A simple temperature-based model for scheduling long-cane blackberry crops

Dormant containerized blackberry plants grown as long-canes are forced in protected environments, such as plastic tunnels or greenhouses, to schedule harvesting for important market weeks. The time needed to produce a crop is mainly a function of temperature. Objectives were to quantify temperature effects on plant development rates for long-cane blackberry and develop simple models predicting the time from forcing dormant plants to first open flower and ripe fruit as a function of mean daily temperature (MDT). The crop time and MDT at first flower and fruit were measured for cultivars ‘Natchez’, ‘Ouachita’, ‘Prime-Ark^® Traveler’, and ‘Prime-Ark^® Freedom grown as long-canes during a greenhouse and high tunnel experiment, and the days to flower and fruit were converted to rates by calculating the reciprocal. Nonlinear models relating flowering and fruiting rates to MDT were developed for each cultivar using a combination of the experimental data and base (6°C), optimum (25°C), and maximum (35°C) temperature parameters derived from a previous blackberry heat unit study. Model accuracy was evaluated by comparing the predicted to observed time to first flower and fruit per cultivar. Validation consisted of testing model accuracy with data from a separate long-cane experiment using the same cultivars with plants forced under differing environmental conditions. Results from the validation experiment suggested MDT had a dominant influence on crop timing, shown by a strong positive correlation (r=0.97) between predicted and observed days to flower/fruit. Model accuracy within ±7 days was found to be 80 to 85% across cultivars. This study provides a framework for modeling temperature effects on crop timing for long-cane blackberry and suggests methods to improve model accuracy and precision. These models can also be used for general training purposes to help educate growers on how temperature influences crop scheduling during long-cane blackberry production.