Orchard Outlook Newsletter Vol. 24, No 8

Tuesday, June 4, 2024

Today's newsletter reports average king fruitlet diameters on varieties ranging from 5.8 mm to 9.5 mm... so welcome to the window of opportunity for chemical fruitlet thinning! This week's temperature forecast is currently showing ideal weather for thinning and the trees are expected to have a slight carbohydrate surplus; the implications on chemical thinning are discussed. In terms of diseases, primary apple scab infections are still possible but the end is in sight. We discuss Sharda Captan to clarify any confusion about product rates. Please be aware of the presence of rattail flowers and flowers on young trees and develop a strategy because the risk of fire blight blossom infection approaches late this week. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2024 Degree Day Accumulations
  • Precipitation
  • Apple Buds
  • Pear and Stone Fruit Buds
  • Apple - Scab
  • Apple - Powdery Mildew
  • Fire Blight Prevention
  • Apple and Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Apple Insects
  • Stone Fruit Pests
  • Pear Insects

Fruitlet Thinning

  • Apple Fruitlet Thinning
  • Defruiting Young Trees
  • Pear Fruitlet Thinning

  • Cover Crops
  • Grafting
  • Mowing
  • Weed Management
  • Pruning and Training
  • Nursery Trees

Events and Notices

  • 2024 Virtual Orchard Meetups Series

Online Pest Management Guide



2024 Degree Day Accumulations

The degree day accumulations for base 5°C plant development and base 10°C insect development are still slightly more than the 5- and 10-year averages (Figure 1). 
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 3 for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 11% more plant development heat units compared to the 5-year average, and 10% more compared to the 10-year average.
  • Approximately 18% more plant development heat units compared to 2023, and 3% less compared with 2022.
  • Approximately 14% more insect development heat units compared to the 5-year average, and 8% more compared to the 10-year average.


Throughout the months of April and May the Kentville area has received a total of 84 mm of rain which is about half of average and therefore we are experiencing a precipitation deficit this spring.

Bud Development

Apple Buds

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on June 3, ten king fruitlets of each of the following varieties were measured to get a rough average (size of side fruitlets is irrelevant). The Idared measured 9.5 mm, Honeycrisp 7.0 mm, and Ambrosia 5.8 mm (Figure 2). 

Typically fruitlets grow about 1 mm each day in average temperatures. Growth was slowed to 0.5 mm/day during cold temperatures over the last week. Early varieties are still within the thinning window of opportunity but action should be taken soon. Refer to the thinning section later in the newsletter for more information. Note that rattail bloom is showing up on many varieties and young trees are in bloom (Figure 3).

Although pollination weather appeared to be excellent, not all fruit have set. Some of the side fruitlets can be easily dislodged at this point showing that they have not set. It may be that daily maximum temperatures were too high for excellent fertilization or that the snowball bloom caused competition between the flowers. Regardless, in most situations there should still be plenty of fruit considering that trees need to set only 5% of flowers for a commercial crop.

Figure 2: Fruit bud development in an early region on Middle Dyke Road in Kentville on June 3. Shown from left to right: Idared (9.5 mm), Honeycrisp (7.0 mm), and Ambrosia (5.8 mm). The king fruitlet is measured to represent fruit stage for thinning and the size of the side fruitlets is irrelevant.

Figure 3: Photos taken on Monday, June 3 show rattail bloom and bloom on young trees.

It has been noted that stems on Gala look especially long this year. The phenomenon may not have any practical implications but in case you're curious, it could be related to chilling experienced before bloom. Ian Willick explains that in certain tulips the stems elongate in response to low temperatures prior to bloom. This is just a theory as it relates to apple stems but may offer some explanation.

Pear and Stone Fruit Buds

Yesterday on June 3 at an early region in Greenwich, the pear buds measured 10.4 mm (Figure 4). Stone fruit are beyond shuck fall with measurements of peach 1.5 cm and European plum 1.2 cm.

Figure 4: Bud development in an early region in Greenwich on June 3. Shown from left to right: pear (10.4 mm), peach (1.5 cm), and European plum (1.2 cm).


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 28 to June 4, 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, total seasonal ascospores are expected to mature to 100% on Saturday, June 8 and then a wetting event would need to release the final spores. Therefore, primary infections are still a risk according to the model and leaf tissue should stay protected on 5-7 day intervals. There is still some time before it is safe to reduce fungicide spray intervals. Models are not completely accurate so wait 2 weeks after ascospores are depleted.
  • Some of you may have questions about using Sharda Captan 48 that is a liquid product with a 48% content of the active ingredient captan. If you usually use 3 kg/ha of Captan 80% (2.4 kg of active ingredient) then you would need 5 L/ha of Sharda Captan (2.4 kg of active ingredient) to be equivalent. The Sharda label allows up to 5 L/ha per application. Please note that this liquid format might improve uptake and also increase the risk of leaf injury. You may want to be especially careful with tank mixing especially if you are using foliar nutrients that are also formulated for increased uptake.
  • Let's revisit some considerations for product options at this time of the year:
    • Captan may be used as long as it is not applied within 7-14 days of an oil such as Agral 90 (worse if applied after oil that preconditions leaves). The REI for hand thinning fruit in high-density systems is 15 days and in low-density systems it is 24 days. The product has activity on summer diseases. For high density, do not use more than 10 applications per year and for low density do not use more than 2 applications per year.
    • Allegro may be applied as long as oil has not been applied within 3 days (including Fontelis and Agral 90). The REI is short at 24 hrs. 
    • Do not apply: Folpan/Follow and Syllit should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting. 
    • Buran may be considered again. But remember that the product is registered for only suppression of apple scab and must be used post-infection only. Summer disease control is not likely strong.
    • Note that single site products in group 3 are not expected to provide control of apple scab due to resistance. For other single site products, check the label for rates required for apple scab control because for Luna Tranquility the high rate is needed unless it is tank mixed with another product for scab control.
    • Several of the single site products do not have activity on scab after petal fall (fruit scab). Such products include Senator, Fullback, Nova, Cevya, Aprovia, Sercadis, Excalia, Scala, and Vangard.
  • Pears: For pear scab, Allegro and mancozeb are NOT registered uses. Captan may be used 2 times for low density and 10 times for high density. Note that for pears, Scala and Luna Tranquility have a 72 day preharvest interval. The registered products are listed in the online guide under Tree Fruit and Pears.

Apple – Powdery Mildew

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


  • Apply a protectant during petal fall to bearing blocks with a history of powdery mildew pressure. The forecast would suggest that this week offers the opportunity for infections to happen.
  • If you're using Luna Tranquility for powdery mildew, concurrent activity for scab control is only provided at the high rate. If you're using a full rate of Nova, Fullback or Cevya, no scab activity is expected due to resistance. If using Nova, the water soluble packaging should not be mixed with oil or boron.
  • Avoid more than two consecutive applications of products with a group 3, 7, or 11. Powdery mildew resistance to group 11 products was reported in a survey done in 2013 so success is unlikely. Group M products do not have activity on powdery mildew. 
  • Buran is registered for control of powdery mildew in apples under low to moderate disease pressure and local research is ongoing. Apply with 0.1% Agral 90. This product does not have protectant scab activity so will only provide scab protection post-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.

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.
  • 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. Remember that any remaining flowers are susceptible to infection if the EIP becomes high.

Apple and Pear – Fire Blight Blossom Blight

Current and Forecast Blossom Blight Risk
  • Industry alerts will continue while rattail bloom and bloom in young plantings is present. 
  • The risk of bacterial growth on flowers is low for now but it is forecast to begin increasing. On Thursday, June 6 and Friday, June 7 the bacteria may grow to high levels. An alert email will be sent when predictions become clear.
  • 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.


    • Note that varieties known for protracted bloom like Gala still have unopened flower buds. Their long bloom period is one of the reasons why they are high risk for fire blight. Do not underestimate the risk of infections on late flowers. By the time of late flowers there is already plenty of bacteria established throughout the environment.
    • How many blooms per tree is a concern for fire blight? This could be rephrased to read, how many infections could you tolerate per tree? The answer is none.
    • Have a strategy for rattail bloom. You may pinch the flowers on dry days or rely on an antibiotic.

    Fire Blight - Shoot Blight Management


    • If you applied Apogee/Kudos during bloom, follow up with a second application applied around 14 days later. You may question if you need two applications for fire blight management. I recommend the two applications because the product has activity for three to four weeks following application and then it is degraded by the plant.
      • When you re-apply Apogee/Kudos it extends the period of activity to give season-long protection of terminal shoot growth by thickening cell walls. (A third application may be needed for very vigorous trees).
      • Two weeks are required for the product to slow growth. By making the second application two weeks after the first, the second application will become active four weeks after the first application so there is no gap in activity. Successive application will ensure that all terminal shoot growth will have thickened cell walls to slow the progression of fire blight bacteria in case blossom or shoot infection occurs.
      • The industry had high risk of infection during the full bloom period so any efforts to proactively slow fire blight infections will be worthwhile. The symptoms of any blossom infections that might have occurred around May 23 are not yet visible. Better to be safe than sorry!
    • Apogee/Kudos (prohexadione calcium) supress shoot 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.
    • 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 – Black Rot


      • Based on our limited knowledge, the highest risk of infections is theoretically between petal fall and 4-6 weeks after bloom.
        • A 10 hr wetting period at 16°C to 32°C allows infection. 
        • 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 this group 7 + 11 product should not be used more than 4 times each year. Folpan has activity but should not be applied until 30 days after petal fall to avoid russet. 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 fruit cuticle is sensitive to damage at this stage. Be cautious with spray mixtures (calcium, foliar nutrients). 


      Apple Insects

      Pesticide options for post-bloom insects are listed in the table. 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 petal fall insecticide decision table for a quick overview of your choices for apple trees.
      (Click image to access full size PDF file for printing)

      In addition:
      • The biofix date for codling moth is still in the process of being determined by Erika Bent, APM.
      • 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 water volumes are needed for effectiveness.

      Stone Fruit Pests


      • Treatment for plum curculio may be reapplied 10 days after the first application if needed.
      • 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. Note that pyrethroids are best used at moderate temperatures (20°C or less) and lose efficacy at around 25°C.
      • Plum curculio will target apples if stone fruit are nearby.
      • For stone fruit, monitor for green peach aphids and black cherry aphid.
      • Peaches are susceptible to peach scab infections from shuck fall to 4-6 weeks before harvest. Symptoms are visible on the bark. Periods of wet weather will require additional protection until 4-6 weeks before harvest.

      Pear 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 younger tissues. 
        • 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.

      Fruitlet Thinning

      Apple Fruitlet Thinning

      Please note that 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 to 12 mm.

      This year a new thinner called Accede is registered and has activity at up to 25 mm fruitlet diameter but supposedly works best at 18 mm.  Product supply is limited but you may wish to try it on a small scale.


      • 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. The danger zone is when temperatures will exceed 29°C. This week the forecast is currently moderate and within the range of ideal temperatures for thinning (nighttime temperatures are below 18°C and daytime temperatures are no higher than 26°C). 
        • Thinning may begin anytime now. The long-term forecast has been unpredictable this year and currently the next few days are a good opportunity for thinning. Next week the forecast is for rain and cool weather... but who knows!?
      • If you are concerned about overthinning, it might help to calm your fears by reflecting on the high temperatures observed in 2020 and 2021.
          • 2020: Average daytime temp was 27.9°C with two of those days (June 18 and 19) above the danger zone of 29°C. The temp got higher than forecast and it fooled us. 
          • 2021: There were also two days above the danger zone (June 7 and 8). 
        • As promised, here are some comments about the carbohydrate status of the trees this week. 
          • Due to the cool and moderate temperatures, the trees are expected to have a slight carbohydrate surplus. Due to the accumulation of resources, less competition between the fruitlets will theoretically lead to less response from chemical thinning.
          • Using this consideration of carbohydrate status, you may adjust your usual rate of Fruitone +10-20% if you need additional thinning.
        • Any chemical thinning done on Saturday, June 1 was less than ideal due to the cold weather at a high of 13°C.

        Product Overviews:

        Fruitone and Sevin are considered rainfast within 2 to 3 hours. Information varies on rainfastness, so up to 6 hours would be an even more cautious approach.

        Sevin XLR
        • Does not overthin so it is mild and reliable.
        • Undissolved Sevin remains active. Damp and drizzly weather that keeps tissue wet but does not wash off product results in more thinning.
        • Often combined with Fruitone for a synergistic effect resulting in more thinning than either product used alone.
        • Temperatures at application should be above 17°C.
        • 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.

        Fruitone L
        • Strong thinner that is very effective in Nova Scotia and is rate-responsive. Higher rates thin more.
        • Unabsorbed residue on leaves is inactivated by sunlight. Slow drying conditions cause more absorption. Therefore, nighttime applications are usually more effective.
        • Temperatures at application should be above 16°C.

        MaxCel/Cilis Plus
        • Product is most likely effective when weather conditions cause a carbohydrate deficit. The thinning effectiveness has been limited in Nova Scotia and it may be because in many years the trees are not stressed during chemical thinner application.
        • This product can be used to increase fruit size (20g/fruit) beyond the influence of thinning by stimulating cell division but the timing matters. According to research:
          • When applied at 10-15 mm, it increases fruit weight 80% of the time.
          • When applied at 5 mm, it increases fruit weight 25% of the time.
          • When applied at petal fall, there is generally no increase in fruit size.
        • Temperatures at application should be above 18°C.

        Defruiting Young Trees

        • Defruiting young trees can be accomplished with a combination of Sevin XLR at 2.5 L plus Maxcel/Cilis Plus 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 anyway.
        • 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.

        Pear Fruitlet Thinning

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


        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.


        • Bark typically slips from pink to bloom at which point grafting can begin. The local business Maple Grove Nursery made a video this 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


        • Keeping the orchard floor cover mowed to 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).

        Weed Management

        • 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.
          • Create a plan for the whole year. Put on residual products before weeds emerge and use the post-emerge products as backup.
        • If using glyphosate alone, consider coarse droplets and low pressure to reduce drift. Use Ignite during hot days in full sun if possible.
        • In young plantings, weed control is essential. If newly planted trees have received a settling rain then you may consider a residual herbicide before the next rain.
        • Understand and consider using more Venture for grass control in young orchard. Venture is slow to work (2-3 wks) but you can check for activity by removing the flag leaf on treated grass and examining the base of that shoot for rot.
        • Add Prowl H2O or Dual II Magnum to improve your grass control spectrum in young orchard. These pre-emerge products won’t work for bluegrass species however.
        • Sinbar is good for pre-emerge grasses in young orchard.
        • Lontrel is a great post-emergent for vetch, clovers, and sheep sorrel.
        • Chateau has activity on Ragweed whereas Authority does not.

        Pruning and Training

        • Start selecting strong terminals on young trees and remove competing terminals to single the tops if there are no re-entry intervals active.
        • Pruning and training practices should be done on dry and sunny days, especially in blocks with high risk of fire blight. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
        • 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 requires frequent application to new growth and after rainfall.
        • 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).

        Nursery Trees

        • Consider staking to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
        • Treat for tarnished plant bug and 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.

        Events and Notices

        2024 Virtual Orchard Meetups Series

        Every Thursday from June 6 to June 27 at 8:00 PM Atlantic time
        Since 2021, the North American Summer Virtual Meetup Program has brought together growers, researchers, extension, and government to have a conversation about important tree fruit topics. Connecting industry leaders across North America, over 20 experts are involved in these 90-minute online forums, interacting with more than 1,000 participants.

        The fourth series will focus on "Water Wisdom: Navigating Tree Fruit Production Through Drought and Deluge". Over the past decade, growers have experienced unpredictable rainfall, water availability challenges, droughts and deluges. We want to explore methods for adapting to these challenges and discuss alternatives for efficient irrigation practices, including advances in irrigation technologies that help growers produce high quality fruit.

        In addition to the primary speakers, viewers are invited to share solutions, ask questions, and interact with the specialists and grower panelists. Preregistration is not required to attend. To join, simply go to the Meet-Up Zoom Site. If you can't access, copy and paste the URL in your browser. https://bit.ly/2024-virtual-meetup


        Online Pest Management Guide

        Beginning this year, all of the pest management guides are available from an online tool. On the tool you will find guides for organic and conventional apples, pears, peaches/nectarines, plums, and sour/sweet cherries. You can search and filter the information and/or print. If you wish to view growth regulators only, then under the 'Advance Search' for 'Pesticide Type' choose growth regulator. To help you navigate the guide, we have developed a brief tutorial video as well as a how to use guide.

        This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Jeff Franklin, Larry Lutz, Danny Davison, Suzanne Blatt, Ian Willick, Joan Hebb, Shawkat Ali, Keith Fuller, Mathew Vankoughnett, and Jessica D'Entremont.

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

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