima and Sinaloa between August 2011 and September 2012. Samples were then evaluated for phytoplasmas and CLas by PCR, using primers that respectively target the genes for the 16S ribosomal RNA and 50S ribosomal protein of the β operon (rplA-rplJ). Out of 86 HLB-symptomatic citrus plants, 54 were positive for CLas, 20 were positive for phytoplasmas, 7 were found in mixed infections with both pathogens and 19 samples were negative for CLas and phytoplasmas. Actual and virtual RFLP analyses of the 16S rDNA sequences enabled us to classify two HLB phytoplasma strains as members of the aster yellows group (16SrI) ‘Candidatus Phytoplasma asteris’, which was confirmed by phylogenetic analysis. The HLB phytoplasma strain identified from Nayarit (HLBpc-Nay-IB) belongs to subgroup B (16SrI-B), and the strains identified from Colima (HLBpc-Col-IS) and Sinaloa (HLBpc-Sin-IS) belong to subgroup S (16SrI-S). The partial ‘Ca. L. asiaticus’ rplA-rplJ gene sequences were 100% identical to the ‘Ca. L. asiaticus’ strains isolated from several countries affected by HLB. These results confirm the association of ‘Candidatus Phytoplasma asteris’ with HLB-like symptoms in citrus groves in Mexico. Nonetheless, further studies are required to fully describe the ‘Ca. L. asiaticus’ and ‘Ca. P. asteris’ interactions in citrus, which will greatly assist the design of efficient management strategies.

Insecticide sprays, natural enemy assemblages and predation on Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae).

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama is considered a key citrus pest due to its role as vector of 'huanglongbing' (HLB) or citrus greening, probably the most economically damaging disease of citrus. Insecticidal control of the vector is still considered a cornerstone of HLB management to prevent infection and to reduce reinoculation of infected trees. The severity of HLB has driven implementation of intensive insecticide programs against ACP with unknown side effects on beneficial arthropod fauna in citrus agroecosystems. We evaluated effects of calendar sprays directed against this pest on natural enemy assemblages and used exclusion to estimate mortality they imposed on ACP populations in citrus groves. Predator exclusion techniques were used on nascent colonies of D. citri in replicated large untreated and sprayed plots of citrus during the four major flushing periods over 2 years. Population of spiders, arboreal ants and ladybeetles were independently assessed. Monthly sprays of recommended insecticides for control of ACP, adversely affected natural enemy populations resulting in reduced predation on ACP immature stages, especially during the critical late winter/early spring flush. Consequently, projected growth rates of the ACP population were greatest where natural enemies had been adversely affected by insecticides. Whereas, this result does not obviate the need for insecticidal control of ACP, it does indicate that even a selective regimen of sprays can impose as yet undetermined costs in terms of reduced biological control of this and probably other citrus pests.

Biology of the Huanglongbing vector Diaphorina citri (Hemiptera: Liviidae) on different host plants.

Although many studies have been conducted on the development and reproductive potential of Diaphorina citri Kuwayama, 1908 (Hemiptera: Liviidae) in different host species, few have evaluated these parameters on different varieties of the same host species. This study evaluated the influence of five commercial varieties of citrus (Citrus spp. L.)--Hamlin, Natal, Pêra, Ponkan, and Valencia-and orange jasmine [Murraya exotica (L.) Jack] on the development of D. citri. Survival rates for the egg stage were highest on orange jasmine (85.7%) and on Valencia (83.3%). The lowest viability of the nymphal stage was also observed on Hamlin, averaging 57.4%. Values for total viability ranged from 65.9 to 32.6%, and were highest on Valencia. The longest egg-adult development time was on Natal, with a mean of 18.4 d; the shortest total development time was on orange jasmine, with a mean of 17.3 d. Based on the fertility life table, the net reproductive rate (Ro) of D. citri was 2.5 times higher when reared on Valencia than on Hamlin. The other parameters (duration of each generation [T], finite rate of increase [lambda], and innate capacity to increase in number [r(m)]) also demonstrated that Valencia is best suited to this insect. The results obtained for the biological parameters and the fertility life table indicate that Valencia and orange jasmine were the most suitable hosts, whereas Hamlin was least suitable for the development of D. citri. These results provide information for the installation of new citrus groves, especially in the choice of varieties to be planted and the location of different varieties within the groves, with a view toward the management of Huanglongbing or HLB.

Nitrogen‐fertilizer forms affect the nitrogen‐use efficiency in fertigated citrus groves

AbstractThe fertigated area of the Brazilian citrus industry has grown rapidly during recent years, and an efficient management of nitrogen (N) application at these sites is required for sustainable citrus production. Therefore, a field trial with Valencia orange trees [Citrus sinensis (L.) Osbeck] on Swingle citrumelo rootstock (Citrus paradise Macfad. x Poncirus trifoliata L. Raf.) was conducted for 8 years to evaluate the effects of N rates (80, 160, 240 and 320 kg ha–1 y–1) applied by fertigation, either as ammonium nitrate (AN) or calcium nitrate (CN), on soil solution dynamics, fruit yield, nutritional status, and N‐use efficiency (NUE) of trees. The maximum fruit yield was reached with 240 kg N ha–1 for AN, whereas a linear response and greater fruit yield was observed for N supplied as CN. The NUE was reduced for both N forms with increasing N rates. However, the NUE for CN was 14 to 38% greater than the NUE for AN. The lower fruit yield and NUE for AN compared to CN‐treated trees was associated with the increased acidification of the soil solution with increased AN rates (pH ≤ 4.0). This limited nitrification resulted in a high ammonium (NH$ _4^+ $) concentration in the soil solution and a reduction in the net absorption of cations by the trees, particularly calcium (Ca). Due to the improved ion balance as well as the higher pH of the soil solution (pH ≥ 6.3) and diminished NH$ _4^+ $ availability, gains in both fruit yield and NUE in fertigated citrus groves in tropical soils can be obtained with the use of CN as a source of N.

First report of the fungus Fomitiporia maxonii Murrill causing citrus wood rot in commercial orange and grapefruit groves in Cuba

Cuban citriculture has recently been affected by important pests and diseases including black citrus aphid Toxoptera citricida Kirkaldy, citrus leafminer Phyllocnistis citrella Stainton, Asiatic citrus psyllid Diaphorina citri Kuwayama, Citrus tristeza disease, and huanglongbing. This complex of ‘invasive species’ is thought to be contributing to the increasing decline of commercial citrus groves. During several surveys carried out in commercial citrus areas of several provinces in Cuba, symptoms of dieback, characterized by the presence of abundant dry branches and wood rot were detected on Criolla Valencia orange, Marsh grapefruit trees on sour orange, and Cleopatra mandarin rootstocks. Samples of branches and trunk wood were processed and a fungus was isolated from all samples. Morphological, physiological and molecular characterization demonstrated that the isolated agent is Fomitiporia maxonii Murrill. The incidence of affected trees was high in most surveyed groves, reaching 100% in old groves. Symptoms similar to the ones found in naturally infected trees were reproduced on trees inoculated with pure cultures of the fungus, and the fungus was recovered in culture from inoculated trees, thus fulfilling Koch's postulates. This is the first report of an association of F. maxonii with citrus wood rot in Cuba.

Host Range Testing of <I>Tamarixia radiata</I> (Hymenoptera: Eulophidae) Sourced From the Punjab of Pakistan for Classical Biological Control of <I>Diaphorina citri</I> (Hemiptera: Liviidae: Euphyllurinae: Diaphorinini) in California

ABSTRACT Tests evaluating the host range of Tamarixia radiata (Waterson) (Hymenoptera: Eulophidae), a parasitoid of the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), sourced from the Punjab of Pakistan, were conducted in quarantine at the University of California, Riverside, CA. Seven nontarget psyllid species (five native and two self-introduced species) representing five families were exposed to T radiata under the following three different exposure scenarios: 1) sequential no-choice tests, 2) static no-choice tests, and 3) choice tests. Nontarget species were selected for testing based on the following criteria: 1) taxonomic relatedness to the target, D. citri; 2) native psyllids inhabiting native host plants related to citrus that could release volatiles attractive to T. radiata; 3) native psyllids with a high probability of occurrence in native vegetation surrounding commercial citrus groves that could be encountered by T. radiata emigrating from D. citri-infested citrus orchards; 4) a common native pest psyllid species; and 5) a beneficial psyllid attacking a noxious weed. The results of host range testing were unambiguous; T radiata exhibited a narrow host range and high host specificity, with just one species of nontarget psyllid, the abundant native pest Bactericera cockerelli Sulc, being parasitized at low levels (< 5%). These results suggest that the likelihood of significant nontarget impacts is low, and the establishment of T. radiata in southern California for the classical biological control of D. citri poses negligible environmental risk.

Impact of some alternative methods to chemical control in controlling aphids (Hemiptera: Sternorrhyncha) and their side effects on natural enemies on young Moroccan citrus groves

Aphid control in Moroccan citrus orchards is based mainly on carbamate and neonicotinoid sprays, especially methomyl and imidacloprid. The extensive use of these insecticides may have side effects on natural enemies and environment quality and raises human health concerns. This research aimed to assess the control of aphids with insecticidal soap, kaolin and augmentative biological control using the indigenous predator Adalia decempunctata L. (Coleoptera: Coccinellidae). The insecticides were applied and the predators were released in April 2009 and 2010. Under field experimentation, the methomyl and imidacloprid foliar pulverization were very effective against aphids. In contrast, the insecticidal soap and kaolin application were less efficient while A. decempunctata adults were effective only in the first week after release. The side effects on beneficial insects were also assessed and discussed. The possibility of employing A. decempunctata in an integrated pest management package in citrus groves is discussed in relation to effectiveness and side effects on beneficial arthropods.

First Quantitative Estimates of Carbon Retention by Citrus Groves under Cuba’s Conditions

Citrus is one of the major fruit crops in Cuba. Its perennial nature, the planted area and the time of productive exploitation turn it into a potential sink of atmospheric carbon. The present study was focused on the obtainment of two models that allow the quantitative estimation of carbon retention by citrus groves. The research was done in two commercial groves: orange [Citrus sinensis (L) Osbeck] cv. “Valencia Late” and grapefruit (Citrus paradisi Macf.) cv. “Marsh Seedless” both on sour orange (Citrus aurantium L.) and planted on a typical red ferralitic soil of Artemisa province. Groves are located at 22°55' North and 82°40' West. Cuba’s climate is tropical, seasonally humid, with sea influence and semicontinentality features. Three issues were dealt with: 1) Determination of the total mean quantity of retained carbon by the aerial part of the trees using a destructive sampling method (Pattern Method) to estimate: the total volume of the tree, wood densities and green and dry biomass; 2) Determination of the total mean quantity of retained carbon by the aerial part of the trees using two Allometric Methods; and 3) Determination of the most effective Allometric Method to estimate the carbon retention by the aerial part of the trees. From the results, it is concluded that the evaluated methods were effective to reach a first quantitative approximation to carbon retention by citrus groves and under equal conditions, the Allometric Method 2 was more accurate to estimate the Total Carbon Content in “Valencia Late” orange, while for “Marsh Seedless” grapefruit the Allometric Method 1 provided the best estimate.

重信川流域における栄養塩流出特性に関する調査研究

Run off characteristics of nutrients from small basins in Sigenobu river catchment area were invested in detail. These characteristics are summarized by using L-Q curve relationship, and first flush phenomenon in which nutrients concentration increased quickly during the early stage were observed in the cases of SS, T-P, PO4-P, and T-N. Detail observation was conducted in Yuwatari area in which urbanized area, citrus grove, and forest exist. SS and phosphorus concentration in discharged water increased with the increase of flow rate of discharged water, which means the pattern of the loading rate of SS and phosphorus was "washout type". Run of amounts of T-P and T-N were calculated and 84% of T-P, and 61% of T-N were discharged during rainy days. Management of catchment area in rainy days is more important than in fine days in the area.

Incidence and Severity of Asiatic Citrus Canker on Diverse Citrus and Citrus-related Germplasm in a Florida Field Planting

Xanthomonas citri ssp. citri (Xcc) is the causal agent of Asiatic citrus canker (ACC), a commercially important disease in Florida citrus as well as in many other regions. In this study we evaluated occurrence of foliar lesions from ACC on progenies of 94 seed-source genotypes (hereafter called “parent genotypes”) of Citrus and Citrus relatives in the field in east–central Florida to identify the relative susceptibility to ACC. Eight seedlings per parent genotype were planted in a randomized complete block planting, but the number of plants assessed in some genotype groups was reduced by mortality at some or all sampling dates. Plants experienced ambient exposure to high Xcc inoculum pressure and plants were assessed in Sept. 2010, July 2011, Oct. 2011, May 2012, and Sept. 2012. The incidence and severity of ACC lesions were assessed and evaluated using non-parametric analyses to compare progeny from the 94 parent genotypes. Progeny of 14 parent genotypes did not exhibit ACC symptoms at any date. All were in genera other than Citrus with only Microcitrus and Eremocitrus being cross-compatible with Citrus. The kumquat hybrid C. halimii, two accessions of C. reticulata, C. nobilis, and C. sunki were the only Citrus species in the group that had a low severity (percent total leaf area showing symptoms) on each date of assessment. The aforementioned accessions had an average incidence and severity of ACC lesions of less than 4% in 2011 and 2012, but 26% to 38% in 2010 when no chemical control for ACC was applied in the adjoining citrus groves at our field site. Fourteen of the 16 progeny of C. reticulata and related parent genotypes were in the group with the lowest incidence and severity of ACC on two or more assessment dates. However, for analysis of only the most symptomatic leaves on each plant, 10 C. reticulata parent genotype progenies were in the most resistant category on the Sept. 2012 assessment despite having a low incidence and severity of ACC symptoms overall. Progeny of Poncirus and its hybrids as well as those of C. maxima, C. limon, and related species were the most severely diseased at all assessment dates. There were few instances in which progeny of different accessions of the same species had markedly different responses to ACC: progeny of C. reticulata ‘Fremont’ displayed more severe ACC compared with several other C. reticulata groups and C. aurantium ‘Zhuluan’ displayed much lower incidence and severity of ACC compared with several other accessions designated C. aurantium. Information on ACC susceptibility in diverse Citrus and Citrus relatives may prove useful for breeding programs aimed at reducing ACC susceptibility and will be of value to researchers interested in mechanisms of ACC resistance and susceptibility.

Quantitative Distribution of Candidatus Liberibacter asiaticus in the Aerial Parts of the Huanglongbing-infected Citrus Trees in Texas

The Asian citrus psyllid, Diaphorina citri Kuwayama, one of the known vectors for citrus greening disease or Huanglongbing (HLB) pathogens, has been present in Texas for over a decade, but the detection of the disease is recent. HLB has been confirmed in only two adjacent commercial citrus groves of grapefruit and sweet orange. A study was conducted to compare the population of Candidatus Liberibacter asiaticus (CLas) cells in different plant parts including peduncle, columella, leaves, seeds, young shoots, flower buds, flowers, and bark of 6-year-old known infected grapefruit and sweet orange trees. The bacterial population was estimated using a previously described grand universal regression equation Y = 13.82 – 0.2866X, where Y is the log of the target copy number and X is the Ct (threshold cycle) of the assay. Except for bark tissue, there was no significant difference in the concentration of CLas cells in other plant parts between the two cultivars. Within the cultivar, the bacterial concentration also varied with the plant part, with peduncle, columella, midrib having significantly higher titer of CLas compared with other plant parts. The obtained results here are in agreement with previous studies conducted on Florida samples, but the consistently lowest bacterial titer recorded in young shoots, leaf blade, and especially leaf margins relative to the midrib has never been previously reported.

“We Always Tell Our Children They Are Americans”: Mendez v. Westminster and the Beginning of the End of School Segregation

“We Always Tell Our Children They Are Americans”: Mendez v. Westminster end the Beginning of the End of School Segregation PHILIPPA STRUM Soledad Vidaurri walked up to the schoolhouse door, five little children in her wake. It was a warm September 1943 day in Westminster, California, thirty-five miles south of Los Angeles in the heart of citrus­ growing country, home to some 2,500 residents. American soldiers were still fight­ ing overseas—there were almost two more years of battles ahead before World War II would end—but Orange County was peace­ ful, and bustling economically because ofthe wartime demand for agricultural products and war factory materiel. Mrs. Vidaurri had gone to the Westminster Main School to enroll her two daughters, Alice and Virginia Vidaurri, and her niece and two nephews—Sylvia Mendez, Gonzalo Mendez, Jr., and Geronimo (Jerome) Mendez—in the neighborhood pub­ lic school. Mrs. Vidaurri was welcomed to the school and told that her daughters could be registered. Their father had a French ancestor and their last name sounded acceptably French or Belgian to the teacher in charge of admissions. Besides, the Vidaurri girls were light-skinned. The Mendez children, however, were visibly darker and, to the teacher, their last name was all too clearly Mexican. They would have to be taken to the “Mexican” school a few blocks away. Little Gonzalo Jr. would remember the teacher telling his aunt, while indicating the two Vidaurri girls, ‘“We’ll take those . . . but we won’t take those three,”’ because “We were too dark.”1 “No way,” an outraged Mrs. Vidaurri replied, and marched all the children home. Her equally outraged brother, Gonzalo Mendez, simply refused to send his children to the “Mexican” school. Two years later the Mendezes would lead a group of Mexican-American parents into federal court, 308 JOURNAL OF SUPREME COURT HISTORY challenging the segregation of their children, and legal history would be made. Their case became the first in which a federal court declared “separate but equal” schooling to be unequal. Mendez v. Westminster was the 1946 predecessor to Brown v. Board ofEducation, and can in fact be seen as the Latino/a version of that better-known decision.2 There had been Mexican-Americans in California since the United States annexed California in 1848, although their numbers were relatively few. The combination of political turmoil in Mexico in the first decades ofthe twentieth century andjob opportunities in the United States, however, led to largescale immigration. Official census figures indicated that 661,538 Mexicans entered the United States between 1910 and 1930. Scholars of Latino history put the number as closer to one million, suggesting that 1/8 to 1/10 of the entire Mexican population moved north.3 Many ofthem found work in agricultural fields. In the decades after the end of the American Civil War, railroads had expanded into the West. Simultaneously, advances in irrigation enabled Western growers to pro­ duce large quantities of fruits and vegetables, which could be transported in the newly invented refrigerator cars on the railroads that now crisscrossed the United States. That became the pull for Mexican immigrants, as the need ofboth growers and the railroads for cheap farm workers increased exponentially.4 In 1930, the U.S. Chamber of Commerce stated that Mexicans picked more than eighty percent of the Southwest’s crops. By 1940 Mexican immigrants and their American descendants were almost 100 percent of the picking force in southern California.5 Many ofthem lived in what amounted to ghetto neighborhoods—colonias—next to citrus groves or vegetable fields, on the outskirts of cities such as Santa Ana, California. Santa Ana is the county seat of Orange County, where the Mendez story takes place. The Mexican farm laborers in Orange County in the 1930s found themselves in neighborhoods that for the most part lacked sewers, gas for cooking and heating, paved streets, or sidewalks. Many families built their own two-room wooden houses and could afford very little furniture. There were no refrigerators; heat came from wood-burning kitchen stoves. Clothes were made on pedalpowered sewing machines and cleaned in washtubs. The families might have small food gardens and raise chickens, goats or ducks...

Development of a Web-Based System to Optimize Copper Fungicide Application in Citrus Groves

<abstract><title><italic>Abstract. </italic></title> Copper fungicides are commonly used for protective applications against foliar fungal and bacterial diseases in citrus groves. Management of these products must be finely balanced between disease prevention, application costs, fruit blemishes caused by copper phytotoxicity, and toxic accumulation of copper in the soil. The traditional schedule for copper sprays in Florida is an every 21-day post-bloom application. However, our computer simulation analysis showed that this traditional schedule is inefficient and leaves the grove unprotected in wet years and applies unnecessary copper sprays in dry years. In order to facilitate the copper management for the citrus growers, a user friendly internet-based decision support system was developed. This system is capable of estimating the copper residue on the fruit based on rainfall records and spray details. This allows producers to plan the copper applications in order to minimize unprotected periods while avoiding unnecessary applications in dry years.

Identification and determination of the number of immature green citrus fruit in a canopy under different ambient light conditions

Yield mapping for tree crops by mechanical harvesting requires automatic detection and counting of fruits in tree canopy. However, partial occlusion, shape irregularity, varying illumination, multiple sizes and similarity with the background make fruit identification a very difficult task to achieve. Therefore, immature green citrus-fruit detection within a green canopy is a challenging task due to all the above-mentioned problems. A novel algorithmic technique was used to detect immature green citrus fruit in tree canopy under natural outdoor conditions. Shape analysis and texture classification were two integral parts of the algorithm. Shape analysis was conducted to detect as many fruits as possible. Texture classification by a support vector machine (SVM), Canny edge detection combined with a graph-based connected component algorithm and Hough line detection, were used to remove false positives. Next, keypoints were detected using a scale invariant feature transform (SIFT) algorithm and to further remove false positives. A majority voting scheme was implemented to make the algorithm more robust. The algorithm was able to accurately detect and count 80.4% of citrus fruit in a validation set of images acquired from a citrus grove under natural outdoor conditions. The algorithm could be further improved to provide growers early yield estimation so that growers can manage grove more efficiently on a site-specific basis to increase yield and profit.