Orchard Outlook Newsletter Vol. 23, No 10

Tuesday, June 20, 2023

Today's newsletter reports fruitlet sizes ranging from 12.4 mm to 18.5 mm with only a limited opportunity to finish thinning late varieties or in late regions. Cell division is occurring right now and the forecast heat will help to encourage greater potential fruit size. We discuss a serious tank mix incompatibility when using Captan solupacks and boron. In terms of diseases, please check new plantings for open blossoms because bacterial levels are expected to be high beginning on Thursday, June 22 in conjunction with the heat. We review look-alikes that can be mistaken for fire blight blossom blight. Thanks to the ongoing commitment of the Orchard Outlook Committee members. 

Table of Contents:

  • 2023 Degree Day Accumulations
  • Apple Bud Growth
  • Apple - Scab
  • Apple - Fire Blight Blossom Blight
  • Fire Blight - Infection Management
  • Apple - Fire Blight Look-Alike (Blossom Blast and Sap Guttation)
  • Apple - Black Rot
  • Apple - Brooks Spot
  • Apple - Flyspeck and Sooty Blotch
  • Apple Insects
  • Codling Moth: Degree Day and Treatment Timing Predictions
  • Pear Insects

Fruitlet Thinning

  • Apple Fruitlet Thinning
  • Defruiting Young Trees

  • Solstice Reminders
  • Weeds and Root Sucker Management
  • Cover Crops
  • Mowing
  • Pruning and Training
  • On-farm Nursery

Events and Notices

  • Spotted Lanternfly - Invasive Species
  • Funding Programs

Pest Management Guides 2023

  • Decision Tables
  • Guides



2023 Degree Day Accumulations

Over the last week there has been very little change in the degree day accumulations relative to average. The trend of cumulative degree days being below the 5- and 10-year averages continues for plant and insect development (Figure 1). So far the month of June has been about 2°C below average. 

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 19 for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 9% less plant development heat units compared to the 5-year average, and 10% less compared to the 10-year average.
  • Approximately 17% less plant development heat units compared to 2022, and 22% less compared with 2021.
  • Approximately 16% less insect development heat units compared to the 5-year average, and 17% less compared to the 10-year average.

Tree Growth

Apple Bud Growth

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on June 19, I measured twenty king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 18.5 mm, Honeycrisp measured 16.2 mm, and Ambrosia measured 12.4 mm (Figure 2). Over the last week, Ambrosia fruitlets grew at a rate of 0.7 mm/day and Idared and Honeycrisp grew at a rate of 0.9 mm/day.

Figure 2: Bud growth in an early region on Middle Dyke Road in Kentville on June 19. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Why are apple fruitlets growing about 1 mm in diameter each day? Because the cells that make up the fruit are currently dividing to create millions of cells that steadily increase the size of the fruit. This period of rapid cell division happens after fertilization and up to about 3 to 5 weeks after bloom. The cell number is then set and the remainder of fruit growth happens because the given cells expand. Several research studies have concluded that cell division controls the final fruit size. At harvest the small fruit have similar cell size as large fruit but with fewer total cells.

We cannot control the weather but it is helpful to understand its influence. Cool weather is expected to prolong the cell division phase but less cell division will occur. Alternatively, warm weather results in a short cell division phase with numerous cells. So far the weather has been cool but the heat in the forecast would be welcome to encourage more cell division for greater potential fruit size.


Apple – Scab

Table 1: Primary apple scab infection events in Kentville from June 14 to June 20, 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.


  • Ascospore maturity reached 100% and theoretically the final spores were released in the June 14 rain. Models are not completely accurate so wait 2 weeks after ascospores are depleted before you lengthen your spray intervals. Also note the risk of summer diseases if spray programs are stretched to the limit.
  • Where primary lesions are present, secondary infections have been occurring and will continue during wetting events of sufficient duration. The minimum wetting required for secondary infections is 3 hours less than the wetting required for primary infections.
  • 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.
  • Folpan/Follow should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting.
  • The 2023 Fungicide Decision Table can be used to compare fungicide products.

Tank Mix Incompatibility - Solupacks/Water Soluble Packaging (WSP)
A grower has shared their cautionary tale with solupacks to help prevent the trouble for everyone else. Captan WSP was put into the tank and when they thought the packaging was fully dissolved they added boron to the tank. They had three main filters and each one was plugged solid. They lost a full day with one sprayer because everything had to be taken apart and flushed (Figure 3). This story is shared to prevent people from thinking that it won't happen to them. Sometimes it works if sprayers have enough agitation but when it doesn't work, it fails terribly. Do not put boron in the tank when using solupacks/WSP!

Figure 3: Clogged filters from using Captan WSP and then adding boron to the tank. Photos submitted.

Apple – Fire Blight Blossom Blight

Check new plantings for open blossoms. Bacterial levels will be high and approach the threshold level of 100 beginning on Thursday, June 22. Due to the heat, bacterial growth could be rapid on newly opened flowers. Multiple applications of antibiotics may be necessary during the expected period of heat.

  • Rain is in the forecast and wetting will trigger an infection. Wetting can be a heavy dew, 0.25 mm of rain, or high water volume sprayed on open flower blossoms.
  • When the EIP is high, do not spray high water volumes on trees in bloom unless an antibiotic has been applied.
  • Kasumin is best applied in the evening due to UV sensitivity and at least a few hours before any rain. Streptomycin may be applied at least a few hours prior to rain. 
  • Ideally you can monitor your own farm-specific conditions and improve your management decisions using PomeBlight that was developed for Nova Scotia apple and pear growers.

Fire Blight - Infection Management

Blossom blight infections have not been reported yet as far as I am aware. However, it may be possible that any infections from May 28 could be showing symptoms. 


  • As soon as you find fire blight infections, an application of Apogee/Kudos (prohexadione calcium) can help to suppress the progression of infection that buys you time for cutting it out. Use a lower rate if trees have not filled their space or the full rate if tree growth is not an issue.
  • Do not break off branches with fire blight infections as you navigate the orchard. Research shows that the bacteria becomes systemic in the tree because branches are not adequately removed. There are then a high number of new infections and significantly more canker tissue and cankers on structural wood. 
  • Prune out fire blight infections on young trees in the current year, don't wait for winter.
  • Remove fire blight strikes at least 2-4 ft below active infections to remove the leading edge of the bacteria. The younger the tree, the deeper the cut. Being aggressive at the first sign of symptoms will help prevent the re-occurrence of symptoms and the need for continuous cutting back. Repeat tree inspections.
  • If you feel confident that you can monitor the formation of a canker on a stub cut for later removal, then a stub cut may be appropriate. A 4-inch stub cut causes a canker to form on the stub before reaching structural wood like the leader of the tree. However, do not forget to remove the stub because otherwise the canker will serve as a source of bacteria. Mark the tree for revisiting.
  • Cut out infections when a period of 2 dry days are in the forecast. Leave prunings in orchard laneways to let dry thoroughly for several weeks. If cutting a whole tree consider letting it dry while attached to the trellis. Don’t make piles that will prevent the wood from drying. 

Apple – Fire Blight Look-Alikes

Fire blight is a serious disease that warrants quick management action and can have a major economic impact. So if you are unsure about the symptoms you observe, please let me know and I can take a look and lab testing is also available. There are diseases and physiological processes that can mimic fire blight symptoms.

Pseudomonas Blossom Blast
This year, there have been some cases of collapsed apple blossoms caused by the bacteria Pseudomonas syringae and the infection is known as blossom blast (Figure 4, top). Blossom blast can also affect pear. The infections were in low lying areas that experienced freezing conditions during bloom, which tends to be associated with infection by Pseudomonas. Our Plant Health Lab confirmed the infection by growing the bacteria and then confirming that it glows under UV light (Figure 4, bottom). Ooze is never present for blossom blast infections and it is most likely to occur during cool and wet bloom periods.

The Pseudomonas blossom blast infections do not extend more than 5 cm into the spur. Prune the infections 15 cm below the symptoms and remove infected tissues from the orchard. The disease will not spread to new infection sites after bloom.

Figure 4: Top: Blossom blast infections on apple clusters caused by Pseudomonas observed in June, 2023. Bottom: Bacteria grown (left) and observed glowing under UV light (right). 

Sap Guttation
There is a phenomenon when sap flow can leak out of pores on young trees known as guttation (Figure 5, left). In this case, the sap is watery unlike the sticky globs of fire blight. The phenomenon has been observed locally several times in the past and it is believed to happen when the plant tries to restore balance in water content. We may expect to see guttation this year because of cool conditions that slow growth but plenty of water supply. 

Finally, there are fungal infections like nectria twig blight that can resemble fire blight (Figure 5, right). In the case of fungi, they tend to kill the shoots from the base to the tip. 

Figure 5: Watery sap can run out of pores in the wood when sap flow seems to exceeds growth during cool conditions (left). Fungal infections can mimic fire blight but typically kill the shoot from the base to the tip (right).  

Apple – Black Rot


    • The highest risk of infections is between petal fall and 4-6 weeks after bloom.
      • A 10 hr wetting period at 16°C to 32°C allows infection. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.
      • The optimum temperature for infection is 20°C to 24°C. 
      • There are few management options to cover such a long risk period. Captan has activity but note the REI for orchard activities. Merivon has activity but any group 7 + 11 product should not be used more than 4 times each year.  Folpan may have activity but it should not be used until 30 days after bloom.
    • Minimize lenticel cracking by:
      • The fruit cuticle is sensitive at this stage. Be cautious with spray mixtures (calcium, foliar nutrients).

    Apple - Brooks Spot

    Brooks spot is caused by a fungus that creates sunken, dark green lesions on the fruit. It is a minor disease that has been an issue on Honeycrisp in the past. The symptoms of Brooks Spot can resemble lenticel breakdown and bitter pit which are also common on Honeycrisp. Include a product for cover sprays that is labelled for brooks spot such as Inspire Super and Aprovia Top (or Folpan 30 days after petal fall).

    Apple - Flyspeck and Sooty Blotch

    These summer diseases develop on the surface of the fruit in midsummer until harvest. They are caused by fungi that overwinter in dead twigs and the fungi tend to cause more infections under conditions of moderate temperature, high humidity and rainfall. Include a product for cover sprays that is labelled for flyspeck and sooty blotch such as Captan, Maestro, Inspire Super, Aprovia Top, Allegro, Pristine, and Merivon (or Folpan 30 days after petal fall).


    Apple Insects

    Choose insecticides by considering what you are targeting and what the products control. Often your hardest to control pest will determine what you need to use, then check the label of that product for all pests that are also controlled by the product. Please refer to the 2023 petal fall insecticide decision table for a quick overview of your choices for apple trees.

    (Click on the image to access the full size PDF file for printing)

    Codling Moth: Degree Day and Treatment Timing Predictions

    The biofix dates for this season are June 2 for early and June 8 for late regions determined by Erika Bent, APM. Jeff Franklin, AAFC, ran the degree day model to predict when degree day thresholds will be met for treatments. The models were run on Monday, June 20 with a degree day threshold of 10°C.

    Please Note:
    If you are using egg hatch products, codling moth do not lay eggs during cool nights. Timing of products this year might not be straightforward. Males do not fly or mate when temperatures at dusk are below 15°C. Therefore, the risk to fruit is low during these cool dusk temperatures. 

    Codling Moth Treatment with Egg Hatch Products
    Assail, Calypso, Delegate, Intrepid, Altacor, and Exirel
    Timing: The treatment timing for egg hatch products is 100 degree days Celsius from biofix.
    Prediction: According to the current forecast, the 100 degree day threshold is expected to occur by June 23 for early regions and June 24 for late regions.

    Codling Moth Treatment with Organophosphate
    Caution: Newly amended labels came into effect on October 30, 2022. Now all hand thinning activities must be completed prior to application. No hand thinning can occur on trees treated with Imidan.
    Timing: Control of codling moth with Imidan is typically slightly later at 140 degree days after biofix.
    Prediction: According to the current forecast, the 140 degree day threshold is expected to occur by June 28 for early regions and June 29 for late regions.


    • These are approximate dates. The North Medford region is typically cooler by a day or two. 
    • Codling moth lay eggs and hatch over a period of time. Late application may miss the first egg hatch and could result in a few codling moth entries. 
    • A heavy rain just after application is more concerning than a late application because heavy rain would wash off and reduce the residual life of the insecticide. 
    • Approximately a week after application of an OP insecticide, clean out the trap and start monitoring the trap. The capture of an additional 10 or more moths would indicate that a second treatment is required.

    More Insects:

    • Monitor for white apple leafhopper. Sevin XLR applications for thinning in mature blocks will control leafhopper but monitor non-bearing plants for leafhopper. If treatment is required, a neonicotinoid, Sivanto Prime, or Exirel would control leafhopper.
    • Monitor for rosy apple aphid and green aphid in young trees and nursery plantings where feeding can disrupt shoot growth. If leaves are curling high, high water volumes are needed for effectiveness. Green aphid will move back into orchards that were treated previously so continue to monitor. Assail and Calypso also have activity on codling moth, apple maggot and leafhoppers. Be cognizant of REIs if installing trellis.
    • Second generation veafrollers and codling moth may be less likely due to the lack of heat observed so far this year.

    Pear Insects

    • Pear Psylla: Refer to the management guide for product options.
    • Pear rust mite: Pear rust mite can go unnoticed until heavy russeting extending from the base to the top of the fruit. Growers that apply Agri-mek for pear psylla control would also obtain pear rust mite control. Nexter or Envidor would be other options for pear rust mite control.
    • Codling moth: Refer to the above degree day timing given for apples.

    Fruitlet Thinning

    Apple Fruitlet Thinning

    • The next few days are the final opportunity for chemical thinning on late varieties and/or in late regions. The forecast heat will certainly help if thinners are applied beforehand.
    • Most farms started thinning only about 8-9 days ago. Usually it takes at least 7 days to notice the effect of a thinner. The size difference among the fruitlets in the cluster will start to differ more greatly. The fruitlets growing at a slow rate will eventually fall off. 


    • Late applications of Fruitone/Maintain may lead to more mummy fruitlets and increase the risk of black rot next year.
    • MaxCel/Cilis Plus may be applied when the average king fruit diameter is up to 15 mm and it can contribute to increased fruit size. Especially with the forecast heat, it may be a good option for late thinning this year.
    • Earlier this year I put together a summary of Nova Scotia crop load management studies on Honeycrisp and Gala. For Honeycrisp, using Fruitone + Sevin is our industry standard and showed fairly consistent local results. For Gala, Fruitone alone and Fruitone + Sevin decreased fruit set and crop load, usually without increasing fruit size. For Gala, the combination of MaxCel + Sevin thinned and increased fruit size. Contact me if you need help selecting a rate. 
    • 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.
    • When using Sevin in high density orchard do not exceed 3.22 L of product/ha/year. In low density orchard do not exceed 2.15 L of product/ha/year. Sevin is a thinner but note that it is also an insecticide and care should be taken to avoid contact with bees.

    Defruiting Young Trees

    • 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 (avoid Gala, Ambrosia, Golden Delicious, Red Delicious). 
      • 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. A second application will likely still miss some fruit so consider that hand thinning may still be required.
    • Choosing to use Fruitone (NAA) in this mixture instead of MaxCel will result in chemical pinch at the terminal bud that stunts growth.
    • Using currently available products, the amount of product that would be needed to completely defruit trees in our climate would likely negatively affect tree growth. Therefore, expect that hand thinning will still be required.


    Solstice Reminders

    • Top dressing is not recommended after the end of June. Late release will prevent trees from hardening off before the winter. 
    • Around July the trees are storing reserves in the roots for next year’s growth. When they are storing reserves, late glyphosate applications can be damaging if taken up by root suckers and transported to the root system. Avoid the risk by avoiding glyphosate applications after the end of June.

    Weeds and Root Sucker Management

    • Note that 2,4-D has an 80-day PHI. Eighty days from now is September 8.
    • Broadcasting grass seed is not recommended for establishing grass in the alleyway. Direct seeding is recommended to confine the grass seed to the alleyway and avoid spread to the tree row. The herbicide gramoxone used to provide good control of bluegrass species but post-emerge products for grass control are now limited.
    • Remove root suckers. Suckers compete with the main tree for water and nutrients. They harbour pests, and they are an entry point for fire blight. Pull or break off suckers because otherwise cutting them would let them rebound. AIM herbicide is registered for control of suckers but avoid drift onto young trees and apply only near mature brown bark.
    • Please note there are local reports that the new rootstock G890 has plenty of root suckers and they can show up about 4 ft from the tree.


    • Consider if nitrogen as soon as possible if tree foliage appears pale. Leaching may have occurred during recent heavy rains, especially on sandy soils. Apply a half application of granular nitrogen fertilizer if trees are looking chlorotic. 
    • This year's degree days are tracking similar to those of 2019 and soil temperatures are similarly cool at 30 cm depth. Nutritional deficiencies were observed in 2019 so it is a possibility to keep in mind.

    Cover Crops

    • Perennia has a series of videos about cover crops by Sonny Murray and Rosalie Gillis-Madden that can be accessed from our website.
    • Summer grasses such as pearl millet and sorghum-sudangrass that have been growing in popularity lately can be planted from mid-June until early August.


    • Keeping the orchard floor cover mowed pre-bloom will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.
    • Mowing and herbicide strips help to prevent issues with two-spotted spider mite (John Michael Hardman).

    Pruning and Training

    • Young trees are gaining foliage that turns them into a sail in the wind. It is becoming increasingly important to install trellis and tie trees. Work in the trees during dry weather and 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).
    • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Prior to deer fencing, the product Bobbex may be used as a deer repellent but it must be applied proactively and requires frequent application to new growth and after rainfall. Ideally, install deer fencing the year prior to planting.

    On-Farm Nursery

    • Consider staking to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury. Tying may be considered soon.
    • Monitor for green aphids.
    • 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!

    Events and Notices

    Spotted Lanternfly - Invasive Species

    The Spotted lanternfly (Lycorma delicatula) is a plant hopper indigenous to parts of China and Vietnam. It was introduced to Japan by accident in 2009 and has since spread to the United States. It was detected in Pennsylvania in 2014 and has spread to several states, some of which boarder Southern Ontario, Canada. The Canadian Food Inspection Agency have now included this on their invasive species list, and we need to be on the look out for this pest as it can be devastating to our grape, pome fruit and soybean industries. A link to the Canadian Food Inspection Agency, spotted lanternfly fact sheet has been provided. Please be on the lookout and notify Perennia specialists or the NSDA - Plant Protection Coordinators if you have any concerns. Spotted lanternfly (Lycorma delicatula) - Fact sheet - Canadian Food Inspection Agency (canada.ca)

    Funding Programs

    Please check the NSDA website for all programs under the Sustainable Agricultural Partnership: https://novascotia.ca/programs/. As this is a new 5-year agreement moving into the Sustainable Canadian Agricultural Partnership programs, producers will need to fill in a new Program Funding Registration Form.

    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: Joan Hebb, Jeff Franklin, Larry Lutz, Mathew Vankoughnett, Suzanne Blatt, Danny Davison, Ian Willick, Heather Rand, Jeff Wentzell, Karen Burgher, Keith Fuller, and Jill MacDonald.

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

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