Assessment of Leaf Area, Vine Vigor, and Grape Yield and Quality of Phylloxera-Infested and Non-Infested Grapevines in Napa County and Their Relationship to Leaf Reflectance, Chlorophyll, and Mineral Content

摘要

Grape Phylloxera will cause the California wine industry to lose over one billion dollars by the year 2000. Grape growers with grape phylloxera- infested soils graft scion varieties onto what are popularly termed 'resistant rootstocks.' Rootstocks, however, differ in their suppression of phylloxera: some do not support the insect at all, while other support low populations. In addition, phylloxera biotypes vary in their growth on different rootstocks. In California's Napa and Sonoma county vineyards, about 75 of the vines have AXR#1 rootstock that tolerates phylloxera biotype A. In the early 1980's biotype B emerged there. It so devastates AXR#1 that the vineyards must be replanted with rootstocks resistant to biotypes A and B. Timing replanting is difficult because vineyards do not decline uniformly. A patchwork of uninfested vines, infested but asymptomatic vines, declining but productive vines', and unproductive vines typifies most vineyards. The grower must determine the proportion of vines in each category and estimate the yield loss the stressed vines will suffer. During 1993, 1994 and 1995 the NASA-Ames GRAPES study used remotely sensed leaf reflectance, temperature, and canopy size data and geographic information system (GIS) technology to study infestations in Napa County vineyards. As part of this study a vineyard with a range of phylloxera induced stress and accompanying symptoms -- reduced growth, less chlorophyll, and lower reflectance of near infrared:red light -- was investigated to determine the degree to which stress measurements predict the current and following season's yields from stressed vines relative to healthy vines. Such yield estimates could enable a grower -- before obtaining actual yields -- to calculate the economics of replanting. A grower who decided to replant would have 2-14 months additional lead time to plan and prepare.