Plan for Multiple Fire Blight Conditions, Be Agile | WSU Tree Fruit

Written by Tianna Dupont, WSU Extension; Ken Johnson, OSU, April 6, 2020. Last updated March 5, 2023.

Make a plan now to be ready to prevent fire blight in your orchard this year.

Think about which are your high-risk blocks: blocks with sensitive varieties, high value varieties or a history of fire blight. Those are blocks where you may want a more intensive program. Consider how different each season can be. Have a plan for moderate temperatures and extended bloom as well as flash bloom. Remember if temperatures are warm and wet risk is high. If temperatures are cool and dry you may not need to manage blight. Below is an example of a set of plans a grower might design to choose from for different blocks and conditions.

Apples
Conventional		Organic
*Cut and remove fire blight cankers. Good sanitation is essential for successful fire blight management.*
Low to Moderate Risk	High Risk high value varieties history of blight	Easy to thin varieties	Hard to thin varieties/ short bloom period	Hard to thin varieties/ long bloom period
Watch the model. If an infection event is projected apply an antibiotic within 24 hours before wetting. Repeat every 2-3 days during warm wet risk periods to cover newly opening flowers rotating FRAC.^d Continue weekly apps 1-2 weeks post petal fall during warm wet risk periods. ^e	Blossom Protect + Buffer Protect 50-80% bloom preventative. Use antibiotic mixes: oxytetracycline+ kasugamycin or antibiotic + Actigard. ^d Cover every 2-3 days during warm conditions during bloom rotating FRAC. ^d Acidify spray tanks to improve antibiotic efficacy to at least 5.5. New research shows to 4.0 may improve further. ^b Continue weekly apps 1-2 weeks post petal fall if warm and wet. ^e	Blossom Protect/ Buffer Protect early. ^a Lime sulfur (+ oil). Blossom Protect/ Buffer Protect. Depending on the model and cultivar russet risk soluble copper (Previsto 3 qt, Cueva 4 qt, Cueva 3 qt + Serenade Opti, Instill, MasterCop). Petal fall + 1-2 weeks Serenade Opti (most fruit safe) or 2% lime sulfur (red apples). ^{c, f}	Lime sulfur (+ oil) 2-3 applications. Depending on the model and cultivar russet risk soluble copper (Previsto 3 qt, Cueva 4 qt, or Cueva 3 qt + Serenade Opti, Instill, MasterCop). ^g Petal fall + 1-2 weeks Serenade Opti (most fruit safe) or 2% lime sulfur (red apples). ^c	Lime sulfur (+ oil). Blossom Protect + Buffer Protect.^a Lime sulfur (+ oil). Blossom Protect + Buffer Protect. Depending on the model and cultivar russet risk soluble copper (Previsto 3 qt, Cueva 4 qt, or Cueva 3 qt + Serenade Opti, Instill, MasterCop). Petal fall + 1-2 weeks Serenade Opti or 2% lime sulfur (red apples).^c

^aApply to every row. Two applications between 50-100% bloom have the best efficacy.

^bSpray tank acidification has been most significant for oxytetracycline products (e.g. Mycoshield).

^cLime sulfur at this timing can interfere with oil sprays for mites.

^dRotate. Rotation is necessary for resistance management. Rotate as necessary to comply with application intervals for individual products. Do not apply Actigard at closer than 7-day interval (label restriction). Streptomycin should be used NO MORE than one time per season.

^eDo not make more than 4 applications of KASUMIN 2L per year. Post petal fall restriction has been removed (March 2021).

^fBlossom Protect+ Buffer Protect, then Previsto (full bloom), then Serenade (petal fall) best organic combination in 13 trials at 83% relative control (Johnson) similar to antibiotics.

^gRemember Blossom Protect yeast need about 12 hours to grow on the flower to protect blooms before a wetting event.

Pears
Conventional		Organic
*Cut and remove fire blight cankers. Good sanitation is essential for successful fire blight management.*
Low to Moderate Risk	High Risk	Easy to Mark Varieties Anjou/ Comice	Marking Tolerant Varieties Bosc
Watch the model. If an infection event is projected apply an antibiotic within 24 hours before wetting. Repeat every 2-3 days during warm wet risk periods to cover newly opening flowers rotating FRAC. ^d Continue weekly apps 1-2 weeks post petal fall during warm wet risk periods. ^e	Use antibiotic mixes: oxytet+ kasumamycin or antibiotic + Actigard. Cover every 2 days during warm conditions during bloom rotating FRAC.^d Acidify spray tanks to improve antibiotic efficacy to at least 5.5.^b New research shows to 4.0 may improve further. Continue weekly apps 1-2 weeks post petal fall.^e	2 applications of Blossom Protect + Buffer Protect during early bloom to petal fall (70-80% bloom if single treatment). ^a Follow with Serenade Opti at petal fall to reduce russet risk from Blossom Protect yeast.	2 applications of Blossom Protect + Buffer Protect during early bloom to petal fall (70-80% bloom if single treatment). ^a Follow with soluble copper (Cueva 4 rt, Previsto 3 qt, or Cueva 3 qt + Serenade Opti) if the model indicates risk (warm/wet).

Additional Information

Fire Blight Website

Fire Blight

Tianna DuPont, Tim Smith. Washington State University. See updated efficacy reports at the bottom of the page.

Decision Aid System

Visit for the recent model projections of blossom blight risk at your site.

Crop Protection Guide

Crop Protection Guide recommendations are updated on an annual basis.

Cougar Blight Model

A description of the Cougar Blight Model for determining fire blight risk.

Contact

Tianna DuPont

WSU Extension Specialist, Tree Fruit

tianna.dupont@wsu.edu

Office: (509) 293-8758

Mobile: (509) 713-5346

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