Effective use of ethylene-releasing agents to prevent spread of eastern dwarf mistletoe on black spruce.

Ethephon, ethanedial dioxime, etacelasil, 2-chloroethyl-methylbis (phenylmethoxy)-silane and 1-aminocyclopropane-1-carboxylic acid applied to Arceuthobium pusillum infections on Picea mariana promoted premature abscission of mistletoe shoots. Concentrations of the chemicals ranged from 12 to 5000 mu g/g. Surfactants (Ortho X- 77 and PGFI-100) were also evaluated. The treatment combination that consistently resulted in 74-100% abscission of dwarf mistletoe shoots was August applications of 2500 mu g/g ethephon plus either surfactant. Abscission of dwarf mistletoe shoots prevents spread of the disease in black spruce for 2 yr and for at least 4 yr in some western conifers.-from Authors