Orchard Outlook Newsletter Vol. 22, No 6

Tuesday, May 17, 2022

Hopefully you didn't blink over the last few days or you would have missed a lot of tissue growth! Today's newsletter discusses the usual diseases but also jumps into fire blight blossom blight and shoot blight management and offers reminders about black rot management. We also consider ongoing insect risks. The pros and cons of blossom thinning are discussed. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2022 Degree Day Accumulations

  • 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)
  • Stone Fruit - Brown Rot Blossom Blight
  • Pre-Bloom Insecticides (spring caterpillar complex, European apple sawfly, tarnished plant bug, leafroller)
  • Nematode (Pre-plant samples)

  • Weed Management
  • Pollination
  • Grafting
  • Mowing
  • Pruning
  • Fertilizing
  • Liming
  • Planting
  • On-farm Nursery
  • Wild apple trees

Pest Management Guides 2022

Events and Notices

  • Perennia - 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 ahead of the 5 and 10-year averages for base 5°C heat units for plant development (Figure 1). The long-term forecasts suggests that temperatures could be in the mid to high 20s again later in the week. Also note the rapid accumulation of base 10°C heat units for insect development so that this year has now caught up to average.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 16 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 12% more plant development heat units compared to the 5-year average, and 7% more compared to the 10-year average.
  • Approximately 7% less plant development heat units compared to 2021, and 73% more compared with 2020.
  • Approximately 4% more insect development heat units compared to the 5-year average, and 9% less compared to the 10-year average.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. What a change a few hot days can make! Yesterday on May 16, the Idared buds were at about 50% king bloom, Honeycrisp was at bud separation, and Ambrosia was at late tight cluster (Figure 2).

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on May 16. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Orchard Outlook committee members report that in the Melvern Square area, Jonagold, Honeycrisp and Ambrosia are around bud separation to pink. In the Morristown area, Honeycrisp is at bud separation and Ambrosia is at late tight cluster. In general, cherries, peaches, and pears are in full bloom.

King buds damaged by the frost are visibly small at this point and they will not survive (Figure 3). Also note that vegetative growth of the terminals is continuing, which is worth watching for upcoming applications of prohexadione calcium (Apogee/Kudos) for management of fire blight shoot blight (Figure 3).

Figure 3: A Honeycrisp cluster with a dead king bud in the centre that is visibly smaller than surrounding lateral fruit (left). A terminal shoot on Idared measuring 2 cm in length.  


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 10 to May 17, 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 15 and on the morning of May 17 but according to the modified mills table, an infection was unlikely for short leaf wetness periods. Regardless, the May 15-16 infection was reason enough to be protected.


  • By the weekend, the total seasonal ascospore maturity is expected to reach 76.4%.
  • If you are due for a protectant fungicide, it is recommended that protection be maintained especially at this 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


  • Ideal conditions for infection may occur during this warm and relatively dry week. 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. 
  • Apply two sprays targeting powdery mildew prior to bloom on the re-application schedule noted on the product being used (usually 7-14 days). Coverage during the pink to bloom stage prevents fruit infection.
  • 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.
  • Practice resistance management:
    • Powdery mildew: Group Ms do not have activity on powdery mildew so they will not help prevent powdery mildew resistance development. Products in the groups 3, 7 and 11 are registered for control of PM. Resistance to group 11 products was reported in a survey in 2013. Therefore, whenever the remaining groups 3 & 7 are used, careful consideration must be given to rotating the groups to slow resistance development. Avoid more than two consecutive applications of a single group.
    • Scab: The Group M fungicides (mancozeb and captan) provide scab control so tank mixing them with single-site fungicides is a great strategy to slow resistance development in the apple scab population. Although Group 3 fungicides Nova and Fullback are labeled for apple scab, they are not expected to provide control because of resistance in the scab population.

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 is used to predict blossom blight infections.

Monitoring Regions for Maryblyt Alerts

This year, all NSFGA-owned weather stations will be used for industry alerts. Those weather stations are located in the following communities: Atlanta, Aylesford, Grafton, Grand Pre, Melvern Square, Morristown, Moschelle, North Medford, Windsor, and Woodville.

Short notice Maryblyt alerts will be delivered directly to your email inbox. Periods with high fire blight bacterial populations are defined by Maryblyt as having an Epiphytic Infection Potential (EIP) greater than 100. Notifications will be sent as soon as it is evident that the EIP will approach 100 for apples and pears.

The first email alert was sent this morning. If you did not receive an alert and you wish to, please let me know at mcortens@perennia.ca or sign up online. Alerts will be delivered on weekends and holidays.

Current and Forecast Blossom Blight Risk

Open blossoms must be present for a blossom blight risk to exist. The first wave of blossoms opened on May 13 and 14 in early apple varieties and in pears. This morning's alert email shared details on infection risk for some regions.

According to the forecast, after today the EIP is expected to stay low for a few days. However, warm temperatures near the end of the week are forecast to increase the risk and infection events are possible around Sunday, May 22. Stay tuned because predictions can change on short notice.



  • Consider the ongoing risk of blossom blight infection on flowering apples and pears.
  • Wondering about the daily EIP risk even if you do not receive an alert? Tomorrow I will start to post updated daily screenshots in a folder online to make model predictions easily accessible. Access apple and pear predictions. 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.


  • Streptomycin 17 will provide excellent efficacy on blossom blight and is best used up to 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.
  • 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. 

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. 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.

Stone Fruit – Brown Rot Blossom Blight

Brown rot infection of the flowers during bloom provides secondary inoculum for fruit infections later on.


  • Fungicide protection from brown rot should be maintained during periods of warm, wet weather. 
  • Rotating classes of brown rot fungicides is key to slow resistance development. There are many options in the management guide.
  • The new formulation of Captan limits the number of applications to one per year on stone fruit.



  • Some regions might still have an opportunity to treat for insects if blossoms have not opened. 
  • 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.

Pre-Bloom Insecticides

Spring Caterpillar Complex

(winter moth, green pug moth, eyespotted bud moth, speckled green fruitworm)

  • Evidence of feeding includes tiny holes in new leaves and flower buds, and black specks of frass. Begin scouting procedures described in Perennia’s Best Management Practices. Monitor your scouting reports for notes on WM, GPM, and other caterpillars for those with scouting services.
  • Note that there is a lower tolerance for WM than GPM. Green Pug Moth do not feed directly on developing fruitlets.
  • If a treatment for just WM is required, then a Bt product (e.g. Dipel or Bioprotec) with Upside applied at bud separation is effective with a minimum impact on beneficial insects.

European Apple Sawfly

  • In orchards with a history of damage and high numbers of EAS catches, an application of Altacor, Assail/Aceta, Calypso, Minecto Pro, Cormoran or Exirel is recommended to control the adults prior to egg laying.
  • In blocks with low to moderate pressure, control of EAS can occur at petal fall.

Tarnished Plant Bug

  • If history of tarnished plant bug damage indicates that pressure is moderate to high, a prebloom insecticide can be beneficial.
  • Pyrethroids (group 3) and the group 4 products Closer, Cormoran, and Twinguard, are registered for control.


  • Obliquebanded leafroller is often controlled by pesticides that are applied at this time of year.
  • If leafroller alone requires treatment, the ecdysone disrupter products Intrepid and Confirm have a low risk of toxicity to bees.
  • If treatments for OBLR are required at pink, the treatments will also have some activity on WM and GPM. 

General Notes

  • Monitor for rosy apple aphid populations.
  • If a pyrethroid is applied for tarnished plant bug at pink, it will also have activity on WM and GPM. Similarly, pyrethroids are expected to have some activity on EAS if being applied for other pests.
  • As a reminder, pyrethroids are best used at moderate temperatures (20°C or less) and are harsh on beneficial insects and predator mites. They should only be used where potential losses justify their application.
  • In stone fruit, monitor for black cherry aphid. Dr. Suzanne Blatt reports that leaves are not yet curling in Kentville.

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.

Blossom Thinning

The caustic thinner ammonium thiosulphate (ATS) is the first chemical thinning opportunity of the growing season. ATS reduces pollen germination, interfering with fertilization. 


  • May lead to increased fruit size and return bloom compared to later fruitlet thinning. ATS would be a good consideration for early thinning of small fruited varieties (e.g. Ambrosia and Gala). 
  • The caustic activity of ATS does not depend on the temperature at application, unlike fruitlet thinners.


  • This year there was frost injury to king buds. This is a complication because blossom thinning attempts to thin after the king bud is set to target killing side buds. Without a king bud, the differentiation between side buds is challenging. Know how many buds are viable before blossom thinning by taking a close look at king buds (Figure 3 above). 
  • Beware that if the fire blight risk is high (infection pending a wetting event) an antibiotic is needed prior to ATS or wait until the risk has decreased.
  • You are thinning with an unknown crop load (before fertilization). 
  • There is potential for foliar spray injury. If ATS is applied to dry leaves then there is less chance of injury. Some foliar and petal burn is normal and suggests the concentration is effective for thinning. 
  • It can increase fruit russet so avoid sensitive varieties as a precaution.
  • Blossom thinning cannot compensate for a lack of bud removal during pruning.


  • ATS can be applied towards the later part of full bloom (80-100% FB), at which point adequate pollination of king flowers has occurred. This strategy can produce variable results by being too late if it gives most flowers the time needed for fertilization.
  • The goal is to apply ATS when the king flower has had enough time to become fertilized but prior to the lateral flowers becoming fertilized. For more accurate timing, consider that in order to become fertilized, a pollen grain must germinate on the stigma and grow a pollen tube to the base of the style to reach the ovary. In cool temperatures of 13°C, fertilization of open flowers takes 5 days and in warm temperatures of 24°C, fertilization takes 2.5 days. Therefore, time the ATS application for several days after the desired percentage of bloom has opened. Please ask me for more information if interested (and if you want to measure stigmas).
  • In Nova Scotia, ATS has been used at 5.5 L in 100 gal/acre (13.6 L ATS in 935 L/ha). The concentration is what matters for its activity so don’t concentrate it by spraying a lower volume. Keep records to learn from your results. If you are not familiar with the product, be conservative with the rates, use it on a small area first, and talk to someone with experience about rates.


Weed Management

  • 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.


  • Honeybees should be moved into the orchard for pollination when king flowers open.
  • Monitor bee activity to estimate fruit set.


  • Bark typically slips from pink to bloom at which point healing of grafts is quick and most successful. Grafting has started.


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


  • Ensure that youngest blocks are pruned first so growth is directed into desirable leader and terminal extension. Avoid heavy pruning to avoid weakening trees.
  • 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:
    • Boron: Applied pre-pink. Do not use water soluble pesticide bags in a tank mix with boron and rinse the tank well before and after boron. Do not use boron with oil or Epsom salts.
    • Magnesium: Epsom salts are applied starting at pink. Do not use with oil or boron.
    • 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.
    • When foliar nutrients are applied in slow drying conditions, about 40% is absorbed in 6 hours. When applied in dry and winter conditions, about 75% can be lost in 48 hours.
    • Foliar nutrients are not well-absorbed at below 10°C.


  • Be cautious because a lime spreader intended for fields with tall beaters at high speeds can damage the leaf tissue and buds on tree fruit.
  • Lime especially if a site is being planted this year. When applied in spring the lime works best when applied as soon as possible to get the product working in the top layer of soil. 
  • Surface applied lime will take a number of years to adjust pH of the soil profile so it is best to apply annually or biannually where needed. If soil testing for pH, measure during the same time each year as pH can change over the growing season. 
  • The provincial limestone trucking assistance program is open.


More information was provided in the May 3 newsletter.
  • 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.
  • Remember to document the quality of your nursery trees with pictures and notes. 
  • Avoid letting trees dry out.
  • Bundles of trees sitting in water awaiting planting can asphyxiate, especially in stagnant water and/or warmish water.
  • Tilth should be friable enough to avoid air pockets for good root to soil contact.
  • If you fumigated last fall, remember to practice tillage within the same direction as fumigated rows and not across.
  • Remember the risk of dipping roots in a shared water solution.
  • Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Watering-in or rainfall soon after planting can help to fill air gaps.

On-Farm Nursery

  • 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.

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: Jeff Wentzell, Joan Hebb, Dr. Suzanne Blatt, Larry Lutz, Dr. Mathew Vankoughnett, Dr. Ian Willick, Crystal MacRae, Dr. Vicky Levesque, Dustin MacLean, Danny Davison, Jeff Franklin, and Colin Hirtle.

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

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