Avocado Orchards Research Articles

Avocado fertilization: Matching the periodic demand for nutrients

Abstract The main objective of this study was to assess the seasonal nutrients requirement of ‘Hass’ avocado trees grown in lysimeters, especially during flowering and the early period of fruit development that may affect later on the fruitlet abscission and determine crop yield. The experimental design included three fertigation treatments applying a fixed nutrient solution at three different starting dates of fertigation: (a) T1 – continuous fertigation, including macro nutrients (N-P -K) and micronutrients application, all over the year; (b) T2 – no fertilization (only irrigation) until 15 March, and fertigation as T1 since then; (c) T3 - no fertilization (only irrigation) until 15 May, and fertigation as T1 since then. Absence of fertilization during the winter period induced leaf-chlorosis while healthy, dense and plenteously green leaves characterized the fertilized trees (T1). The beneficial effect of early fertigation on fruit yield was statistically significant, mostly because of higher fruit number. Leaf analyses are commonly used in the avocado industry as a guide for fertilization yet; fruits rather than leaves are the main products of avocado orchards. Consequently, fruit rather than leaf analyses should determine fertilization management. Based on fruit growth data and nutrient concentration in the fruit, the N, P and K quantities removed by ‘Hass’ avocado fruit yield of 30 t ha−1 were 120, 25 and 240 kg ha−1. Taking into account common efficiency consideration (nutrient quantities removed by fruit yield divided by quantities added), the annual quantities of N, P and K required for attaining high quality avocado yield are 250–300, 80–120 and 500–600 kg ha−1, respectively. Thus, fertilization rate together with nutrient combination should be modified in order to insure optimal fruit development.

Spatial Distribution of Bactrocera dorsalis and Thaumatotibia leucotreta in Smallholder Avocado Orchards along Altitudinal Gradient of Taita Hills and Mount Kilimanjaro.

Avocado (Persea americana) fruits are an important source of income and a nutritious food for small-scale growers and other stakeholders involved in farming along the Afrotropical highlands of Taita Hills and Mount Kilimanjaro in Kenya and Tanzania, respectively. Avocado fruits are infested by several insect pests, namely the Asian invasive fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), and the false codling moth, Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae). However, there is inadequate information on the distribution patterns of these pests in small-scale avocado cropping systems in the East African highlands. This study was initiated to generate a spatial distribution map of B. dorsalis and T. leucotreta in avocado orchards at Taita Hills and Mount Kilimanjaro in Kenya and Tanzania, respectively. The two pests were monitored by using their respective parapheromone lures for two years between August 2012 and July 2014. Fruit damage was assessed by computing the proportion of infested fruits for B. dorsalis, whereas the damage score was used for T. leucotreta. Our results indicated that the mean number of B. dorsalis per trap per day differed significantly across elevation, being highest in lowland zone for both Taita Hills (15.90) and Mount Kilimanjaro (24.45). Similarly, the percentage infestation of ground collected fruits by B. dorsalis varied with altitude, being lowest at highlands above 1500 m.a.s.l. (0.66% and 0.83% for Taita Hills and Mount Kilimanjaro, respectively). Conversely, the mean number of T. leucotreta did not vary with altitude in either study area. However, the damage score for T. leucotreta infestation was significantly lower in the highlands of both transects (7.0% and11.1% for Taita Hills and Mount Kilimanjaro, respectively). These findings describe spatial trends that are important in formulating strategies aimed at suppressing the populations of B. dorsalis and T. leucotreta in East African avocado cropping systems.

Effect of Honey Bee (Apis mellifera L.) Density on Pollination and Fruit Set of Avocado (Persea americana Mill.) Cv. Hass.

Abstract The objective of this research was to determine the effect of honeybee density on pollination and fruit set of the Hass avocado. The research was carried out in the municipality of Popayán, Colombia. Three avocado orchards were selected, each one with an area of one hectare and trees with an age of six years. The treatments were: 1) four hives/ha, 2) six hives/ha, and 3) control without hives. Treatments of six and four hives/ha presented significant differences with respect to the control, with a honeybee density per tree of 7.72, 6.04 and 2.72, pollination rate of 60, 55 and 50%, pollination efficiency of 7.57, 6.04 and 5.98 grains of pollen per stigma, 6.11, 4.13 and 3.54% fruit set initial, 0.058, 0.048 and 0.028% fruit set final, 231, 212 and 137 of fruits per tree, 46.2, 38.2 and 21.6 kg fruit per tree, respectively. The results obtained show an increase of honey-bee density per tree, pollination rate, pollination efficiency, % fruit set, % fruit set final, number of fruits per tree and total fruit weight per tree when six and four bee hives/ha are introduced in the avocado crop.

Isolation and pathogenicity of Phytophthora species and Phytopythium vexans recovered from avocado orchards in the Canary Islands, including Phytophthora niederhauserii as a new pathogen of avocado

Root rot, caused by Phytophthora cinnamomi , is the most important disease of avocado, but few studies have determined whether other Phytophthora or oomycete species are involved in crop decline. Avocado orchards in the Canary Islands were surveyed for the presence of Phytophthora and Phytophthora -like oomycetes. Isolates obtained were identified morphologically and by sequence analysis of their internal transcribed spacer (ITS) regions, and their pathogenicity was tested by root and stem inoculation of avocado seedlings. Phytophthora species were isolated in 41 of 99 orchards sampled, and 10% of orchards were infected with more than one species. The species most frequently isolated was P. cinnamomi , which was detected in 26 orchards. In addition, P. multivora (ten orchards), P. niederhauserii (four orchards), P. nicotianae (four orchards), P. palmivora (one orchard) and Phytopythium vexans (20 orchards) were isolated. Phytophthora nicotianae and P. palmivora have been previously reported as pathogens of avocado, but P. niederhauserii, P. multivora and Pp. vexans are reported for the first time to be associated with this host. Phytophthora niederhauserii was the most virulent of these species. It was isolated from declining trees, and root rot severity was comparable to that caused by P. cinnamomi in two independent pathogenicity tests. In addition, P. niederhauserii caused cankers after stem inoculation. The pathogenicity results for P. multivora and Pp. vexans varied depending on isolates and pathogenicity tests. This study increases the knowledge of oomycetes associated with avocado, highlighting the potential threat posed by P. niederhauserii to this important fruit crop.

Vertical Distribution and Daily Flight Periodicity of Ambrosia Beetles (Coleoptera: Curculionidae) in Florida Avocado Orchards Affected by Laurel Wilt.

Ambrosia beetles have emerged as significant pests of avocado ((Persea americana Mill. [Laurales: Lauraceae])) due to their association with pathogenic fungal symbionts, most notably Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the causal agent of the laurel wilt (LW) disease. We evaluated the interaction of ambrosia beetles with host avocado trees by documenting their flight height and daily flight periodicity in Florida orchards with LW. Flight height was assessed passively in three avocado orchards by using ladder-like arrays of unbaited sticky traps arranged at three levels (low: 0-2 m; middle: 2-4 m; high: 4-6 m). In total, 1,306 individuals of 12 Scolytinae species were intercepted, but six accounted for ~95% of the captures: Xyleborus volvulus (Fabricius) (Coleoptera: Curculionidae), Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae), Euplatypus parallelus (Fabricius) (Coleoptera: Curculionidae), Xyleborus bispinatus Eichhoff (Coleoptera: Curculionidae), Xyleborus affinis Eichhoff (Coleoptera: Curculionidae), and Hypothenemus sp. (Coleoptera: Curculionidae). The primary vector of R. lauricola, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae), was not detected. Females of X. volvulus showed a preference for flight at low levels and X. bispinatus for the low and middle levels; however, captures of all other species were comparable at all heights. At a fourth orchard, a baiting method was used to document flight periodicity. Females of X. saxesenii and Hypothenemus sp. were observed in flight 2-2.5 h prior to sunset; X. bispinatus, X. volvulus, and X. affinis initiated flight at ~1 h before sunset and Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae) at 30 min prior to sunset. Results suggest that ambrosia beetles in South Florida fly near sunset (when light intensity and wind speed decrease) at much greater heights than previously assumed and have species-specific patterns in host-seeking flight.

Quantifying the Severity of Phytophthora Root Rot Disease in Avocado Trees Using Image Analysis

Phytophthora root rot (PRR) infects the roots of avocado trees, resulting in reduced uptake of water and nutrients, canopy decline, defoliation, and, eventually, tree mortality. Typically, the severity of PRR disease (proportion of canopy decline) is assessed by visually comparing the canopy health of infected trees to a standardised set of photographs and a corresponding disease rating. Although this visual method provides some indication of the spatial variability of PRR disease across orchards, the accuracy and repeatability of the ranking is influenced by the experience of the assessor, the visibility of tree canopies, and the timing of the assessment. This study evaluates two image analysis methods that may serve as surrogates to the visual assessment of canopy decline in large avocado orchards. A smartphone camera was used to collect red, green, and blue (RGB) colour images of individual trees with varying degrees of canopy decline, with the digital photographs then analysed to derive a canopy porosity percentage using a combination of ‘Canny edge detection’ and ‘Otsu’s’ methods. Coinciding with the on-ground measure of canopy porosity, the canopy reflectance characteristics of the sampled trees measured by high resolution Worldview-3 (WV-3) satellite imagery was also correlated against the observed disease severity rankings. Canopy porosity values (ranging from 20–70%) derived from RGB images were found to be significantly different for most disease rankings (p < 0.05) and correlated well (R2 = 0.89) with the differentiation of three disease severity levels identified to be optimal. From the WV-3 imagery, a multivariate stepwise regression of 18 structural and pigment-based vegetation indices found the simplified ratio vegetation index (SRVI) to be strongly correlated (R2 = 0.96) with the disease rankings of PRR disease severity, with the differentiation of four levels of severity found to be optimal.

Modelización espacial de trips (Insecta: Thysanoptera) en el cultivo de aguacate (Persea americana)

México es el principal productor y exportador de aguacate en el mundo. Los trips son considerados una de las principales plagas de este cultivo, ya que se alimentan del fruto pequeño y forman crestas o protuberancias, las cuales al crecer el fruto son más visibles, y este pierde valor económico. Además de este daño, las heridas causadas por los trips son el principal causante para que entre la enfermedad denominada roña de fruto. Las alternativas de control de los trips han carecido de eficacia debido, entre otras causas, a que se desconoce su distribución espacial dentro de las huertas de aguacate. Este trabajo tuvo por objetivo determinar la distribución espacial de las poblaciones de trips en aguacate mediante el uso de técnicas de estadística espacial que condujeron a la generación de mapas por medio del “krigeado”. Los resultados demostraron que las poblaciones de trips presentan una distribución de tipo agregada, que fue corroborada por los mapas de densidad. Las infestaciones se distribuyeron en el 100 % de la superficie de las dos parcelas experimentales, lo cual resulta interesante para dirigir las medidas de control sobre áreas específicas de infestación. Se logró determinar estabilidad espacial y temporal a corto plazo de las poblaciones de trips.

Management practices and diversity of flower visitors and herbaceous plants in conventional and organic avocado orchards in Michoacán, Mexico

ABSTRACTDespite alleged advantages of organic over conventional farming, management effects on biodiversity are still little known. We related the diversity of herbs and flower visitors to management indicators in avocado orchards and hypothesized that inputs, practices, and context influence diversity of herbs and flower visitors. Using basic classification units, matrix correlation, and multivariate analysis of variance, we found that low-toxicity insecticides, infrequent herb cutting, and presence of forest areas were related to high biodiversity. Intensification of agricultural management reduced biodiversity both in organic and conventional management type. Our results advocate for an improved, integrative, management classification considering intensification and ecological context, besides input-type criteria.

Using Worldview Satellite Imagery to Map Yield in Avocado (Persea americana): A Case Study in Bundaberg, Australia

Accurate pre-harvest estimation of avocado (Persea americana cv. Haas) yield offers a range of benefits to industry and growers. Currently there is no commercial yield monitor available for avocado tree crops and the manual count method used for yield forecasting can be highly inaccurate. Remote sensing using satellite imagery offers a potential means to achieve accurate pre-harvest yield forecasting. This study evaluated the accuracies of high resolution WorldView (WV) 2 and 3 satellite imagery and targeted field sampling for the pre-harvest prediction of total fruit weight (kg·tree−1) and average fruit size (g) and for mapping the spatial distribution of these yield parameters across the orchard block. WV 2 satellite imagery was acquired over two avocado orchards during 2014, and WV3 imagery was acquired in 2016 and 2017 over these same two orchards plus an additional three orchards. Sample trees representing high, medium and low vigour zones were selected from normalised difference vegetation index (NDVI) derived from the WV images and sampled for total fruit weight (kg·tree−1) and average fruit size (g) per tree. For each sample tree, spectral reflectance data was extracted from the eight band multispectral WV imagery and 18 vegetation indices (VIs) derived. Principal component analysis (PCA) and non-linear regression analysis was applied to each of the derived VIs to determine the index with the strongest relationship to the measured total fruit weight and average fruit size. For all trees measured over the three year period (2014, 2016, and 2017) a consistent positive relationship was identified between the VI using near infrared band one and the red edge band (RENDVI1) to both total fruit weight (kg·tree−1) (R2 = 0.45, 0.28, and 0.29 respectively) and average fruit size (g) (R2 = 0.56, 0.37, and 0.29 respectively) across all orchard blocks. Separate analysis of each orchard block produced higher R2 values as well as identifying different optimal VIs for each orchard block and year. This suggests orchard location and growing season are influencing the relationship of spectral reflectance to total fruit weight and average fruit size. Classified maps of avocado yield (kg·tree−1) and average fruit size per tree (g) were produced using the relationships developed for each orchard block. Using the relationships derived between the measured yield parameters and the optimal VIs, total fruit yield (kg) was calculated for each of the five sampled blocks for the 2016 and 2017 seasons and compared to actual yield at time of harvest and pre-season grower estimates. Prediction accuracies achieved for each block far exceeded those provided by the grower estimates.

Antifungal activity of avocado rhizobacteria against Fusarium euwallaceae and Graphium spp., associated with Euwallacea spp. nr. fornicatus, and Phytophthora cinnamomi.

Plant rhizobacteria have been successfully used as biocontrol agents against fungal phytopathogens. However, their potential to control two important avocado diseases, namely Fusarium dieback (FD) and Phytophthora root rot (PRR), has been poorly studied. FD is an emerging disease triggered by fungi associated with two ambrosia beetle species (Euwallacea fornicatus species complex), while PRR is caused by Phytophthora cinnamomi, a soil-borne oomycete. In the present work, the antifungal activity of bacteria isolated from avocado rhizosphere was tested in dual culture assays against Fusarium euwallaceae, Graphium euwallaceae and Graphium sp., causal agents of FD, and against P. cinnamomi. In 2015, rhizosphere soil samples of FD infested and non-infested avocado trees were collected from a commercial avocado orchard in Escondido, California. In an initial screening, 72 of the 168 assessed bacterial isolates reduced mycelial growth of F. euwallaceae by up to 46%. Eight bacterial isolates showing inhibition percentages larger than 40% were then selected for further antagonism assays against the other fungal pathogens. Five bacterial isolates, determined by 16S rDNA sequencing to belong to the Bacillus subtilis/Bacillus amyloliquefaciens species complex, successfully inhibited the mycelial growth of both Graphium species by up to 30%. The same isolates and an additional isolate identified as Bacillus mycoides, inhibited the growth of P. cinnamomi by up to 25%. This is the first report of avocado rhizobacteria with antifungal activity against pathogens responsible for FD and PRR in avocado.

Evaluación de las tasas de deforestación en Michoacán a escala detallada mediante un método híbrido de clasificación de imágenes SPOT

En las últimas décadas, se han registrado altas tasas de deforestación en el estado de Michoacán. En el presente trabajo se puso en marcha un método de clasificación híbrido que combina procesos automatizados, análisis espacial e interpretación visual, el cual permitió generar cartografía de cubierta/uso de suelo para el estado de Michoacán, a escala 1:50 000, con un área mínima cartografiable de una hectárea para 2004, 2007 y 2014. Adicionalmente, se evaluó la fiabilidad de la cartografía generada. La evaluación del mapa para 2007 indicó que la fiabilidad global fue de 83.3%, con un intervalo de confianza de 3.1%. Las tasas de deforestación en Michoacán han disminuido (i.e., 2004–2007; 0.17%, 2007–2014; 0.07%). No obstante, existen dos focos principales de deforestación donde bosques de pino y pino-encino han sido sustituidos por huertas de aguacate (centro del estado) y selvas bajas y medianas han sido transformadas en pastizales (región sierra-costa)

Insect visitors to avocado flowers in the Bay of Plenty, New Zealand

Insect pollination is key to ensuring adequate fruit yields within avocado orchards. Various bee and non-bee insect species have been considered as potential pollinators of avocado worldwide, but in New Zealand there has been little research into which insect species visit avocado flowers. In the Bay of Plenty, an important avocado production area, flower visitor abundance and diversity data were obtained by conducting observational surveys in four orchards in November 2015. Honey bees were the dominant flower visitors in all orchards surveyed, representing 92.9% of all insects recorded, but there was high variation in numbers among sites. Other common insects observed included the beetle, Zorion guttigerum (3.4%), and bumblebees Bombus spp. (1.6%). A better understanding of the interaction between honey bee stocking rates and flower visitor abundances within orchards could assist in improving pollination recommendations.

Insights from “The Hidden Half”: The impact of root-zone oxygen and redox dynamics on the response of avocado to long-term irrigation with treated wastewater in clayey soil

Treated wastewater (TWW) is a major source of water for agriculture in Israel; however, recent reports indicate a marked yield loss in TWW-irrigated avocado and citrus orchards planted in clayey soils. The association of the yield loss with clayey soils rather than sandy soils suggests that it is associated with conditions in the root zone, and specifically poor aeration. A three-year study (2012–2015) was conducted in an avocado orchard planted in clayey soil, comparing the oxygen and redox conditions in the root zone of TWW-irrigated plots with fresh water (FW)-irrigated plots, together with the physiological status of the trees. Soil parameters included: continuous in-situ measurement of soil-water tension (SWT), soil oxygen, and soil redox potential, and periodic measurements of soil solution composition. Physiological parameters included: mineral composition of plant tissue from the leaves, trunk xylem and roots, root growth, yield, fruit setting, plant volume, and yield. TWW-irrigated plots were found to endure longer periods of low SWT indicating higher water content, accompanied by lower oxygen levels and more reduced conditions in comparison to FW-irrigated plots. The differences in these soil parameters between treatments were greater during the irrigation season than during the rainy period. The more reduced conditions in the TWW plots did not lead to significant differences in Fe or Mn concentrations in the soil solution or in plant leaves. TWW soil solution had significantly higher Na levels compared with FW. This did not affect the leaf Na content, but was expressed in substantially higher Na content in the root and trunk xylem, with up to seven times more trunk xylem Na in TWW-irrigated plants compared with FW-irrigated plants. Root growth was significantly hindered in TWW-irrigated plots compared with FW-irrigated plots. A negative correlation was found between root growth and the duration of hypoxic conditions, and similarly between root growth and the Na levels in the roots. TWW-irrigated plants had greater fruitlet numbers at the initial fruit-setting stage, but had a smaller number of fruit and a lower yield at harvest. The yield (kg/tree) negatively correlated with the duration of hypoxic conditions in the root zone but not with the Na levels in the roots or xylem. Our findings point towards a substantial role of oxygen deprivation as a major factor leading to the damage to TWW-irrigated orchards in clayey soils. Based on the assimilation of data, we suggest that a downward cascade is instigated in the TWW-irrigated orchards by increased input of Na into the soil, leading to degradation of soil hydraulic properties and reduced aeration. Impaired physiological functioning of the roots due to limited oxygen supply results in less roots growth, lower water uptake and impaired selectivity against Na uptake, thus imposing a negative feedback to increase soil water content, reduce aeration and root-zone oxygen availability for the roots, and further impair plant resistance to the high Na levels.

Diversidad de la herpetofauna en huertos de aguacate y hábitats conservados en Michoacán, México

The transformation of natural habitats to monocultures is a widespread phenomenon. Therefore, it is important to implement studies to evaluate the impact of this phenomenon on biodiversity of different groups, including the herpetofauna. In this study we carried out an intensive survey of amphibians and reptiles in 3 sites in avocado orchards and 3 sites in pine forest (the original vegetation in sites of avocado orchards). Additionally, since it is a widespread vegetation type in the municipality of Uruapan, Michoacán, México, 3 sites of tropical dry forest were surveyed. Our results indicated that the herpetofauna in avocado orchards presented intermediate levels of diversity between pine forests and tropical dry forest. Furthermore, we found a marked species turnover among habitats, since avocado orchards only shared 23% of species with pine forest and 18% with dry tropical forest. Avocado orchards, immersed in a matrix of the original vegetation, with low levels of management and not exposed to agrochemicals showed potential to maintain several herpetofaunistic elements, including threatened species.

Annual Capture of Two Elachistidae Moth Species UsingStenoma cateniferSex Pheromone in Criollo Avocado (Persea americana) at Chiapas, Mexico

Abstract. Native varieties of avocado (Persea americana Mill) called “Criollo” grow in Mexico, but little is known of their association with the seed borer moth, Stenoma catenifer (Walsingham). S. catenifer is the best-known pest of ‘Hass’ avocado fruit. The S. catenifer sex pheromone was used to capture male S. catenifer in Criollo avocado orchards at different elevations at Chiapas, Mexico from September 2012 to August 2013. Polynomial regression analysis was used to assess the relationship between numbers of moths caught and weather factors (precipitation and temperature). We thought temperature and precipitation might affect the moths captured. Initial S. catenifer captures coincided with crop flowering and presence of avocado fruit, independently of the altitude at the site. S. catenifer was caught frequently at the low-altitude site from December to January, while captures increased from February to May at higher altitude. Moths captured and precipitation were positively correlated at the low-altitu...

Responses of avocado production to variation in irrigation levels

The effects of four irrigation regimes on fruit production and size were evaluated for three seasons in a mature ‘Hass’ avocado orchard (Persea americana Mill.). The research was conducted in Chile’s Central Valley on a clay loam soil at the surface and sandy loam from 0.3 to 0.9 m. Climate zone is sub-humid, Mediterranean-type. A completely randomized block design was used with four applied water treatments (25, 50, 75, and 100% of reference evapotranspiration, ETo), estimated on the basis of mean daily pan evaporation of the previous week, and four replicates each consisting of six trees. Avocado size and production increased significantly as applied water increased to the level equivalent to 75% ETo. Avocado production differed during the three seasons. For the 2005/2006 and 2007/2008 seasons, the highest yield were 29.6 and 26.9 t ha−1 with 10,071 and 8887 m3 ha−1 season−1, respectively. The lowest production was observed for the 2006/2007 season when climatic conditions were adverse, and the highest production was obtained with 100% ETo. Production was consistently less in the ‘off-crop’ years due to alternate bearing for all treatments. However, yield of the 25% and 50% ETo represented only 22% of the yield obtained in the two ‘on-crop’ years, whereas the yield of 75 and 100% ETo in the off year reached 42% of the average yield of the 2 years of high production. The increasing trend in alternate bearing in the drier treatments emphasizes the need to maintain adequate water supply in avocado even in off-crop years.

Distribution, Pest Status and Fungal Associates of Euwallacea nr. fornicatus in Florida Avocado Groves.

Members of a complex of cryptic species, that correspond morphologically to the ambrosia beetle Euwallacea fornicatus (Eichhoff) (Coleoptera: Curculionidae: Scolytinae), were recently found attacking avocado (Persea americana Mill.) in Israel and California. In early 2016, an outbreak of another member of this species complex was detected infesting approximately 1500 avocado trees in an avocado orchard at Homestead, Florida. An area-wide survey was conducted in commercial avocado groves of Miami-Dade County, Florida to determine the distribution and abundance of E. nr. fornicatus, to identify different populations of E. nr. fornicatus and their fungal associates, and to assess the extent of damage to avocado trees. Ewallacea nr. fornicatus were captured in 31 of the 33 sampled sites. A sample of 35 beetles from six different locations was identified as E. nr. fornicatus sp. #2, which is genetically distinct from the species causing damage in California and Israel. Eleven fungal associates were identified: an unknown Fusarium sp., AF-8, AF-6, Graphium euwallaceae, Acremonium sp. Acremonium morum, Acremonium masseei, Elaphocordyceps sp. and three yeast species. The unknown Fusarium isolates were the most abundant and frequently found fungus species associated with adult beetles and lesions surrounding the beetle galleries. In addition to fungal associates, three bacteria species were found associated with adult E. nr. fornicatus. Visual inspections detected significant damage in only two orchards. A large number of beetles were captured in locations with no apparent damage on the avocado trees suggesting that E. nr. fornicatus are associated with other host(s) outside the groves or with dead trees or branches inside the groves. More research is needed to determine the potential threat E. nr. fornicatus and its fungal associates pose to the avocado industry and agricultural and natural ecosystems in Florida.

TEJIDOS ALTERNATIVOS AL FOLIAR PARA EVALUAR LA RESPUESTA A LA FERTILIZACIÓN CON ZN O B EN AGUACATE HASS

Las deficiencias de zinc (Zn) o boro (B) en frutos y hojas de aguacate (Persea americana Mill.) cv. Hass son comunes en la región productora del estado de Nayarit, México. El seguimiento de la concentración foliar de estos micronutrimentos en respuesta a la fertilización no siempre proporciona un diagnóstico adecuado. El objetivo de esta investigación fue evaluar el efecto de la fertilización al suelo con Zn o B sobre la concentración de estos nutrimentos en el tejido de diferentes estructuras de la planta de aguacate Hass. El estudio se realizó en un huerto comercial de Hass cultivado sin riego en clima semicálido subhúmedo de Tepic, Nayarit. Los tratamientos fueron aplicados al suelo, anualmente del año 2001 al 2005, durante la estación lluviosa (julio y septiembre) y fueron (g por árbol por año): (T-1) dos aplicaciones de 750 g ZnSO4 (35.5 % Zn); (T-2) dos aplicaciones de 29.5 g Boronat® (32 % B); (T-3) testigo, sin aplicación de Zn o B. Los tejidos muestreados fueron: inflorescencias en estado “coliflor”, inflorescencia completa en antesis, flores en antesis, raquis de la inflorescencia en antesis, pedúnculo + pedicelo del fruto en madurez fisiológica, pulpa del fruto y hojas del flujo vegetativo de invierno de seis meses de edad. Los tejidos que mejor reflejaron la respuesta a la fertilización con Zn fueron el raquis de inflorescencias en antesis y la pulpa del fruto en madurez fisiológica. En el caso del B lo fueron las inflorescencias completas en antesis y el pedúnculo + pedicelo del fruto en madurez fisiológica.

Characterisation and pathogenicity of fungal species associated with branch cankers and stem-end rot of avocado in Italy

Branch cankers and stem-end rot are two of the most important threats to avocado production. During the autumn of 2013, sampling was conducted in the main avocado growing area in eastern Sicily to study the occurrence and establish the causal agents of branch canker and stem-end rot. A total of 94 fungal isolates, recovered from four avocado orchards, were identified by morphological characterisation, DNA sequencing and phylogenetic analyses as belonging to the genera Colletotrichum, Neofusicoccum or Diaporthe. The majority of the isolates were identified as Neofusicoccum parvum (70.2 %), with the remaining isolates being Colletotrichum gloeosporioides or C. fructicola (16 %), and Diaporthe foeniculacea or D. sterilis (13.8 %), respectively. Pathogenicity tests showed N. parvum was the most virulent species (P = 0.05), whereas Diaporthe isolates were the least so. An intermediate virulence was observed for C. gloeosporioides and C. fructicola, which were associated only with stem-end rot of fruit. Regarding cultivar susceptibility of fruit to these pathogens, ‘Hass’ was more susceptible to infection by C. fructicola and D. foeniculacea compared with ‘Bacon’ whereas no significant differences were detected for the remaining pathogens. To our knowledge, this is the first account of the pathogens causing branch canker and stem-end rot of avocado in Italy, and the first studies comparing the relative virulence of each species involved.

Spatial Dependence and Sampling of Phytoseiid Populations on Hass Avocados in Southern California.

Research on phytoseiid mites has been critical for developing an effective biocontrol strategy for suppressing Oligonchus perseae Tuttle, Baker, and Abatiello (Acari: Tetranychidae) in California avocado orchards. However, basic understanding of the spatial ecology of natural populations of phytoseiids in relation to O. perseae infestations and the validation of research-based strategies for assessing densities of these predators has been limited. To address these shortcomings, cross-sectional and longitudinal observations consisting of >3,000 phytoseiids and 500,000 O. perseae counted on 11,341 leaves were collected across 10 avocado orchards during a 10-yr period. Subsets of these data were analyzed statistically to characterize the spatial distribution of phytoseiids in avocado orchards and to evaluate the merits of developing binomial and enumerative sampling strategies for these predators. Spatial correlation of phytoseiids between trees was detected at one site, and a strong association of phytoseiids with elevated O. perseae densities was detected at four sites. Sampling simulations revealed that enumeration-based sampling performed better than binomial sampling for estimating phytoseiid densities. The ecological implications of these findings and potential for developing a custom sampling plan to estimate densities of phytoseiids inhabiting sampled trees in avocado orchards in California are discussed.