Evaluation of biological control materials for the control of fire blight on Buckeye Gala apples in Michigan, 2018

摘要

Treatments were applied at 300 gal per acre with a handgun sprayer at 200-250 psi to a block of 6-year-old Buckeye Gala trees on M106 rootstock at East Lansing, MI to evaluate fire blight control. Treatments were replicated four times in single-tree plots. Spray dates and respective growth stages for the treatments were as follows: 7 May (spread cluster); 12 May (pink); 17 May (70% bloom); 17 May (80%); 18 May (80-90% bloom); 19 May (full bloom) and 24 May (petal fall). Trees were inoculated when themajority of blossoms were at the 80% bloom stage on 18 May by spraying the outer perimeter of each tree with a 3-gallon sprayer containing an aqueous suspension of Erwinia amylovora strain Ea110 containing 1.0 x 106 cfu per ml. Inoculation was carried out during the evening to ensure optimal conditions for bacterial survival. Blossom blight was evaluated on 14 Jun followed by a shoot blight evaluation on 8 Aug. A total of 100 blossom clusters and 100 shoots from each treatment rep. were evaluated for incidence of fire blight infection. Data were analyzed using the analysis of variance and LSD mean comparison function of ARM (version 9.3; Gylling Data Management Inc., Brookings, SD). Percentage data were subjected to an arcsine square root transformation before analyses. For the 93-day period between 14 May and 15 August, there were 86 days with high temperatures above 70 °F, and 9 days with high temperatures above 90 °F. There were also 41 days with measurable precipitation, although the total measured precipitation was only 6.8 inches. During the bloom period between 13 May and 23 May, high temperatures ranged from 60 to 78 °F with a daily maximum relative humidity reaching above 90 % for all 11 days. Measurable precipitation was recorded for eight out of the 11 days during the bloom period. Temperatures were moderate during the late afternoon to evening inoculation on 18 May, ranging from 67 to 74 °F. After inoculation, daily high temperatures were between 60 and 72 °F for the next four daysand then above 80 °F for the subsequent 10 days. Minimum temperatures after inoculation on 18 May through petal fall on 24 May ranged from 44 °F on 21 and 23 May to 55°F on 19 May.