Spray Programs Research Articles

Compounds alone and in combination with yeasts to control Colletotrichum acutatum in apples

In New Zealand summer rots caused by Colletotrichum acutatum Simmonds (bitter rot) result in significant loss. This pathogen is currently controlled by fungicide sprays. This project was initiated to investigate if populations of naturally occurring yeast biological control agents could be enhanced by application of benign compounds in the field as an alternative means of control. Calcium chloride (CaCl2) and calcium carbonate (CaCO3) enhanced the biocontrol activity of applied yeasts against C. acutatum in detached fruit assays. Combining these compounds with yeasts resulted in a reduction of lesion size following inoculation by C. acutatum that was additive for some of the yeast-CaCl2 combinations and synergistic for some of the yeast-CaCO3 combinations. Calcium chloride was applied in the field in two trials conducted in different seasons and different regions. Disease incidence in the field was reduced by the application of CaCl2 in both trials. Results in a commercial orchard using CaCl2 at a rate of at 0.33 kg product /100 L were comparable to a standard fungicide spray programme. Investigation of the mode of action suggests direct fungistatic suppression by CaCl2, although there was evidence that treatment with CaCl2 increased resistance to infection in one apple variety.

WALNUT BLIGHT MANAGEMENT USING XANTHOMONAS ARBORICOLA PV. JUGLANDIS DORMANT BUD POPULATION SAMPLING

Four years of surveying walnut blight and the causal pathogen in Tehama County California (Ca.) and three years in Butte County (Ca.) revealed a linkage of a history of Xanthomonas arboricola pv. juglandis populations in orchards with current season disease and temporal dynamics explained by differences in disease control measures. In the Tehama County (Ca.) orchards, walnut blight control has been very good and aggressive spray programs are maintaining bud pathogen populations at low levels. In the Butte County (Ca.) locations, although there are only three years of data, less effective spray programs have allowed disease damage and the initial inoculum overwintering in dormant buds to increase. The incidence of walnut blight damage differed greatly between different trees in a linear transect through a ‘Vina’ orchard and disease was strongly related to the population of pathogen in the developing buds, suggesting that the disease history of individual trees also varies, and is predictive of the risk of disease on those trees and that spatial segregation of disease occurs within an orchard. Assessments of the population sizes of the pathogen in dormant buds is thus a good predictor of the risk of walnut blight in a given year since the walnut buds are the primary source of initial inoculum that can spread to susceptible leaf and nut tissues after they open.

Diversity in the erg27 Gene of Botrytis cinerea Field Isolates from Strawberry Defines Different Levels of Resistance to the Hydroxyanilide Fenhexamid.

The hydroxyanilide (Hyd) fenhexamid has played a major role in gray mold management in Florida strawberry fields since 2000. Recent monitoring of the sensitivity of Botrytis cinerea to fenhexamid indicated that resistance has emerged. In this study, mutations in the target gene erg27 encoding the 3-keto reductase enzyme were investigated and the shift in fenhexamid sensitivity over time was evaluated in 630 isolates collected between 2005 and 2013 from locations sprayed with different spray programs. Overall, 227, 155, 48, and 200 isolates were sensitive (HydS), had reduced sensitivity (HydR2), or were moderately (HydR3-) and highly (HydR3+) resistant, respectively. Analysis of complete sequences of the erg27 gene from 70 isolates revealed seven and five mutations and one deletion in the HydR3- and HydR3+ isolates, respectively, at eight and five different codons, respectively. In addition to the three mutations (F412S, -I, and -V) reported previously at codon 412, two new mutations from glycine to arginine at codon 170 (G170R, two isolates) and from alanine to glycine at codon 210 (A210G, eight isolates) were detected for the first time in HydR3+ isolates from Florida. These isolates were not controlled on detached fruit sprayed with the recommended field rate of fenhexamid, whereas all HydS, HydR2, and HydR3- isolates were controlled on detached fruit. Overall, there was no clear correlation between the spray frequency of fenhexamid and the frequency of resistant phenotypes. This study provides an overview of the current distribution of erg27 genotypes in Florida and will serve as a baseline for future studies on shifts in population diversity and resistance. The frequency of fenhexamid-resistant populations has increased progressively in different strawberry fields but has not reached a plateau yet, indicating that the effective life of fenhexamid could be extended if appropriate rotation and management strategies are implemented. Sensitivity to other sterol biosynthesis inhibitors is discussed.

The rising threat of fungicide resistance in plant pathogenic fungi: Botrytis as a case study.

The introduction of site-specific fungicides almost 50years ago has revolutionized chemical plant protection, providing highly efficient, low toxicity compounds for control of fungal diseases. However, it was soon discovered that plant pathogenic fungi can adapt to fungicide treatments by mutations leading to resistance and loss of fungicide efficacy. The grey mould fungus Botrytis cinerea, a major cause of pre- and post-harvest losses in fruit and vegetable production, is notorious as a 'high risk' organism for rapid resistance development. In this review, the mechanisms and the history of fungicide resistance in Botrytis are outlined. The introduction of new fungicide classes for grey mould control was always followed by the appearance of resistance in field populations. In addition to target site resistance, B. cinerea has also developed a resistance mechanism based on drug efflux transport. Excessive spraying programmes have resulted in the selection of multiresistant strains in several countries, in particular in strawberry fields. The rapid erosion of fungicide activity against these strains represents a major challenge for the future of fungicides against Botrytis. To maintain adequate protection of intensive cultures against grey mould, strict implementation of resistance management measures are required as well as alternative strategies with non-chemical products.

Negative cross resistance mediated by co-treated bed nets: a potential means of restoring pyrethroid-susceptibility to malaria vectors.

Insecticide-treated nets and indoor residual spray programs for malaria control are entirely dependent on pyrethroid insecticides. The ubiquitous exposure of Anopheles mosquitoes to this chemistry has selected for resistance in a number of populations. This threatens the sustainability of our most effective interventions but no operationally practicable way of resolving the problem currently exists. One innovative solution involves the co-application of a powerful chemosterilant (pyriproxyfen or PPF) to bed nets that are usually treated only with pyrethroids. Resistant mosquitoes that are unaffected by the pyrethroid component of a PPF/pyrethroid co-treatment remain vulnerable to PPF. There is a differential impact of PPF on pyrethroid-resistant and susceptible mosquitoes that is modulated by the mosquito’s behavioural response at co-treated surfaces. This imposes a specific fitness cost on pyrethroid-resistant phenotypes and can reverse selection. The concept is demonstrated using a mathematical model.

Eupalopsellidae and Stigmaeidae (Acari: Prostigmata) within citrus orchards in Florida: species distribution, relative and seasonal abundance within trees, associated vines, and ground cover plants.

Seven citrus orchards on reduced- to no-pesticide spray programs were sampled for predacious mites in the families Eupalopsellidae and Stigmaeidae (Acari: Prostigmata) in central and south central Florida. Inner and outer canopy leaves, fruit, twigs, and trunk scrapings were sampled monthly between August 1994 and January 1996. Open flowers were sampled in March from five of the sites. Two species of eupalopsellid mites (Exothorhis caudata Summers and Saniosulus harteni (van-Dis and Ueckermann)) were identified from 252 specimens collected within citrus tree canopies within the seven citrus orchards of which 249 were E.caudata. Only two E. caudata were collected from ground cover plants within five of the seven orchards. Eight species of Stigmaeidae were identified from 5,637 specimens: Agistemus floridanus Gonzalez, A. terminalis Gonzalez, Eustigmaeus arcuata (Chandhri), E. sp. near arcuata, E. segnis (Koch), Mediostigmaeus citri (Rakha and McCoy), Stigmaeus seminudus Wood, and Zetzellia languida Gonzalez were collected from within citrus tree canopies from seven orchard sites. Agistemus floridanus was the only species in either family that was abundant with 5,483 collected from within citrus tree canopies compared with only 39 from vine or ground cover plants. A total of 431 samples from one or more of 82 vines and ground cover plants were sampled monthly between September 1994 and January 1996 in five of these orchards and one or more eupalopsellids or stigmaeids were collected from 19 of these plants. Richardia brasiliensis (Meg.) Gomez had nine A. floridanus from 5 of 25 samples collected from this plant. Solanum sp. had five A. floridanus from three samples taken. Both eupalopsellid and stigmaeid species numbers represented <1% of the total numbers of phytoseiid species taken from the same plants. The two remaining orchards were on full herbicide programs and ground cover plants were absent. Agistemus floridanus was more abundant in the citrus orchards with on-going or recent herbicide programs compared with orchards having well-developed ground cover plants. Agistemus floridanus was most abundant on inner leaves between January and April and again during September through November. Additional collection records of E. caudata, S. harteni, A. terminalis, M. citri, Z. languida, and Zetzellia sp. near silvicola within Florida citrus orchards between 1989 and 2004 are included. Four species of Eupalopsellidae and ten species of Stigmaeidae occur within Florida citrus orchards.

Managing Phytophthora crown and root rot on tomato by pre-plant treatments with biocontrol agents, resistance inducers, organic and mineral fertilizers under nursery conditions

Five trials were carried out under greenhouse conditions to test the efficacy of spray programmes based on biocontrol agents, phosphite-based fertilizers and a chemical inducer of resistance (acibenzolar-S-methyl, phosethyl-Al) to control crown and root rot of tomato incited by Phytophthora nicotianae . The best disease control, under high disease pressure resulting from artificial inoculation, was obtained with three pre-plant leaf sprays at 7 d intervals with acibenzolar-S-methyl and with two mineral phosphite-based fertilizers. The disease reduction achieved was similar to that obtained with a single application of azoxystrobin and metalaxyl-M. Phosetyl-Al and the biocontrol agents Glomus spp. + Bacillus megaterium + Trichoderma , B. subtilis QST713, B. velezensis IT45 and the mixture T. asperellum ICC012 + T. gamsii ICC080 provided a partial disease control. Brassica carinata pellets did not control the disease.

Release of Erysiphe necator Ascospores and Impact of Early Season Disease Pressure on Vitis vinifera Fruit Infection

Populations of <i>Erysiphe necator</i> cleistothecia can dehisce and release ascospores over an extended period ranging from fall through late spring and are an important source of primary inoculum for grapevine powdery mildew epidemics. The temporal distribution of ascospore maturity was monitored and measured as ascospore release from field-stored samples in a controlled environment assay. Assays were conducted over multiple seasons, in multiple locations, using multiple source populations. The influence of primary inoculum quantity and how that influences subsequent fruit disease severity was assessed. Cumulative ascospore release was positively correlated with accumulated wetting events and heat units; however, in most situations, &gt;50% of the season-total ascospores were released before the date of local budbreak of <i>Vitis vinifera</i>. Both abbreviated and season-long fungicide programs suppressed mildew on fruit across a 100-fold gradient of inoculum dose when seasonal weather was relatively unfavorable for epidemic development. Suppression was degraded with progressive 10-fold increases of ascosporic inoculum dose when seasonal weather was more conducive to epidemic development. Combined, these findings suggest that differences between severe and mild years in grape powdery mildew can relate to the amount of primary inoculum present in the vineyard, that the levels of primary inoculum can be influenced by pre-budbreak weather conditions, and that effectiveness of spray programs at controlling primary infection events is related to the favorability of in-season weather conditions.

Validation of the Phenology Model for the Codling Moth,Cydia pomonella(Lepidoptera: Tortricidae), in South African Pome Fruit Orchards

The codling moth, Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is a key pest of pome fruits in the Western Cape, South Africa. Up to 1993, the industry recommendation for commencement of the codling moth spray programme was at 75 % petal fall in order to avoid the negative impact of organophosphate sprays on bees during bloom. However, codling moth can emerge, mate and oviposit before and during full bloom in pome fruit orchards. Consequently, petal-fall does not necessarily correspond with the commencement of egg-laying or first egg hatch. The availability of insecticides with a softer environmental profile made it possible to apply sprays earlier than 75 % petal-fall. The development of phenology models provided a means of accurately predicting biological events such as the initiation of egg-laying and first egg hatch. Using lower and upper development thresholds of 10 °C and 32 °C, respectively, and hourly temperature recordings, phenology models were evaluated by comparing the number of degr...

Sensitivities of Baseline Isolates and Boscalid-Resistant Mutants of Alternaria alternata from Pistachio to Fluopyram, Penthiopyrad, and Fluxapyroxad.

Resistance of Alternaria alternata to boscalid, the first succinate dehydrogenase inhibitor (SDHI) fungicide labeled on pistachio, has become a common occurrence in California pistachio orchards and affects the performance of this fungicide. In this study, we established the baseline sensitivities of A. alternata to the new SDHIs fluopyram, fluxapyroxad, and penthiopyrad and assessed their cross resistance patterns with boscalid. Examination of the effective fungicide concentration that inhibits mycelial growth to 50% relative to the control (EC50) for 50 baseline isolates revealed that the majority were sensitive to boscalid, penthiopyrad, fluopyram, and fluxapyroxad. Analysis of EC50 values for boscalid for 117 A. alternata isolates originating from boscalid-exposed orchards showed that 44, 3, 1, and 69 isolates had sensitive, reduced sensitivity, moderately resistant, and highly resistant boscalid phenotypes, respectively. Molecular investigation of the occurrence of known SDH mutations showed that, among the 69 isolates highly resistant to boscalid, 44, 2, 14, and 1 isolates possessed the mutations leading to the H277Y, H277R, H134R, and H133R amino acid substitutions in AaSDHB, AaSDHB, AaSDHC, and AaSDHD subunits, respectively. Some SDHB or SDHC mutants displayed highly sensitive, sensitive, or reduced sensitivity phenotypes toward penthiopyrad or fluxapyroxad, whereas other had low, moderate, or high levels of resistance to these fungicides. In contrast, all the SDHB mutants were sensitive to fluopyram, while 10, 5, and 1 SDHC mutants had sensitive, reduced sensitivity, and moderately resistant fluopyram phenotypes, respectively. The SDHD mutant had reduced sensitivity to fluopyram and penthiopyrad but was highly resistant to fluxapyroxad. The discrepancies of cross-resistance patterns between SDHIs suggest that their binding sites in complex II may differ slightly and that additional mechanisms of resistance to these compounds are likely involved. Ultimately, the findings of this study should lead to the rational and sustained deployment of new SDHIs in Alternaria late blight spray programs.

Development of a concentrated oil spray programme on avocados to control insect and mite pests

Best practice guidelines have been developed in recent years for application of low volume concentrated pesticide sprays to avocado orchards Oil sprays an important component of spray programmes on avocado orchards have been excluded from the concentrate programme because of the risk of damage to the crop Two unreplicated trials were undertaken on commercial orchards one each in Northland and Bay of Plenty from December 2012December 2013 Each plot consisted of a single orchard block (ca 1 ha) per treatment Dilute (05 oil) high volume sprays (up to 3000 litres/ha) were compared with concentrated (15 oil) lowvolume sprays (up to 1000 litres/ha) containing a horticultural superspreader adjuvant Monitored pest populations were comparable in both treatments throughout the year with no detrimental impacts of concentrate oil sprays on either export packout rates or storage quality of fruit after harvest Safe use of concentrate oil sprays on avocados is practical using a horticultural superspreader adjuvant

Evaluation of epidemics and weather-based fungicide application programmes in controlling anthracnose fruit rot of day-neutral strawberry in outdoor field and protected cultivation systems

Anthracnose fruit rot caused by Colletotrichum acutatum is an economically important disease of strawberry in Ontario. Three years of experiments (2009–2011) were conducted at the University of Guelph’s Cedar Springs Research Station in Blenheim, ON to understand anthracnose fruit rot epidemics in outdoor field and protected production systems and to evaluate different fungicide spray programmes for disease control in day-neutral strawberry. Weather-based fungicide timing programmes were compared with calendar spray programmes in two day-neutral cultivars, ‘Seascape’ and ‘Albion’. Incidence of disease in high-tunnels was very low in all 3 years, even in fungicide non-sprayed plots, indicating that cultivation of day-neutral strawberry in high-tunnels could be an alternative strategy for controlling anthracnose fruit rot with minimal use of fungicides. In outdoor fields, disease incidence was greatly influenced by leaf wetness duration, rainfall and temperature. The use of a weather-based model to determine the timing of fungicide treatments reduced the number of sprays and was as effective as a calendar-based spray at 7-day intervals to reduce the disease and increase marketable fruit yield. Rotating fungicides with different modes of actions (pyraclostrobin, myclobutanil and boscalid + pyraclostrobin) was more effective in reducing disease than regular sprays of captan. The outcomes of this research will be useful to develop decision support tools and select proper fungicides and cultivation systems to manage anthracnose.

Evaluation of Ongoing Indoor Residual Spray Programme in Some Malaria Endemic Districts of Andhra Pradesh, India

A survey was conducted in four malaria endemic, tribal dominated districts of Srikakulam, Vizainagaram, Visakhapatnam and West Godavari in Andhra Pradesh, to note the quality of ongoing Indoor Residual Spray (IRS). Both concurrent and consecutive supervision was done to find out house coverage, room coverage, house and room refusal rates, technical knowledge of spray crew and condition of pumps. A very high room refusal rate varying between 74.6 to 88.8 per cent was noted in the study areas. Outer surface of the houses and cattle sheds were sprayed with the insecticide which diluted the objective of IRS. There is a need to generate mass awareness through Behavioral Change Communication (BCC) about IRS operations in order to overcome the shortcomings.IRS operations should be carried out in accordance with World Health Organization (WHO) and National Programme guide lines on the subject under strict supervision.

Potential secondary inoculum sources ofBotrytis cinereaand their influence on bunch rot development in dry Mediterranean climate vineyards

Epidemiological studies have described the life cycle of B. cinerea in vineyards. However, there is a lack of information on the several infection pathways and the quantitative relationships between secondary inoculum and bunch rot at harvest. Over two seasons, different spray programmes were used to determine key phenological stages for bunch rot development. Secondary inoculum sources within the bunch were also studied. The relative importance of flowering was evidenced in the given conditions, as treatments that included two fungicide applications at flowering were the most effective. In 2010, under conducive meteorological conditions for B. cinerea development after veraison, an extra application provided significantly higher control. Infections of necrotic tissues inside the bunch and latent infections developed mainly during flowering, while very low quantities of B. cinerea conidia were recovered from the fruit surface at veraison. Regression analysis correlated the incidence of latent infections and B. cinerea incidence on calyptras and aborted fruits at veraison with incidence of Botrytis bunch rot at harvest, presenting R2 = 0.95 for the overall regression model. This work points out key phenological stages during the season for bunch rot and B. cinerea secondary inoculum development and relates quantitatively inoculum sources at veraison to bunch rot at harvest. Recommendations for field applications of antibotrytic products are also suggested.

Foliar Nutrition to Enhance Horticultural Crop Production and Quality: An Introduction

F oliar nutrition is an important management strategy to improve performance of vegetable and fruit crops. This technology has been used for decades to enhance nutrient absorption and utilization in three critical conditions of crops, namely: 1) during high-demand periods, especially when the soil cannot supply nutrients fast enough for rapid tissue expansion; 2) when fertilizer application to the soil is impossible or the environmental conditions would reduce its effectiveness; and 3) when application of a given fertilizer source to the soil could result in high nutrient fixing and unavailability. The objectives of the workshop were 1) to provide the science framework for using foliar nutrition in vegetable and fruit crops and 2) to discuss the conditions for its implementation. On the first objective, the physiological and environmental aspects of foliar nutrient application, absorption, and assimilation were discussed over a broad range of crops, with special emphasis on vegetables and fruit trees. On the second objective, the practical application of fertilizer sources, application techniques, deficiency monitoring and correction, and limitations of the technologies were presented. Four out of the six papers are presented in this publication of the workshop, including research on diverse foliar fertilization aspects, such as the effects of timing of nitrogen fertilization on avocado (Persea americana) and citrus (Citrus sp.) in California, foliar nutrient uptake and nitrogen and calcium application on apple (Malus ·domestica), potassium and iron sources on muskmelon (Cucumis melo), and tomato (Solanum lycopersicum) in Texas and Florida, respectively. These papers illustrate the current challenges and potential future practices on foliar fertilization of horticultural crops. The article on timing of foliar fertilization in avocado and citrus discussed the most important aspects of this type of fertilization on fruit trees and the needed conditions for success. Also, it dealt with identification of stages in tree phenology when application of low-biuret urea improves fruit yield and quality. The effects of this fertilizer source on inflorescence and ovule viability were also discussed. Another paper described recent research on developing foliar spray programs that enhance nutrient availability, reduce nutrient requirements, and minimize release of potentially deleterious elements into the environment. The influence of foliar urea and calcium sprays on apple was also examined. On the vegetable side, a paper on muskmelon described the effects of potassium foliar sources on important fruit traits, such as soluble solids, ascorbic acid, beta carotene, sugar, aroma, appearance, and texture. The authors emphasized the influence of environmental conditions and production practices on the timing of foliar potassium application, as well as the suitability of potential sources. The last paper focused on corrective foliar applications of iron in tomato using several organic and inorganic sources. Considerations on soil pH and organic matter content modifications to improve absorption were presented. Workshop

Control of spotted wing drosophila, Drosophila suzukii, by specific insecticides and by conventional and organic crop protection programs

Spotted wing drosophila, Drosophila suzukii, is an invasive insect pest that has spread into many fruit production regions of the world. Strategies to protect fruit from infestation by this insect are currently dominated by insecticide applications, so producers need information on relative efficacy and residual activity of insecticides to be able to select effective treatments. Semi-field bioassays in which highbush blueberry shoots with berries were treated then exposed to adult flies at different times after application revealed that fresh residues of organophosphate, pyrethroid, and spinosyn insecticides have strong initial activity on flies, with varying levels of residual protection against fruit infestation. An organic pyrethrum insecticide was not effective, whereas the neonicotinoid insecticide acetamiprid was found to have activity for up to five days. Rainfall after application greatly reduced the level of control achieved by some insecticides. Field-scale evaluation of conventional and organic spray programs initiated in response to capture of D. suzukii flies in monitoring traps indicated that both types of management provide significant fruit protection compared to untreated fields, with less larval detection in the conventionally-produced berries.

A Review of Current Knowledge of Resistance Aspects for the Next-Generation Succinate Dehydrogenase Inhibitor Fungicides

The new broad-spectrum fungicides from the succinate dehydrogenase inhibitor (SDHI) class have been quickly adopted by the market, which may lead to a high selection pressure on various pathogens. Cases of resistance have been observed in 14 fungal pathogens to date and are caused by different mutations in genes encoding the molecular target of SDHIs, which is the mitochondrial succinate dehydrogenase (SDH) enzyme. All of the 17 marketed SDHI fungicides bind to the same ubiquinone binding site of the SDH enzyme. Their primary biochemical mode of action is the blockage of the TCA cycle at the level of succinate to fumarate oxidation, leading to an inhibition of respiration. Homology models and docking simulations explain binding behaviors and some peculiarities of the cross-resistance profiles displayed by different members of this class of fungicides. Furthermore, cross-resistance patterns among SDHIs is complex because many mutations confer full cross resistance while others do not. The nature of the mutations found in pathogen populations varies with species and the selection compound used but cross resistance between all SDHIs has to be assumed at the population level. In most of the cases where resistance has been reported, the frequency is still too low to impact field performance. However, the Fungicide Resistance Action Committee has developed resistance management recommendations for pathogens of different crops in order to reduce the risk for resistance development to this class of fungicides. These recommendations include preventative usage, mixture with partner fungicides active against the current pathogen population, alternation in the mode of action of products used in a spray program, and limitations in the total number of applications per season or per crop.

Alternative Disease Assessment Method for Cercospora Spot (Pseudocercospora purpurea (Cooke) Deighton) of Avocado (Persea americana Mill.)

The most serious pre-harvest disease of avocado in South Africa is still Avocado Black spot (Cercospora spot). Two methods were compared to assess Cercospora infection. The conventional assessment method (CA) relies on a disease intensity rating system that classifies fruit as local, export or rejects market quality. The disease incidence and severity assessment method (ISA) combines spore release intensity (through a weather based prediction formula) with disease intensity on fruit (as measured for specific lesion sizes representing different infection periods). In the current study, Fuerte avocado fruit from the Limpopo Province in South Africa was subjected to both CA and ISA. Data obtained through CA proved to be very limited and only reflected total disease control at the end of the season. ISA allowed a more detailed assessment of the spray program and it was possible to evaluate the efficiency of individual spray applications. Both the effect of environmental influences on disease severity and the resulted disease intensity can also be evaluated through ISA visualization.

EFFECT OF BORDEAUX MIXTURE SPRAY ON FRUIT QUALITY OF 'KYOHO' GRAPE AND COPPER ACCUMULATION IN THE SOIL

In 2008, residual copper contents in soils of Korean vineyards under different Bordeaux mixture spray programs were determined. In all 25 vineyards tested, copper contents in the soil were below the 50 mg kg-1 soil maximum contamination standard. However, as the number of sprays increased, the residual copper content also increased. The effects of Bordeaux mixture on ‘Kyoho’ grape quality and incidence of downy mildew were also investigated. Grape quality was improved in many Bordeaux mixture treated blocks because most leaves were not infected with downy mildew (Plasmopara viticola). The effect of bagging ‘Kyoho’ grape bunches before spraying with Bordeaux mixture was also determined. Grape bunches without paper bags had poor appearance, which reduces the market price, and elevated copper levels in the grape juice. Copper concentration in the naked bunches sprayed with Bordeaux mixture was close to the maximum limit of 20 mg kg-1 fruit for table grapes.

Frequency of symptomatic trees removal in small citrus blocks on citrus huanglongbing epidemics

Among the recommended measures for citrus Huanglongbing (HLB) management, the systematic elimination of symptomatic trees is the most argued and difficult to be accepted and accomplished by citrus growers. Elimination of recently affected HLB trees represents a short term yield loss and cost increase due to the need of frequent inspections and removal operations. This work aimed to evaluate the effect of different frequencies of inoculum reduction applied at individual citrus blocks scale (or local inoculum reduction) on HLB temporal progress. Eight experiments were carried out in new planted and older citrus blocks with 504–1290 trees/plot. In all experiments, inspections to detect symptomatic trees were done in a fortnightly or monthly frequency. The treatments of frequencies of local inoculum reduction varied from fortnightly to 6 months. Annual disease progress rate was estimated by logistic model for each plot. No difference on HLB progress rates among treatments was observed, except in experiments 1 and 3 where less frequent tree removal resulted in higher disease progress rate. This ineffectiveness of local inoculum reduction on the disease progress rate was explained by the higher weight of primary spread on HLB epidemics than the secondary spread within plots associated with small size and narrow shape of treated plots (except for experiments 1 and 3), high dispersal capacity of HLB-insect vector among plots and groves, and strong control of psyllid within the plots (except for experiment 1, with poor insecticide spray program). Also, the high amount of inspections to detect symptomatic trees before the eradication treatment, which reduced the escapes (asymptomatic and non visual detectable diseased trees) contributed for these results. It is important to note that these results were obtained with only small citrus plots (0.8–2.9 ha) and they cannot be extended to larger groves and farms amenable to HLB management by the symptomatic tree removal and vector control.