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Geostatistical Analysis of Dollar Spot Epidemics Occurring on a Mixed Sward of Creeping Bentgrass and Annual Bluegrass

^a Dep. of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061
^b Dep. of Plant Pathology, Michigan State Univ., East Lansing, MI 48824
^c Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824. This work was supported by a Project GREEEN grant (GR00-037) from the Mich. Agric. Exp. Stn., East Lansing

View larger version (12K): [in this window] [in a new window]   Figure 1. Schematic layout of 200 regular grid sampling areas for 2000 with black squares () denoting the center of each 0.09-m2 sampling area at the Robert Hancock Turfgrass Research Center, East Lansing, MI.

View larger version (22K): [in this window] [in a new window]   Figure 2. Schematic layout of 800 regular grid and 88 randomly located sampling areas for 2001 and 2002 with black squares () denoting the center of each 0.023-m2 sampling area at the Robert Hancock Turfgrass Research Center, East Lansing, MI.

View larger version (18K): [in this window] [in a new window]   Figure 3. Overall disease progress of dollar spot epidemics on a mixed sward of creeping bentgrass and annual bluegrass from 2000 to 2002 as measured by the average number of dollar spot foci per square meter. Area under the disease progress curve (AUDPC) values calculated from dollar spot foci counts are shown in upper right of graph.

View larger version (17K): [in this window] [in a new window]   Figure 4. Variograms of dollar spot epidemic caused by S. homoeocarpa on a mixed sward of creeping bentgrass and annual bluegrass on six dates in 2000 selected to be representative of changes in disease progress (Fig. 3) throughout the growing season.

View larger version (16K): [in this window] [in a new window]   Figure 5. Variograms of dollar spot epidemic caused by S. homoeocarpa on a mixed sward of creeping bentgrass and annual bluegrass on six dates in 2001 selected to be representative of changes in disease progress (Fig. 3) throughout the growing season.

View larger version (15K): [in this window] [in a new window]   Figure 6. Variograms of dollar spot epidemic caused by S. homoeocarpa on a mixed sward of creeping bentgrass and annual bluegrass on six dates in 2002 selected to be representative of changes in disease progress (Fig. 3) throughout the growing season.

View larger version (11K): [in this window] [in a new window]   Figure 7. Proportion of structural variance (PSV) (C/(Co + C), where C = sill value-nugget variance, and Co = nugget variance) displayed over time for spherical variogram models based on geostatistical analysis of dollar spot epidemics on a mixed sward of creeping bentgrass and annual bluegrass from 2000 to 2002. Dotted lines in the plot area represent the area where structural variance accounted for between 30 and 60% of the total variation present.

View larger version (45K): [in this window] [in a new window]   Figure 8. Spatial pattern of dollar spot disease incidence on (A) 28 June 2000, (B) 2 Aug. 2000, (C) 22 June 2001, (D) 30 Aug. 2001, (E) 2 July 2002, and (F) 30 Aug. 2002, representing dates early (A, C, and E) and late (B, D, and F) in disease epidemics of each year. Decile scale to the right of each map represents block estimates of dollar spot foci 0.08–1 m–2. Maps generated by kriging of disease incidence data from sampling locations shown in Fig. 1 and 2. Maps are oriented with north at top, and east and north coordinates on x and y axes.