Phenology is the study of seasonal biological development. The progress of plants and animals can be quantified, based on prevailing weather. Many models of development have been tested for various species of crops and insects. Each gives a mathematical formula that is supposed to be linear with development. These formulas use maximum and minimum daily temperatures as arguments, and most require threshold and cutoff temperatures as parameters to constrain growth outside ideal conditions. All predict growth due to the amount of heat present in the environment to speed development. This is expressed as a product of temperature and time: Growing Degree-Days.
Orchard with Flowering Apricot-Trees (1888, van Gogh)
As cumulative Growing Degree-Days increase throughout the season, milestones in development of each species are passed when biological treatments and controls may be enacted. The needs of the past are observed, and the effort and material required to secure future crops are minimized by applying resources at optimal times.
This document supersedes the one written for the Cydia WeeWX Extension. The Cydia Extension is obsolete. The Phenology WeeWX Extension is written in Python 3 and has been tested with WeeWX 4.2.0 and subsequent versions.
Disclaimer: I am a sales associate for a world-wide discount retailer. I am a systems analyst by training, and I have worked in the field for a regional grocery distributor, a worldwide consumer electronics manufacturer, and a "Big 10" university. Beyond tending a backyard orchard, I have no credentials whatever in the life sciences. The information herein is drawn from sites publicly available on the Internet.