Project Title: Predicting Key Phenological Stages for Grapevines: A Simple but Scientific Approach for Management and Site Selection
Date: December 12, 2016

Principal Investigator(s): Melba R. Salazar-Gutierrez
Organization: AgWeatherNet
Address: 24106 North Bunn Rd
Telephone: 509-786-9201
Email: [email protected]

CO-PI(s): Gerrit Hoogenboom
Organization: AgWeatherNet
Address: 24106 North Bunn Rd
Telephone: 509-786-9371
Email: [email protected]

CO-PI(s): Markus Keller
Organization: IAREC
Address: 24106 North Bunn Rd
Telephone: 509-786-9263
Email: [email protected]

Cooperator(s): Boushey Vineyards
Description of Participation: advice, access to the vineyards for data collection

Cooperator(s): Hogue Ranches
Description of Participation: advice, historical data, access to the vineyards for data collection

Project Summary:

Plant development is primarily controlled by temperature which plays a role in determining the appearance of phenological stages and the length of the phenophases (Johnson and Thornley 1985, Kwon et al. 2008). In this way, phenology can be modeled in function of temperature to characterizing differences among species (Parker et al. 2013) and predicting plant development under different environmental conditions (Caffarra and Eccel 2010). Using the degree-days model (DD) which is is calculated as the difference between daily mean air temperature and a threshold value known as base temperature (Tb) (Arnold 1959). Below the Tb the plant development ceases (Arnold 1959, Snyder et al. 1999).

Most of the thermal time models that have been implemented so far applied the same Tb for different phonological stages but an accurate prediction of the critical phenological events during a crop’s cycle requires the determination of the an appropriate Tb (Hoover 1955, Parker et al. 2013). Tb can be estimated as Moncur (1989) exposing the plants under controlled environments, and finding differences between the occurrences of phenological stages. However, less uncertainty has been found in the methods that estimate Tb using phenology timing and temperature data collected under field conditions for several years or locations, and the selection of Tb is based on finding the temperature that provides the minimum variability in DD (Yang et al. 1995).

In grapevines, budbreak, flowering, veraison, and harvest are the most important stages, and the timing among these phenological stages varies between cultivars, climate and location (Jones and Davis, 2000). An accurate prediction of the occurrence of these stages can help with executing crop management practices and scheduling labor requirements and equipment. As example, knowing the occurrence of budbreak beforehand may assist in planning pruning that is needed to adjust crop load; after fruit set, leaf removal and cluster thinning is performed to improve vine balance and berry size; before and after veraison, irrigation is applied to control crop growth, enhance desired fruit traits and ensure vine health.

The goal of this study was to predict the appearance of budbreak, bloom, and veraison for 17 red and white grapevine cultivars through determining Tb and duration in thermal time required to reach each phenological stage and to implement these Tb and DD parameters for predicting the successive appearance of the three key stages as a function of grapevine cultivar.

Read more by downloading the full report above.

Climate // Viticulture //