Residue Levels of Daminozide in Apple Trees Sprayed the Preceding Spring and Summer

Abstract

Daminozide residue levels in fruit and vegetative parts of apple trees were determined the year following foliar spray treatments with daminozide at recommended rates and times and at excessive rates and times closer to harvest than recommended. Trees were sampled in December, March and August following spraying. Daminozide residues were found in all vegetative plant parts, with the highest residue levels found in the buds, bark and xylem of spurs, and in terminal and lateral buds; the lowest residue levels were found in the bark and xylem of stems. Residue levels were affected by both rate and time of application. Residue levels increased as application rates increased, but the response to rate was less when treatments were applied 21 d after bloom (125 d before harvest) than when treatments were applied closer to harvest. The highest residue levels were from treatments applied the day of harvest. Higher residue levels were found in March samples than December samples. Residues had been dissipated to low levels by the August sampling date. No daminozide residues were found in apple fruit from trees treated the previous year with recommended levels of daminozide applied at the recommended time. However, low residue levels were found in fruit treated with 2 × and 4 × rates of daminozide at times closer to harvest than recommended.