Influence of harvest date on bull’s eye rot of ‘cripps pink’ apple and control chemical strategies

Abstract

The influence of four different harvest times on the bull’s eye rot of ‘Cripps Pink’ apple caused by Neofabraea spp. was investigated in two orchards harvested at four different times. In addition, a control strategy based on chemical treatments performed in preharvest or post- harvest was evaluated. Regression analysis between harvest time and disease incidence revealed high r2 values (>0.75). All preharvest fungicide treatments significantly (P < 0.0085) reduced the bull’s eye rot incidence; however, thiophanate-methyl (achieving >87% con- trol) was more effective than a mixture of pyraclostrobin and boscalid ‘Cripps Pink’ apple (Malus domestica Borkh.), which originated from a cross between ‘Lady Williams’ and ‘Golden Delicious’, is a late-maturing and long-storing cultivar, superior in size, appearance, and flavor relative to those of other late-maturing cultivars (Cripps et al. 1993). Since 1990, this cultivar has been cultivated in major apple-producing areas of the world (IPLA 2015). Although Cripps Pink apple represents a small portion of world apple production (1%), it frequently commands a premium value. In Europe, to achieve the best fruit color for marketing, Cripps Pink apple is generally harvested in a period that extends from the end of October to the end of November. Cripps Pink apple is fairly resistant to bitter pit and, if harvested at the correct maturity stage and stored in a controlled atmosphere, it also shows a low susceptibility to superficial scald (Cripps et al. 1993). After storage for 3 to 4 months at 0°C, Cripps Pink fruit frequently develops bull’s eye rot, which is caused by several species of Neofabraea (Soto-Alvear et al. 2013; Spotts et al. 2009; Verkley 1999). Previous in- vestigations (Edney 1964; Spotts 1990; Verhoeff 1974; White and Wilkinson 1962) have well documented that the pathogen infects apple fruit in the orchard prior to harvest and remains latent in the fruit for several months. Although Neofabraea spp. can produce cankers in the twigs (Henriquez et al. 2006), fruit remains symptomless in the field, developing lesions only during storage. Initially, the symptoms are restricted to lenticels as circular necrotic areas, usually flat or slightly concave, dark, and firm. The incidence of disease varies considerably, depending on weather conditions; however, in humid areas with abundant rain and persistent fog close to harvest, bull’s eye rot can affect over 50% of the fruit (Spotts et al. 2009). Partial control of bull’s eye rot can be achieved by repeated applications of fungicides such as captan, phenyl-pirroles, and strobilurines during the 2 months preceding harvest (Giraud and Bompeix 2012; Henriquez et al. 2006; Minář 2006). Late-season and postharvest use of fungicides on apple, however, is under scrutiny by the (<80.7%) or fludioxonil (<57.6%), in all trials. Compared with non- treated control fruit, a postharvest treatment with the ethylene inhibitor 1-methylcyclopropene (1-MCP) halved the incidence of infection in three of four experiments. However, a combination of two preharvest treatments with a mixture of pyraclostrobin plus boscalid and one post- harvest 1-MPC treatment suppressed bull’s eye rot to a significantly (P < 0.00001) greater degree (achieving >87.5% control) than the single treatments with pyraclostrobin and boscalid (<65%) and 1-MCP (<80%) tested alone.