A Model of Damping-off and Root Rot of Douglas-Fir Seedlings Caused byFusarium oxysporum

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Abstract
The mathematical relationships required to construct a model of damping-off and root rot of Douglas-fir seedlings caused by F. oxysporum were derived from the literature, unpublished data and experiments. A time and space frame of 180 days from sowing, in plots 0.1-0.2 m2 .times. 20 cm deep containing up to 100 seedlings, was selected. Simplifications and assumptions in the model included use of temperature as the main environmental factor, subdivision of time into 5-day periods and space into 2-cm intervals, with 1 vertical and 1 horizontal dimension and natural variation based on pseudo-random selections from normal distributions. Using chi-squared goodness-of-fit, model predictions of germination, root growth and root rot mortality were not significantly different from nursery results in 4 yr. Predictions of number of seedlings and seedling roots infected were 72-120% of nursery results.