South African Avocado Growers ’ Association Yearbook 1998. 21:22-25 Soil Boron Application for Control of Boron Deficiency in the Avocado

Studies indicated tentatively that foliar boron applications were ineffective and falsely inflated annual boron analysis results. In spite of sprays, mean leaf boron concentrations varied from 28-33 mg/kg. Soil analyses from four growing areas in KwaZulu-Natal, reveled deficient levels of B, all showing concentrations of less than 1 mg/kg. Glasshouse trials showed that Edranol was 40 % more efficient at boron uptake than the widely used Duke 7 rootstock. Field trials, experiments with soil boron (in the form of Borax) application rates in the range of 5-60 g/m2/year showed all treatments successfully raised leaf boron concentration, highest application rates causing toxicity 15 months after initial application. Successful treatments in younger trees resulted in a 4 % increase in mean fruit mass, and a consequent 10 % increase in yield with no significant difference i