Fire blight blossom blight suppression by experimental and registered products on Idared apple

摘要

Treatments involving Actigard (FRAC P1), Serenade Optimum (FRAC 44), and Regalia (FRAC P5) and integrated schedules with streptomycin (FRAC 25, Firewall/Harbour) were compared to streptomycin alone for blossom blight control and fruit finish effects.The test was established in four randomized blocks on 31-yr-old trees using single-tree replications with border rows between treatment rows. Our general test strategy was to make applications in the morning before inoculating in the evening in anticipation of a relatively warm day to follow. All treatments were applied to both sides of trees with a Swanson Model DA-400 airblast sprayer at 100 gallons per acre 11 Apr (Pk, Trt. #6 only, early pink);18 Apr (B1, early bloom); 23 Apr (B2, full bloom);1 May(B3, late bloom); 10 May (PF, petal fall, Trt. #6 only); 18 May (1C, 1st cover, Trt. #6 only). Four selected branches per tree, each with about 25 blossom clusters, were inoculated by spraying to wet with a bacterial suspension containing 1x106 streptomycin- sensitive Erwinia amylovora cells/ml. Inoculation was done the evenings of 18 Apr, 23 Apr, and 1 May, the same days as the three bloom applications. Trees were not inoculated after the fourth and fifth applications (to Trt. 6). Infection data were based on counts of number of blossom clusters present on the inoculated branch at the time of the first inoculation. A cluster was rated as infected if it had at least one blossom with any fire blight symptoms on 16 May. Maintenance insecticides were applied to the entire block with a commercial airblast sprayer. Fruit finish was rated on 25 fruit per replication after harvest 24 Sep.