RELATIVE EFFECTIVENESS OF, AND RESIDUE DECLINATION VALUES FOR DICHLORPROP, FENOPROP AND NAPHTHALENEACETIC ACID USED TO CONTROL PREHARVEST DROP OF McINTOSH APPLES

Dichlorprop [2-(2,4-dichlorophenoxy)propionic acid] sprays, at concentrations of 20–40 ppm, provided generally satisfactory protection against preharvest drop of McIntosh apples (Malus sylvestris Mill.) in each of three seasons. The protection was comparable to that provided by 10–20 ppm fenoprop (2,4,5-trichlorophenoxy propionic acid) and frequently superior to 20 ppm naphthaleneacetic acid (NAA). An examination of residue levels in fruits harvested 2 h to 10 days after spraying showed that dichlorprop is quite persistent whereas NAA residues decline rapidly in fruits on the tree.