Boron Deficiency in California Vineyards

Abstract

Boron deficiency has been found in certain Caifornia vineyards leached by excessive seasonal rainfall in the unirrigated coastal region, and by low-boron irrigation water on sandy alluvial soils of granitic origin along the east side of the San Joaquin Valley. The foliage symptoms and effects on fruit production are descriped and illustrated by six photographs; they are in complete agreement with symptoms described in reports from other grape-growing regions of the world. Boron levels of representative foliage tissue are presented. Chlorotic leaves have values averaging about 7 to 9 ppm. Bloomtime petioles adjacent to clusters, taken from deficient Carignane and Thompson Seedless vines, show boron levels of 20 to 28 ppm. It is suggested that vineyards of these two varieties may respond to borax treatment (using any of several available materials at rates equivalent to 10 pounds of boric oxide per acre) when bloomtime petioles drop below 30 ppm, and that visual symptoms are likely if values are 25 ppm or less.