Field Runner: A Disease Incidence, Severity, and Spatial Pattern Assessment System

Sugarcane mosaic is a historically important disease in Louisiana currently caused by sorghum mosaic virus (SrMV). Successful breeding for resistance reduced the disease to low incidence in commercial cultivars. However, mosaic was detected in experimental clone evaluations at multiple locations, leading to uncertainty concerning the current distribution and incidence in the state. Field surveys were conducted from 2016 to 2018 in breeding program yield trials and experimental clone seed cane increase fields. Mosaic symptomatic plants were observed in a newly released cultivar, HoCP 09-804, in three of five production areas, with incidences ranging from 0 to 10%. Mosaic also was observed in nine additional experimental clones. Single leaf samples were tested for SrMV using reverse transcription PCR. All symptomatic samples and a low percentage (0.3%) of asymptomatic samples tested positive for SrMV, confirming that it continues to be the causal species. Runs analysis detected aggregation of infected plants within at least 70% of rows in 94% of surveyed fields. The spatial pattern and geographical distribution of disease incidence suggested that infected seed cane was the source of the disease. Surveys conducted in the same fields of HoCP 09-804 through two subsequent crops detected disease incidence increases in some fields and decreases in the others in first ratoon, but observed incidence was lower compared with plant cane in all fields in second ratoon. The results indicated that disease increase owing to aphid transmission did not occur under the prevailing conditions.

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Effects of Initial Epidemic Conditions, Sporulation Rate, and Spore Dispersal Gradient on the Spatio-Temporal Dynamics of Plant Disease Epidemics

Phytopathology ◽

10.1094/phyto.1998.88.10.1000 ◽

1998 ◽

Vol 88 (10) ◽

pp. 1000-1012 ◽

Cited By ~ 58

Author(s):

X.-M. Xu ◽

M. S. Ridout

Keyword(s):

Spatial Pattern ◽

Power Law ◽

Temporal Dynamics ◽

Initial Conditions ◽

Disease Incidence ◽

Disease Status ◽

Spatio Temporal ◽

Disease Epidemics ◽

Sporulation Rate ◽

The Relationship

A stochastic model that simulates the spread of disease over space and time was developed to study the effects of initial epidemic conditions (number of initial inocula and their spatial pattern), sporulation rate, and spore dispersal gradient on the spatio-temporal dynamics of plant disease epidemics. The spatial spread of disease was simulated using a half-Cauchy distribution with median dispersal distance μ (units of distance). The rate of temporal increase in disease incidence (βI, per day) was influenced jointly by μ and by the sporulation rate λ (spores per lesion per day). The relationship between βI and μ was nonlinear: the increase in βI with increasing μ was greatest when μ was small (i.e., when the dispersal gradient was steep). The rate of temporal increase in disease severity of diseased plants (βS) was affected mainly by λ: βS increased directly with increasing λ. Intraclass correlation (κt), the correlation of disease status of plants within quadrats, increased initially with disease incidence, reached a peak, and then declined as disease incidence approached 1.0. This relationship was well described by a power-law model that is consistent with the binary form of the variance power law. The amplitude of the model relating κt to disease incidence was affected mainly by μ: κt decreased with increasing μ. The shape of the curve was affected mainly by initial conditions, especially the spatial pattern of the initial inocula. Generally, the relationship of spatial autocorrelation (ρt,k), the correlation of disease status of plants at various distances apart, to disease incidence and distance was well described by a four-parameter power-law model. ρt,k increased with disease incidence to a maximum and then declined at higher values of disease incidence, in agreement with a power-law relationship. The amplitude of ρt,k was determined mainly by initial conditions and by μ: ρt,k decreased with increasing μ and was lower for regular patterns of initial inocula. The shape of the ρt,k curve was affected mainly by initial conditions, especially the spatial pattern of the initial inocula. At any level of disease incidence, autocorrelation declined exponentially with spatial lag; the degree of this decline was determined mainly by μ: it was steeper with decreasing μ.

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Determining the Spatial Pattern of Blackleg Diseased Potato Plants in the Field and Simulated Post-Harvest Tuber Infections in Potato Crates

Potato Research ◽

10.1007/s11540-021-09529-6 ◽

2021 ◽

Author(s):

Thomas H. Been ◽

Johanna E. Beniers ◽

Jan M. van der Wolf

Keyword(s):

Spatial Pattern ◽

Disease Incidence ◽

Random Pattern ◽

Field Surveys ◽

Infected Seed ◽

Seed Potatoes ◽

Potato Plants ◽

Global Positioning ◽

Before And After ◽

Random Distributions

Abstract Experiments were carried out in 2012 and 2013 to answer two basic questions in the testing of potato blackleg causing agents before and after harvest. Firstly, what is the spatial distribution of symptomatic plants in the field. Secondly, what is the distribution of infected tubers over the crates and the resulting detection probability using the standard method of collecting 200 tubers from the top crates in storage. In both years, ten farmers were equipped with a global positioning system (Garmin GPSMAP 62) and asked to register the position of blackleg diseased plants every time they scouted their potato lot for diseases. To answer the second question, potatoes marked with four nails (only visible internally after harvest) and potatoes with a different skin colour were added to one-hectare (ha) fields of seed potatoes in different patterns of aggregation ranging from random, to aggregated distribution, up to one big hotspot prior to harvest. The invisibly marked tubers were used for the unbiased collection of twenty 200-tuber samples from the storage crates, while the coloured skin tubers were used to ascertain, when the potatoes were graded, the distribution of ‘infected’ potatoes over the storage crates. The experiment was carried out with 0.05 and 0.1% disease incidence, in 2012 and 2013, respectively. Twenty two out of 26 fields proved to have a random pattern of diseased plants at harvest, which indicates that the blackleg diseased plants came into the field as infected seed potatoes. Two of the four aggregated patterns detected, started out as random distributions but became aggregated later in time, indicating spread in the field. A random spatial pattern in the field at harvest proved to result in a uniform distribution of infected tubers in the crates and, consequently, sampling of only the top crates for the 200-tuber sample does not introduce any bias. Fifty percent of the infected farmer lots were detected by the Nederlandse Algemene Keuringsdienst inspectors performing their official field surveys, which was a better performance than the 18% detection obtained by the standard 200-tuber sampling method. Only 6 out of 80 samples from the ‘infected’ lots with 0.05% disease incidence level, and 22 out of 80 samples at the 0.1% disease incidence level were detected by the latter method. It was concluded that intensifying the field survey would be cheaper and more successful than enlarging the tuber sample size to increase the probability for detection of infected seed lots.

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Quantification of Within-Field Spread of Soybean Mosaic Virus in Soybean Using Strain-Specific Monoclonal Antibodies

Phytopathology ◽

10.1094/phyto.1998.88.9.895 ◽

1998 ◽

Vol 88 (9) ◽

pp. 895-901 ◽

Cited By ~ 22

Author(s):

Forrest W. Nutter ◽

Patricia M. Schultz ◽

John H. Hill

Keyword(s):

Monoclonal Antibodies ◽

Spatial Pattern ◽

Mosaic Virus ◽

Logistic Model ◽

Disease Incidence ◽

Soybean Mosaic Virus ◽

Spatial Spread ◽

Field Virus ◽

Temporal And Spatial ◽

Spread Analysis

Strain-specific monoclonal antibodies were used to follow the temporal increase and spatial spread of soybean mosaic virus (SMV) strain G-5 released from a point source. The use of strain-specific monoclonal antibodies allowed discrimination of within-field temporal and spatial spread of SMV strain G-5 from non-G-5 SMV isolates that originated from exogenous field sources. SMV isolates originating from exogenous sources have potential to alter the temporal and spatial pattern of within-field virus spread, which could potentially affect the choice of models used to quantify within-field pathogen spread. Analysis of SMV epidemics in field-plot experiments indicated that the logistic model was the most appropriate model to describe and compare the temporal spread of SMV among years. On the basis of ordinary runs analyses, within-field spread of SMV strain G-5 was random in 1991 and 1994, but was mostly aggregated in 1992 and 1993. Non-G-5 SMV isolates arising from exogenous sources displayed a random spatial pattern over time. This is the first study in which pathogen incidence (detection of SMV using strain-specific monoclonal antibodies) as opposed to disease incidence (based on symptoms) was employed to monitor and model SMV spread in time and space.

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Spatiotemporal Attributes and Crop Loss Associated with Tan Spot Epidemics in Baby Lima Bean in New York

Plant Disease ◽

10.1094/pdis-07-17-1096-re ◽

2018 ◽

Vol 102 (2) ◽

pp. 405-412

Author(s):

Sarah J. Pethybridge ◽

Frank S. Hay ◽

Adrienne Gorny ◽

Julie R. Kikkert

Keyword(s):

New York ◽

Spatial Pattern ◽

Leaf Area ◽

Disease Incidence ◽

Lima Bean ◽

Tan Spot ◽

Spatiotemporal Patterns ◽

Green Leaf ◽

Incidence Data ◽

Green Leaf Area

Tan spot, caused by the pycnidial fungi Didymella americana and Boeremia exigua var. exigua, is a foliar disease affecting processing baby lima bean production in New York. Tan spot epidemics are prevalent, occur annually, and may result in substantial defoliation. The disease is controlled by the prophylactic application of fungicides to maximize green leaf area. Information on yield losses due to tan spot on baby lima bean yield and the benefits of fungicide applications is needed to justify investments in disease management. Four small-plot, replicated trials were conducted over 2 years in commercial baby lima bean fields to evaluate the efficacy of fungicides for tan spot control at Piffard and Leicester, NY. Applications of pyraclostrobin or boscalid significantly reduced tan spot incidence and severity compared with nontreated plots, and increased the number of leaves per stem. In 2016, the increase in green leaf area associated with fungicide application was also documented in canopy reflectance values at 830 nm. Despite the decrease in tan spot incidence and corresponding increase in crop health obtained from fungicides, this effect did not translate into significant increases in pod yield. This finding suggested that the relationship between green leaf area and yield is highly variable in baby lima bean. The spatial and spatiotemporal patterns of naturally occurring tan spot epidemics were also characterized in baby lima bean fields across western New York using disease incidence data collected in transects and grids. The spatial pattern of data collected in transects was analyzed using median runs analysis. Disease incidence data collected in two-dimensional grids were analyzed to quantify spatial pattern using spatial analysis by distance indices (SADIE). The association function of SADIE was used to quantify the spatiotemporal patterns of tan spot epidemics after crop emergence and at harvest. These findings suggested that tan spot is likely to initiate at relatively frequent, randomly positioned foci, and that subsequent, limited spread results in significant local aggregation. Hypotheses for inoculum sources and recommendations for tan spot control in baby lima bean fields in New York are discussed.

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Monitoring methods and spatial patterns of European canker disease in commercial orchards

New Zealand Plant Protection ◽

10.30843/nzpp.2016.69.5883 ◽

2016 ◽

Vol 69 ◽

pp. 213-220 ◽

Cited By ~ 2

Author(s):

R.E. Campbell ◽

S. Roy ◽

T. Curnow ◽

M. Walter

Keyword(s):

Spatial Pattern ◽

Disease Control ◽

Spatial Patterns ◽

Disease Incidence ◽

Systematic Sampling ◽

Monitoring Methods ◽

Canker Disease ◽

Single Row ◽

Changes Over Time ◽

Over Time

European canker (Neonectria ditissima) kills trees and decreases production in apple orchards To determine a level of disease control or the extent of its spread in commercial orchards efficient monitoring methods are required In this study we investigated two monitoring methods sampling a single row and systematic sampling of an orchard block The spatial pattern of disease within blocks and whether this changes over time was also investigated The accuracy of singlerow monitoring depended on the level of canker in the orchard and the patchiness of the distribution of infected trees However singlerow monitoring tracked changes over time in incidence severity and type of canker sufficiently well and was efficient The spatial patterns of disease incidence across the blocks were nonrandom but showed hotspots which did not change significantly over time

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Dynamics of Lettuce Drop Incidence and Sclerotinia minor Inoculum Under Varied Crop Rotations

Plant Disease ◽

10.1094/pd-90-0269 ◽

2006 ◽

Vol 90 (3) ◽

pp. 269-278 ◽

Cited By ~ 6

Author(s):

J. J. Hao ◽

K. V. Subbarao

Keyword(s):

Spatial Pattern ◽

Spatial Patterns ◽

Field Experiments ◽

Disease Incidence ◽

Inoculum Density ◽

Crop Rotations ◽

Sclerotinia Minor ◽

Progressive Decline ◽

Fallow Period ◽

Lettuce Drop

Field experiments were conducted to determine the population dynamics of Sclerotinia minor and incidence of lettuce drop at two sites during 1995 to 1998. Rotation treatments at the Spence site, which had a low density of inoculum (<7 sclerotia per 100 cm3 of soil) that was distributed randomly, included: continuous lettuce (LLL), lettuce rotated with broccoli (LBL), and lettuce followed by a fallow period (LFL). Treatments at the Hartnell site, which had a high density of inoculum (>7 sclerotia per 100 cm3 of soil) that was distributed uniformly, included: continuous lettuce (LLLL), alternate crops of broccoli and lettuce (BLBL), continuous broccoli or lettuce (BBLL), and fallow-lettuce-fallow-lettuce (FLFL). Under continuous lettuce cropping (LLLL) at the Hartnell site, a progressively aggregated spatial pattern of inoculum distribution developed, despite the initial uniform distribution of high inoculum density. In the fallow treatment (FLFL), the spatial pattern tended to be aggregated following a lettuce crop and less aggregated or random when left fallow. In contrast to these two treatments, treatments involving rotations with broccoli (BLBL and BBLL) exhibited consistently random spatial patterns of inoculum regardless of the crop in the field. The marginal increases in the number of sclerotia contributed by the few diseased lettuce plants were offset by the significant reductions in the number of sclerotia by the broccoli residue. Spatial patterns of disease incidence reflected the pattern of inoculum distribution in the soil at the Hartnell site. Higher inoculum density coupled with an aggregated distribution was associated with an aggregation in disease incidence. At Spence, this correlation was poor in most seasons because of progressive decline in the lettuce drop incidence and lack of treatment differences. In greenhouse experiments, the competence volume for S. minor sclerotia was quantified, which was calculated to be 25 3 for 100% infection and 200 cm3 for 50% infection. Thus, in 100 cm3 of soil, a minimum of four to five sclerotia are needed for 100% of infection, explaining the high correlation between inoculum density and disease incidence.

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Spatial Pattern, Inoculum Density-Disease Incidence Relationship, and Population Dynamics of Sclerotium rolfsii on Apple Rootstock

Plant Disease ◽

10.1094/pd-71-0719 ◽

1987 ◽

Vol 71 (8) ◽

pp. 719 ◽

Cited By ~ 2

Author(s):

S. F. Tomasino

Keyword(s):

Population Dynamics ◽

Spatial Pattern ◽

Disease Incidence ◽

Sclerotium Rolfsii ◽

Inoculum Density ◽

Apple Rootstock

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Rhynchosporium leaf scald disease incidence: seed source and spatial pattern

Plant Pathology ◽

10.1111/ppa.13019 ◽

2019 ◽

Vol 68 (6) ◽

pp. 1179-1187 ◽

Cited By ~ 2

Author(s):

C. F. E. Topp ◽

G. Hughes ◽

I. M. Nevison ◽

A. Butler ◽

S. J. P. Oxley ◽

...

Keyword(s):

Spatial Pattern ◽

Disease Incidence ◽

Seed Source ◽

Leaf Scald

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Spatial Pattern of Trees Affected by Black Spot in Citrus Groves in Brazil

Plant Disease ◽

10.1094/pd-91-0036 ◽

2007 ◽

Vol 91 (1) ◽

pp. 36-40 ◽

Cited By ~ 31

Author(s):

M. B. Spósito ◽

L. Amorim ◽

P. J. Ribeiro ◽

R. B. Bassanezi ◽

E. T. Krainski

Keyword(s):

Spatial Pattern ◽

Disease Incidence ◽

Black Spot ◽

Monte Carlo Test ◽

Ripley’S K Function ◽

Ripley’S K ◽

Citrus Groves ◽

Ripley's K ◽

K Function ◽

Orange Trees

Citrus black spot (CBS), caused by Guignardia citricarpa, is the most important fungal disease of orange trees in Brazil. The spatial pattern of CBS-symptomatic trees was evaluated using the binomial dispersion index (D), Ripley's K function (K), and a Monte Carlo test for minimum mean distance (d) to understand the distribution of the pathogen. Disease was monitored in 7,790 citrus trees from four commercial groves. In one grove, disease incidence was assessed from 1999 to 2001 and, in the others, disease assessments were conducted only in 2002. Infected trees were aggregated based on the three statistical analyses used (D, K, and d) regardless of the CBS incidence. The binomial index of dispersion (D) indicated aggregation of CBS-affected trees for all groves and for various quadrat sizes (2 by 2, 3 by 3, 4 by 4… up to 10 by 10). According to Ripley's K function, the dependence among symptomatic trees comprised two to three neighboring trees. Disease dispersion occurred at distances below 24.7 m according to the test for d. This suggests that the dispersion of inoculum is highly important over short distances. As a consequence, the required sample size to achieve a level of accuracy of C = 20% increases exponentially with the decrease in incidence of CBS below 15% infected plants.

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