Spatial distribution of environmental stress indicators in Concord grape vineyards

Abstract

Concord grapes ( Vitis labrusca L.) in Washington, USA suffer from ‘blackleaf’ disorder, which darkens the foliage to purplish-brown and black in sun-exposed leaves of the outer canopy. Recently, blackleaf has been related to ultraviolet radiation in combination with water-deficit stress, although blackleaf development varies within and among vineyards. This study used digital image analysis, mapping, and semivariogram models to determine if blackleaf or its reciprocal greenness, demonstrates spatial variability within Washington vineyards, and if so, to characterize development of that spatial structure throughout the growing season. In 1998, digital color images were taken in one commercial and one research vineyard. Images taken directly above the vines were captured at key phenological stages (fruit set, veraison, and harvest). Individual images were analyzed for blackleaf symptoms, demonstrated by a low proportion of greenness, and each measurement was associated with a vine location for use in geostatistical procedures and mapping. Declines in greenness occurred throughout the growing season in both vineyards. Spatial auto-correlation was strongest early in the season with 39–51% of the variation explained by spatial location. Results suggest greenness is spatially dependent early in the season, but as the season progresses and the canopy expands, greenness loses its association with spatial location until blackleaf expression becomes more pervasive late in the season. This research presents insight into the seasonal and spatial development of blackleaf in an agroecosystem. It also presents a method for detecting and mapping early to mid-season indications of environmental stress to facilitate site-specific management practices.