Orchard Outlook Newsletter Vol. 22, No 7

Tuesday, May 24, 2022

Here we are with the majority of full bloom across varieties and regions! Today's newsletter discusses the usual diseases including frequently asked questions about fire blight blossom blight. We also look ahead to post-bloom insect management. Chemical thinning is discussed. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2022 Degree Day Accumulations
  • Soil Temperatures and Precipitation

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Calyx or Blossom End Rot
  • Apple - Black Rot (Advance Notice)
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects
  • Nematode (Pre-plant samples)
  • Apple fruitlet thinning
  • Pear thinning
  • Weed Management
  • Pollination
  • Grafting
  • Mowing
  • Pruning and training
  • Fertilizing
  • Planting
  • On-farm Nursery
  • Wild apple trees

Pest Management Guides 2022

Events and Notices

  • Perennia May 24 - Weather station apps and website training session
  • 2022 Virtual orchard meetup series



2022 Degree Day Accumulations

This past week's above seasonal temperatures have put us well ahead of the 5 and 10-year averages for base 5°C and 10°C heat units (Figure 1). Essentially, this year's degree day accumulations are now tied with 2021.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 23 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 17% more plant development heat units compared to the 5-year average, and 12% more compared to the 10-year average.
  • Approximately 1% less plant development heat units compared to 2021, and 63% more compared with 2020.
  • Approximately 25% more insect development heat units compared to the 5-year average, and 13% more compared to the 10-year average.

Soil Temperatures and Precipitation

Soil temperatures this year are ahead of the 10-year mean and the 2021 temperature. Jeff Franklin suspects that the higher soil temperatures, "is due to the drier than average conditions as so far we have received only 26.5 mm of rain in May compared to the 10-year average of 69.3 mm (for the entire month of May). As a comparison, in 2021 we had 106.0mm of rain in May."

Figure 2: Soil temperatures at 35 cm depth at the Kentville Research Station from 2017 to 2022. Provided by Jeff Franklin (AAFC).

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 23, the Idared buds were at about early petal fall, Honeycrisp was at late full bloom, and Ambrosia was at full bloom (Figure 3). 

Figure 3: Bud development in an early region on Middle Dyke Road in Kentville on May 23. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Orchard Outlook committee members report that in the Melvern Square area, Jonagold was at early petal fall and Honeycrisp was near full bloom. In the Morristown area, Honeycrisp and Ambrosia were at 80% full bloom.

Across the Valley, a fairly compacted bloom period is occurring with regions and varieties all being around full bloom. So far, pollination conditions have seemed good with sunny days, moderate temperature, and bee activity.

Kings County is under a frost advisory for overnight on May 24. The advisory says minimum temperatures of zero degrees are possible in low lying areas. Apples in full bloom should be hardy to -2.2°C before injury (see full chart). 


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 17 to May 24, based on the Modified Mills Table. 
1 For a high inoculum orchard, a significant number of spores can be released during darkness, so begin calculating leaf wetting regardless of the time of day when the wetting event started. An orchard is considered to have a high inoculum load if last season it had 100 or more scabby leaves observed over 600 shoots.
2 Assuming a green tip date of Sunday, April 17th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
3 All forecasts are estimates. Observe forecasts daily for more accurate predictions.
Note: The environmental conditions for an infection are listed in the Modified Mills Table.

A couple of hours of wetting also occurred on the morning of May 17 due to heavy rain but it was followed by sunlight, wind and quick drying within about 6 hours. Also, on May 23 rain occurred and wetting varied by microclimate although it was not prolonged. Spores would have been released but infections were unlikely for short leaf wetness periods. The risk of such events will depend on the microclimate and protective programs should be maintained. The May 19-20 infection was reason enough to be protected.


  • Currently, cumulative ascospore maturity is theoretically at about 84.3%. By the weekend, the total seasonal ascospore maturity is expected to reach 97.3%.
  • If you are due for a protectant fungicide, it is recommended that protection be maintained especially at this continues to be a critical time in the season. Waiting for rain is a gamble with the hopes that protection is applied in time.
  • Re-apply a protectant fungicide to green tissue prior to an infection event on a 7-day interval, with a shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
  • Always tank mix single site fungicides with a group M for resistance management.
  • Be careful mixing water soluble packaging (WSP) with other products. Do not use WSP in a tank mix with boron and rinse the tank well before and after boron.

Apple – Powdery Mildew


  • Powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected, and not prior to heavy rain. 
  • Where powdery mildew pressure is historically high, a third application is often recommended by petal fall. 
  • Remember to treat young plantings because severe infections can reduce shoot growth, which is most concerning for young, non-bearing orchards.
  • Pay particular attention to susceptible and high-value varieties such as Honeycrisp and Gala.

Apple & Pear – Fire Blight Blossom Blight

Fire Blight Biology

Open blossoms must be present for a blossom blight risk. Fire blight bacteria are transported from overwintering canker sites to open flowers by the action of insects and rain. These bacteria then reproduce on the stigma of flowers and are washed down into the base of the flower by a wetting event – a minimum of just 0.25 mm of rain or heavy dew – which then initiates an infection if adequate bacterial populations are present. An average daily temperature of at least 15.6°C is needed to establish infections and the infection potential rises with consecutive hours above 18.3°C. Blossom blight risk increases with warm temperatures between 23°C and 27°C, especially when occurring over consecutive days because this temperature range is ideal for bacterial reproduction. The Maryblyt model takes into account all of these factors and is used to predict blossom blight infections.

Current and Forecast Blossom Blight Risk

An alert was sent for Sunday, May 22 for all regions being monitored and that had open blossoms on apples and pears. 

  • Bacterial populations built rapidly in a single day during high forecast temperatures. Even new blossoms that opened on May 22 and that were colonized by bacteria were susceptible to infection. For future reference, only blossoms open at the time of an antibiotic spray are protected from infection.
  • Wetting occurred on May 23 and could possibly have produced infections.
  • Applying protection on May 22 or 23 reduced bacterial populations (EIP) and then populations are not expected to grow for the next few days. 
  • If protection was not applied on May 22, bacterial populations remain high for the next several days.

According to the forecast, warm temperatures near the end of the week are forecast to increase the risk and infection events are possible on open blossoms around Saturday, May 28. Stay tuned because predictions can change on short notice.



  • Consider the ongoing risk of blossom blight infection on flowering apples and pears.
  • This year, all NSFGA-owned weather stations are used for industry alerts. If you are not receiving email alerts and you wish to, please let me know at mcortens@perennia.ca or sign up online. Alerts will be delivered on weekends and holidays. I also post daily screenshots in a folder online to make model predictions easily accessible. Predictions are updated daily. Access apple and pear predictions and click on the images to expand.
  • At bloom, to run the Maryblyt model using your own temperature, rainfall, bloom and spray dates, download the Maryblyt desktop software. Need a refresher on how to use Maryblyt? Watch the 2020 Perennia Maryblyt video tutorial
  • You can use the daily max and min temperature data from the NSFGA weather stations to run Maryblyt. Do so by logging in to the NSFGA account on www.weatherlink.com, choose the weather station, select the tab "data" and then choose the view "Monthly Summary". Enter the given values into Maryblyt.


  • If pinching buds on young trees, leave at least 1-2 warm days for the wounds to heal prior to rain. Do not pinch flowers when tissues are wet, even in a morning dew.
  • Streptomycin 17 will provide excellent efficacy on blossom blight and should not be used more than 24 hours prior to an infection event. If necessary, it may be used after infection and is best used within 12-18 hours but can still be helpful if delayed longer. It is recommended that you keep Strep on the farm at this time of year to respond quickly. Streptomycin 17 may be used up to 3 times each year.
  • Streptomycin and Agral 90 are best applied with little else in the tank to prevent incompatibility issues that would reduce efficacy. However, if manzate is applied it has a spreader-sticker so reduce the use of Agral 90 by at least half to avoid strep burn.
  • Kasumin also has excellent efficacy and may be used up to 4 times each year during bloom. Consider using Kasumin if you need to re-enter a block because it has a short REI of 12 hours. However, the PHI for Kasumin is 90 days, which can be challenging for early varieties like Paula Red. Note that Kasumin is not partially systemic and should not be used for post-infection control or after a trauma event.
  • For on-farm nurseries, consider applying a copper product at the lowest labeled rate prior to training trees and follow the labeled REI. Make cuts on only dry and sunny days. 

Blossom Blight - Frequently Asked Questions

Does water wash away bacteria? 
(Shared in 2021) No. Bacteria use water to disperse and colonize new flowers. The Maryblyt model does not reset after a rain because there is still a lot of bacteria present. Rain also helps to maintain bacterial survival. Sometimes a rain will correspond with cooler temperatures in which case it is the cooler temperatures that are responsible for less bacterial growth.

When are flowers no longer at risk of a blossom blight infection?
(Shared in 2021) As flowers age, the stigmas become less susceptible hosts for E. amylovora. HOWEVER, petal fall on the entire tree is the only time we can be sure that the bacteria cannot grow on stigmas to be washed into the flowers. Therefore, flower protection until at least petal fall is recommended.

Can we micromanage fire blight?
No. The Maryblyt model is a daily model, not an hourly model. A prediction of the bacterial population (EIP) is therefore made for the entire day, taking into account the forecast maximum and minimum temperatures. When it takes 12 hours to cover an entire orchard, hourly predictions are not often helpful anyway. BUT, my point is that our model is a daily snapshot whereas bacterial growth is a continuum. We might not have experienced rain on May 22 to trigger an infection in the model, but during dew and rain soon afterwards on the morning of May 23 the bacteria was still present and we do not know at what population levels during that particular point in time. With such a risk and uncertainty, protection is the best option.

What is the rainfast period for Streptomycin and Kasumin?
(Shared in 2021) If strep dries then it will absorb and have good activity. Kasumin does not absorb so it needs a couple of hours for activity to knock back bacteria. If rain happens soon after application then Kasumin is likely washed away before it has a chance to reduce bacterial levels. Especially if the rain is a downpour. A light rain might be okay. Activity of both products it not immediate and happens over a few hours.

Fire Blight - Shoot Blight Management


  • Apogee/Kudos (prohexadione calcium) supress shoot blight. The timing of the first application at 2.5-7.5 cm of new shoot growth is critical to success. We are likely in the window of opportunity right now. Follow up with a second application applied around 14 days later.
  • Apogee should be put on with higher water volumes to cover all new leaves and growing tips.
  • Include Agral 90 at 500 mL per 1000 L of water. Do not exceed this amount of surfactant. 
  • If applying Agral 90 there may be a risk of burn if using Captan.
  • Apogee should also be applied with spray grade ammonium sulphate (AMS) in an equal 1:1 ratio with the amount of Apogee used (e.g. 500 g Apogee = 500 g or 0.5 L of ammonium sulphate). This is not the blossom thinning product ammonium thiosulphate (ATS)!

Apple  Calyx or Blossom End Rot

Infections develop toward the end of bloom and appear about one month after petal fall as a brown discolouration surrounded by red on the calyx end of the fruit. The lesion is usually sunken and a corky rot develops in the flesh. When in storage, blossom end rot can lead to moldy core. 

Blossom end rot is more likely in years when the weather is warm (15 to 25°C) and wet during and shortly after bloom. The disease is most common on Paulared, Delicious, Cortland, Honeycrisp and McIntosh.


  • Captan is a good product for blossom end rot and black rot management. Note the new WSP formulation changes to REI and maximum number of applications if using the product.
  • If calyx or blossom end rot has been an issue in the past, consider using a captan product during full bloom. 
  • If applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.

Apple  Black Rot (Advance Notice)

Although early, I think this is a good time to consider how to reduce the risk of black rot. This past spring we heard from Dr. David Rosenberger and the following suggestions from him might be helpful to consider:
  • Black rot can survive on prunings. Flail mow prunings in row middles where they will degrade more quickly.
  • Minimize lenticel cracking by:
    • Avoiding drought stress with irrigation
    • Being cautious with spray mixtures (folpet, calcium, foliar nutrients). Be especially cautious when heavy rains follow drought conditions because rapid fruit expansion can break lenticels and allow product to cause more damage than usual, making it susceptible to fungal infection.
  • The black rot fungus infects fruit during warm rains from petal fall to harvest:
    • A 10 hr wetting period at 16°C to 32°C allows infection. 
    • The optimum temperature for infection is 20°C to 24°C. 
    • Based on our limited knowledge, the highest risk of infections is theoretically around 4-6 weeks after bloom.



  • Fungicide, antibiotic, and growth regulator sprays are best applied early morning or late evening when bees are not actively foraging. Be aware that dandelion blooms are open until about dusk.

Apple Insects

In anticipation of upcoming petal fall, pesticide options are listed in Table 2. Registered insecticide options and label rates for calyx stage of apples are listed in the Pome Fruit Management Guide.

Table 2: Pesticides options for calyx stage of apples in Nova Scotia (revised May 2022) with input at original publication from Erika Bent (APM). Products are rated from 1 (poor) to 4 (excellent).

Stone Fruit Insects

Plum curculio is a weevil that begins laying eggs in stone fruit at shuck fall. Mated females will deposit their eggs in the developing fruit leaving the characteristic crescent-shaped scar. Activity of PC is increased in temperatures above 16°C.


  • Treatment for PC should be applied at petal fall before shuck split to obtain optimal control. Treat between petal fall and shuck split. A second application is usually needed about 10 days later.
  • The insecticides available for managing plum curculio include Assail (Neonicotinoid) and Exirel (Diamide). The neonicotinoids kill plum curculio on contact, and they are also systemic so they deter egg laying and feeding. Their systemic activity will also kill eggs and larvae that are present in the fruit.
  • Plum curculio will target apples if stone fruit are nearby.
  • Be aware of bee toxicity warnings on pesticide labels and take precautions while nearby crops are in bloom.
  • For stone fruit, monitor for green peach aphids and black cherry aphid.
  • Tarnished plant bug and stinging bugs cause catfacing of peaches. This stinging takes place around shuck split/fall and one to two insecticide applications may be required to reduce the incidence of catfacing if pressure is high. Apply one to two applications of one of the pyrethroids listed in the Stone Fruit Management Guide. Repeat treatment in 5-7 days if additional stings are detected.

Pear Insects

  • Petal fall is the ideal treatment timing for winter moth and fruit worm in pear. Treatment should be based on need determined by monitoring. 
  • Apple curculio is difficult to monitor for and its presence often is not observed until damage on fruitlets shows up. Treatments for this pest should go on when pears have reached calyx. Use of one of the products registered for plum curculio should also control apple curculio.
  • If you are planning to use Agri-Mek + Oil for pear psylla control, it is best to apply it at petal fall or ideally within 2 weeks. Agri-Mek has better residual control when applied to younger tissues. Do not apply Agri-Mek with any bloom around as this product is highly toxic to bees. Do not use Captan/Maestro as a fungicide for pear scab within 14 days of Agri-Mek + Oil. Minecto Pro (Abamectin and Cyantraniliprole) is a new formulation that is registered for control of pear psylla with the same recommended application time.

Nematode (pre-plant samples)

Root and soil samples are best collected in the spring (May-June) or during the fall (September-October), both of which avoid the heat or drought conditions in summer. Soil temperatures at sampling should be above 10°C for adequate nematode presence in the upper soil levels.

Chemical Thinning

ATS is NOT recommended for defruiting young trees
The question of using ATS to defruit young trees comes up every year. I do not recommend the practice because of concern about foliar spray injury to young trees. In order to eliminate all blossoms, the ATS would need to be applied multiple times to target flowers that open at successive times. The frequent number of applications would increase the risk of foliar spray injury. The leaves of young trees are also very tender.

Apple Fruitlet Thinning


  • The optimal temperature for thinner activity is between 21-24°C (within fruit sizes of 5 to 18 mm and most effective from 7-12 mm).
  • Note that the PHI for Sevin is 75 days and this may be challenging for early varieties like Paula Red. The REI is 0.5-17 days depending on the activity. For a comparison between products, review the Thinning and Growth Regulation Guide.
  • Varieties prone to biennial bearing that had a low crop load last year should be thinned adequately and early enough this year to enable bud initiation (for Honeycrisp this is within 45 days after bloom). Thin to escape the biennial bearing cycle!
  • Defruiting young trees can be accomplished with a combination of Sevin XLR at 2.5 L plus Maxcel at 5.0 L per 1000 L of water applied using dilute nozzles to the point of drip. A few litres of oil (10.6 L/1000 L water) can also be added as a spreader sticker to this combination unless the variety is sensitive to oil. This mixture should cover more than an acre of young trees. Apply from petal fall until 8-10 mm. A second application can be done before 18 mm if additional thinning is needed. Hand thinning may still be needed.

Pear Thinning

  • The Maxcel thinning window is 8-14 mm and early treatments are most effective.


Weed Management

  • Currently there is still a good flush of active growth that would uptake herbicide well.
  • Due to herbicide shortages, it seems that weed management in young plantings will be reliant on consistent and vigilant use of burnoff products. Note the risk of frequent use of Agral 90 for bark blistering on Delicious varieties.
  • Studies have shown maintaining weed free strips from bud break to 30-days after full bloom has the greatest impact on tree growth and yield. Timely herbicide application will ensure you make the most of the weed free window.
  • Note that residual herbicides can damage single tree replacements. 
  • Residuals need an activating rain of 0.5 inches within 7-10 days of application.
  • When mixing residual herbicides, agitation is important to keep the product in solution. If the herbicide settles in the tank then it can be delivered in a high concentration and possibly result in crop injury.
  • If weeds are already present, add a post-emerge to a residual herbicide to achieve control. 
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees.


  • Monitor bee activity to estimate fruit set.


  • Grafting is underway.


  • Keeping the orchard floor cover mowed pre-bloom will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.

Pruning and Training

  • Summer pruning is the next best opportunity if pruning is not complete by bloom.
  • Train and support young trees as soon as possible. Work in dry weather especially if the block has historically high risk of fire blight. This year is expected to be an active hurricane season.
  • Pruning practices should be done on dry and sunny days, especially in high risk fire blight blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.


  • Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.
  • Foliar nutrients to correct nutrient deficiencies:
    • Nitrogen: Urea may be used from pre-pink to mid-June as a nitrogen supplement. Sprays near bloom give a boost of nitrogen when it is needed most. Urea used from tight cluster to mid-July can remedy a nitrogen shortage. However, limit foliar nitrogen later in the season.


More information was provided in the May 3 newsletter.

  • Tilth should be friable enough and stamp trees in to avoid air pockets for good root to soil contact, especially under current conditions of limited rainfall. 
  • Warm soil temperatures mean that roots will grow immediately. Start fertilizer programs as soon as possible after planting.
  • Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Under currently dry conditions, watering with drip tape if possible especially under sandier situations is recommended. Keith Fuller also notes that M26 wilts very easily and that water provided in replant situations can reduce stress from replant disease. A dry season compounds replant disease symptoms.
  • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees.
  • Newly planted trees should be pruned for tree structure and supported as early as possible after planting. Prioritize trees that are known to be brittle at the union, including many of the new Geneva rootstocks (G.11, G.41, G.16 etc).
  • If fumigating in the spring, observe the warnings on the label prior to planting to avoid crop injury. Leave the soil undisturbed for 10 to 14 days or longer in wet weather.

On-Farm Nursery

  • Strip leaves from rootstock soon for budding. Strip non-varietal buds from last year's rootstock soon.
  • Monitor for tarnished plant bug and green aphids.
  • Remember the importance of weed control in nurseries. Management practices now will impact the outcome of the final tree. Encourage the growing point to be successful!

Wild Apple Trees

  • Wild apple trees harbour pests, in particular apple maggot, that can then spread to nearby orchards. Now that wild apple trees are in bloom, it’s a good time to flag trees on your own property so that you can find them later in the season for removal.

Pest Management Guides 2022

All changes new to 2022 are made in red text directly on the guides. The information on all changes was summarized in a blog post on April 8th.

Events and Notices

For upcoming events, visit the ‘Events’ tab on the NS Tree Fruit Blog. Specific events will be described here when available.

May 24 Weather Station Apps and Website Training Session

This training session is intended for producers who have purchased weather stations from Perennia under the Nova Scotia Weather Station Assistance Program and is also open to anyone who would like to learn more about the weather stations and how they work. It will provide an overview of the Davis weather station components, basic maintenance and using the apps and software tools.

Date: May 24th from 7:00- 8:30 PM

For more info and to register for the session, please visit this link: https://www.perennia.ca/eventer/weather-station-apps-and-website-training-session/edate/2022-05-24/

2022 Virtual Orchard Meetup Series

Last year various extension specialists across the United States put together a virtual apple meetup series, focusing on ‘Honeycrisp’ apples. This year, the series will focus on labour and technology in the orchard with representation from across the U.S. and Ontario. Register at bit.ly/orchardmeetups.

Orchard Efficiency: Labour and Technology (4PM PST, 7PM EST)
June 2. Labour – Grower Experiences
June 16. Labour – Specialist Panel
June 30. Technology – Growers Experiences
July 14. Technology – Specialist Panel

These meetups will provide an opportunity to review challenges, best practices, and new recommendations for orchard labor and technology. Led by a panel of scientists, growers, and other experts in labor and technology across North America.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Colin Hirtle, Joan Hebb, Larry Lutz, Jeff Franklin, Jeff Wentzell, Keith Fuller, Dr. Suzanne Blatt, Danny Davison, Dr. Vicky Levesque, Dr. Ian Willick, and Dr. Mathew Vankoughnett.

Perennia Food and Agriculture Inc.
Edited by Michelle Cortens, Tree Fruit Specialist

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