Prediction of a District's Grape-Ripening Capacity Using a Latitude-Temperature Index (LTI)

Abstract

A district's grape-ripening capacity has previously been related to the area's growing degree days (DD) or the mean temperature of the warmest month (MTWM). It has been observed that grape cultivars ripened in parts of New Zealand where they did not fulfill the DD or MTWM criteria used for Europe or North America; thus, an attempt was made to find a more universal index. Cultivars were divided into four distinct groups, based on their ripening requirements, and 14 indices were tested for their ability to relate the groups to the districts in which they are known to ripen. Seventy-eight locations in Europe, North America, Australia, and New Zealand were used. Three groups of locations were adequately separated using DD or MTWM and a different three by latitude. All groups were separated, by an index combining latitude and MTWM. This is termed the latitude-temperature index (LTI) and has more general usefulness for all areas than any other index tested. LTI = MTWM (60 - latitude).