Aćimović, Srđan G.Meredith, Christopher L.Santander, Ricardo DelgadoKhodadadi, Fatemeh2022-01-032022-01-032021-12-030191-2917http://hdl.handle.net/10919/107315To reduce the severity of shoot blight and prevent the resulting development of cankers on perennial apple wood, we evaluated eight fire blight postinfection spray programs of prohexadione-calcium (PCA) alone or with acibenzolar-<i>S</i>-methyl (ASM) over 2 years. On mature trees of cultivar Royal Court, a single application of the high PCA rate (247 mg/liter) at 2 to 3 days after inoculation resulted in 89.5 and 69.5% reduction of shoot blight severity after inoculation. Two applications of PCA 247 mg/liter 12 or 14 days apart, with the first one applied 2 to 3 days after inoculation, resulted in 78.8 and 74.5% reduction of shoot blight severity in both years. A 100% control of canker incidence on perennial wood from infected shoots in both years was achieved with a single application of PCA (247 mg/liter) applied at 2 or 3 days after the inoculation, and three applications of PCA (125 mg/liter) + ASM (25 mg/liter) 12 to 16 days apart reduced canker incidence by 83.5 and 69% in the 2 years. The other programs with lower PCA rates and frequencies of application reduced shoot blight severity 50.8 and 51.8% (PCA) and 62.6 to 72% and 59.3% (PCA + ASM) over 2 years, respectively. Reduction of canker incidence on wood by the other programs was 66.5% and 69 to 90.4% in the two years, respectively. As fire blight cankers lead to death of dwarf apple trees and serve as primary sources of inoculum, our effective PCA and PCA + ASM programs could serve as viable postinfection management options. These treatments can reduce or prevent canker development and thus significantly abate tree losses in high-density apple orchards after fire blight epidemics occur.Pages PDIS08201744REapplication/pdfenIn CopyrightErwinia amylovoraacibenzolar-S-methylfire blightpost-infection controlprohexadione-calciumrescue treatmentshoot blight0605 Microbiology0607 Plant Biology0703 Crop and Pasture ProductionPlant Biology & BotanyArticle - Refereed2022-01-03https://doi.org/10.1094/pdis-08-20-1744-reAćimović, Srđan G. [0000-0002-0710-2339]342320521943-7692