Orchard Outlook Newsletter Vol. 25, No 7

Tuesday, May 27, 2025

Bud development has been at an almost standstill over the last week. In today's newsletter, we consider bee pollination and flower fertilization. In terms of disease management, primary apple scab spores are still maturing (but we are nearing the end!), and a fire blight blossom blight risk is anticipated later this week. Join me for a popup fire blight meeting on Wednesday at noon to discuss the current situation and frequently asked questions. With petal fall approaching it will soon be time to consider post-bloom insecticides for insects that hatch during bloom like stinging bugs and while apple leafhopper. Thanks to the ongoing commitment of the Orchard Outlook Committee members.



Table of Contents:


Weather
  • 2025 Degree Day Accumulations
  • Apple Buds
  • Pear and Stone Fruit Buds
  • Bee Pollination and Flower Fertilization
  • Apple - Scab
  • Apple - Powdery Mildew
  • Fire Blight Prevention and Shoot Blight Management
  • Apple and Pear - Fire Blight Blossom Blight
  • Apple - Calyx/Blossom End Rot
  • Apple - Postbloom Insects
  • Stone Fruit Insects
  • Pear - Postbloom Insects

Thinning

  • Apple Fruitlet Thinning (Advance Notice)
  • Pear Fruitlet Thinning (Advance Notice)

  • Suckers
  • Grafting
  • Mowing
  • Root Pruning
  • Pruning and Training
  • Weed Management
  • Nursery Trees
  • Wild Apple Trees

Events and Notices

  • Popup Fire Blight Webinar
  • Marbicon Pesticide Courses

Pest Management Guide



  

Weather


2025 Degree Day Accumulations

The cumulative degree days remain ahead of the 5- and 10-year averages (Figure 1). However, recent below-average temperatures have narrowed the gap between this year and the averages. Soil temperatures have also decreased slightly.


Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 26 for the past 17 seasons. Provided by Jeff Franklin (AAFC Plant Physiology).
  • Approximately 12% more plant development heat units compared to the 5-year average, and 16% more compared to the 10-year average.
  • Approximately 1% less plant development heat units compared to 2024, and 27% more compared with 2023.
  • Approximately 6% more insect development heat units compared to the 5-year average, and 8% more compared to the 10-year average.



Bud Development


Apple Buds

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Development was essentially at a standstill over the last week. Yesterday on May 26, the Idared buds were at the early petal fall stage, Honeycrisp was at late king bloom and Ambrosia was at late king bloom (Figure 2). There appears to be a lot of variation in bud stage throughout individual trees with some clusters at full bloom and others with many unopened lateral buds. Many of the king blossoms that were open throughout the period of cool weather look weathered.

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on May 26. Shown from left to right: Idared (early petal fall), Honeycrisp (late king bloom), Ambrosia (late king bloom).

Terminal shoot growth has also progressed slowly with Idared measuring about 10.0 cm, Honeycrisp at 5.0 cm and Ambrosia at 4.0 cm to the growing point (Figure 3). For now we are still at the early timing for Apogee/Kudos (2.5-7.5 cm shoot growth) on many varieties. Likely terminal growth will proceed quickly in the upcoming heat.

Figure 3: Terminal shoot growth in an early region on Middle Dyke Road in Kentville on May 26. Shown from left to right: Idared (10.0 cm), Honeycrisp (5.0 cm), Ambrosia (4.0 cm).

Pear and Stone Fruit Buds

Yesterday on May 26 at an early region in Greenwich, the pear buds were at early petal fall, peach was at petal fall, and European plum was at petal fall (Figure 4). Pears are at full petal fall in other regions.

Figure 4: Bud development in an early region in Greenwich on May 26. Shown from left to right: pear (bloom to petal fall), peach/nectarine (petal fall), and European plum (petal fall).

Bee Pollination and Flower Fertilization

Everyone has been aware this year that wild bee activity has been low under the cool and wet conditions. Last week there was limited to no wild bee activity even during breaks in the rain, leading us to question pollination of open flowers. 

During my bee surveys I noticed that honeybee hives were more active during the cloudy and cool weather. If hives were placed at a good density throughout the orchard, then flower visitation was acceptable for fruit set (over 5 flower visits in 5 minutes on 3' X 3' floral area). Due to the significant difference in bee activity near hives we might see some variability in fruit set such as more fruit near hives and less with distance from hives, as has been noted in the past. Thankfully pollination conditions turned better starting on Monday afternoon and will be good for the next few days.

Flowers that were pollinated last week theoretically had a prolonged fertilization period (9 days). In the heat over the next few days, pollinated flowers will be fertilized in a few short days (2-3 days).

Crop insurance records suggest that the year 2004 was notable for claims of pollination issues. The 2004 weather pattern during pollination was quite similar to this year with 60% of days with rainfall, and only 30% of days above 15 degrees C. The 2004 Orchard Outlook newsletter reported, “fruit bud development practically on hold” and they were “questioning cross pollination as a result of cool, damp weather” but noted there were a few good pollination days.

Fruit set will not be straightforward this year and so far we will have to wait and assess. In 2004, there was poor fruit set in some orchard blocks and very good crop load in other blocks. It will likely mean assessing fruit set a couple of times as the size differential between the king and side fruitlets becomes more pronounced. We should also bear in mind the common trend that initially fruit set looks low but then by harvest the crop load is good or too much.



Diseases



Apple – Scab


Table 1: Apple scab infection events in Kentville from May 21 to May 27, 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 April 20. 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.

Recommendations:

  • Again, fungicide residues should have lasted throughout the weekend wetting period if they were applied prior to the prolonged wetting event because rainfall amounts totalled 23.5 mm (less than 50 mm residue depletion). Although we didn't get excessive new growth, rain removed some of the residues and it looks like another prolonged wetting event may occur this weekend so reapplication is warranted.
  • According to the forecast, ascospores are maturing at a rate of 1-2% per day. An additional 9% of spores might mature by the end of this weekend, bringing us to a seasonal spore maturity of 99%.
  • Do not apply captan within 7-14 days of an oil such as Agral 90 (worse if applied after oil that preconditions leaves).
  • Folpan/Follow should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting.


Apple – Powdery Mildew


Typically, conidia are released around the tight cluster stage. Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.

Recommendations:

  • So far the weather this year has not been very conducive to powdery mildew infections. An infection was possible around mid-May and the next few warm days might present another infection risk.
  • Our research last year suggested that post bloom applications have protective value. If one of the typical pre bloom applications was missed, the powdery mildew products may be applied starting again at petal fall and 10-14 days later.
  • New products registered this year for apple powdery mildew with unique chemical groups include: 
    • Migiwa group 52, control of scab, short REI of 12 hrs, max 3 apps total.
    • Gatten group U13, no activity on scab, short REI of 12 hrs, max 4 apps total.
    • Property group 50, no activity on scab, short REI of 12 hrs, max 4 apps total.
  • Some notes about industry-standard products:
    • The chemical group 3 products Nova/Fullback are very effective. Fullback and Nova are systemic and given a long drying period of 24 hrs they should be well-absorbed into the plant. (Fullback and Nova will not provide scab protection due to industry-wide fungicide resistance.)
    • If you're using Luna Tranquility for powdery mildew, concurrent activity for scab control is only provided at the high rate.
    • There is no expected resistance to chemical group 3 and 7 products so the products are expected to be effective. 
    • There is industry resistance to group 11 products such as Flint so it should not be used for powdery mildew management. 
  • Do not use any products with powdery mildew activity more than two times consecutively to avoid resistance development. 
  • 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.


Fire Blight Prevention and Shoot Blight Management


Recommendations:

  • 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.
  • Even if bacterial EIP populations are low, do not pinch flowers in wet weather. Pinching causes open wounds like a trauma event and bacteria are transported to wounds in wet weather. 
  • Apogee/Kudos (prohexadione calcium) supress shoot blight. Apogee/Kudos is first applied at 2.5-7.5 cm of shoot growth which has been reached by now. Follow up with a second application applied around 14 days later. 
    • The product takes 10 days to become active so for the maximum effect on fire blight suppression it should be applied before fire blight symptoms appear. Early application might even thicken cell walls of the flower pedicels giving some added protection from blossom blight.
    • When Apogee/Kudos are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still slow fire blight progression.
    • The product is not systemic so good coverage with high water volume is required.
    • 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)!
    • Use low rates on young apple trees to avoid delaying growth too much.


Apple and Pear – Fire Blight Blossom Blight


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. 


Blossom Blight Risk
  • A blossom blight alert email was sent this morning as an early warning for the risk of blossom infections on Thursday/Friday. 
  • Now that the temperature is rising, bacterial growth will occur gradually on flowers over the next few days. Currently it looks like bacterial levels will become risky on Thursday (EIP 97) and Friday (EIP 109) for open apple and pear blossoms. Wetting would trigger an infection and there are showers in the forecast. An updated alert will be sent tomorrow. If you would like to join the alert contact list, please let me know or sign up online. 
  • I am hosting a popup webinar tomorrow on Wednesday, May 28 at noon to review current conditions and answer frequently asked questions about fire blight. See the information below under Events.
  • 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. A Quickstart video is available here.


Apple – Calyx/Blossom End Rot


Recommendations:

  • Infections occur when weather conditions are warm (15 to 25°C) and moist during bloom and shortly after bloom. 
  • The only product with activity on calyx/blossom end rot is captan applied 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.
  • Infections can occur in problem blocks as the pathogen can last in the soil for several years. The disease is most common on Paulared, Delicious, Cortland, Honeycrisp and McIntosh.
  • 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.



Insects


BE RESPONSIBLE FOR POLLINATORS – DO NOT SPRAY INSECTICIDES DURING 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 - Postbloom Insects

Choose post-bloom insecticides according to the pest complex on your scouting report. Insects might include the caterpillar complex, stinging bugs (mullein bug), European apple sawfly, green and rosy apple aphids, curculio, European red mite, and white apple leafhopper.

Refer to the Apple Efficacy Guide for product selection. You may begin by determining the product and rate for your most difficult to control pest and then note the other pests that will be managed by your product selection and whether or not additional products are required. Take note of the higher rate required for some pests. 

Recommendations:

  • If you have not already treated for rosy apple aphid, be aware that they thrive in cool and wet springs. For those of you that have treated, it's great to be on top of the issue!
  • Stinging bugs and white apple leafhopper hatch around the bloom period and trees should be checked around petal fall for their presence. 
    • Stinging bugs are checked using limb tap samples when the nymphs are very small. 
    • Leafhoppers can be found feeding on the underside of leaves and they will move forward or backward. Leafhopper nymphs are found on cluster leaves close to the main trunk or large branches, not on terminal shoots. Leafhoppers are often controlled by Sevin insecticide when used as a thinner.
  • Dr. Suzanne Blatt's lab has just put out traps to start monitoring for codling moth flight. You may wait until petals fall to avoid cluttering traps. Moths have not been active in these cool temperatures but warm evenings will eventually encourage their flight. Organic apple growers should have traps in place and consider the timing of mating disruption for codling moth. When using Isomate-CM/OFM for codling moth mating disruption, have the ‘twist ties’ placed in the orchard blocks by petal fall (prior to the start of male moth flight).
 

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.


Recommendations:

  • Be aware of bee toxicity warnings on pesticide labels and take precautions while nearby crops are in bloom.
  • Note that pyrethroids are best used at moderate temperatures (20°C or less) and lose efficacy at around 25°C.
  • Plum Curculio
    • Treatment for PC should be applied at petal fall before shuck split to obtain optimal control. A second application is usually needed about 10 days later.
    • The insecticides available for managing plum curculio include Malathion, Pounce, 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.
  • 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 Online Pest Guide for peaches. Note that Matador is not registered. Repeat treatment in 5-7 days if additional stings are detected. 

Pear - Postbloom Insects

  • 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 young tissues because of rapid penetration. 
    • 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. 
    • Do not use MaxCel in close proximity to AgriMek because the oil will increase thinning activity.
    • Minecto Pro (Abamectin and Cyantraniliprole) is a new formulation that is registered for control of pear psylla with the same recommended application time.
  • 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.



Thinning


Apple Fruitlet Thinning (Advance Notice)

General Comments:
  • The timing of chemical thinning is based on the average size of the king fruitlet. The size of the side fruitlets is irrelevant. After petal fall, fruitlets typically grow about 1 mm each day in average temperatures. Chemical thinning occurs when king fruit are 5 to 18 mm in diameter and is most effective from 7-12 mm. 

    Recommendations:

    • Research has demonstrated that there is a recommended crop load associated with trunk diameters of young apple trees in high density systems. Our ideal crop load for Honeycrisp based on local research is 6 fruit/cm². Our ideal crop load for Gala is 6 fruit/cm² or if you would like larger fruit then 4 fruit/cm². Refer to Table 2 to see how the recommended crop load relates to tree trunk diameter measured about 10 cm above the graft union. For large, old trees, measuring the size of typical limbs might be more appropriate.
    • During the thinning window I will comment on the suspected carbohydrate status of the trees. (The consistent cloudy weather suggests trees are currently in a carbohydrate deficit.)
    • The optimal temperature for thinner activity is between 21-24°C. In cooler temperatures the thinning activity is less and in warmer temperatures the thinning activity is more. At thinning time, consider the weather and then you may adjust your usual rate +/- 20%. 
    • Have a block with trees on and off? Thin according to trees with the heaviest fruit set. Trees with less flowers are less likely to thin anyway because holding onto well-supplied fruitlets.
    • 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).

    Table 2: The recommended crop load for young high density apple trees based on trunk diameter. Honeycrisp and Gala trees can have 6 fruit/cm² or if you would like larger Gala fruit then 4 fruit/cm². For the chosen column, note how many fruit can be cropped based on trunk diameter. For example, at 6 fruit/cm² , a Honeycrisp tree with a 2" trunk diameter would have 122 fruit.




    Pear Fruitlet Thinning (Advance Notice)

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



    Horticulture


    Suckers

    • Suckers are becoming quite strong by now and would be resistant to sucker control using contact herbicides if suckers are taller than a few inches in height. Remove woody suckers by cutting or ripping to avoid resource competition, the risk of systemic herbicide uptake, harbouring pests like fire blight shoot blight.
    • If suckers are more prevalent because of exposed roots due to frost heaving, try to hill the soil to cover the roots.

    Grafting

    • Bark is slipping and grafting has begun.
    • The local business Maple Grove Nursery made a video last year about top working young trees. The video is available on their website called, “Reworking Young Orchard Trees (slow motion)” https://www.maplegrovenursery.ca/grafting-supplies

    Mowing

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

    Root Pruning

    • If you are considering root pruning to reduce excessive vigour, the window of timing is from bloom and up to two weeks later. An article from Michigan State was recommended by a local grower.

    Pruning and Training

    • Pruning has been delayed this year and it might not be possible to prune all blocks. After bloom, making large pruning cuts can weaken trees so you may wait for summer pruning to open up tree canopies. If the orchard is near the end of its life then there is not as much concern about 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).

    Weed Management

    • When burndown products are needed, consider that Reglone works in cool and cloudy conditions whereas Ignite requires warm and sunny conditions. Also, applying Ignite when leaves are wet is ineffective.
    • 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.

    Nursery Trees

    • This week is a good opportunity for a residual herbicide in nurseries prior to the upcoming rain.
    • Treat for tarnished plant bug and green aphids.
    • Consider staking soon to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
    • Remove rootstock leaves when they are tender and before shoots become woody. 
    • For bench grafts, leave some shoots on the rootstock to feed the scion as the callus tissue develops. Locally, rootstock leaves have been stripped when the scion has 8-10 leaves. Early in the season, leave at least an extra scion leader for insurance.
    • 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


    Popup Fire Blight Webinar

    Join me tomorrow on Wednesday, May 28 at noon. A blossom blight risk is forecast for this week so let’s review the disease risk situation together. We will consider answers to common questions including the influence of first bloom dates, the activity of antibiotics prior to rainfall, how to think about modeled risk, and when bacterial growth happens. We will also discuss trauma blight situations and why open wounds have an immediate risk even in cold temperatures. This review will help you consider key management timings with antibiotics.

    There are pesticide points! It is NS Environment Course T2619 worth 0.5 points in Pest Management. No need to register, just join us using this link and passcode: https://perennia.zoom.us/j/89038883166 (Passcode: 680206)


    Marbicon Pesticide Courses

    In-person full-day pesticide applicator exam preparation courses will be offered in mid-June by Marbicon.
    • Jun 9 - Mon – Truro – Colchester Legion Stadium Lounge, 14 Lorne St.
    • Jun 11 - Weds – New Germany – Anglican Hall, 5311 Highway 10.
    • Jun 13 - Fri – Berwick – Berwick Legion Hall, 232 Main St.
    Email/call Jim ( marbicon@eastlink.ca ) or 902-538-7101 to pre-register.
    Pre-exam courses are $130 including HST.
    Instruction starts at 9:00. Expect to be done around 4:00-4:30.
    People sitting in for 5.0 recertification points pay $120 including HST.
    Points people can expect to be done around 3:15.
    Doors open at 8:30 am for registration & settling in. 
    Pay at the door or by corporate/government purchase order.
    If paying by e-Transfer, please add for whom and for which date.
    Sorry, no Visa, MC, or Debit.
    HST is included in the above prices. 
    Food & drink is on your own. 
    A course manual will be provided. Bring a pen.

    NOTE: Pesticide exams are normally written online, NOT at this course. 
    Contact NS Environment for further details on writing the exam.
    A course is not required before challenging the pesticide exam, but it usually helps.

    Cash or cheques (payable to Marbicon Inc.) or e-transfer to marbicon@eastlink.ca
    Contact Jim Jotcham at marbicon@eastlink.ca or at 902-538-7101 for more details and/or to pre-register. 



    Pest Management Guide

    We offer printable PDFs of the guides from our website:

    Online pest guides are also available without login (https://www.perennia.ca/pest-guides/) and with login on your Perennia account (https://www.farmdatatools.perennia.ca/).  Using the online tool you can filter for organic and conventional options, search for key information, and sort based on information of interest. 



    This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Larry Lutz, Danny Davison, Suzanne Blatt, Joan Hebb, Harrison Wright, Shawkat Ali, Ian Willick, and Ariana Willick.

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

    By Michelle Cortens at May 27, 2025
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