Relationships between autumn black spot leaf litter and <i>Venturia inaequalis</i> ascospore production in apple orchards

Abstract

Ascospore production from pseudothecia in apple leaf litter in the spring is a critical step in the disease cycle of Venturia inaequalis Leaf litter management is potentially an important component of an integrated pest and disease management strategy An orchard study was carried out in Hawkes Bay to investigate the relationships between the incidence of black spot on leaves in autumn the density of apple leaf litter on the orchard floor in spring and the number of ascospores produced in spring A total of 22 blocks on eight orchards were surveyed for black spot incidence in autumn 2000 The following spring remaining leaf litter was measured and ascospore production was quantified using spore traps Autumn black spot levels and spring litter levels were accurate predictors of spring ascospore production Management strategies employed on different blocks influenced spring leaf litter and ascospore levels Blocks with high autumn black spot generally had high spring ascospore production Management practices that substantially reduced litter levels resulted in reduced V inaequalis inoculum