Vineyard Response to Phosphate-Zinc Foliar Sprays

Abstract

Five replicated vineyard trials were conducted during a two-year period to test the response of commercial 9Thompson Seedless9 raisin vineyards to foliar sprays of two proprietary nutrient spray materials. Nutra-Phos 24 and Zinc Nutra Spray 50 were applied three times in 1962 and twice in 1963 at equal concentrations of zinc content. Two-inch shoot tip samples were collected throughout the season from before bloom until early harvest stage, and these were analyzed for zinc and phosphorus. Shoots were tagged for growth rates, fruit samples were collected at three dates for quality measurements, and total crop as raisin yield was compared with that from unsprayed controls. Zinc content of tips was increased two- to-threefold by both materials, especially by the prebloom sprays. Increase of total phosphorus was not detectable by either of two analytical methods with precision of ± 100 ppm P. Visual symptoms of zinc deficiency did not develop, and the content of phosphorus in the tissue was about average for the area. There was no measurable benefit from phosphorus <i>per se</i>. In all five trials Zinc Nutra Spray 50 increased raisin yields 3 to 7%, but only one, at plus 6%, was statistically significant; and it was associated with a statistically reduced °Balling of the fruit.