scholarly journals Physical Properties of Container Media and Relation to Severity of Phytophthora Root Rot of Rhododendron

1990 ◽  
Vol 115 (4) ◽  
pp. 564-570 ◽  
Author(s):  
B.H. Ownley ◽  
D.M. Benson ◽  
T. E. Bilderback
Keyword(s):  
Bulk Density ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Total Porosity ◽  
Pine Bark ◽  
Phytophthora Root Rot ◽  
Air Space ◽  
The Media ◽  
One Year ◽  
Water Percent

One-year-old Rhododendron L. `Nova Zembla' were grown in four container media infested with Phytophthora cinnamomi Rands. The media (all v/v) were pine bark, 3 pine bark:1 sand, 3 pine bark:1 peat, and 1 peat: 1 sand: 1 soil. After 20 weeks, plants were evaluated for root rot symptoms and the total porosity, air space, moisture-holding capacity, and bulk density were determined for all media. All media provided adequate moisture-holding capacity for container production of rhododendron in noninfested media. Shoot fresh weight in noninfested media was positively correlated with bulk density and water (percent by volume) held in the 1.0- to 5.0-kPa matric tension range and negatively correlated with total porosity and air space. Root rot severity was greatest in peat: sand: soil, intermediate in pine bark: peat, and least in pine bark and pine bark: sand. Root rot severity was negatively correlated with total porosity and air space and positively correlated with bulk density and water (percent by volume) held in the 5.0- to 10.0-kPa matric tension range.

scholarly journals Physical Properties of Pine Bark and Hardwood Bark Media and Their Effects with 4 Fertilizers on Growth of llex x ‘Nellie R. Stevens’ Holly

1985 ◽  
Vol 3 (4) ◽  
pp. 181-185
Author(s):  
T.E. Bilderback
Keyword(s):  
Particle Size ◽  
Bulk Density ◽  
Total Porosity ◽  
Dry Weight ◽  
Pine Bark ◽  
Foliar Nitrogen ◽  
Nitrogen Levels ◽  
Air Space ◽  
Retention Characteristics ◽  
Top Dry Weight

Pine bark (PB) and composted hardwood bark (HWB) were combined into 5 media. Particle size distribution, total porosity, air space, moisture retention characteristics, and bulk density were determined for each medium. Four commercial fertilizers were applied and substrate nitrogen levels, pH, % foliar nitrogen and top dry weight were determined for Ilex x ‘Nellie R. Stevens’ holly. Pine bark had approximately 84% of the particles between 4.75 and 1.0 mm (0.19 and 0.04 in). As HWB was added in 25% increments (by vol) the percent weight of particles in this range decreased. HWB increased bulk density, but did not significantly change total porosity. Hardwood bark and the 1:3 PB:HWB (v/v) medium held more water than other media. Nursery Special raised pH in all media treatments. Plants treated with SulfurKote tended to have the highest foliar nitrogen content. The Sierrablen in PB and SulfurKote in 3 PB:1 HWB and 1 PB:1 HWB (v/v) and HWB produced the greatest top dry weight.

scholarly journals Change in Physical Properties of Pine Bark and Switchgrass Substrates Over Time

2012 ◽  
Vol 30 (3) ◽  
pp. 113-117
Author(s):  
James E. Altland ◽  
Charles Krause
Keyword(s):  
Root Growth ◽  
Physical Properties ◽  
Bulk Density ◽  
Total Porosity ◽  
Pine Bark ◽  
Change Over Time ◽  
Air Space ◽  
Over Time ◽  
Container Capacity

Alternatives to pine bark for nursery crop substrates have been proposed, including the use of straw materials such as switchgrass. While straw substrates can be developed with suitable physical properties measured immediately after mixing, little is known about how the physical properties of straw-based substrates change over time. The objective of this research was to measure the change in air space (AS), container capacity (CC), total porosity (TP), and bulk density (Db) over time of a switchgrass-based substrate compared to a pine bark substrate. Switchgrass and pine bark substrates were packed into 15 cm (6 in) tall aluminum cores and placed in a production greenhouse with or without a single hibiscus plant. Physical properties of the substrates were measured at the beginning of the experiment and 9 to 10 weeks later when the plants were nearly too large for their containers. Air space decreased over time, primarily as a function of root growth and shrinkage. Container capacity increased slightly across all treatments over time. Bulk density changed very little over time. The switchgrass substrate was more prone to shrinkage than the pine bark substrate, although vigorous hibiscus root growth reduced shrinkage in switchgrass substrates.

scholarly journals Cellulase Activity as a Mechanism for Suppression of Phytophthora Root Rot in Mulches

2011 ◽  
Vol 101 (2) ◽  
pp. 223-230 ◽  
Author(s):  
Brantlee Spakes Richter ◽  
Kelly Ivors ◽  
Wei Shi ◽  
D. M. Benson
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Cellulase Activity ◽  
Enzyme Concentration ◽  
Disease Suppression ◽  
In Vitro Assays ◽  
Infested Soil ◽  
Phytophthora Root Rot ◽  
Standard Curve

Wood-based mulches are used in avocado production and are being tested on Fraser fir for reduction of Phytophthora root rot, caused by Phytophthora cinnamomi. Research with avocado has suggested a role of microbial cellulase enzymes in pathogen suppression through effects on the cellulosic cell walls of Phytophthora. This work was conducted to determine whether cellulase activity could account for disease suppression in mulch systems. A standard curve was developed to correlate cellulase activity in mulches with concentrations of a cellulase product. Based on this curve, cellulase activity in mulch samples was equivalent to a cellulase enzyme concentration of 25 U ml–1 or greater of product. Sustained exposure of P. cinnamomi to cellulase at 10 to 50 U ml–1 significantly reduced sporangia production, but biomass was only reduced with concentrations over 100 U ml–1. In a lupine bioassay, cellulase was applied to infested soil at 100 or 1,000 U ml–1 with three timings. Cellulase activity diminished by 47% between 1 and 15 days after application. Cellulase applied at 100 U ml–1 2 weeks before planting yielded activity of 20.08 μmol glucose equivalents per gram of soil water (GE g–1 aq) at planting, a level equivalent to mulch samples. Cellulase activity at planting ranged from 3.35 to 48.67 μmol GE g–1 aq, but no treatment significantly affected disease progress. Based on in vitro assays, cellulase activity in mulch was sufficient to impair sporangia production of P. cinnamomi, but not always sufficient to impact vegetative biomass.

scholarly journals Temporal and Spatial Epidemiology of Phytophthora Root Rot in Fraser Fir Plantations

Plant Disease ◽  
2006 ◽  
Vol 90 (9) ◽  
pp. 1171-1180 ◽  
Author(s):  
D. M. Benson ◽  
L. F. Grand ◽  
C. S. Vernia ◽  
T. R. Gottwald
Keyword(s):  
Spatial Analysis ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Local Area ◽  
Slope Aspect ◽  
Mortality Data ◽  
Phytophthora Root Rot ◽  
Fraser Fir ◽  
Incidence And Mortality ◽  
Over Time

In 1999, 19 plots of Fraser fir (Abies fraseri) with a disease focus were established in commercial plantings grown for Christmas tree production in the mountains of five western North Caro-lina counties. Progress of Phytophthora root rot caused by Phytophthora cinnamomi as estimated by mortality was followed in each plot over 3 to 4 years in an attempt to understand dispersal of inoculum. Slope, aspect, and field production age at the time plots were established were recorded. Rainfall estimated from National Weather Service stations each growing season also was recorded. The relationship of site parameters and rainfall to dispersal and disease was investigated. Disease incidence and mortality were assessed in June and September each year for 3 or 4 years depending on plot. Phytophthora root rot as estimated by mortality counts over time in a logistic regression model progressed in only five of 19 plots over 3 years. None of the site parameters correlated with mortality data, although slightly more disease was found in plots with a north aspect. Rainfall was below normal in the 3 years of the study and did not correlate with mortality in any year. Lack of disease progress in the majority of plots was attributed to drought conditions in the region. In the five plots where mortality increased over time, spatial analysis suggested an aggregated pattern of diseased plants. Aggregation was apparent but not very strong among nearest neighbors, but was considerably stronger among groups of trees within a local area. This aggregation within groups was stronger when larger group sizes were examined by beta-binomial analysis. A spatial analysis by distance indices method (SADIE) indicated the presence of secondary clusters occurring several meters away from the main focus. A stochastic model also was employed that indicated a combination of spatial processes were likely involved, specifically a tendency toward spread within a local area, but not necessarily to the nearest neighboring trees, combined with an influence of background inoculum that could not be accounted for within local areas and may have come from external sources. Thus, all sources of inoculum including infected planting stock, inoculum in soil, infected trees, and contaminated equipment were equally important in epidemics of Phytophthora root rot in Fraser fir and dispersal of P. cinnamomi.

scholarly journals Variation in Disease Severity Caused by Phytophthora cinnamomi, P. plurivora, and Pythium cryptoirregulare on Two Rhododendron Cultivars

Plant Disease ◽  
2018 ◽  
Vol 102 (12) ◽  
pp. 2560-2570 ◽  
Author(s):  
Jerry E. Weiland ◽  
Carolyn F. Scagel ◽  
Niklaus J. Grünwald ◽  
E. Anne Davis ◽  
Bryan R. Beck ◽  
...  
Keyword(s):  
Disease Control ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Severe Disease ◽  
Phytophthora Species ◽  
Relative Resistance ◽  
Inoculum Level ◽  
Phytophthora Root Rot ◽  
Mild Disease ◽  
Comparative Information

Rhododendrons are an important crop in the ornamental nursery industry, but are prone to Phytophthora root rot. Phytophthora root rot is a continuing issue on rhododendrons despite decades of research. Several Phytophthora species are known to cause root rot, but most research has focused on P. cinnamomi, and comparative information on pathogenicity is limited for other commonly encountered oomycetes, including Phytophthora plurivora and Pythium cryptoirregulare. In this study, three isolates each of P. cinnamomi, P. plurivora, and Py. cryptoirregulare were used to inoculate rhododendron cultivars Cunningham’s White and Yaku Princess at two different inoculum levels. All three species caused disease, especially at the higher inoculum level. P. cinnamomi and P. plurivora were the most aggressive pathogens, causing severe root rot, whereas Py. cryptoirregulare was a weak pathogen that only caused mild disease. Within each pathogen species, isolate had no influence on disease. Both P. cinnamomi and P. plurivora caused more severe disease on Cunningham’s White than on Yaku Princess, suggesting that the relative resistance and susceptibility among rhododendron cultivars might be similar for both pathogens. Reisolation of P. cinnamomi and P. plurivora was also greater from plants exhibiting aboveground symptoms of wilting and plant death and belowground symptoms of root rot than from those without symptoms. Results show that both P. cinnamomi and P. plurivora, but not Py. cryptoirregulare, are important pathogens causing severe root rot in rhododendron. This study establishes the risks for disease resulting from low and high levels of inoculum for each pathogen. Further research is needed to evaluate longer term risks associated with low inoculum levels on rhododendron health and to explore whether differences among pathogen species affect disease control.

scholarly journals Incidence of Phytophthora Root Rot of Fraser Fir in North Carolina and Sensitivity of Isolates of Phytophthora cinnamomi to Metalaxyl

Plant Disease ◽  
2000 ◽  
Vol 84 (6) ◽  
pp. 661-664 ◽  
Author(s):  
D. M. Benson ◽  
L. F. Grand
Keyword(s):  
North Carolina ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Disease Incidence ◽  
The State ◽  
Systematic Sampling ◽  
Phytophthora Root Rot ◽  
Fraser Fir ◽  
Phytophthora Spp ◽  
Old Trees

A survey of Fraser fir Christmas trees in North Carolina for incidence of Phytophthora root rot was conducted during 1997 and 1998. Field sites (7- to 13-year-old trees) and nursery transplant beds (4- to 5-year-old trees) selected at random were surveyed based on foliar symptoms of Phytophthora root rot. Field sites were surveyed with a random transect method (>3,000 trees/field) or by counting all trees (<3,000 trees/field). Overall, incidence of Phytophthora root rot averaged 9% over the 58 field sites sampled, with a range of 0 to 75%. No relationship was found between number of years Fraser fir had been planted in the field site and disease incidence. Disease incidence did not increase as field sites were rotated through second or third crops of Fraser fir. Phytophthora spp. were recovered from 1.8% of asymptomatic trees sampled from 58 field sites across the state. P. cinnamomi accounted for 91% of the Phytophthora isolates recovered. In nursery transplant beds where a systematic sampling procedure was used, incidence of diseased trees averaged 2%, with a range of 0 to 12% across 16 locations. Recovery of Phytophthora spp. averaged 1.2% from root samples collected from 50 asymptomatic seedlings at each location. Isolates collected from the field and nursery transplant beds were grown on cornmeal agar incorporated with 0, 1, 1.25, 10, or 100 μg a.i. metalaxyl/ml. All 166 isolates of P. cinnamomi tested were sensitive to metalaxyl at 1 or 1.25 μg a.i. metalaxyl/ml. Although incidence of Phytophthora root rot has not increased in the state compared to a survey done in 1976 to 1977, the disease continues to limit production of Fraser fir in North Carolina.

Control of Phytophthora Root Rot in Field Plantings of Fraser Fir with Fosetyl-Al and Mefenoxam

2006 ◽  
Vol 7 (1) ◽  
pp. 25 ◽  
Author(s):  
D. M. Benson ◽  
J. R. Sidebottom ◽  
J. Moody
Keyword(s):  
Root Rot ◽  
Tree Mortality ◽  
Phytophthora Cinnamomi ◽  
Flood Plain ◽  
Treatment Programs ◽  
Phytophthora Root Rot ◽  
Rainfall Events ◽  
Fraser Fir ◽  
Growing Seasons ◽  
Western North Carolina

Fungicides were evaluated for control of Phytophthora root rot for five growing seasons in two field plantings of Fraser fir (Abies fraseri) affected by Phytophthora cinnamomi in western North Carolina. At the first site, which had a fairly well-drained soil, treatment programs with Aliette (5 lb/100 gal, three applications per year), Subdue Maxx (3.7 fl oz/1.15 gal/1000 ft2, two applications per year), and Subdue GR (5.75 lb/1000 ft2, two applications per year) maintained low rates of mortality (< 10%) for three growing seasons, whereas tree mortality in the untreated plots reached 13 and 37% by the second and third growing seasons, respectively. At the second site, which was in a flood plain, disease did not develop during the first 2.5 years, even in untreated control plots. However, mortality increased rapidly following several high-rainfall events, but none of the fungicides had any effect on disease development. Apparently, at least under conditions not overly conducive to the disease, the fungicide treatment programs can delay the onset of high mortality rates caused by P. cinnamomi in Fraser fir for up to three growing seasons. Accepted for publication 23 February 2006. Published 31 March 2006.

Evaluation of physical properties of several growing media for use in aerial seeding containers

1987 ◽  
Vol 17 (2) ◽  
pp. 165-173 ◽  
Author(s):  
Tanya L. Lennox ◽  
Glen P. Lumis
Keyword(s):  
Water Retention ◽  
Total Porosity ◽  
Linear Increase ◽  
Buffering Capacity ◽  
Tree Seedlings ◽  
Growing Media ◽  
Available Water ◽  
Air Space ◽  
The Media ◽  
Hydrophilic Gel

Several personally blended and commercially prepared growing media were evaluated as potential substrates for coniferous tree seedlings in specialized seeding containers (aerial darts). Water retention curves were developed using a porous pressure plate apparatus. Bark–vermiculite–sand and Ball Growing Mix II retained less water at pressures from 0 to 0.1 MPa than all other media observed. At pressures less than 20 × 10−3 MPa the greatest water retention was in Pro-mix A, while above 33 × 10−3 MPa the greatest water retention was in bark–vermiculite. As the proportion of bark in bark–vermiculite was increased, the air space increased significantly but water retention was unaffected. Addition of a hydrophilic gel to media containing a surfactant significantly increased water retention. The easily available water, water buffering capacity, and air space were unaffected by gel but total porosity increased in some of the media. When the surfactant was excluded the addition of gel at the recommended rate did not significantly increase water retention. As the concentration of gel increased there was an increase in water retention, a linear increase in total porosity, a slight increase in air space, a decrease in easily available water, and no change in water buffering capacity. Media amended with gels of different absorbing capacities retained water similarly, releasing approximately 50% of the absorbed water at pressures less than 10 × 10−3 MPa.

scholarly journals Synergistic effects of a cellulase-producing Micromonospora carbonacea and an antibiotic-producing Streptomyces violascens on the suppression of Phytophthora cinnamomi root rot of Banksia grandis

1996 ◽  
Vol 74 (4) ◽  
pp. 618-624 ◽  
Author(s):  
Khaled A. El-Tarabily ◽  
Melissa L. Sykes ◽  
Ipek D. Kurtböke ◽  
Giles E. St. J. Hardy ◽  
Aneli M. Barbosa ◽  
...  
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Synergistic Effects ◽  
Control Plant ◽  
Pathogenic Fungi ◽  
Plant Pathogenic Fungi ◽  
Selective Isolation ◽  
Phytophthora Root Rot ◽  
Mine Site ◽  
Isolation Techniques

Three polyvalent Streptomyces phages were used to isolate four Micromonospora species (M. carbonacea, M. chalcea, M. purpureochromogenes, and M. inositola) from mine-site rhizosphere soils in Western Australia. Streptomyces violascens was isolated using selective isolation techniques from the same soils. The Micromonspora spp. were examined for their ability to produce cellulases. Micromonospora carbonacea, M. chalcea, and M. purpureochromogenes, which were found to produce the enzyme, caused lysis of Phytophthora cinnamomi hyphae. Glasshouse trials showed that the use of the cellulase-producing M. carbonacea isolate, in conjunction with the antibiotic-producing S. violascens isolate, had a synergistic effect on the suppression of the Phytophthora root rot and in promoting growth of Banksia grandis. The importance of using a number of antagonists with different antagonistic abilities to control plant pathogenic fungi is discussed. Keywords: biological control, Micromonospora carbonacea, Streptomyces violascens, cellulases, Phytophthora cinnamomi.

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