With increasing organic acreage and scrutiny of antibiotics use, alternatives to antibiotics for the control of Erwinia amylovora are of interest to stakeholders. At the same time failures of minimally tested, newly marketed products have resulted in severe infections leading to costly tree and orchard removal. We evaluated antibiotic alternatives in 8 Washington, 3 Oregon, 3 New York and 2 Pennsylvania field experiments conducted 2013 to 2022. Antibiotic alternatives included essential oils (thyme and cinnamon extracts), mineral compounds (potassium aluminum sulfate), oxidizers (peracetic acid-peroxide), soluble coppers (copper octanoate, copper hydroxide, copper sulfate pentahydrate), and biological controls (Aureobasidium pullulans, Bacillus subtilis, bacteriophage). Studies were conducted in ‘Bartlett’ and ‘dAnjou’ pear, ‘Gala’, ‘Cameo,‘ and ‘Red Delicious’ apple with 4 to 6 single-tree replicates arranged in a randomized complete block inoculated with E. amylovora at 80–100% bloom. In summary analysis of 8 Washington trials Alum (potassium aluminum sulfate), Blossom Protect (A. pullulans) and several copper products (Previsto, Mastercop, Instill) provided good disease suppression of 70–73% similar to antibiotic checks. Several essential oil, copper, and peracetic acid-peroxide and biological products (Serenade Opti, Cueva, Oxidate 5.0, Jet Ag, Thyme Guard and Thymox) provided intermediate disease suppression between 45 and 62% significantly better than the water-treated control. In multistate trials Alum with 2–3 applications provided good control in most experiments (means 2019: WA 79%, NY 77%, PA 57%; 2020: OR 86%, NY 65%, WA 28%; 2021: NY 87%, WA 50%). Essential oils with 3–4 applications provided intermediate control NY 2021 81% control 23% thyme oil, 70–85% control NY 2020, 2021 60% cinnamon oil.

Pear psylla, Cacopsylla pyricola (Förster), is the most economically challenging pest of commercial pears in Washington and Oregon, the top producers of pears in the United States. The objective of this study was to quantify economic injury levels and thresholds for pear psylla. We used the relationship between pear psylla adult and nymph densities, and fruit downgraded due to psylla honeydew marking to identify injury levels. We calculated economic injury levels using the cost of downgraded fruit and average management costs (spray materials and labor). Using economic injury levels, we determined economic thresholds for pear psylla, which include predicted pest population growth, natural enemy predation, and anticipated delays between when pest populations are measured and when managers apply interventions. Economic thresholds generated by this study were 0.1–0.3 second-generation nymphs per leaf and 0.2–0.8 third-generation nymphs per leaf depending on predicted price and yield for insecticide applications at 1,300 pear psylla degree days in the second generation and 2,600 pear psylla degree days in the third generation. Natural enemy inaction thresholds identified by this study were 6 Deraeocoris brevis or 3 Campylomma verbasci immatures per 30 trays or 2 earwigs per trap for third-generation optional insecticide applications.

Ten experiments were conducted to evaluate the efficacy of methods to therapeutically remove fire blight cankers from apple trees with different age, vigor, training system and rootstock combinations in Washington, Oregon, Pennsylvania and New York, United States. Removal methods included pruning at varying distances from visible symptoms, utilization of a sanitizing agent and the use of a stub cut to minimize cankers on structural wood. Fire blight removal resulted in reductions of rootstock blight and tree death. Removal treatments resulted in fewer additional cankers compared to the no-treatment control in most trial sites and years. The standard best management practice (BMP) for removing fire blight was branch removal at 30 cm below the proximal edge of visibly cankered tissue with sanitized loppers. This practice significantly reduced the number of new systemically-caused symptoms compared to the no-treatment control in seven of nine experiments with significant reductions in five experiments. Aggressive removal, defined as BMP but branches removed approximately 76 cm from the proximal edge of visibly cankered tissue, generally did not improve the standard practice. Elimination of cutting tool sanitation did not result in more cankers than the standard practice. Breaking off diseased branches by hand provided a rapid removal method, but it resulted in a greater number of cankers in the orchard at the end of the season. In one of five experiments cutting which left a 13 cm stub distal to structural wood significantly reduced the number of cankers on structural wood compared to flush cut or 4 cm stubs.

Erwinia amylovora is a relatively homogeneous species with low genetic diversity at the nucleotide level. However, phenotypic differences and genomic structural variations among E. amylovora strains have been documented. In this study, we identified 10 large chromosomal inversion (LCI) types in the Spiraeoideae-infecting (SI) E. amylovora strains by combining whole genome sequencing and PCR-based molecular markers. It was found that LCIs were mainly caused by homologous recombination events among seven rRNA operons ( rrns) in SI E. amylovora strains. Although ribotyping results identified inter- and intra-variations in the internal transcribed spacer (ITS1 and ITS2) regions among rrns, LCIs tend to occur between rrns transcribed in the opposite directions and with the same tRNA content (tRNA-Glu or tRNA-Ile/Ala) in ITS1. Based on the LCI types, physical/estimated replichore imbalance (PRI/ERI) was examined and calculated. Among the 117 SI strains evaluated, the LCI types of Ea1189, CFBP1430, and Ea273 were the most common, with ERI values at 1.31, 7.87, and 4.47°, respectively. These three LCI types had worldwide distribution, whereas the remaining seven LCI types were restricted to North America (or certain regions of the United States). Our results indicated ongoing chromosomal recombination events in the SI E. amylovora population and showed that LCI events are mostly symmetrical, keeping the ERI less than 15°. These findings provide initial evidence about the prevalence of certain LCI types in E. amylovora strains, how LCI occurs, and its potential evolutionary advantage and history, which might help track the movement of the pathogen.