A population level, two-compartment, temperaturedependent model that predicts date of seedling johnsongrass flowering was formulated. The model consisted of a fourparameter poikilotherm rate equation to describe development rate as a function of temperature and a temperature-independent Weibull function to distribute flowering times for the population. Experiments were conducted to determine the effect of temperature, nitrogen availability, and water availability on development of seedling johnsongrass. Development was most sensitive to temperature while the effect of nitrogen concentration and water availability was minimum and inconsistent. The model was tested against three independent field data sets and provided accurate prediction of flowering dates for each data set.

Research was conducted to formulate a temperature-dependent population level model for johnsongrass seed germination and rhizome bud break. A nonlinear poikilotherm rate equation was used to describe development rate as a function of temperature, and a temperature-independent Weibull function was used to distribute development times for the population. Seed germination and initiation of rhizome bud break of johnsongrass were collected under constant temperature conditions to parameterize the model. Seed germination rate increased with temperature up to 36 C, then declined at 40 C. Rate of rhizome bud break increased with temperature up to 32 C, then rapidly decreased with further temperature increases. Rate of rhizome bud break was higher than for seed germination at temperatures of 32 C or below, but lower at higher temperatures. Time to first germination or bud break event was longer for seed than for rhizomes, but subsequent progression of development was higher for seed. A population level temperature-dependent model was developed by coupling the poikilotherm equation with the Weibull function. The model was validated against two independent seed germination and three independent rhizome bud germination data sets.

Research was conducted to formulate a temperature-dependent population-level model for rhizome johnsongrass flowering. A nonlinear poikilotherm rate equation was used to describe development as a function of temperature and a temperature-independent Weibull function was used to distribute development times for the population. Johnsongrass flowering data were collected under constant temperature conditions to parameterize the poikilotherm rate equation and Weibull function. Coupling the poikilotherm rate equation with the Weibull function resulted in a population level temperature-dependent model. The model was validated against independent field data sets. The model accurately predicted rhizome johnsongrass flowering from plants emerging in the spring. The model performed poorly for plants emerging in summer. Adjustments to the high-temperature inhibition parameter of the poikilotherm rate equation improved model performance in the summer without affecting spring predictions.