SEEDLING EMERGENCE MODEL FOR VELVETLEAF

Consistent postemergence weed control requires information on the timing of weed emergence- information is especially important for velvetleaf (Abutilon theophrasti Medikus), which interferes with many crops over a broad geographic range. The objective of this study was to develop a model that predicts the timing and proportional extent of velvetleaf seedling emergence. Environmental effects on seed germination and seedling emergence, used to construct the model, were determined in growth chambers or from published sources. Two variables drive the model: average daily soil temperature of the seed zone (5-cm soil depth) and daily rainfall. The model requires initialization by four seed zone parameters: (i) soil water content at the start of the simulation period, (ii) soil water holding capacity, (iii) soil bulk density, and (iv) a water retention curve relating percent soil water to soil water potential. The model was validated using field data collected in Illinois in 1967 and 1969 and in Minnesota in 1990. Regressions of predicted and observed seedling emergence resulted in r2 values of 0.91, 0.97, and 0.98 for 1967, 1969, and 1990, respectively. Correspondence (regression coefficients) between predicted and observed seedling emergence was 0.83, 1.01, and 1.01 for 1967, 1969, and 1990, respectively. Both sets of statistics indicate the model predicts velvetleaf seedling emergence reliably.