The Effects of Simulated Rain and Dew on Fluoride Accumulation by Citrus Foliage

Abstract

Abstract ‘Valencia’ orange trees subjected to a drenching shower twice a week or sprinkled daily with a fine water spray until their leaf surfaces were thoroughly wet were found to accumulate less fluoride than unsprayed trees when exposed to low concentrations of HF gas. In the early stages of leaf development the drenching shower and light sprinkling treatments were equally effective in reducing fluoride uptake. After the foliage was 3 or 4 months old, however, the daily sprinklings had little effect on fluoride uptake whereas the twice weekly 1 hr drenchings effectively prevented fluoride accumulation. Growth responses were inversely proportional to fluoride uptake with maximum growth suppression associated with maximum fluoride uptake. After 9 months of treatment, the drenchings had reduced fluoride uptake by 85% and growth suppression by approximately 87%. In the same period the daily sprinkling treatment had reduced fluoride uptake by 37% and growth suppression by 45%.