Mature Orchard Research Articles

HLB Progress and Yield Sustainability in Mature Sweet Orange Orchards Treated with Nutritional and Elicitor Products

Although the implementation of area-wide inoculum reduction and Asian citrus psyllid control are decisive in controlling Huanglongbing (HLB) epidemics, growers continue looking for enhanced nutritional and/or resistance inducer (ENRI) treatments to mitigate yield damage in HLB-affected trees. Therefore, an experiment was set up in an 8-year-old sweet orange orchard to evaluate the effects of the foliar application of nutrients, phosphite, and salicylate sprayed four to five times per year during flushing periods. The trial had eight treatments in four randomized blocks. HLB incidence and yield were assessed from December 2010 to January 2017. HLB-symptomatic trees with less than 5% HLB severity were selected from each plot in the first (Group 1), second (Group 2), and third years (Group 3) after the beginning of treatments to assess the frequency of trees with different HLB symptoms and micronutrient deficiencies, HLB severity, and fruit yield until January 2017. Twenty asymptomatic trees from each plot were also harvested for comparison each year. ENRI treatments did not reduce the progress of HLB incidence in the plots or the HLB severity progress or frequency of HLB symptoms in the selected trees. ENRI treatments did not improve the yield of symptomatic trees compared with asymptomatic trees. Hence, in a scenario without HLB-symptomatic tree removal in mature orchards, disease severity progress and yield reduction in HLB-affected trees remained regardless of ENRI treatment. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Local and landscape context affects bee communities in mixed fruit orchards in Southern Thailand

Abstract Bees play an important role by contributing to the pollination of a diverse range of crops and wild plants. However, bees are threatened by deforestation and habitat degradation caused by urbanization and agricultural intensification, which reduce floral and nesting resources. In this study, the effects of local (orchard size, flowering plant abundance and richness and floral abundance) and landscape factors (surrounding agricultural, forest and urban cover) on bee richness and abundance in mixed fruit orchards were determined from 28 mature orchards interspersed along a gradient of landscape complexity. Bees were observed for 15 min in 2 × 2 m plots. We categorized all bees into one of the three groups: (a) honey bees, (b) solitary bees and (c) stingless bees. Several local and landscape factors were found to influence bee richness and abundance. Honey bee abundance was positively affected by orchard size, whereas honey bee richness was not. Stingless bee richness and abundance were positively correlated with floral abundance. Forest cover within a 3‐km radius positively affected solitary bee richness. Solitary bee abundance was positively affected by forest cover within a 3‐km radius and negatively impacted by urban cover within a 1.5‐km radius. In our study area, small forest patches are found in abundance; thus, the high proportion of forest edge, relative to the forest interior, greatly supports solitary bee abundance and richness in this landscape. Moreover, most solitary bees are soil‐nesting species that may be excluded from environments that are converted from natural to anthropogenically developed areas. Recommendations to protect pollinators included conserving existing forest patches, especially forest margins; restoring forest patches within farmland landscapes; maintaining a diversity of herbs and grasses within mixed fruit orchards; establishing live fences composed of diverse plant species and retaining dead trees within farmland. For urban areas, augmenting floral resources in green spaces is suggested.

Evaluation of Removed and Recycled Mineral Nutrients in Italian Commercial Persimmon Orchards

Persimmon is a typical fruit crop of the Mediterranean region and, since it is considered a minor species, little information is available on its nutrients need. In the present experiment, it was estimated the quantity of removed and recycled nutrients by Kaki Tipo and Rojo Brillante, the two main varieties of persimmon grown in Emilia-Romagna region (Po Valley, Italy). Plants from ten mature orchards were selected and harvested; organs (leaves in summer, fruits at harvest, abscissed leaves, roots and skeleton) biomass and mineral composition were determined. The yearly uptake of macronutrients was similar for the 2 varieties, accounting for (kg ha−1): N 89-91, P 10-11, K 79-91, Ca 132-162, Mg 22-26 and S 9. While K was mostly found in fruits, Ca and Mg were mainly partitioned to leaves. Among micronutrients, Mn and Fe showed the highest values (1.1–1.3 and 1.2–2.1 kg ha−1, respectively), followed by B (370 g ha−1), while Cu and Zn showed the smallest amounts (less 100 g ha−1). Nitrogen, Ca, Mg and S were those more recycled than removed, while K showed an opposite trend; among the microelements, the annual recycled fractions of B and Mn were higher than that removed.

Impact of rhizobacteria community of citrus root on Tylenchulus semipenetrans and on Citrus plant growth

ABSTRACT Tylenchulus semipenetrans Cobb, is a parasitic nematode of citrus, causing significant reduction in citrus growth and yield. Biological antagonists including bacteria and fungi have been used to control citrus nematodes. Citrus rhizosphere bacteria were collected from mature orchards in Tunisia and they have been studied to evaluate their nematicidal potentials on citrus nematode and abilities to stimulate plant root growth. Sixty bacterial strains isolated from egg masses of citrus nematode, citrus roots and associated to nematode trapping fungi, were tested for their abilities to parasitize T. semipenetrans and their impact on citrus growth parameters. The data analysis revealed that Bacillus weihenstephanensis, Lysinibacillus sphaericus, Bacillus subtilis, Bacillus thuringiensis, Bacillus pumilus and Bacillus cereus showed the highest effectiveness on T. semipenetrans juvenile (J2) causing up to 85% mortality of juveniles (J2) after 6 days of exposure in vitro. B. subtilis, B. amyloliquefaciens, B. pumilus and B. weihenstephanensis also inhibited egg hatching of citrus nematode in vitro. Furthermore, the majority of these rhizobacteria significantly stimulated citrus growth parameters. The application of B. weihenstephanensis, B. cereus, B. mycoides, B. thuringiensis, L. sphaericus, and Alcaligenes faecalis stimulated sour orange root growth in vitro compared to the control. Citrus rhizosphere bacteria must be studied further due to their diversity, abundance, and ability to effectively control T. semipenetrans.

Studies on physiological and productive effects of multi-leader training systems and Prohexadione-Ca applications on apple cultivar 'WA 38′

The release of new apple varieties able to improve consumer satisfaction provides the opportunity to modernize orchards and transition them away from unlucrative plantings towards highly productive, high-value cultivation systems. Top-working an existing, unprofitable mature orchard by grafting a new variety allows the orchardist to take advantage of an existing root system to achieve early bearing and reduce the establishment cost. Often, the scion in a new top-grafted orchard can present excessive vigor in the years following the grafting due to the abundance of reserves stored in the mature root system that become available for the new variety at the beginning of the season. This case study focuses on ‘WA 38′, an apple variety released in 2017 to Washington State growers. ‘WA 38′ can show variable vigor levels depending on the choice of rootstock, training system, planting density, pruning technique, water availability, and soil characteristics. Prohexadione-calcium (Pro-Ca, Apogee®) has been utilized for years in apple and other crops as a growth regulator with inhibitory activity on gibberellin synthesis, with the common effect of reducing shoot growth and canopy development and other potential physiological effects depending on genetics of the variety, timing, and rate of applications. This study investigated the physiological responses of ‘WA 38′ scion top-grafted on an 8-year-old Granny Smith/M.9 orchard and then trained to 1, 2, and 3-axis systems—suitable for modern mid-high-density planting—with and without the application of Pro-Ca for two consecutive years. The growth regulator was applied in post-bloom at a 250 ppm rate, starting at approximately 12-cm shoot length for three sprays per season. The parameters assessed to evaluate the impact of Pro-Ca on the variety in three training systems were: one-year-shoot length, internode length, dormant pruning weights, number of flower clusters per tree, photosynthetic carbon assimilation rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, chlorophyll determination (by SPAD and chemical extraction), leaf mineral analysis (macro and micro-nutrients), yield per tree, fruit size distribution and packout. The present results confirmed the effectiveness of the Pro-Ca in reducing the canopy growth and vigor in ‘WA 38′, with diminished internode length, total shoot length, and lower amount of pruned material. Leaf gas exchange parameters and chlorophyll quantification highlighted an alteration of tree physiology by Pro-Ca application with increased transpiration, stomatal conductance, intercellular CO2 concentration, and higher concentrations of chlorophyll a and b with respect to untreated trees. Pro-Ca-treated- ‘WA 38′ trees did not show any negative effect on productivity; rather, an increased average fruit mass and an enhanced proportion of apples in the extra-large size category compared to control. Fewer significant differences were found in the comparison between the training systems. Overall, the 3-axis system showed a higher yield and greater number of flower clusters per tree with a lower average area of each leader in comparison to 1-axis. Further investigations will shed light on ‘WA 38′ tree performance, productivity, and fruit quality after multiple years of Pro-Ca treatment to offer orchard management recommendations for a modern, top-worked, machine-friendly orchard.

Analysis of soil water potential characteristics of wheat croplands and apple orchards in an agroforestry ecosystem based on the van Genuchten model

Due to intense droughts and water shortages, soil water deficit limits agricultural production in arid and semiarid areas, such as China’s Loess Plateau region. Yet the effects of different cover crops on soil water in these areas have received insufficient attention. This study was conducted in the Weibei rainfed highland to investigate soil water potential dynamics in an agroforestry ecosystem comprising winter wheat (<i>Triticum aestivum</i> L.) and apple (<i>Malus domestica</i>) trees over the apple growth period (March to September of 2020). Soil water characteristic curves (SWCCs) of cropland topsoil (0 to 40 cm), orchard topsoil (0 to 40 cm), dark loessial subsoil (40 to 80 cm), and loess parent material (80 to 150 cm) were determined using the centrifuge method and water vapor equilibrium method. The van Genuchten model was used to fit SWCCs and then convert volumetric soil water content monitored in field plots to soil water potential. A quantitative analysis was conducted to evaluate soil water stress in wheat croplands and apple orchards. The model performed well in fitting SWCCs for all tested soils, yielding a robust accuracy (<i>R</i>² &gt; 0.96). Compared to apple trees, wheat was more threatened by drought. From mid-March to early July, the 0 to 100 cm soil layers of croplands all exhibited high water stress with matric suction pF &gt; 3.98, and unavailable water occurred in the 0 to 20 cm and 0 to 80 cm soil layers in late March to late April and mid-May to mid-July, respectively. Drought threat in apple orchards increased with an increase in tree age. In young orchards (&lt;10 y), high water stress was found only in surface soil layers (0 to 20 cm) in mid-March to late April and late May to early July, which spread to a depth of 70 cm in early June to early July. In mature orchards (10 to 20 y), high water stress was similarly observed in the surface soil layers in mid-March to early May and late May to early July, which extended to the 80 cm depth in late May to early July. In old orchards (&gt;20 y), high water stress initially emerged in the surface soil layers in early April to mid-April and then reached the 70 cm depth in late May to mid-July, whereas unavailable water occurred in the 0 to 60 cm soil layers in mid-June to mid-July. The results indicated that soil water stress zones with low water potential were formed intermittently at different soil depths of apple orchards depending on tree age and growth stage. However, compared to wheat croplands, apple orchards were less influenced by drought stress, so that converting croplands to orchards could alleviate drought threats in the Weibei area.

Soil Quality Index of Young and Differently Managed Almond Orchards under Mediterranean Conditions

Sustainable agriculture has drawn attention to the maintenance and enhancement of soil health. However, research on soil quality has been carried out mainly in field crops and, to a lesser extent, in mature orchards, neglecting the relevance of assessing the soil quality status in the first years of tree plantations. Therefore, the aim of this study was to assess the soil quality index of young almond orchards located in marginal lands and managed under different practices. The survey was carried out in the Teruel Province (Northeast Spain), in three almond orchards: Alacón (2 years old, 0.75 ha, rainfed, conventionally managed), San Martín (1 year old, 0.4 ha, irrigated, organically managed), and Valdealgorfa (6 years old, 0.2 ha, rainfed, organically managed). The composite soil samples were taken from three spots within each orchard. To determine the soil quality index, four main soil functions were considered: filtering and buffering, nutrient supply, water relations, and crop limitation. The soil quality indices were 0.55, 0.75, and 0.54 for Alacón, San Martín, and Valdealgorfa orchards, respectively. These values suggested that the evaluated soils are adequate for almond production, although they require management actions to improve their quality (for instance, the application of organic amendments) and increase the sustainability of these agroecosystems. Furthermore, this work provides a framework for the assessment of the soil quality in tree orchards at a young stage.

Pruning and Water Saving Management Effects on Mango High-Density and Mature Orchards

Water is getting scarce and irrigation practices should become more efficient. Mango orchards require great quantities of water, and policies in developing countries are substituting surface gravity irrigation by pressurized systems. A commercial orchard having mature 25-year-old trees and a 10-year-old HD high-density section were irrigated with micro sprinklers using 100% ETc (crop evapotranspiration) and reduced deficit irrigation treatments of 75% and 50% ETc. Water soil measurements were made with EC-5 probes at 10 and 35 cm in depth to study the effect of the different irrigation treatments. After the 2020 harvest, mature trees were trimmed without achieving pruning severity greater than 1.3. Canopy volume, mango size, fruit yield and water-use efficiency WUE were analyzed during 2020 and 2021. Sporadic storms produced sprinkler watering problems as weeds proliferated within trees. A controller with a fuzzy algorithm optimized orchard management and saved water in trees without decreasing yield and fruit size. It was found that one year after mature trees were trimmed by taking away the larger internal branch, more light penetrated the canopy, increasing yield by 60%; pruning in HD trees presented a yield increase of 5.37%. WUE (water-use efficiency) also increased with pruning and its value increased to 87.6 when the fuzzy controller and the 50% DI treatments were used in mature trees. This value was 260% greater than the one obtained in pruned trees without the controller. HD trees presented a lower WUE and yield per hectare than mature trees.

Simulation of soil desiccation effects and production water footprint of apple orchards in different precipitation areas of the Loess Plateau, China

To clarify the desiccation effect of deep soil and water footprint of crop production in two typical dry-farming apple orchards on the Loess Plateau of China, with Luochuan County in semi-humid region and Mizhi County in semi-arid region as two typical apple planting areas, we used the WinEPIC model to quantitatively simulate and analyze the variations of soil moisture from 0 to 15 m and water footprint of apple production during 1980-2020. The results showed that annual yield of mature orchards in Luochuan and Mizhi followed an "S" curve, with the average annual values being 24.64 and 18.42 t·hm-2, respectively. The average annual evapotranspirations of Luochuan and Mizhi were 623.82 and 458.97 mm, the average annual drought stress days of Luochuan and Mizhi were 20.4 and 52.73 days, and the water overconsumption were 167.94 and 121.15 mm, respectively. The available soil water contents in Luochuan and Mizhi showed a sharp decline from 1 to 25 years old and from 1 to 23 years old, respectively, with average annual soil desiccation rates being 64.6 and 68.03 mm·a-1, respectively. The dry layer of deep soil for the orchards of Luochuan and Mizhi appeared at the 13th and 7th years, and would be stable after 23 and 22 years, respectively. The formation and stability time of the soil dry layer in the area with high precipita-tion was later than that with low precipitation. Long-term soil moisture deficit would result in irreversible soil dry layer. Water footprint of apple production in Luochuan and Mizhi were low in the early stage and high in the later stage, with the average annual values being 0.187 and 0.194 m3·kg-1, respectively. Both apple yield and production water footprint were affected by precipitation. To ensure the sustainable and healthy development of apple industry, it was recommended that the optimal planting age of apple trees is about 23 years on the Loess Plateau where water sources is limited, and the maximum should not exceed 25 years.

Measurement and modeling of canopy interception losses by two differently aged apple orchards in a subhumid region of the Yellow River Basin

Canopy interception (Ic) of rainwater is an important component of hydrological cycles, and its measurement and modeling are essential for understanding water balances and formulating scientific strategies of management in different ecosystems. Large areas of traditional agricultural crops have been replaced with apple orchards in the Yellow River Basin, while few studies were conducted to quantify and model canopy interception for apple orchards with different ages. In this work, we measured rainfall, stemflow and throughfall and calculated Ic for young and mature apple orchards from May to September 2013–2016 in Changwu County on the Loess Plateau in the Yellow River Basin. The revised Gash model was applied to the two orchards. The results revealed that annual Ic for the young (range 22.2–29.2 mm) and mature (range 26.8–39.7 mm) orchards varied between years. During the past four years, cumulative modeled Ic was 7.6 ± 1.0 and 10.5 ± 0.9% higher than cumulative measured Ic for the young and mature orchards, respectively. Evaluation parameters the mean root mean square error and bias values (0.1719 mm and 0.0372 mm, respectively) between the measured and modeled Ic implied that the revised model performed better for the young orchard. For both orchards, the revised model was most sensitive to the ratio of mean evaporation rate to mean rainfall intensity and canopy storage capacity each year. The good agreement between the measured and modeled Ic indicated that the revised model was suitable for predicting Ic for apple orchards with different ages under our climatic conditions or similar conditions.

Efficiency of irrigation and fertigation in a mature apple orchard: a Latvia experience

Efficiency of irrigation and fertigation in a mature apple orchard: a Latvia experience

Deep soil water storage and drainage following conversion of deep rooted to shallow rooted vegetation

Deep soil water management is important for agroforests to combat frequent droughts. However, little is known about how deep soil water (up to 15.0 m) and its deep drainage after trees fell evolves with time (< 20 years) in deep vadose zone. Therefore, this study was aimed at evaluating the impact of orchards removal on the replenishment of deep soil water and its deep drainage in a sub-humid region on the Loess Plateau, China (LPC). We established paired experimental plots between cultivated farmlands after deforested land and mature/aged orchards. Soil water storage and deep drainage were calculated from the measured soil water contents based on deep soil sampling (down to 6–15.0 m). Then, the time evolution of soil water storage and deep drainage rates were obtained based on the space for time substitution. Results showed that the replenishing front (indicated by the increase of soil water) deepened with time after orchard removal, which progressively increased deep soil water content. The drainage rates increased suddenly right after orchard removal and attained a constant value of 22.0 ± 3.1 mm yr−1 after the conversion. With this deep drainage rate, deep soil water deficit created by prior mature orchards would require 48–69 years of annual crop cultivation. Therefore, this study helps improve the further understanding of ecohydrological process under land use and management of deep soil water storage for increasing resiliency of agroforests to climate change.

Rootstock and Nutrient Imbalance Leads to ‘‘Green Spot’’ Development in ‘WA 38’ Apples

‘WA 38’ is a new apple (Malus domestica Borkh.) cultivar, released by Washington State University (WSU) in 2017. An unknown disorder, ‘‘green spot’’ (GS), dark green halos in the epidermis, with necrotic, corky, and oxidated cortical tissue underneath the damaged epidermis, leads to unmarketable fruit and has become a threat to the adoption and profitability of ‘WA 38’, with young and mature orchards exhibiting up to 60% incidence in 2020. Given the apparent susceptibility of ‘WA 38’ to GS, this research investigated GS relation with nutrient levels in fruit. Research was carried out in 2018 and 2019 in a ‘WA 38’ apple block planted in 2013, on ‘Geneva 41’ (‘G.41’) and ‘M.9-Nic 29’ (‘M.9’) rootstocks. In both years, fruit number per tree, fruit weight, and fruit diameter were evaluated in 18 trees per treatment, from both rootstocks. From each tree, fruit were classified for presence or absence of GS, and subsequently analyzed for nutrient concentration in the peel and in the flesh, nutrient extraction, and total nutrient content, on an individual apple basis. Apples with GS had higher nitrogen (N) and magnesium (Mg) levels in the peel, regardless of year and rootstock. Apples grown on ‘G.41’ rootstock exhibited higher GS incidence and reduced crop load in both years; reduced size and fruit diameter were exhibited only in 2018. Fruit on ‘G.41’ had higher N, potassium (K), and Mg in the flesh and higher N and Mg in the peel, with lower levels of calcium (Ca) in the flesh and peel; however, only in 2018, with no differences in 2019. GS in ‘WA 38’ apples appears to be another Ca-related disorder in which excessive vigor, rootstock, and N and Mg excess are predisposing factors for its development.

Soil chemical quality assessment and spatial distribution of pomelo orchards in acidic red soil hilly regions of China.

Soil quality assessment is a critical strategy for determining optimum fertilization in intensive pomelo production. In this study, we evaluated the soil quality status and mapped the spatial distribution of 347 soil samples collected from pomelo orchards in Pinghe County, southern China. We analyzed nine chemical parameters and an altitude indicator. The mean soil quality index (SQI) was 0.355 in the total data set (TDS) and 0.292 in the minimum data set (MDS). Available Ca (Avail-Ca), pH value, organic matter and altitude were selected as indicators of soil quality in the MDS. The SQI in mature orchards (>10 years) was higher than that in young orchards (<10 years), while no differences between soil types and altitude gradients were identified. We detected a significant positive correlation between the SQI based on TDS (SQITDS ) and the SQI based on MDS (SQIMDS ), and the spatial distribution of soil properties and SQITDS showed a uniform pattern, except for Avail-N, Avail-B and SQIMDS . Overall, unfavorable soil quality indicators, including rich in Avail-P, deficient in Avail-Ca, -Mg and -B, soil acidification and high altitude, were considered to be limiting factors for pomelo production. The soil chemical quality in pomelo orchards is generally low, indicating that integrated management by controlling acidification, reducing planting altitude, regulating fertilization and monitoring soil properties is required for sustainable pomelo production. © 2021 Society of Chemical Industry.

Stand age and precipitation affect deep soil water depletion of economical forest in the loess area

Success of afforestation efforts hinges on better understanding of roles of water in the deep unsaturated zone in plant water uptake. But previous studies have deep soil water measurement either not deep, or not long enough to understand annual deep soil depletion rate for reforested forests, especially the effect of stand age or precipitation year on annual deep soil water depletion rate. To address this question, we selected, in 2016, four apple orchards planted on cropland in 2008, 2005, 2001, and 1994 (i.e., young orchard AP2008, mature orchards AP2005 and AP2001, and old orchard AP1994, respectively) in a thick loess area. Soil water contents were measured in 2016 - 2020 to the depth of 19 m with an in-situ neutron probe technique. Meanwhile, leaf area indexes were measured in 2017 and 2019 to represent each orchard water demand. Results showed annual deep soil water in 5-19 m showed a peak depletion rate of 160 mm yr−1 at around 14 years of orchard age. After the age effects are removed, mature orchards AP2005 and AP2001 showed significant depletions in 5-19 m deep soil water in the dry year 2016; in normal years 2017/2018, the depletion rates were reduced; and no significant deep soil water depletions were found in all orchards in the wet year 2019. The greater deep soil water uses in mature orchards AP2005 and AP2008 agreed with greater leaf area indexes. The depleted deep soil water contributions to actual evapotranspiration (AET) were 27.0% and 13.6% in the dry year 2016 for orchards AP2005 and AP2001, respectively; but their respective contributions were 15.1% and 7.9% in normal years 2017/2018. This indicates both the rainwater supply and the stand age affect deep soil water use, which suggests that more rainwater saving strategies and branch pruning are needed to avoid excess deep soil water depletion in dry and normal precipitation years for the mature forest on the Chinese Loess Plateau.

Title: Selective limb removal pruning and reflective ground covers improve light and crop distributions in the lower zone of ‘Nonpareil’ almond trees but not total yield

Conventional planting and management systems for almond (Prunus dulcis (Mill.) D. A. Webb) orchards involve trees trained from an early age to produce multiple large scaffold branches, which in mature orchards form closed light inefficient canopies. Treatments included a single round of selective limb removal pruning applied at the start of the research to remove the large scaffold branches that cause shading between trees. Treatments were applied to two groups of 5-year-old ‘Nonpareil’ trees on ‘Nemaguard’ rootstock planted at 6 × 3 m spacing (556 trees/ha) in the Riverland region of South Australia. Each year, reflective ground covers were installed beneath one group of pruned trees to reflect light back into the lower canopy zones. A third group of control trees were left unpruned without reflective ground covers. Yield, kernel quality and light transmission within canopy zones were monitored for 3 subsequent years. Results demonstrated that in control trees, less than 10% of incoming sunlight was transmitted to lower canopy zones. This was insufficient to ensure cropping in these zones. Although pruning selected limbs and using reflective ground covers increased the amount of light and thus yields in the lower canopy zones, this was not sufficient to increase total tree yield nor improve kernel quality. Furthermore, the fruit in these lower zones were not ready for harvest until 2–3 weeks after the main crop.

Fungal Pathogens Associated With Canker Diseases of Almond in California.

Almond canker diseases are destructive and can reduce the yield as well as the lifespan of almond orchards. These diseases may affect the trunk and branches of both young and mature trees and can result in tree death soon after orchard establishment in severe cases. Between 2015 and 2018, 70 almond orchards were visited throughout the Central Valley of California upon requests from farm advisors for canker disease diagnosis. Two major canker diseases were identified, including Botryosphaeriaceae cankers and Ceratocystis canker. In addition, five less prevalent canker diseases were identified, including Cytospora, Eutypa, Diaporthe, Collophorina, and Pallidophorina canker. Seventy-four fungal isolates were selected for multilocus phylogenetic analyses of internal transcribed spacer region ITS1-5.8S-ITS2 and part of the translation elongation factor 1-α, β-tubulin, and glyceraldehyde 3-phosphate dehydrogenase gene sequences; 27 species were identified, including 12 Botryosphaeriaceae species, Ceratocystis destructans, five Cytospora species, Collophorina hispanica, four Diaporthe species, two Diatrype species, Eutypa lata, and Pallidophorina paarla. The most frequently isolated species were Ceratocystis destructans, Neoscytalidium dimidiatum, and Cytospora californica. Pathogenicity experiments on almond cultivar Nonpareil revealed that Neofusicoccum parvum, Neofusicoccum arbuti, and Neofusicoccum mediterraneum were the most virulent. Botryosphaeriaceae cankers were predominantly found in young orchards and symptoms were most prevalent on the trunks of trees. Ceratocystis canker was most commonly found in mature orchards and associated with symptoms found on trunks or large scaffold branches. This study provides a thorough examination of the diversity and pathogenicity of fungal pathogens associated with branch and trunk cankers of almond in California.

Contribution of understorey vegetation to evapotranspiration partitioning in apple orchards under Mediterranean climatic conditions in South Africa

Orchard evapotranspiration (ET) is a complex flux which has been the subject of many studies. It often includes transpiration from the trees, cover crops and weeds, evaporation from the soil, mulches and other orchard artefacts. In this study we investigated the contribution of the orchard floor evaporative fluxes to whole orchard ET focusing on the transpiration dynamics of understorey vegetation which is currently not well known. Data on the partitioning of ET into its constituent components were collected in apple (Malus Domestica Bork) orchards with varying fractional canopy cover. The study orchards were in the prime apple growing regions in South Africa. The orchards were planted to the Golden Delicious/Reinders and the red cultivars (i.e. Cripps’ Pink/ Royal Gala/Fuji). Tree transpiration was quantified using the heat ratio method and the thermal dissipation sap flow techniques. Understorey transpiration was measured at selected intervals using micro stem heat balance sap flow gauges calibrated against infrared gas analyser readings. Orchard ET was measured using an open path eddy covariance system while the microclimate, radiation interception, and soil evaporation were also monitored. Orchard floor evaporative fluxes accounted for as much as 80% of the measured ET in young orchards with dense understorey vegetation that covered most of the orchard floor. In these orchards the understorey transpiration was of the same order of magnitude as the bare moist soil evaporation suggesting that water use by the understorey vegetation was substantial. However, in mature orchards with a high canopy cover (>55% fractional cover), orchard floor water losses were less than 30% of the measured ET. Understorey transpiration rates were much lower, contributing less than 10% of the whole orchard ET. Significant volumes of water can be saved, especially in young orchards, by keeping the orchard floor vegetation short, reducing the area occupied by understorey vegetation, and by reducing the wetted ground surface area.

The influence of citrus orchard age on the ecology of entomopathogenic fungi and nematodes

ABSTRACT A three-year survey of the ecology of entomopathogenic nematodes (EPN) and entomopathogenic fungi (EPF) was undertaken on soils from citrus orchards of different ages to determine the influence of orchard age on the ecology of entomopathogenic fungi and nematodes. The influence of mulch and irrigation method on the occurrence of EPN and EPF was also determined. Most of the isolates recovered (n = 810) were Beauveria sp. (87.88% of all isolates), followed by Metarhizium sp. (11.87% of all isolates). Only 0.24% of soil samples collected during this study tested positive for EPN. All EPN isolates recovered were Heterorhabditis bacteriophora. No significant differences in EPF occurrence were recorded between orchards under drip and micro-sprinkler irrigation. EPF occurrence was significantly lower (P = 0.016) in orchards covered by mulch (31.85% ± 2.07% occurrence) than in orchards with no covering (38.57% ± 1.57% occurrence). EPF occurrence of 40.33 ± 2.13% was highest in non-bearing orchards, followed by mature orchards (nine years or older) (36.76 ± 2.05% of samples) with the lowest EPF occurrence of 25.30 ± 2.02% reported in juvenile orchards (four to eight years old). Juvenile orchards sustain significantly less EPF than mature and non-bearing orchards because of the combined negative impact of less favourable environmental conditions (lower shade density) and fungicide applications.

Effects of salinity and sodicity on the seasonal dynamics of actual evapotranspiration and surface energy balance components in mature micro-irrigated pistachio orchards

This article presents findings from a field research study conducted in the San Joaquin Valley of California in 2016–2018 to appraise the effects of soil salinity and sodicity on evapotranspiration and energy balance components of micro-irrigated pistachio orchards. Actual evapotranspiration (ETa) and tree physiologic parameters were measured during consecutive growing seasons in mature orchards grown on non-saline and saline/sodic soils. Salinity and sodicity decreased pistachio water use by about 30%, with ETa reductions varying along the growing season. Accurate information on the dynamics of ETa and energy balance components along the growing season can improve water management for nut orchards exposed to long-term saline-sodic conditions. Results show that the main driver of ETa was the net radiation (Rn), which supplied most of the energy to vaporize water, irrespective of the growth period and level of salinity/sodicity. Field observations revealed that Rn was lower for salt-affected trees due to smaller canopies, which intercepted less light than non-saline trees. Secondarily, the exchange of sensible heat (H) between the ambient air and tree canopies was affected by the interaction between salinity–sodicity and seasonality. Early in the season, salinity and sodicity affected ETa mainly through the reduced canopy growth, which decreased the available energy (Rn–G) for ETa and reduced the water uptake as a result of the lower soil water potential. Late in the season, an increase in H and a decrease in the contribution of the aerodynamic component (β coefficient) to the latent heat flux (LE) occurred, which determined a further reduction of ETa due to a physiological response. The decrease in the β coefficient during the late season was associated with a direct impact of ion accumulation on leaf functionality. Collecting data on the contribution of the aerodynamic component to LE offers a low-cost method to detect and quantify physiological stress, while providing useful information for managing irrigation in salt-affected orchards. The results presented in this article provide insights to improve irrigation management of salt-affected pistachio through integration of weather measurements, energy balance components, and plant-based parameters.