Orchard Outlook Newsletter Vol. 23, No 9

Tuesday, June 13, 2023

Today's newsletter reports fruitlet sizes ranging from 7.6 mm to 12.4 mm that are clearly in the window of opportunity for chemical thinning. The recent heat should lend support to the activity of thinners and the tree's response is not likely to be excessive. Please note that ALL regions are now at risk of blossom blight infections today on rattail bloom or flowers on young trees due to observing more heat than forecast. The codling moth biofix has been set by APM and treatment timing predictions based on degree days are provided by Jeff Franklin. Thanks to the ongoing commitment of the Orchard Outlook Committee members. 

Table of Contents:

  • 2023 Degree Day Accumulations
  • Soil Temperature in Relation to Moisture
  • Apple Bud Growth
  • Apple - Scab
  • Apple - Fire Blight Blossom Blight
  • Fire Blight - Infection Management
  • Apple - Black Rot
  • Apple Insects
  • Codling Moth: Degree Day and Treatment Timing Predictions
  • Pear Insects

Fruitlet Thinning

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

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

Events and Notices

  • 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).

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 12 for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 10% less plant development heat units compared to the 5-year average, and 12% less compared to the 10-year average.
  • Approximately 20% less plant development heat units compared to 2022, and 25% less compared with 2021.
  • Approximately 18% less insect development heat units compared to the 5-year average, and 21% less compared to the 10-year average.

Soil Temperature in Relation to Moisture

If you are wondering how deeply the 130 mm of rainfall from early June might have traveled in the soil profile, Jeff Franklin offers this graph of soil temperature over the period of heavy rainfall. Soil temperature at 50 cm depth appeared to respond to the cooling effect of the rainfall meaning that moisture likely reached 50 cm depth. 

Figure 2: Soil temperatures at various depths at the Kentville Research Station in 2023 in relation to the 130 mm of rainfall in early June.

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 12, I measured twenty king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 12.4 mm, Honeycrisp measured 9.7 mm, and Ambrosia measured 7.6 mm (Figure 3). In Rockland, Honeycrisp also measured 9.7 mm and in Lakeville the Gala measured 7.5 mm. In the current average temperatures, fruitlets are expected to grow about 1 mm each day (especially when further from petal fall that can cause some lag time).

Fruit set looks good where bloom was present. The size difference between fruitlets within a cluster is becoming more apparent (Figure 4).

Figure 3: Bud growth in an early region on Middle Dyke Road in Kentville on June 12. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Figure 4: Fruit set appears good where bloom was present so fertilization was largely successful. On Honeycrisp, aborting fruitlets are becoming more clear now, circled in red (left). Gala is showing typically heavy fruit set (right).


Apple – Scab

Table 1: Apple scab infection events in Kentville from June 7 to June 13, 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 100%. The model predicts that the final 0.1% matured since the last rain so primary spores are still available for infection. Models are not completely accurate so wait 2 weeks after ascospores are depleted before you lengthen your spray intervals.
  • 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

Due to higher than forecast temperatures, all regions are now at risk of blossom infection according to the following EIP values:

Atlanta: 182 Infection
Aylesford: 121 Infection
Grafton: 158 Infection
Grand Pre: 170 Infection
Melvern Square: 121 Infection
Morristown: 158 Infection
Moschelle: 109 Infection
North Medford: 145 Infection
Windsor: 182 Infection
Woodville: 158 Infection

  • Open blossoms are required for a blossom infection so this alert applies to rattail bloom and newly planted trees. Do not underestimate the risk of infection on late blossoms now that bacteria has had plenty of time to distribute in the environment.
  • 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. If absolutely necessary, streptomycin may be applied up to 20 hours after wetting (although it is risky to assume weather conditions will allow).
  • 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


  • 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 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. 
  • 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.

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 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.

    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.

    The models were run on Monday, June 12 with a degree day threshold of 10 degrees (C). Stay tuned for updates as the model will be recalculated with changes in the forecast.

    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.

    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

    • The ideal temperature for thinner activity is between 21-24°C (within fruit sizes of 5 to 18 mm and most effective from 7-12 mm).
    • I would expect that the carbohydrate surplus from the cool weather is being used up recently in the warm temperatures and soon to be cloudy weather. Conditions are likely conducive to average thinning responses. Although daytime temperatures have been near 27°C, nighttime temperatures have been below 18°C so the thinning response is not expected to be excessive. Many have been applying thinners since Sunday, especially because of the forecast of extended rain.
    • Fruitlets typically grow about 1 mm each day in average temperatures.


    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. 
    • 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.


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

    • 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.


    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

    • 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 must be applied proactively and requires frequent application to new growth and after rainfall. Ideally, install deer fencing the year prior to planting.
    • 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, Larry Lutz, Joan Hebb, Danny Davison, Dustin MacLean, Suzanne Blatt, Mathew Vankoughnett, Jeff Wentzell, Karen Burgher, Ian Willick, Keith Fuller, and Shawkat Ali.

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

    Blog Archive