Reduced Tree Vigor Research Articles

High-Density Espalier Trained Mangoes Make Better Use of Light

Mango productivity and fruit quality in Australia can be improved through transforming low-density plantings to high-density plantings and intensive training systems. Several planting density and training systems were established in Australia to investigate optimizing light interception and distribution, yield and fruit quality, and to reduce tree vigor and biennial bearing through the manipulation of canopy architecture. In this research, we studied light relations and yield in conventional low-density commercial orchards of different ages and investigated light relations and yield of ‘National Mango Breeding Program NMBP1243’, ‘Keitt’ and ‘Calypso’ grafted to ‘Kensington Pride (KP)’ rootstock in a replicated experiment. Trees were trained to five planting systems: high-density espalier and conventional, medium-density single leader and conventional, and low-density conventional. Our study in commercial orchards showed that maximum yield was ~16,000 kg/ha when light interception reached ~49% and declined at higher levels of light interception. In the high-density intensive training systems, we found that light interception increased with canopy volume, with high-density espalier training systems intercepting more available light compared to medium-density training systems and low-density conventional trees. Yield/ha increased to ~50,000 kg/ha in espalier training systems when light interception was ~40%. Light interception, canopy volume and yield/ha varied between varieties.

Reviewing the Current Understanding of Replant Syndrome in Orchards from a Soil Microbiome Perspective

Replant syndrome (RS) of fruit and nut trees causes reduced tree vigor and crop productivity in orchard systems due to repeated plantings of closely related tree species. Although RS etiology has not been clearly defined, the causal agents are thought to be a complex of soil microorganisms combined with abiotic factors and susceptible tree genetics. Different soil disinfection techniques alleviate RS symptoms by reducing the loads of the deleterious microbiome; however, the positive effect on crop growth is temporary. The goals of this paper are: (1) to conceptualize the establishment of the syndrome from a microbiome perspective and (2) to propose sustainable solutions to develop a beneficial microbiome to inhibit the onset of RS.

A Mini Review of Citrus Rootstocks and Their Role in High-Density Orchards.

Dwarfing is an important agricultural trait for intensive cultivation and effective orchard management in modern fruit orchards. Commercial citrus production relies on grafting with rootstocks that reduce tree vigor to control plant height. Citrus growers all over the world have been attracted to dwarfing trees because of their potential for higher planting density, increased productivity, easy harvest, pruning, and efficient spraying. Dwarfing rootstocks can be used to achieve high density. As a result, the use and development of dwarfing rootstocks are important. Breeding programs in several countries have led to the production of citrus dwarf rootstocks. For example, the dwarfing rootstocks 'Flying Dragon', 'FA 517', 'HTR-051', 'US-897', and 'Red tangerine' cultivated in various regions allow the design of dense orchards. Additionally, dwarf or short-stature trees were obtained using interstocks, citrus dwarfing viroid (CDVd) and various chemical applications. This review summarizes what is known about dwarf citrus rootstocks and the mechanisms underlying rootstock-scion interactions. Despite advances in recent decades, many questions regarding rootstock-induced scion development remain unanswered. Citrus rootstocks with dwarfing potential have been investigated regarding physiological aspects, hormonal communication, mineral uptake capacity, and horticultural performance. This study lays the foundation for future research into the genetic and molecular mechanisms underlying citrus dwarfing.

How Is Global Warming Affecting Fruit Tree Blooming? "Flowering (Dormancy) Disorder" in Japanese Pear (Pyrus pyrifolia) as a Case Study.

Recent climate change has resulted in warmer temperatures. Warmer temperatures from autumn to spring has negatively affected dormancy progression, cold (de)acclimation, and cold tolerance in various temperate fruit trees. In Japan, a physiological disorder known as flowering disorder, which is an erratic flowering and bud break disorder, has recently emerged as a serious problem in the production of the pome fruit tree, Japanese (Asian) pear (Pyrus pyrifolia Nakai). Due to global warming, the annual temperature in Japan has risen markedly since the 1990s. Surveys of flowering disorder in field-grown and greenhouse-grown Japanese pear trees over several years have indicated that flowering disorder occurs in warmer years and cultivation conditions, and the risk of flowering disorder occurrence is higher at lower latitudes than at higher latitudes. Susceptibility to flowering disorder is linked to changes in the transcript levels of putative dormancy/flowering regulators such as DORMANCY-ASSOCIATED MADS-box (DAM) and FLOWERING LOCUS T (FT). On the basis of published studies, we conclude that autumn–winter warm temperatures cause flowering disorder through affecting cold acclimation, dormancy progression, and floral bud maturation. Additionally, warm conditions also decrease carbohydrate accumulation in shoots, leading to reduced tree vigor. We propose that all these physiological and metabolic changes due to the lack of chilling during the dormancy phase interact to cause flowering disorder in the spring. We also propose that the process of chilling exposure rather than the total amount of chilling may be important for the precise control of dormancy progression and robust blooming, which in turn suggests the necessity of re-evaluation of the characteristics of cultivar-dependent chilling requirement trait. A full understanding of the molecular and metabolic regulatory mechanisms of both dormancy completion (floral bud maturation) and dormancy break (release from the repression of bud break) will help to clarify the physiological basis of dormancy-related physiological disorder and also provide useful strategies to mitigate or overcome it under global warming.

Assessment of Ponderosa Pine Vigor Using Four-Band Aerial Imagery in South Central Oregon: Crown Objects to Landscapes

Ponderosa pine is an integral part of the forested landscape in the western US; it is the dominant tree species on landscapes that provide critical ecosystem services. Moderate drought tolerance allows it to occupy the transition zone between forests, open woodlands, and grasslands. Increases in stand density resulting from wildfire suppression, combined with lengthening, intensifying, and more frequent droughts have resulted in reduced tree vigor and stand health in dry ponderosa pine throughout its range. To address a management need for efficient landscape-level surveys of forest health, we used Random Forests to develop an object-oriented classification of individual tree crowns (ITCs) into vigor classes using existing, agency-acquired four-band aerial imagery. Classes of tree vigor were based on quantitative physiological and morphological attributes established in a previous study. We applied our model across a landscape dominated by ponderosa pine with a variety of forest treatments to assess their impacts on tree vigor and stand health. We found that stands that were both thinned and burned had the lowest proportion of low-vigor ITCs, and that stands treated before the 2014–2016 drought had lower proportions of low-vigor ITCs than stands treated more recently (2016). Upland stands had significantly higher proportions of low-vigor trees than lowland stands. Maps identifying the low-vigor ITCs would assist managers in identifying priority stands for treatment and marking trees for harvest or retention. These maps can be created using already available imagery and GIS software.

Recent Advances on Citrus yellow vein clearing virus in Citrus

Citrus yellow vein clearing virus (CYVCV) is the causal agent of yellow vein clearing disease, a significant and devastating disease of most citrus species including lemon and sour orange. CYVCV, a single-strand positive-sense RNA virus containing six ORFs (Open Reading Frames), represents a new species in the genus Mandarivirus of the Alphaflexiviridae family. The virus can cause particularly serious damage, resulting in reduced tree vigor, lower yields, and decreased marketability of fruit production, and it has been found in India, Turkey, Pakistan, China and Iran. Here we described the geographical distribution of the virus, its transmission mode by grafting, mechanical inoculation, and insects, as well as currently available techniques for detection. In addition, we also discussed practical measures aimed at controlling the disease and provided theoretical guidance to prevent the acquisition and spread of the disease that is a significant step toward ensuring the health of the citrus industry.

First Report of Neoscytalidium dimidiatum Causing Black Canker and Root Rot of Walnut in Turkey

Walnut (Juglans regia L.) is a commercially important crop with about 87,670 ha grown in Turkey, the fourth largest producer worldwide. During summer 2018, unfamiliar and serious decline symptoms associated with stem and branch cankers were observed in walnut trees in two orchards in Sanliurfa Province, Southeastern Anatolia Region. In a 3-year-old orchard of 450 trees (cv. Chandler) in Kayseri, Siverek District, about 62% of trees had deep, large, and black cankers in the trunks and on main branches, drastically reduced tree vigor, and yellowing, wilting, and browning of the leaves, followed by leaf drop. In a 12-year-old orchard with 30 trees (cv. Kaman), in Yaylak, Bozova District, 40% of trees had similar symptoms. Symptoms were first noticed in trunks. Bark cracks, cankers in trunks, and dark discoloration or a black sooty, dusty mass of fungal spores under peeling bark on the trunk and main branches were the most striking symptoms. Deep cankers expanded longitudinally, extending along trunks and into the phloem of the trees, which consequently died, and occasionally laterally extending into the sapwood. Declining trees had dry root rot symptoms, with black necrosis on the surface, and under the cracked and coarse bark extending from the taproot and some large roots to the crown, and black rot and loss of fine roots. Samples were taken from under the bark of trunk cankers, crown tissues, and root tissues of five trees per orchard. The sections of samples were surface sterilized in 2% NaOCl for 2 min and rinsed twice in sterile distilled water, blotted dry with sterilized filter paper, placed on PDA, and incubated at 28°C. A fungus with identical cultural characteristics was consistently isolated. On PDA, the mycelium growth was white and then turned black with age. Rapidly growing colonies (average, 40 mm/day) produced mycelia that disarticulated into 0- to 1-septate, cylindrical-truncate or rod-shaped, thick-walled, hyaline to brown arthroconidia occurring singly or in arthric chains and averaged 9.6 ± 3.7 × 5.5 ± 1.6 μm with a length/width ratio of 1.79. These characteristics were consistent with the description of the arthric synanamorph of Neoscytalidium dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). The rDNA internal transcribed spacer (ITS) and large subunit (LSU) genes of two single conidial isolates (one from under bark tissues; one from root tissues) were amplified with ITS6/ITS4 and NL1/NL4 primer pairs, respectively, and the amplicons sequenced. The ITS and LSU sequences deposited in GenBank (ITS, MK430050 and MK430051; LSU, MK430056 and MK430057) had 100% identity with many sequences of N. dimidiatum, including recently available ones (Turkolmez et al. 2019; ITS, MH114591; LSU, MH114592), in line with the morphological features. Pathogenicity tests were performed on 20 replicates of 1-year-old container-grown J. regia ‘Chandler’ seedlings with a N. dimidiatum isolate by removing a 5-mm-diameter bark plug from the stem with a cork borer and placing an equivalent-sized 7-day-old culture disc of N. dimidiatum onto the exposed vascular cambium. The wound was covered with wet, autoclaved cotton wool and sealed with Parafilm. Treated plants were maintained in a growth chamber with a 16/8-h light/dark photoperiod at 26°C and 55% RH and watered on demand. Within 3 weeks, average lesion lengths under the bark of all inoculated stems were >150 mm, and the lesions were covered with a black sooty layer. Leaf blight was also observed, similar to naturally affected trees. Control plants remained healthy. N. dimidiatum was reisolated only from lesions of inoculated stems, fulfilling Koch’s postulates. In Turkey, N. dimidiatum has been reported as a destructive new blight of tomato (Turkolmez et al. 2019) and canker, shoot blight, and root rot of pistachio (Dervis et al. 2019). This is the first report of N. dimidiatum infection of walnuts in Turkey. By the end of 2018, all symptomatic trees had died. Recent occurrence of this severe disease suggests it could have a significant potential for limiting walnut production.

Field Identification and Management of Greasy Spot Disease

Greasy spot is a disease that's frequently found in tropical and semitropical regions where citrus cultivars are grown. The disease is caused by Mycosphaerella citri. Symptoms appear as yellow to dark brown to black lesions occurring first on the underside of mature citrus leaves (Fig. 1). As the lesions develop on the underside of the leaves, they become darker and a corresponding chlorotic spot will appear on the upper leaf surface. These yellow (chlorotic) spots occur when infected cells fail to develop chlorophyll. Lesions are more yellowish and diffuse on lemons and grapefruit and more raised and darker on tangerines. Affected leaves fall prematurely from the tree during the fall and winter resulting in reduced tree vigor and yield. Greasy spot also infects the fruit of grapefruit trees producing rind blotch. This document is HS-1016, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date May 2005.
 HS-1016/HS263: Field Identification and Management of Greasy Spot Disease (ufl.edu)

Apple blotch disease (Marssonina coronaria (Ellis & Davis) Davis) – review and research prospects

Apple blotch, caused by Marssonina coronaria, is a serious and widely distributed fungal disease that causes huge losses to apple production especially in South and East Asia. The pathogen causes black spots on apple fruits, leaves and premature defoliation, resulting in weakened physiological balance of the host, reduced tree vigor and decreased yield. It is not clear when the pathogen first occurred in Europe but the disease has become increasingly important in Europe due to its unexpected occurrences in European organic orchards in the last decade. Hence, information on the pathogen host range and geographical distribution, symptoms, biology and disease cycle, as well as epidemiology is vital in developing control strategies. Only the asexual stage of the pathogen has been observed in Europe to date. Therefore, mating and sexual recombination mechanism of the pathogen as well as its overall evolutionary potential is unknown. Altogether, population genetics, importance of primary inoculum, overwintering and the time point of disease outbreak are less researched issues of this pathogen. Host resistance is thought to be the most reliable means to prevent the further spread of this pathogen in organic orchards. However, knowledge about the disease and its interaction with the host is a prerequisite for breeding durable resistant apple cultivars. This review highlights the information available from previous research on M. coronaria and its occurrence on apple.

Does propagation method affect the field performance of peach trees?

Worldwide, peach propagation has been performed mainly by grafting scions of desirable cultivars on rootstocks obtained from seeds. There are, however, other potential propagation methods not widely adopted due to the limited reports on the field performance of the resultant trees. This study addressed this knowledge gap and investigated the field performance of peach trees of the cultivar Maciel that were established in an orchard (5.0 m × 1.4 m spacing) in 2011. The trees were trained in a "Y" system, with seedlings from three propagation techniques: 1) Conventional System (CS) - vegetative bud grafting of the scion on the rootstock of the Okinawa cultivar obtained from seed; 2) Rootstock by Minicutting (RM) - vegetative bud grafting of the scion on the rootstock of the Okinawa cultivar obtained by minicutting in a semi-hydroponic system; 3) Self-Rooting (SR) - self-rooting of the scion in a semi-hydroponic system. The vegetative, productive, and fruit quality parameters were assessed during 2012 and 2013. The Maciel peach trees that were propagated by the SR technique were found to have similar or even superior field performance to those propagated by the CS. The RM propagation method was also found to be an important potential alternative to peach propagation, since this it combines two techniques (cutting and grafting) to reduce tree vigor, especially if the goal is high-density planting.

Does propagation method affect the field performance of peach trees?

Worldwide, peach propagation has been performed mainly by grafting scions of desirable cultivars on rootstocks obtained from seeds. There are, however, other potential propagation methods not widely adopted due to the limited reports on the field performance of the resultant trees. This study addressed this knowledge gap and investigated the field performance of peach trees of the cultivar Maciel that were established in an orchard (5.0 m × 1.4 m spacing) in 2011. The trees were trained in a "Y" system, with seedlings from three propagation techniques: 1) Conventional System (CS) - vegetative bud grafting of the scion on the rootstock of the Okinawa cultivar obtained from seed; 2) Rootstock by Minicutting (RM) - vegetative bud grafting of the scion on the rootstock of the Okinawa cultivar obtained by minicutting in a semi-hydroponic system; 3) Self-Rooting (SR) - self-rooting of the scion in a semi-hydroponic system. The vegetative, productive, and fruit quality parameters were assessed during 2012 and 2013. The Maciel peach trees that were propagated by the SR technique were found to have similar or even superior field performance to those propagated by the CS. The RM propagation method was also found to be an important potential alternative to peach propagation, since this it combines two techniques (cutting and grafting) to reduce tree vigor, especially if the goal is high-density planting.

Suppression of greasy spot disease caused by Mycosphaerella citri Whiteside on grapefruit trees in an organic orchard using an aqueous organic mixture of composted cornmeal, humic acid, molasses, and fish oil versus vegetable oil

Greasy spot disease of citrus, caused by the fungus Mycosphaerella citri Whiteside, afflicts citrus trees in all citrus-growing areas of the United States, eastern Mexico, Central America, and the Caribbean islands, causing premature defoliation, blemished fruit, and reduced tree vigor, yield, and fruit size. This three-year study investigated the effects of organic, nonconventional tactics using an aqueous organic mixture, steeped for 10 h, of composted cornmeal, humic acid, molasses, and fish oil and an aqueous suspension of vegetable oil, separately and in combination, for greasy spot suppression in an organic grapefruit, Citrus paradisi Macfad., orchard in the Lower Rio Grande Valley of Texas. The extent of greasy spot infection on each tree was consistently reduced by each of the treatments throughout much of every growing season. The organic mixture had a more consistent, though lesser, effect on greasy spot reduction when precipitation was relatively high in the spring than when spring rains were relatively light. In four of five field experiments conducted during this study, late season bare patches on the tree canopies were more extensive on the control trees than on treated trees. While fruit yield was not consistent in terms of treatment effects, the organic mixture and vegetable oil treatments each protected foliage from greasy spot infection to limited extents during years with wet springs. The greatest protection was observed during a year with a relatively dry spring.

Desempenho produtivo de macieiras 'Royal Gala' e 'Fuji' submetidas a diferentes densidades de plantio e porta-enxertos

Resumo: O objetivo deste trabalho foi avaliar a influência da densidade de plantio e de porta-enxertos sobre o desempenho produtivo de macieiras 'Royal Gala' e 'Fuji'. O trabalho foi realizado de 1996 a 2007, com as cultivares Royal Gala e Fuji, na região de São Joaquim, SC. Os tratamentos consistiram de dois porta-enxertos (M9 e M26) e três densidades de plantio (1.667, 2.500 e 5.000 plantas por hectare), dispostos em arranjo fatorial 2x3, com seis tratamentos por cultivar. Utilizou-se o delineamento de blocos ao acaso, com quatro repetições. O aumento da densidade de plantio aumenta a produtividade e diminui a produção e o número de frutos por planta, independentemente da cultivar. Além disso, o aumento da densidade de plantio reduz o vigor das plantas (seção transversal do tronco) e a massa de fruto. A produtividade induzida pelo M26 é maior do que a induzida pelo M9, porém, este produz frutos maiores em razão, possivelmente, da menor carga de frutos das plantas com esse porta-enxerto.

First Report of the Dagger Nematode Xiphinema diversicaudatum in Citrus Orchards in Morocco

Xiphinema species are migratory ectoparasitic nematodes that feed on an extensive range of hosts, and several species are vectors of nepoviruses. In May 2012, during a survey of the citrus-growing areas in the Gharb region of Morocco, several Xiphinema nematodes were detected in three locations: Kénitra (INRA, plot P1), Sidi Kacem, and Sidi Slimane. Samples were taken 30 cm deep at 50 cm distance from the tree trunks, in 40-year-old orange groves planted with the variety Maroc Late, grafted on rootstocks of Sour Orange and Citrange Carrizo. The trees showed yellowing of leaves, reduced tree vigor, and swellings at the tips of the roots. There were no weeds or grasses in the sampled area. Nematodes were extracted from soil using an automated centrifuge for extracting free-living nematode stages (2) and identified morphologically and by sequencing. All specimens were identified as Xiphinema diversicaudatum based on key morphological features from females and males. The average measurements of six females were: body length 4.1 mm, body width 60.4 μm, odontostylet 133.5 μm, odontophore 64.0 μm, spear 197.5 μm, tail length 45 μm, body width at anus 31 μm, and vulval position 48%. The females had two genital branches of similar length and structure, which contained a pseudo-Z differentiation. The average measurements of four males were: body length 4.3 mm, body width 51 μm, odontostylet 139 μm, odontophore 70 μm, spear 209 μm, tail length 45 μm, body width at anus 35 μm. To confirm the morphological identification, molecular observations were made. DNA was extracted from one nematode of each location. The D3 expansion region of the 26S rRNA gene was amplified using the primers D3A (5'-GACCCGTCTTGAAACACGGA-3') and D3B (5'-TCGGAAGGAACCAGCTACTA-3') (1). The PCR products were purified and sequenced (Macrogen, Inc., Seoul, Korea). All sequences obtained (GenBank Accession Nos. KF057879, KF057880, and KF057881) were compared with sequences available from the GenBank database including several species of Xiphinema. This comparison revealed a sequence similarity of 99 to 100% with X. diversicaudatum. Morphological and molecular identification demonstrated that the isolates of dagger nematodes from three citrus growing areas in Gharb belonged to X. diversicaudatum. An average of six X. diversicaudatum per 100 cm3 soil were found. This is the first report of this species in Morocco. X. diversicaudatum can transmit Arabis mosaic and Strawberry latent ringspot viruses (3). Arabis mosaic virus is of great economic importance in viticulture as it is associated with grapevine fanleaf degeneration disease, together with Grapevine fan leaf virus transmitted by X. index (4). As vineyards are planted amid citrus orchards in the Gharb region, particular attention should be given to this nematode, especially to the risk of its spread by soil. Our finding of X. diversicaudatum in a citrus orchard does not necessarily imply that X. diversicaudatum causes damage in citrus. However, its presence indicates that this nematode species can survive in this environment from where it could spread to other, more susceptible, crops.

Involvement of Phytophthora cryptogea in sweet cherry decline in Turkey

Sweet cherry is a major commercial crop in Turkey, the most important producer of the fruit worldwide. Sweet cherry decline was observed in an orchard in Ankara province of Turkey. Affected young trees exhibited reduced tree vigor, yellowing and wilting of leaves, and dieback symptoms resulted in tree death. A Phytophthora sp. was consistently isolated from necroses that appeared on taproots and crowns. The pathogen was identified as Phytophthora cryptogea based on several morphological features and DNA sequence of the internal transcribed spacer (ITS) region. P. cryptogea was pathogenic on excised shoots and 1-year-old cherry rootstocks. This is the first report of P. cryptogea causing disease of sweet cherry in Turkey.

Coarse Woody Debris in a Southern Appalachian Spruce-fir Forest of the Great Smoky Mountains National Park

Abstract Spruce-fir forests in the southern Appalachian Mountains receive high atmospheric nitrogen inputs and have high nitrate levels in soil solution and streamwater. High levels of excess nitrogen have been associated with reduced tree vigor. Additionally, the balsam woolly adelgid (Adelges piceae Ratz.) has killed the majority of endemic Fraser fir [Abies fraseri (Pursh) Poir.] trees, resulting in large amounts of coarse woody debris. As part of a biogeochemical study in the Great Smoky Mountains National Park, coarse woody debris was sampled to determine volume, mass, change in density, and change in concentration and content of carbon and nitrogen over the decomposition process. Dead wood volume was highly variable across the watershed, ranging from 4.5 m3 ha−1 to 306.8 m3 ha−1 for standing boles and from 21.2 m3 ha−1 to 402.7 m3 ha−1 for down boles. Wood density decreased significantly for all three major overstory species [red spruce (Picea rubens Sarg.), yellow birch (Betula alleghaniensis Britt...

First Report of Root and Collar Rot by Phytophthora cryptogea on Sweet Cherry in Italy.

Sweet cherry (Prunus avium L.) cultivation has increased in Italy and ≈30,000 ha are now in production. In the spring of 2006, a disease survey was conducted in orchards of central Italy. Decline symptoms of Prunus avium 'Durone' grafted on wild rootstocks of Prunus avium consisted of reduced tree vigor, yellowing of leaves, and development of root and collar rot. A reddish brown discoloration of the inner bark and wood was observed on symptomatic trees. Symptoms were recorded in three cherry orchards seasonally submitted to soil saturation conditions. In one orchard, symptoms were observed on approximately 30% of 170 surveyed trees. A Phytophthora species was consistently isolated on PARPH-V8 medium (2) from collar lesions of five cherry trees over nine trees randomly chosen among symptomatic trees in the three orchards. Colonies (20) were isolated and all appeared fluffy on potato dextrose agar and did not grow at 35°C. The morphological characteristics fit the descriptions of Phytophthora cryptogea Pethybr. & Lafferty (1). Sequence analysis of the internal transcribed spacers region of isolates shared 100% homology with P. cryptogea (GenBank Accession Nos. EF418948.1, EF418943.1, and EF153671.1). Pathogenicity of two P. cryptogea isolates (AN1 and AN2, Accession Nos. EF661576 and EF661577, respectively) was tested by soil infestation in a growth chamber at 22°C using 15 1-year-old rooted seedlings of wild rootstock of Prunus avium for each isolate. Noninoculated seedlings (15) were used as negative controls. The inoculum was produced by growing isolates on autoclaved millet grains moistened with V8 juice for 4 weeks. Each plant was inoculated with 30 cm3 of inoculum per liter of soil. Each seedling was randomly assigned to isolates AN1, AN2, or the noninoculated control and arranged in a complete random design. All plants were flooded for 24 h every 2 weeks for 8 weeks. At the end of the experiment, all inoculated seedlings showed crown wilting and root rot. Control plants showed no symptoms. Percentage of necrotic lateral roots expressed as dry weight (±SE) was 19.9 ± 0.6, 17.5 ± 0.2, and 4.4 ± 0.5, respectively, for seedlings inoculated with isolates AN1, AN2, and controls (analysis of variance F = 7.48, P < 0.01). Values of inoculated seedlings were significantly different from the control plants with the Tukey Post-Hoc test. No difference in virulence was observed between the two isolates. P. cryptogea was always reisolated from the roots of inoculated plants. Although pathogenicity of P. cryptogea on sweet cherry has been reported in the United States and other European countries (3,4), to our knowledge, this is the first record of P. cryptogea on sweet cherry orchards in Italy. The presence of P. cryptogea in cherry orchards is of significant concern because of its aggressiveness to this host and woody hosts such as apple, apricot, peach, walnut, and kiwi.

STEWARDSHIP MONITORING AND CONTROL OF ALDICARB APPLICATION TO FLORIDA CITRUS

Temik. (aldicarb) is a nematicide that has been used widely in the Florida citrus industry as nematodes significantly reduce tree vigor, growth, and fruit productivity. However, concerns about groundwater contamination have led to regulations requiring a 91.4-m (300-ft) buffer around all potable water wells and a 304.8-m (1000-ft) buffer for wells in highly vulnerable soils. To provide documentation of proper application, two DGPS-based approaches were considered for implementation on current pneumatic dry granular applicator units. The first was a black-box DGPS/system status data logger. A second level system was developed for data logging and control through a hand-held pocket PC using Farmworks variable rate technology (VRT) software. Electronic sensors, interfacing, and signal conditioning were incorporated into a pneumatic discharge granular applicator unit to demonstrate these technologies for both ground wheel driven and pulse width modulation (PWM) motor-based dispensing. The DGPS unit used for both applications was a wide area augmentation system (WAAS) corrected Trimble 106 antenna. Additional sensors were implemented for measuring material discharge rates and ground speed for PWM control. Performance data, logged at 1 Hz for both systems and a general error analysis, are presented. Factors, such as well-spotting accuracy and product delivery times, are included.

Growth of Young Douglas-Fir Plantations Across a Gradient in Swiss Needle Cast Severity

Abstract During the past decade, Swiss needle cast (SNC) damage has intensified in many Douglas-fir plantations in the Coast Range of Oregon, particularly along the immediate north coast. In plantations with severe symptoms, growth losses and reduced tree vigor are evident, but the magnitude of growth losses associated with varying intensities of damage is not known. A growth impact study was conducted in 1997 to quantify retrospectively the relationship between growth losses and visual symptoms in 10- to 30-yr-old Douglas-fir plantations in coastal northwestern Oregon, a population totaling 75,700 ha. A random sample of 70 Douglas-fir plantations was selected from the population and evaluated for Swiss needle cast severity. One 0.02 ha plot was destructively sampled in each plantation to reconstruct past height and basal area growth trends and to characterize foliage loss and distribution. The SNC “effect” was assessed by comparing growth of plantations with varying degrees of Swiss needle cast to growth of those that retained maximal amounts of foliage, after correcting for initial stand density, Douglas-fir growing stock, age, and site index. Of numerous possible SNC indices, mean needle retention (yr) explained the largest amount of variation in both basal area and top height growth. Prior to 1990, top height growth was similar across all plantations after correcting for site quality and plantation age; but, by 1992, top height growth losses appeared and were proportional to apparent foliage losses. In 1996, top height growth was reduced by up to 25% relative to plantations with little or no SNC. Basal area growth reductions began to appear around 1990, and in 1996 basal area growth of the most heavily damaged plantations was 35% less than the growth that would be expected in absence of SNC damage. The inferred volume growth loss for 1996 averaged 23% for the 75,700 ha target population, but this loss averaged as high as 52% for the most severely impacted plantations. West. J. Appl. For. 17(2):86ߝ95.

Effect of Four Training Systems on Growth and Productivity of `Cortland'/M.9 EMLA Apple Trees

`Cortland'/M.9 EMLA trees were planted in 1991 at 1.8 ×4.2-m spacing. The trees were trained to one of four systems: 1) Vertical Axis; 2) Y trellis; 3) Solen; or 4) Palmette trellis. Tree survival was 86% for Palmette trees and approached 100% for the other three systems. Annual yield and cumulative yield per tree of Vertical Axis and Y trellis was twice that of Solen or Palmette. Tree vigor was sub-optimal relative to planting distance in this study. Trunk cross-sectional area of Vertical Axis trees was larger than that of trees trained to Solen or Palmette, while trees trained to Y trellis were intermediate in trunk growth. Canopy volumes of Vertical Axis and Y trellis trees were similar, and greater than that of Solen or Palmette trees. Fruit size on Solen and Palmette trees was larger than that of Y trellis trees in 1995 and 1996, while fruit size on Vertical Axis trees was intermediate. Cumulative yield per cubic meter of canopy volume was the same for all four systems, suggesting that differences in productivity among systems were attributable to the effects of tree training practices on tree size, not to differences among systems in precocity or efficiency. The low heading cut needed to establish the lowest tier of branches on the Palmette system reduced tree vigor and in some cases, resulted in mortality. The horizontal training of the primary branches of the Solen severely reduced tree vigor. In this study, where tree vigor was sub-optimal due to rootstock selection, the additional restrictions in tree growth resulting from restrictive training methods resulted in a significant loss in productivity.