Efficacy of fire blight management in pome fruit in northern Israel: copper agents and their effect on yield parameters

Abstract

Erwinia amylovora causes fire blight, a bacterial disease of pome fruits. For 15 years, fire blight management in Israel was based solely on the antibiotic oxolinic acid but, in response to decreased disease-control efficacy, copper agents were added in 2014. However, concern was raised as to whether repeated applications of copper might have impaired pollen germination and thereby impaired yields. In Israel, apple cultivars, except for the early-blooming cultivar ‘Cripps pink’ (trademark Pink Lady), appeared to be markedly less sensitive to the infection than pear cultivars (‘Spadona’ and ‘Costia’). The aims of the present study were to monitor the effects of treatments with copper-based agents during blossoming in reducing fire blight damage, while recording their effects on pollen-tube germination and fruit-yield parameters. Copper tribasic sulfate and copper hydroxide reduced disease levels by more than 70% compared with uninfected controls. Pollen-tube germination rates in both apples and pears were significantly reduced after two successive daily applications of copper tribasic sulfate, but usually they recovered to control levels after introduction of a single-day interval. Four to seven seasonal applications of copper agents on apple and pear blossoms did not significantly reduce fruit weight and size, seed number, seed-set or fruit-set. The efficacy of oxolinic acid, applied either alone or tank-mixed with copper, resembled that of copper alone. In summary, copper application against fire blight in pears and apples during their blooming in Israel is both effective and harmless to yields.