Spatial Pattern of Phomopsis Cane and Leaf Spot Symptoms in Commercial Vineyards in Ohio

Spatial patterns of incidence of Phomopsis cane and leaf spot were examined using 57 data sets obtained from a statewide survey of grape vineyards in Ohio from 2002–2004. To characterize small‐scale patterns at the vine scale or below, discrete‐distributional analyses were used to quantify the heterogeneity of disease incidence within vineyards. The number of diseased leaves and internodes (out of 15) per sampling unit was better fitted by the beta‐binomial than the binomial distribution in 67% and 91% of the cases, respectively. The index of aggregation was significantly >1 for 78% and 98% of the cases for diseased leaves and internodes, respectively. These results indicated aggregation of this disease at an individual vine scale (or lower). Conversely, there was little evidence of aggregation at scales larger than a vine (e.g. disease foci extending beyond individual vines) for most vineyards based on Spatial Analysis by Distance IndicEs (SADIE). SADIE analysis suggested a random pattern of the count of diseased leaves and internodes in the majority (>86%) of the cases. Based on SADIE, there was significant (P ≤ 0.05) evidence of association between leaf and internode disease counts per vineyard in 75% of cases, indicating that the dispersal of inoculum from the previously infected wood tissues (canes) affected both leaf and internode in the same manner. In contrast, association of disease counts from one year to the next was only significant in approximately 15% of the cases, indicating the difficulty in predicting the level of disease in a section of a vineyard based on the previous year’s observations alone.