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

Written by Tianna Dupont, WSU Extension; Ken Johnson, OSU, April 6, 2020. Updated March 5, 2023. Last update March 5, 2024.

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 – Low to moderate risk

Cut and remove cankers.
Watch the model.
If an infection event is projected apply an antibiotic within 24 hours before
Repeat every 2-3 days during warm wet risk periods to cover newly opening flowers rotating.^d
Continue weekly apps 1-2 weeks post petal fall.^e

Conventional – High risk, high value varieties, history of blight

Cut and remove cankers.
Use antibiotic mixes: oxytetracycline + kasugamycin or antibiotic + Actigard.^d
Cover every 2-3 days during warm conditions during bloom rotating.^d
Acidify spray tanks to 5.5 to improve antibiotic efficacy. New research shows to 4.0 may improve further.^b
Continue weekly apps 1-2 weeks post petal fall.^e

Organic – Easy to thin varieties

Cut and remove cankers.
Blossom protect/ Buffer protect
Lime sulfur (+ oil)
Blossom Protect/ Buffer Protect ^a
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). Essential oils (Cinnerate, Thymegard), peracetic acids (Oxidate 5.0, Jet Ag)^{c, f}

Organic – Hard to thin varieties, short bloom period

Cut and remove cankers.
Lime sulfur (+ oil) 2-3 applications.
Depending on the model and cultivar russet risk soluble copper (Previsto 3 qt., Cueva 4 qt., Cueva 3 qt. + Serenade Opti, Instill, MasterCop).^g
Petal fall + 1-2 weeks Serenade Opti (most fruit safe) or 2% lime sulfur (red apples). Essential oils (Cinnerate, Thymegard), peracetic acids (Oxidate 5.0, Jet Ag).^c

Organic – Hard to thin varieties, long bloom period

Cut and remove cankers.
Lime sulfur (+ oil).
Blossom Protect + Buffer Protect
Lime sulfur + oil.
Blossom Protect + Buffer Protect. ^a
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).Essential oils (Cinnerate, Thymegard), peracetic acids (Oxidate 5.0, Jet Ag).^c

^aRemember Blossom Protect yeast need about 12 to 24 hours to grow on the flower to protect blooms before a wetting event.

^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. Rotate as necessary to comply with application intervals for individual products. Do not apply Actigard at closer than 7-day interval (label restriction).

^eKasumin. Do 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 Opti/Aso (petal fall) best organic combination in 13 trials in Oregon at 83% relative control (Johnson) similar to antibiotics.

PEARS

Conventional – Low to moderate risk

Cut and remove cankers.
Watch the model.
If an infection event is projected apply an antibiotic within 24 hours before
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

Conventional – High risk, sensitive varieties, history of blight

Cut and remove cankers.
Use antibiotic mixes: oxytetracycline + kasumamycin or antibiotic + Actigard.^d
Cover every 2 days during warm conditions during bloom rotating^d
Acidify spray tanks to at least 5.5 to improve antibiotic efficacy. New research shows that 4.0 may improve further.^b
Continue weekly apps 1-2 weeks post petal fall.^e

Organic – Easy to mark varieties (Anjou/ Comice)

Cut and remove cankers.
2 applications of Blossom Protect + Buffer Protect during early bloom to petal fall (70%-80% bloom if single treatment).
Follow with Serenade Opti at petal fall to reduce russet risk from Blossom Protect yeast.

Organic – Marking tolerant varieties (Bosc)

Cut and remove cankers.
2 applications of Blossom Protect + Buffer Protect during early bloom to petal fall (70%-80% bloom if single treatment).
Follow with soluble copper (Cueva 4 qt., Previsto 3 qt., Cueva 3 qt + Serenade Opti, Instill, MasterCop) if the model indicates risk (warm/wet).
Petal fall options include essential oils (Cinnerate, Thyme Guard), Peracetic acids (Oxidate 5.0, Jet Ag)

^aRemember Blossom Protect yeast need about 12 to 24 hours to grow on the flower to protect blooms before a wetting event.

^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.

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

Contact

Tianna DuPont
Tree Fruit Extension Specialist
Washington State University
(509) 293-8758
(509) 713-5346 cell
tianna.dupont@wsu.edu

Additional information

Fire Blight Website

Fire Blight of Apple and Pear

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.

Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.

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