1023 MANAGING BORON NUTRITION IN DECIDUOUS TREE FRUIT ORCHARDS

Abstract

Boron (B) is an essential micronutrient that is often in inadequate supply in many deciduous tree fruit orchards and must therefore be added as fertilizer. It can also occur at phytotoxic levels because of over-fertilization, use of high-B irrigation water, or naturally in arid soils that are natively high in B. Tree B status is usually characterized by leaf analysis although other diagnostic criteria are being evaluated. Several tests are used to characterize soil B status. Symptoms of B deficiency include blossom blast, poor fruit set and development, shortened internodes, terminal bud death, and shoot dieback. To ameliorate deficiency, B fertilizer may be broadcast or sprayed over the soil surface or sprayed on tree canopies. In some regions, maintenance applications of B fertilizer are made to prevent development of B deficiency. Sodium borates or orthoboric acid are usually used. Fertilizer rates and timing vary with location and farming practices. Symptoms of B excess include reduced or no yield, impaired fruit quality, leaf marginal chlorosis and necrosis, defoliation, and shoot dieback. Boron toxicity is alleviated by leaching B-enriched soil to move B below the root zone.