Epidemiology / Épidémiologie Temporal and spatial dynamics of mycosphaerella blight [Mycosphaerella pinodes] in field pea

The temporal and spatial patterns of epidemics of mycosphaerella blight, [Mycosphaerella pinodes] in field pea in western Canada were characterized during 2000 and 2001, using mathematical models and geostatistical analysis. The logistic model well described the disease progress over distances and in various directions from the inoculum source. The temporal disease progress rates measured by the linear form of the logistic model ranged from 0.187 d–1 for disease progress at the inoculated area to 0.288 d–1 for disease progress at 18 m from the inoculum source, and from 0.136 to 0.265 d–1 in various directions. By the end of the epidemic in both years, the steepest disease gradient was located upwind, in the north to northwest section of the field, while gradients in the east to south section became flatter. The disease gradients ranged from –0.009 m–1 in the downwind direction (south) to –0.183 m–1 in the upwind direction (north). The final disease gradients in the field ranged from –0.043 to –0.050 m–1. Disease severity declined by 50% within 1.8 to 15 m and by 90% within 7 to 62 m from the inoculum source in the upwind directions. Disease declined by 50% within 16 to 44 m and by 90% within 55 to 222 m in the downwind directions. On the basis of the final disease gradients in both years, the disease severity declined by 50% and 90% within 8 to 14 m and 40 to 51 m, respectively. Geostatistical analysis showed that the range of the spatial dependence of sampling sites in the field was 18 m within rows in 2000 and across rows in both years. The range of spatial dependence was 22 m in the 45° direction in both years and in the 135° direction in 2000. It was 32 m in the 135° direction in 2001, but no range of spatial dependence was detected within rows in 2001.