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Managing Fire Blight in 2021

May 3, 2021

by Isabella Yannuzzi & Kerik Cox, PPPMB, Geneva, NY and Janet van Zoeren, CCE, Lake Ontario Fruit Program

2020 fire blight season recap. In 2020, there were devastating fire blight outbreaks in NY and much of New England. The season was characterized by hot dry weather from the end of bloom into petal fall, which were the perfect conditions for systemic shoot blight. In the second half of May many sites experienced extreme risk for fire blight when bloom was apparently over and rainfall, dew, and humidity were scarce. Many growers were mystified with the subsequent outbreaks of shoot blight and perplexed as to how blossom infections could occur with the lack of moisture during high-risk periods. This is a common occurrence in the pacific northwest where fire blight devastates apple production despite a dry climate. Indeed, it may take only the slightest bit of internal canopy humidity or water from a nutritional or fungicide application to start an epidemic in exceptionally warm weather. We should remain cautious with vigorous growth during warm weather in the 2021 season, particularly as we approach petal fall and as shoots elongate.


2021 season outlook. In Western NY, king bloom could occur this week for many varieties, and there is more warm weather in high 60s/low 70s in the long-term forecast. Despite the potential for a warm bloom, weather can change suddenly, and it will be important to watch weather forecasts and follow extension specialists' alerts and fire blight risk predictions. If you are concerned with carry over inoculum from fire blight last season, consider the prohexadione-calcium (Apogee/Kudos) at pink to slow the migration of bacteria through tissues as the plants grow.


Forecasting Infection Events

Keep track of first blossom open dates for each of your varieties, especially those that are susceptible to fire blight. Make a note on a piece of paper or in notes on your phone. Use your farm's open blossom dates to run the NEWA fire blight model to increase precision. As you consider disease forecasting outputs from NEWA or other forecasting models, here are some things to consider before making applications of antibiotics or other costly materials for managing blossom blight:

  1. Predictions and forecasts are theoretical. The theoretical models predicting disease risk use weather data collected (or forecasted) from the weather station location. These results should not be substituted for actual observations of plant growth stage and disease occurrence determined through scouting or monitoring.
  2. Consider the history of fire blight in the planting. If there was no fire blight the previous season or if you have never had fire blight do not let excessive model predictions or extension alerts (including this article) "intimidate you" into applying unnecessary antibiotics each time an alert is released.
  3. Consider the age and susceptibility of your trees. Age and variety can play a large role in the development of fire blight. Presently, none of the models consider these factors in a formal sense. Adjust your interpretations - if you have a young planting of a highly susceptible variety, it may be more important to protect these blocks based on model predictions than a 15-year-old 'McIntosh' planting on resistant rootstocks. A listing of susceptible cultivars and rootstocks is linked from the NEWA model page for fire blight.
  4. The models only identify risk of infection based on weather conditions. This includes temperature and moisture conditions. All wetting events are now color-coded light blue in NEWA to draw attention to the weather factors that promote bacterial ingress into the flowers. Despite the use of words like "extreme" and "infection" colored in vibrant red, the models only predict infections based on favorable weather conditions. If the apple variety is not highly susceptible, if there is no prior history of fire blight, and if the trees aren't being pushed into high vigor with nitrogen, the actual risk of fire blight infection may be low to non-existent.
  5. Weather forecasts and predictions can change frequently. Model predictions are based on weather predictions, so when forecasts change, the model predictions and corresponding risk will also change drastically. Bacteria double about once every 20 minutes under optimal conditions; for fire blight this is warm weather >60F. The models use hourly weather data, rather than daily summaries, to accommodate the rapid growth rate of these pathogens. Check the fire blight predictions, especially those in the forecasts, frequently. The 1- and 2-day forecasts are the most reliable; those at 3-, 4- and 5-days are less accurate predictors.
Eight general guidelines for 2021 management of fire blight in apples.

1.  At late 'Tight Cluster' or 'Early Pink', preventative applications of prohexadione-calcium (PhCam Apogee or Kudos) for blossom blight and early shoot blight may be helpful, especially on highly vigorous plantings of highly susceptible apple varieties. If you have a low vigor block, these programs may not provide benefit as the trees need to be actively growing for the plant growth regulator to work. Also, consider applying PhCa during warmer temperature above 65F to improve absorption and metabolism of this PGR. In all, this use practice should not be a substitute for a robust blossom blight program (see 5). 

         a.   An application of prohexadione-calcium at pink at 6 oz/100 gal may reduce blossom blight and subsequent shoot blight in high vigor blocks.

        b.  Applications of prohexadione-calcium of 2 oz/100 gal mixed with 1oz /100 acibenzolar S-methyl at both 'Pink' and 'Petal Fall' may similarly be effective

2.  During bloom, follow a blossom blight forecasting system such as the ones offered in NEWA ( Time applications during high risk weather only. Regardless of model predictions, it is rarely necessary to make more than three applications for blossom blight.

3.  Operations with No Recent History (> 3 Seasons) of Streptomycin Resistance.

         a.   At 'Bloom' begin antibiotic applications for blossom blight with a single application of streptomycin at 24 oz/acre. Consider including the penetrating surfactant Regulaid (1 pt/100 gal of application volume) in the first streptomycin spray to enhance the effectiveness of streptomycin. Regulaid would be especially beneficial when applied under rapid drying conditions. Regulaid can be omitted from subsequent applications to minimize the leaf yellowing that is sometimes associated with repeated applications of streptomycin.

         b.  If later antibiotic applications are needed, streptomycin or kasugamycin (Kasumin 2L 64 fl oz/A in 100 gallons of water) should be used. Consider making at least one application of Kasumin 2L for resistance management purposes. If there are concerns about the effectiveness of streptomycin or kasugamycin, contact one of the people listed on the last page to discuss the product failure and determine if it would be necessary to submit a sample for antibiotic resistance testing. The presence of shoot blight later in the season isn't necessarily an indication that antibiotics applied during bloom failed due to resistance.

5.  Operations with Streptomycin Resistance.

          a.  At 'Bloom' begin antibiotic applications for blossom blight with a single application of kasugamycin (Kasumin 2L) at 64 fl oz/A in 100 gallons of water. Consider including the penetrating surfactant Regulaid (1 pt/100 gal of application volume) to enhance the effectiveness of kasugamycin. Regulaid would be especially beneficial when applied under rapid drying conditions. Do not use alternate row middle spraying and apply after petal fall. (The PHI is 90 days and REI is 12 hours).

          b.  If a later antibiotic application is needed, Blossom Protect (1.25 lbs/A + 8.75 Buffer Protect; OMRI listed) or Oxytextracycline at the highest rate should be used.  

          c.  If three application are needed, consider using Kasumin 2Lfor the first and last application. Use Blossom Protect during bloom and avoid using it as trees go into petal fall.

6.  In the two weeks following bloom, scout for and prune out fire blight strikes promptly. Destroy pruned strikes by burning or leaving them out to dry. It is best to prune well back into healthy wood, at least 12 inches behind the water-soaked margin. Take care as summer pruning may stimulate active shoot growth leading to new susceptible tissues that could later become infected. If fire blight reaches the central leader, the tree should be removed. However, the spot may be safely replanted.

7.  Preventative applications of prohexadione-calcium (Apogee or Kudos) for shoot blight should be seriously considered, especially on vigorous blocks of highly-susceptible apple varieties during shoot elongation which begins in late bloom.

          a.  For maximum effectiveness, prohexadione-calcium should be applied at 6-12 oz/100 gal (3-6 oz/100 gal for tree <5 years) when trees have 1-2" of shoot growth. A second application should be made 14-21 days later.

8.  Preventative applications of copper can be used post-bloom and during the summer to protect against shoot blight infections. Copper must be applied before infection occurs as it will only reduce bacteria on the surface of tissues. It will have no effect on existing shoot blight infections and may cause fruit russet in young developing fruit. Apply with adequate drying time and use hydrated lime to safen copper. Terminal shoots can outgrow protective residues of copper. A low rate fixed copper program consists of applications on a 7-10 day schedule during high risk weather until terminal bud set.

9.  It may be possible to save plantings on resistant rootstocks that have a moderate amount of shoot blight. Apply prohexadione-calcium at the highest rate for the planting (6-12 oz/100 gal) and allow 5 days for the product to take effect. Afterwards, prune out existing and newly developing shoot blight every two weeks for the rest of the season and remove any trees where fire blight has reached the central leader. If pruning stimulates additional shoot growth, a second application of prohexadione-calcium could be warranted.

10.  If you need to interplant apple trees in existing orchards where trees were killed by fire blight and removed, replant these missing trees 'skips' in late fall to synchronize next season's bloom with established trees. 

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Upcoming Events

Good Agricultural Practices (GAPs) Training & Food Safety Plan-Writing Workshop

February 2 - February 3, 2023
Newark, NY

Goals of this workshop:

  • Understand how GAPs (Good Agricultural Practices) impact produce safety, and how you can improve practices on your farm to reduce the risk of microbial contamination
  • Learn the difference between a FSMA Inspection and a GAPs audit, and learn what is needed to have a USDA GAP/GHP audit and the 2 types (Basic & Harmonized)
  • Begin writing a farm food safety plan that complies with a USDA GAP/GHP Audit

This workshop is targeted at Mott's growers who need to have a successful GAP audit for the 2023 harvest. However, all farms and organizations are invited to attend.  

We will have several breaks, including a lunch break, scattered throughout the day, but feel free to step away whenever you need to. Lunch and snacks provided. Note: All times are approximate. Time spent on each topic varies depending on audience and questions/discussion. There will be time for questions at the end of each section and a final opportunity for questions when we close for the day.  

Instructors Confirmed: Craig Kahlke (CCE-LOF), Robert Hadad (CCE-CVP), Caroline Boutard-Hunt (CCE-Yates), Judy Wright (CCE-Seneca), and Representatives from NYS Dept. of Ag & Mkts.

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How Profitable Will My New Orchard Investment Be? 1-day, hands-on skills class

February 7, 2023
Highland, NY

The Eastern NY Commercial Hort Team and the Lake Ontario Fruit Team are offering a 1-day, hands-on course at 5 locations in NYS in January and February for tree fruit farms on using farm financial information and other resources to make decisions about long-term investments or changes to their business.  We will apply the techniques covered in the 8-part webinar series in December to scenarios using sample financial data from fruit farms in NYS.

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Apple Leafcurling Midge IPM - Webinar

Event Offers DEC Credits

February 16, 2023

In recent years, the apple leafcurling midge (ALCM) has become an increasingly problematic pest in many orchards across the northeast.

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Save the Date! - Scroll down for Upcoming Events

Have you missed a meeting recently? All recorded LOFP hosted webinars can be found on our YouTube Channel

NOW - please scroll down to find the link to the short NY Herbicide Resistance Survey!

Courses Available All Year - Cornell Small Farms Program New Season of Online Courses-Enroll Now!


26 Jan - Innovative new technology to implement PACMAN (Part 2) & How's your adoption going?- 12pm (Eastern) - online - registration required

16 Feb - Apple Leafcurling Midge IPM - Webinar - 1:30-2:30pm - Registration Now Open

27 & 28 Feb - WNY Winter Fruit Conference - Registration Now Open

14 Mar - USDA/RMA Listening Session - Spring 2023 Apple Grower Meeting -
The Risk Management Agency (RMA) is inviting interested parties to participate in a listening session to discuss the proposed changes to the apple crop insurance program. Free - Rochester

15 Mar - Fire Blight Informational Webinar Series - Using biopesticides to help control fire blight - 7-8PM

13 Jun - Fire Blight Informational Webinar Series - Pruning and sanitation strategies to reduce fire blight - 7-8PM

18 Oct - Fire Blight Informational Webinar Series - Using weather and environmental conditions to optimize biologicals and biopesticides for bloom production - 7-8PM

Food Safety Virtual Office Hours

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Past recorded virtual office hours can be found on YouTube:

Webinar Recordings

Check out the recordings of some recent webinars:


Employment Opportunities

The CCE-LOF Program has created a space to share Lake Ontario Fruit Region local employment opportunities. See listings and details for sharing listings at|business

Pollinator Resouces

Now available Pollinator Resource Links

Meeting Recordings Now Available

Did you miss the recent meeting?  Check and see if we recorded it and added it to our website or Lake Ontario Fruit Program YouTube Channel.

Honeycrisp Meetup recordings available here.

Why are my trees growing so poorly? recording available here.

Additional Recorded Webinars listing with recording and resource link are available at|crops|apples|crop*38

New Publication on Growing Pawpaws

Are you a fan of pawpaws? These custardy fruits can be hard to come across, so this guide provides information on how to grow your own pawpaw from seed, and how to care for grafted seedlings. Pdf on growing now available.​|crops|unusual_fruit|crop*50

New Weed Management Technology Survey

Want to move away from herbicide reliance? Are you using novel technologies to manage weeds? We want to know about it to inform our weed science research. A team of weed scientists from University of California Davis, Oregon State University, and Cornell University are asking berry, tree fruit, tree nut, and vine crop growers to take 5 to 10 minutes and answer this short and anonymous survey. Weed Technology Survey link:

For more information on this survey please visit

Pollinator Webinar Series - Summer 2020

The Pollinator Webinar Series presented by Penn State cover bee health and pollination services.

Bloom Pesticides for Pollinator Health

A reference table created by Janet van Zoeren and Anna Wallis, is now available at|pests.