Learn About and Submit Samples Here: https://blogs.cornell.edu/coxlab/disease-sample-submission-forms/

Survey Efforts led and Graphics and Content developed by Isabella Yannuzzi

• 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. An effective removal practice is quickly cut the tree off below the graft union hang on the wire and dry out until you have time to remove it. Dead trees will not continue to ooze, but if trees are oozing, they should be promptly removed to avoid inoculum spread. Fortunately, the location may be safely replanted in later years.
• Post-bloom applications of prohexadione-calcium (Apogee or Kudos) for shoot blight management should be considered, especially on vigorous blocks of highly-susceptible apple varieties during shoot elongation which begins in late bloom.
  • For maximum effectiveness, prohexadione-calcium (Kudos, Apogee, etc.) 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.
• Preventative applications of copper can be used post-bloom and during the summer to protect against the spread of 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 reduce the potential of phytotoxicity from copper. Remember 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.
• It may be possible to save plantings on resistant rootstocks that have a moderate amount of shoot blight. Apply prohexadione-calcium (Kudos, Apogee, etc.) 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, but 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.
• 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 better synchronize next season’s bloom with established trees.

Forecasting Infection Events. Keep track of first blossom open dates for each of your varieties, especially those susceptible to fire blight. Make a note on a piece of paper or in a note application on your phone. Make sure to use these dates in the NEWA fire blight models to increase precision (https://newa.cornell.edu/fire-blight). Avoid using the less-accurate model default dates or generalized, region-wide dates if you have access to precise bloom information.

As you consider disease forecasting outputs from NEWA or other forecasting models, here are some things to consider before making costly applications of antibiotics or other materials for managing blossom blight:

• 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.
• 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.
• 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 of model predictions based on tree age, variety, and rootstock. 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, which may not warrant the same level of protection during bloom. A listing of susceptible cultivars and rootstocks is linked from the NEWA model page for fire blight.
• 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.
• 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 populations double about once every 20 minutes under optimal conditions; for Erwinia amylovora, the bacterium causing fire blight, this is temperatures above 60° The models use hourly weather data, rather than daily summaries, to accommodate the rapid growth rate of these pathogens. Check the fire blight predictions frequently, especially those in the forecasts. The 1- and 2-day forecasts are the most reliable; those at 3-, 4- and 5-days are less accurate predictors. NEWA uses the National Weather Service forecasts which you can compare to your favorite local weather forecast provider and what you see happening in the area.

• A: Operations with No Recent History (> 3 Seasons) of Streptomycin Resistance.
  • Before high-risk (‘Extreme’ or ‘Infection’) weather 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 its effectiveness. 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.
  • 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 your regional specialist to discuss the product failure and determine if it would be necessary to submit a sample for antibiotic resistance testing (https://blogs.cornell.edu/coxlab/disease-sample-submission-forms/). The presence of shoot blight later in the season isn’t necessarily an indication that antibiotics applied during bloom failed due to resistance.
• B: Operations with confirmed Streptomycin Resistance.
  • Before high-risk (‘Extreme’ or ‘Infection’) weather 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). Kasugamycin may rapidly breakdown with exposure to sunlight, take care to apply this antibiotic in the evening or on overcast days.
  • 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. It’s entirely possible to have an effective program consisting of only applications of Blossom Protect. This is the best option for organic production systems.
  • If three applications are needed, consider using Kasumin 2L for the first and last application to reduce populations. Use Blossom Protect for the remaining applications during bloom and avoid using it as trees go into petal fall.

2023 fire blight season recap. The 2023 fire blight season was light with outbreaks. We received an “all-time” low number of samples for streptomycin resistance testing as the disease was generally easy to manage throughout the state. The season was characterized by a cool “low-risk” and “early” bloom that started mid-April. Bloom seemed to linger through mid-May where we got a burst of warm weather that pushed us to petal fall. Afterwards, it became cool again until the end of May. The end of May was met with hot, stormy “high-risk” weather finally, but by the time this high-risk weather arrived, any early fire blight infections were well managed. This left little inoculum for shoot blight epidemics in the summer.  In past years, where fire blight was devastating, exceptionally hot weather rainy weather occurred about the end of petal fall and into the thinning period. Should this happen again, growers need to be prepared to start and finish strong at bloom and petal fall with their most effective options.

Present season. Presently, the spring is cool, and if these trends continue, we could have another light fire blight season, especially on Long Island and Hudson Valley, which are in early bloom or on the cusp of bloom.  Temperatures have been cold and we’re presently and this will continue for the next couple of days. However, temperatures will be approaching the low 70s by the end of the week. In Western NY, king bloom may occur this late weekend if we get days in the low 70F. If you are concerned with carryover inoculum from fire blight last season, consider applying prohexadione-calcium (Kudos, Apogee, @ 3-6 oz/100 gal) with (2 oz/100 gal PhCa) or without Acibenzolar-S-methyl (Actigard @ 1 oz/100 gal) at tight pink to slow the migration of infecting bacteria through tissues should infection occur later in early bloom.

General guidelines for season-long management of fire blight in apples

• All fire blight strikes and shoots with larger cankers should be removed during winter pruning. Remove any trees where the central leader or main trunk has become infected. Infected wood should be removed from the orchard and either burned or placed where it will dry out rapidly. The fire blight pathogen can withstand cold temperatures but is intolerant to drying.
• Copper should be applied at ‘Silver Tip’ and ‘Green Tip’. Processing varieties can be protected with copper as late as ½ inch green depending on requirements of the label.
• At late ‘Tight Cluster’ or ‘Early Pink’, preventative low-rate applications of prohexadione-calcium growth regulator (Apogee or Kudos) with or without Acibenzolar-S-methyl (Actigard) 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 prohexadione-calcium during warmer temperature above 65 °F to improve absorption and metabolism. In all, this practice should not be a substitute for a robust blossom blight program.
  • An application of prohexadione-calcium (Kudos, Apogee, etc.) at pink at 6 oz/100 gal may reduce blossom blight and subsequent shoot blight in high vigor blocks.
  • Applications of prohexadione-calcium (Kudos, Apogee, etc.) of 2 oz/100 gal mixed with 1oz /100 acibenzolar S-methyl (Actigard) at both ‘Pink’ and ‘Petal Fall’ will similarly be effective.