Refinement of Nonantibiotic Spray Programs for Fire Blight Control in Organic Pome Fruit.

Area of Science:

• Agricultural Science
• Plant Pathology
• Organic Farming

Background:

• Certified organic pome fruit production in the Pacific Northwest faces challenges with fire blight (Erwinia amylovora) due to the ban on antibiotics.
• Alternative nonantibiotic treatments for fire blight often carry a risk of phytotoxicity, specifically fruit russeting, or have limited efficacy.
• The critical period for fire blight control is between full bloom and petal fall, requiring effective and safe suppression strategies.

Purpose of the Study:

• To evaluate nonantibiotic spray programs for fire blight suppression in organic pome fruit production.
• To determine the optimal sequencing of materials to maximize disease control and minimize fruit russeting.
• To assess the impact of spray programs on epiphytic pathogen populations, biocontrol efficacy, and fruit quality.

Main Methods:

• Orchard trials were conducted to test various sequences of nonantibiotic materials, including yeast biocontrol (Aureobasidium pullulans), soluble coppers, and Bacillus-based biorationals.
• Evaluations included measuring Erwinia amylovora populations, yeast biocontrol populations, floral pH, fire blight infection incidence, and fruit russeting.
• Specific application timings (70% bloom, full bloom, petal fall) were investigated for their impact on efficacy and fruit safety.

Main Results:

• A sequential spray program of Blossom Protect (Aureobasidium pullulans) at 70% bloom, a soluble copper (Previsto) at full bloom, and a Bacillus-based biorational at petal fall provided the best balance.
• This integrated approach effectively suppressed fire blight pathogen while significantly reducing the risk of phytotoxic fruit russeting.
• Individual nonantibiotic treatments showed varying efficacy and russeting risks, highlighting the importance of strategic sequencing.

Conclusions:

• Nonantibiotic spray programs, when strategically sequenced, can effectively manage fire blight in organic pome fruit orchards.
• The combination of yeast biocontrol, soluble copper, and Bacillus-based biorationals offers a viable alternative to antibiotics, mitigating disease and fruit damage.
• Optimizing application timing and material selection is crucial for successful organic fire blight management and maintaining fruit quality.