Temperature Thresholds and Growing-Degree-Day Models for Red Sorrel (Rumex acetosella) Ramet Sprouting, Emergence, and Flowering in Wild Blueberry

Red sorrel is a common herbaceous creeping perennial weed in wild blueberry fields in Nova Scotia that spreads by seeds and an extensive creeping root system. Experiments were established to determine temperature thresholds for ramet sprouting from creeping root fragments and to develop growing-degree-day (GDD) models for predicting ramet emergence and flowering under field conditions in wild blueberry fields in Nova Scotia. Ramets sprouted from root fragments at temperatures as low as 1 C, with an optimum temperature for ramet sprouting around 22 C. Ramet sprouting was completely inhibited at temperatures above 35 C. Cumulative ramet emergence and flowering under field conditions were adequately explained as functions of GDD by a three-parameter power equation (R 2 = 0.98) and a four-parameter logistic equation (R 2 = 0.87), respectively. Ramet emergence began between 110 and 265 GDD and continued throughout the season at each site. Model prediction for the initiation of emergence was 92 GDD, and 50 and 95% emergence were predicted to occur at 1,322 and 2,696 GDD, respectively. Red sorrel ramets began to flower in the field between 308 and 515 GDD. Model prediction for the initiation of flowering was 289 GDD, and 50 and 95% flowering were predicted to occur at 545 and 1,336 GDD, respectively. Model validation was conducted with the use of two additional independent data sets for emergence and flowering and indicated good performance of the proposed models (R 2 and root-mean-square error values ranging from 0.96 to 0.99 and 4.0 to 13.8, respectively). The models allow for direct comparison of red sorrel phenology to that of the wild blueberry and will aid in the development of new management strategies.