Orchard Outlook Newsletter Vol. 23, No 8

Tuesday, June 6, 2023

Today's newsletter reports fruitlet sizes ranging from 5 to 8 mm that might stir thoughts of thinning, but please note the lack of thinning activity expected in cold weather. Chemical thinners are discussed, noting that temperatures at application should be at least 16°C to 18°C depending on the product. In terms of diseases, a heavy apple scab infection occurred and primary infections are still possible. In the cool temperatures, fire blight blossom blight risk is low on rattail flowers and flowering young trees but stay tuned. Thanks to the ongoing commitment of the Orchard Outlook Committee members. 

Table of Contents:

  • 2023 Degree Day Accumulations
  • 2023 Precipitation
  • Apple Bud Growth
  • Peach Tree Observations
  • Apple - Scab
  • Apple - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Apple Insects
  • Pear Insects

Fruitlet Thinning

  • Influence of Weather
  • Apple Fruitlet Thinning
  • Defruiting Young Trees
  • Pear Fruitlet Thinning

  • Cover Crops
  • Mowing
  • Pruning and Training
  • On-farm Nursery

Events and Notices

  • Funding Programs (*new: Agricultural Clean Technology Program)

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 because the extreme heat and extreme cold averaged each other out. Cumulative degree days continue to be slightly behind the 5- and 10-year averages for plant and insect development (Figure 1). According to Environment and Climate Change Canada seasonal forecast prediction, our temperatures this season are expected to be above average.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 5 for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 8% less plant development heat units compared to the 5-year average, and 10% less compared to the 10-year average.
  • Approximately 19% less plant development heat units compared to 2022, and 23% less compared with 2021.
  • Approximately 11% less insect development heat units compared to the 5-year average, and 15% less compared to the 10-year average.

2023 Precipitation

The Kentville weather station recorded 118.2 mm of rain over the last three days and on-farm weather stations recorded even more (notably Grand Pre at 159 mm). Although the year 2023 now has an above-average accumulation of precipitation, there was a deficit in spring that has now been made up all at once (Figure 2). Some runoff was reported during the heavy rain rate.
Figure 2: Both rainfall and the rainfall equivalent from snow at the Kentville Research Station from 2020 to 2023 up to June 6. Provided by Jeff Franklin (AAFC).

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 5, I measured twenty king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 8.1 mm, Honeycrisp measured 6.6 mm, and Ambrosia measured 5.3 mm (Figure 2). Typically fruitlets grow about 1 mm each day but I suspect that the cold temperatures may cause a delay in growth. In some cases, there appears to be more rattail bloom than usual. 

Fruit set looks good from what we can tell but we encourage monitoring in your own orchard. Some king fruitlets are missing due to winter injury but the loss does not appear to be extensive. Terminal shoots on Honeycrisp are around 8 cm in length.

Figure 2: Bud growth in an early region on Middle Dyke Road in Kentville on June 5. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Peach Tree Observations

Early observations suggest that the wood on peach trees is healthy following the cold winter temperatures. Pruning cuts on old and young wood are not showing blackened xylem (Figure 3). Please let me know if you observe blackened wood. Even though wood is healthy, some trees are certainly susceptible to decline. In case of an assistance program, please keep track of any extra labour spent tending to trees with winter injury and if any trees are pulled out. Also note that this year's limited vegetative growth reduces the area to initiate buds for next year's crop. 

Figure 3: Healthy young and old wood on peach trees in 2023 with the absence of blackened xylem.


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 30 to June 6, 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 is currently at 99.4%. According to the forecast, total seasonal ascospores are expected to mature to 99.9% by this coming Saturday.
  • Ascospores responsible for primary infections are still available for release. 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.
  • 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. 
  • 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. Remember that there is also a 2023 Fungicide Decision Table that can be used to compare fungicide products.

Apple – Fire Blight Blossom Blight

Current and Forecast Blossom Blight Risk
  • Industry alerts will continue while rattail bloom and bloom in young plantings is present.
  • 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.
  • The risk of bacterial growth on flowers is low for now and into the foreseeable future. Stay tuned because predictions can change on short notice.


  • Monitor alerts for varieties considered susceptible to fire blight like Paula Red and Gala that may still have blossoms. Their long period of bloom with flowers opening successively is in part responsible for the increased risk of infection. Do not underestimate the risk of infections on late flowers.

Fire Blight - Shoot Blight Management


  • 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.
  • 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 – 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. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.
    • Black rot can survive on prunings. Flail mow prunings in row middles where they will degrade more quickly.
    • Minimize lenticel cracking by:
      • The fruit cuticle is sensitive at this stage. Be cautious with spray mixtures (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 risk of foliar nutrients is not worthwhile at this stage.


    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)

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

    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

    Influence of Weather

    Temperature and sunlight on the 2 days before and more importantly the 4 days after applying thinners determine thinner response. The relationship has been explained in terms of the carbohydrate status of the tree. During sunny days the tree is photosynthesizing unimpaired and when matched with cool nights (<18°C) it is respiring slowly, meaning carbohydrates are plentiful. Reversing the conditions, cloudy days impair photosynthesis and when coupled with warm nights the respiration uses many carbohydrates making them in short supply, causing stress to weak fruitlets.
    • Temperature is a very important factor this year. For now and the next few days, temperatures are too cold to expect thinning activity from available products.
    • Fruitlets typically grow about 1 mm each day in average temperatures but I suspect that growth will be slowed in the cool temperatures, hopefully gaining extra time for thinner application.
    • 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).

    Apple Fruitlet Thinning

    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.

    Fruitone L:
    • Strong thinner that is very effective in Nova Scotia and is rate-responsive.
    • 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.


    • Trees are currently expected to have a carbohydrate surplus that will make fruitlets difficult to thin. In these cool conditions we typically struggle to see efficacy from MaxCel/Cilis Plus.
    • In a block that has trees that are on and off, thin according to the trees with the heaviest fruit set. You want to adequately thin the trees with heavy set and the trees with less set will be less likely to thin anyway (holding onto strong, well-supplied fruitlets).
    • 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.
    • 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

    • As mentioned above, conditions are currently too cold to expect adequate thinning from chemical thinners. Wait for more heat.
    • 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.

    Pear Fruitlet Thinning

    • The Maxcel thinning window is 8-14 mm. Wait for more heat.


    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.
    Figure 4: Summer grasses pearl millet (left) and sorghum sudangrass (right). Photos taken on Aug 23, 2022.


    • 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

    • Pruning 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.
    • Avoid aggressive pruning to avoid weakening trees. 
    • 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).

    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 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. Encourage the growing point to be successful!

    Events and Notices

    Funding Programs

    • The Agricultural Clean Technology Program - Adoption Stream (Act-A) opened on June 1 and is accepting until June 22 or until demand exceeds available funding. Therefore it is recommended that applications be made ASAP. The program supports the purchase and installation of clean technology or equipment upgrades that will reduce greenhouse gas, fertilizer and methane emissions. For more information, visit the AAFC website application page.
    • 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: Jeff Franklin, Joan Hebb, Heather Rand, Suzanne Blatt, Danny Davison, Jeff Wentzell, Karen Burgher, Larry Lutz, Dustin MacLean, Keith Fuller, Ian Willick, Shawkat Ali, and Jill MacDonald.

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

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