Determination of the incidence of postharvest stem decay on cold stored pears and development of control measures

Under conditions of high relative humidity, such as which develops when pome fruit is enclosed in a polyethylene bag liner inside the box for storage, pathogens already present in and on the stems, or surface of pears, proliferate and grow from the infection site, resulting in stems with unsightly brown/black discolouration, or lesions on the surface of the fruit. Alternaria was found to be the main pathogen isolated from Forelle pear stems, followed by Penicillium and Botrytis. Sodium bicarbonate (NaHCO₃) was shown to be a promising treatment to reduce the development of stem decay on Forelle pears. Biox (20 ppm), and a combination treatment of NaHCO₃ (10%) + Sporekill (1 ml/ L) + Biox (10 ppm), also showed promise as a fungicide alternative approach to reduce stem decay. The inhibition of Alternaria on stems was less effective than for Penicillium. The efficacy of control was related to the product applied. Treatment of Forelle pears with iprodione or pyrimethanil effectively confined the incidence of Botrytis stem and fruit decay better than chlorine. Treatment of Forelle pears with iprodione or pyrimethanil effectively confined the incidence of Penicillium stem decay better than chlorine, with only pyrimethanil confining the incidence of Penicillium fruit decay significantly. Hot water application did not improve efficacy of iprodione or pyrimethanil against Botrytis or Penicillium. Alternaria stem and fruit decay incidence could not be reduced significantly by treatment of Forelle pears with iprodione or pyrimethanil, neither with chlorine. Pre-harvest control measures should be sought to confine development of Alternaria stem decay on pears.