Orchard Outlook Newsletter Vol. 23, No 6

Tuesday, May 23, 2023

The newsletter discusses freezing temperatures observed in isolated regions this morning during bloom. In terms of diseases, apple scab spores continue to mature consistently so the risk period is still high. Fire blight infection risk is being monitored but in these cool temperatures the bacterial growth is low and is forecast to remain low - but stay tuned as conditions can change quickly. During bloom, of course do not spray insecticides. We also review blossom thinning and look ahead to fruitlet thinning. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2023 Degree Day Accumulations
  • 2023 Precipitation
  • Apple Bud Growth
  • Spring Frost Injury
  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple - Fire Blight Prevention
  • Apple - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Calyx/Blossom End Rot
  • Apple - Black Rot
  • Pear Insects
  • Nematodes


  • Apple Blossom Thinning
  • Apple Fruitlet Thinning
  • Pear Fruitlet Thinning

  • Weed Management
  • Pollination
  • Grafting
  • Mowing
  • Pruning and Training
  • Fertilizing
  • On-farm Nursery
  • Wild Apple Trees

Events and Notices

  • Introducing the Perennia Plant Health Lab!
  • Funding Programs
  • Pesticide Training Opportunities by Marbicon

Pest Management Guides 2023



2023 Degree Day Accumulations

Cumulative degree days continue to be slightly behind the 5- and 10-year averages for plant and insect development (Figure 1). 

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 22 for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 5% less plant development heat units compared to the 5-year average, and 7% less compared to the 10-year average.
  • Approximately 20% less plant development heat units compared to 2022, and 21% less compared with 2021.
  • Approximately 4% less insect development heat units compared to the 5-year average, and 13% less compared to the 10-year average.

2023 Precipitation

Currently, the Kentville weather station has recorded 31 mm of rain out of the monthly average of 74 mm. The rain on Sunday varied a lot depending on microclimate with anywhere from 4 mm to 24 mm. Higher amounts of precipitation were observed in the western side of the Valley.

There are currently some very good programs available to cost-share your improvements to water resources. 

Tree Growth

Apple Bud Growth

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 22, the Idared buds were at the 50% full bloom stage, Honeycrisp was at king bloom and Ambrosia was at late full pink to early king bloom (Figure 2). Orchard Outlook committee members also report that varieties are at similar stages in Falmouth, Morristown, and a little further along in Melvern Square. Gravenstein is nearing full bloom. Pear is blooming.

Figure 2: Bud growth in an early region on Middle Dyke Road in Kentville on May 22. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Spring Frost Injury

Freezing temperatures were recorded in some regions this morning on May 23. The coldest temperatures were recorded in South Berwick (-2.9°C), Aylesford (-2.1°C), Rockland (-1.9°C), and Windsor (-1.8°C). The critical temperature for frost damage in spring during the stage from full pink to petal fall is -2.2°C at which point 10% kill could occur. More extreme temperatures of -3.9°C would cause 90% bud damage.

Very little damage was observed where temperatures reached -1.9°C. Damage to king buds was observed where temperatures reached -2.9°C.

Figure 3: Healthy bud (left) and damaged bud (right) observed on May 23 after the morning freeze. Damage is not extensive and is more likely on king buds than side buds.

Turning our focus to terminal shoots, they are beginning to elongate. The timing of the first application of Apogee/Kudos is between 2.5 to 7.5 cm of new shoot growth and is critical to success. It is likely that the window of time has been reached.

Figure 4: Terminal shoot growth on Honeycrisp. Taken on May 23, 2023 on trees with king bloom.


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 16 to May 23, 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 Saturday, April 15th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
Note: The environmental conditions for an infection are listed in the Modified Mills Table.


  • According to the forecast, ascospores are expected to mature at a rate of 2-3% per day and within the next five days about 90% of total seasonal ascospores are expected to be mature.
  • We continue to be in a very high risk period. The next apple scab infection will have a significant spore load available. 
  • 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. Otherwise, waiting for rain is a gamble with the hopes that protection is applied in time (and the possibility of relying on post-infection treatment).
  • Folpan/Follow should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting.
  • Remember that there is a new label for Manzate (mancozeb). The product may be applied 4 times/ha/year, the re-treatment interval is 7 days, the REI for hand thinning is 35 days (12 hrs for all other activities), and the PHI is now 77 days.
  • Alternatives to Manzate for resistance management? Captan may be applied if it is not 7-14 days within an oil. Allegro may be applied 1 day after an oil.

Apple – Powdery Mildew

Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.


  • Apply two sprays targeting powdery mildew prior to bloom on the re-application schedule noted on the product being used (usually 7-14 days) and prior to a period of warm and dry weather. 
  • 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.
  • Practice resistance management:
    • When 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: Although Group 3 fungicides Nova and Fullback are also labeled for apple scab, they are not expected to provide control because of resistance in the local scab population. Another product is required for scab protection.

Apple – Fire Blight Prevention


  • Pruning practices should be done on dry and sunny days, especially in high risk blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees. 
  • If interested in pinching buds on young trees the practice can begin around the bud separation stage when it's possible to avoid removing the terminal shoot. Pinching buds becomes risky as bloom begins because fire blight bacteria grow on the flower stigma and are expected to be present in high numbers in warm weather. Do not pinch flowers when tissues are wet. Overall, bud pinching is time-consuming and any remaining flowers are susceptible to infection.

Apple – Fire Blight Blossom Blight

Monitoring for Blossom Blight Alerts
This year, all NSFGA-owned weather stations are being used for industry monitoring and alerts. If you would like to join the alert contact list, please let me know at mcortens@perennia.ca or sign up online. Alerts will be delivered on weekends and holidays.

Ideally you will monitor your own farm-specific conditions and improve your management decisions using PomeBlight that was developed for Nova Scotia apple and pear growers. Contact me if you need a quick refresher or need help setting up. Run the model using your own temperature, rainfall, bloom and spray dates (industry alerts will offer limited scenarios). 

Current and Forecast Blossom Blight Risk
  • Due to cool nighttime temperatures and mild daytime temperatures, the EIP that represents bacterial growth is is currently LOW for open flowers on apples and pears. 
  • According to the forecast, the EIP will remain low into the near future indicating that an infection is unlikely in the next few days. 
  • Stay tuned because predictions can change on short notice.

Quick Refreshers:
  • Does water wash away bacteria? No! Bacteria use water to disperse and colonize new flowers. The 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 actually the cooler temperatures that are responsible for less bacterial growth.
  • When are flowers no longer at risk of a blossom infection? As flowers age, the stigmas become less susceptible hosts for the bacteria Erwinia amylovora. Yet, late blooms are especially important because bacterial populations have had time to build throughout bloom and bees have broadly dispersed the bacteria in the landscape. 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 petal fall is recommended.
  • What is the rainiest period for Streptomycin and Kasumin? 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.


  • 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 20-24 hours. 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 should be put on with higher water volumes to cover all new leaves and growing tips.
  • Apogee is applied dilute so be aware of the fire blight blossom blight risk at the time of application. If the EIP is high, the bacterial population is high and a dilute spray may cause an infection.
  • 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.
  • 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/Blossom End Rot


  • If calyx/blossom end rot has been an issue in the past, consider using a captan product during full bloom. Infections can occur in problem blocks as the pathogen can last in the soil for several years.
  • If applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.
  • Keeping grass and dandelions mowed will allow the soil to dry and reduce the environmental conditions for spore ejection. Other broadleaf weeds are also a host of this disease so weed control prevents the build up of this pathogen.

Apple – Black Rot


    • Based on our limited knowledge, the highest risk of infections is theoretically between petal fall and 4-6 weeks after bloom.
    • 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. 



    • 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.

    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 petal fall. 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.


    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. Samples can be processed by the Agriculture and Food Laboratory (AFL) in Guelph, ON.


    Apple 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 could be a good consideration for early thinning of small fruited varieties (e.g. Ambrosia and Gala). 
    • The efficacy 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.
    • 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. Do not wait much longer and especially don't wait until petal fall because it can be too late.
    • 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.
    • 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.
    • ATS is NOT recommended for defruiting 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.
    • 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 Fruitlet Thinning

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


    Weed Management

    • This week may be a good opportunity for burndown herbicides if needed. If you have not yet acted, act soon because full control is already unlikely as weeds are becoming large.
    • In young plantings, weed control is essential. Local research showed that by year 4, a weedy planting was 39% the trunk cross sectional area of a hoed comparison.


    • Monitor bee activity to estimate fruit set.


    • Bark is expected to begin slipping from pink to bloom.


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

    Pruning and Training

    • Plan ahead and watch re-entry intervals for pruning activities.
    • Continue pruning to reduce crop load but avoid aggressive pruning to avoid weakening trees. 
    • 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).


    • Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.
    • Foliar nutrients to correct nutrient deficiencies:
      • 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.

    On-Farm Nursery

    • Monitor for tarnished plant bug and green aphids.
    • Remove rootstock leaves when they are tender and before shoots become woody. In the case of bench grafts, wait for 1" bud growth before stripping the rootstock and be very careful not to touch the graft union. 
    • Consider staking soon to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
    • 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.

    Events and Notices

    Introducing the Perennia Plant Health Lab!

    Perennia has always known the importance of fast and accurate analytical testing for farm operations. While we have been offering some lab services to diagnose and manage problems in tree fruit, vegetable, berry, field and specialty crops, the Plant Health Lab is transitioning to a more comprehensive service. As such, there are some changes we’d like to outline for Nova Scotia growers.

    To ensure the long-term sustainability of the lab, we are implementing a pay-for-service model with preferred pricing for Nova Scotia registered farmers and some exceptions for in-field diagnoses by our agriculture specialists.

    Perennia specialists can still perform in-field diagnoses of plant health issues for growers. If a Perennia specialist working with our plant pathologist can visually make an identification, no testing will be triggered unless the producer requests and pays for it with discounted rates for Nova Scotia registered farms. In those rare instances when our specialists and plant pathologist are not confident in the diagnosis, they will collect and test a sample free of charge. Regardless of the testing required, our team will work with industry to address with appropriate strategies.

    In all other instances, a pay-per-use system has been implemented to access the Plant Health Lab’s services. This decision was not taken lightly but made to ensure the sustainability of the Lab as well as plan for future investments in the service.

    Please find here an overview of the PHL’s current diagnostic capabilities and pricing, as well as how to submit and pay for samples.

    Thank you for your continued trust in Perennia,

    The Plant Health Lab Team

    Funding Programs

    Pesticide Training Opportunities by Marbicon

    The next series of in-person courses from Marbicon Inc (Jim Jotcham) are confirmed.
    This may be the final courses offered until October/November this fall.
    They will need a minimum of 8 people for any additional courses this spring.

    Pre-exam courses (with 5.0 points available for T2237):
    June 8 - Truro Horsemen’s Club in Bible Hill

    Points workshop (with 5.0 points available for T2236):
    May 24 - Berwick Legion in Berwick
    June 9 - Truro / Douglas Street Rec Centre, limited seating!
    This points workshop is not preparation for the provincial applicator exam.

    Email/call Jim ( marbicon@eastlink.ca ) or 902-538-7101 to pre-register.

    Pre-exam courses are $125 including HST.
    People only sitting in for 5.0 recertification points pay $110 including HST.
    Doors open at 8:30am. Pay at the door. Cash, cheque, or e-Transfers only. No credit/debit cards.
    Food & drink on your own.
    A course manual is provided for pre-exam courses. Bring a pen.

    Pest Management Guides 2023

    All changes new to 2023 are made in red text directly on the guides. The information on all expected changes was summarized in a blog post on March 7. 

    This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Heather Rand, Larry Lutz, Dustin MacLean, Suzanne Blatt, Karen Burgher, Mathew Vankoughnett, Shawkat Ali, Joan Hebb, Jeff Wentzell, Jill MacDonald, Keith Fuller, and Jeff Franklin.

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

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