Foliar Sprays Containing Phosphorus (P) Have Minimal Impact on ‘Pinot noir’ Growth and P Status, Mycorrhizal Colonization, and Fruit Quality

Abstract

Grapevines grown in low-phosphorus (P) soils typical of western Oregon vineyards may benefit from additional P applied to the canopy using foliar sprays. Alternatively, vines may be negatively affected by foliar P sprays because lower root colonization by arbuscular mycorrhizal fungi (AMF) could reduce uptake of other nutrients or increase vine water stress. The impact of foliar P sprays on vine growth, vine nutrient and water status, AMF colonization, and fruit yield and quality was studied in two ‘Pinot noir’ vineyards with a history of low vine P status over 3 years. Three foliar spray treatments [phosphite, phosphate, water (control)] were applied to vines three times each season using a standard air-blast sprayer at a commercial vineyard. Two foliar spray treatments (phosphite, water) were applied using a hand sprayer at a smaller research vineyard. Phosphite sprays increased leaf blade and petiole P concentrations and reduced arbuscular colonization of roots at the research vineyard, but neither phosphate nor phosphite significantly affected these variables at the commercial vineyard. Foliar P sprays had no effect on vine growth, vine water relations (leaf water potential and stomatal conductance), yield, or fruit quality attributes at either site. These results indicate that there is little benefit to spraying the canopy of grapevines with P, even in vineyards with low P status.