Orchard Outlook Newsletter Vol. 22, No 10

Tuesday, June 14, 2022

In today's newsletter you'll find more information on winter injury and weakened trees. In terms of disease, the apple scab model indicates that 100% of ascospores have been released but allow time to evaluate pressure from recent infections before reducing fungicide intervals. There are reports of blossom blight infection symptoms now becoming visible so you may begin monitoring. For insect management, updated codling moth treatment timing predictions are provided. We offer final thoughts on thinning at the tail end of the thinning window of opportunity. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Correction post-publication on June 15 at 9:48 AM: The blossom blight infection symptoms that are showing up now are likely from the May 22 infection and not the May 29 infection as originally published.

Table of Contents:

  • 2022 Degree Day Accumulations
  • Winter Injury to Apple Trees
  • Weather Station Communications

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects
  • Apple fruitlet thinning
  • Defruiting Young Trees
  • Calcium Nutrition
  • Weed Management
  • Mowing
  • Training
  • Planting
  • On-farm Nursery

Pest Management Guides 2022

Events and Notices



2022 Degree Day Accumulations

The cumulative degree days remain above the 5 and 10-year averages for base 5°C and 10°C heat units (Figure 1). Temperatures are expected to continue to cycle around the average. Recent precipitation has been extremely dynamic and unpredictable.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 13 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 13% more plant development heat units compared to the 5-year average, and 9% more compared to the 10-year average.
  • Approximately 6% less plant development heat units compared to 2021, and 25% more compared with 2020.
  • Approximately 15% more insect development heat units compared to the 5-year average, and 9% more compared to the 10-year average.

Winter Injury to Apple Trees

In last week's newsletter it was reported that in some cases trees are lagging in development or collapsing, most likely as a result of winter injury. Southwest injury to the trunk has also been observed. The greatest risk of injury appears to be on Gravenstein and Northern Spy, and in situations with young trees, weakened trees and fall pruned trees. 

Looking back to the winter of 1980-81, temperatures fluctuated and low and injurious temperatures were recorded. We can glean the following information from the historical survey of growers, based on varieties and conditions in the 1980s:
  • Susceptible varieties: Of the injured trees, 42% were Gravenstein, 17% were Northern Spy, and the remainder that were less affected were McIntosh, Cortland, Red Delicious, Idared and others. Gravenstein trees were the main variety affected.
  • Susceptible rootstocks: Of the injured trees, the greatest percentage of injury was observed on BA, M111, M106 and seedling. A smaller percentage of injury occurred on M26, M7, and M106. Large rootstocks appear to be more susceptible although I do not know how widely dwarfing rootstocks were planted at the time.
  • Age groups: Of the injured trees, 13% were 1-5 years old, 26% were 6-10 years old, 25% were 11-15 years old, 24% were 16-20 years old, and the remaining 12% were older than 20 years. Young trees were more susceptible than old trees. 

This year we are also noticing borer activity in injured trees (Figure 2). Winter injury weakens the trees and then stress signals from the trees attract borers. After cold injury in the 1980s, an increase in borer activity was also noted. Local research explored insecticide treatments but it is most likely that after the stressor dissipated and weakened trees died, that borers were no longer an issue.

Figure 2: Trees weakened by winter injury become attractive to borers.

Weather Station Communications

Perennia is contracted to provide maintenance for the ten NSFGA weather stations. A couple of issues are currently being serviced outside of routine maintenance:
  • GRAND PRE (NSFGA): Replacing the battery and resetting features of the station were unsuccessful. The issue with this station is still under investigation. Please do not rely on minimum temperatures being reported by the Grand Pre NSFGA weather station. Other nearby stations that are publicly accessible from the WeatherLink app are Grand Pre (NSW014) and Avonport (Luckett's). Grand Pre (NSW014) is being used for fire blight Maryblyt alerts. 
  • NORTH MEDFORD (NSFGA): The leaf wetness sensor is not yet operational.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on June 13, I measured ten king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 19.6 mm, Honeycrisp measured 16.7 mm, and Ambrosia measured 13.4 mm (Figure 3). Honeycrisp in the Billtown area measured 17.8 mm. Keep in mind that fruitlets grow about 1 mm each day. 

Figure 3: Bud development in an early region on Middle Dyke Road in Kentville on June 13. Shown from left to right: Idared, Honeycrisp, Ambrosia.


Apple – Scab

Table 1: Apple scab infection events in Kentville from June 8 to June 14, 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 Sunday, April 17th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
3 All forecasts are estimates. Observe forecasts daily for more accurate predictions.
Note: The environmental conditions for an infection are listed in the Modified Mills Table.


  • As of June 10, cumulative ascospore maturity theoretically reached 100% according to the model. Therefore, the last primary infection event is currently occurring. Secondary infection events will continue until harvest.
  • Do not reduce fungicide spray intervals until you can identify your pressure from scab lesions. This requires waiting at least 2 weeks after the last primary infection event.
  • The pre-harvest interval for EBDC fungicides (e.g. Manzate, Dithane) for fruit destined for the United States is 77 days versus 45 days for the domestic market. An application of EBDC on June 14 would require until August 30 to meet pre-harvest requirements for the United States.
  • Do not use folpan until 30 days after petal fall to avoid fruit russeting. Also note that new to this year is a 6-day REI for hand thinning fruit.
  • Re-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.
  • Always tank mix single site fungicides with a group M for resistance management.
  • 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.

Apple – Powdery Mildew


  • Powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected, and not prior to heavy rain. 
  • Do not apply more than two consecutive applications of a group 3 or group 7 fungicide.
  • 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.

Apple & Pear – Fire Blight Blossom Blight

Past and Forecast Blossom Blight Risk

  • Multiple alerts were sent for new plantings that were in bloom. Blossoms were under high risk and infection risk for several days beginning around June 9.
  • Antibiotic protection applied on June 11 or June 12 provides protection for several days and then bacterial growth is expected to slow for several days in cool forecast temperatures. 
  • Moderate temperatures are then forecast to increase the risk. Currently it appears as though the EIP will approach or exceed the 100 threshold around June 17.
  • When concerning EIP values are imminent, alerts will be sent for the purpose of protecting late blossoms on new plantings.

Please note: The Epiphytic Infection Potential (EIP) is a representation of the bacterial population that is growing on only the floral stigma that is relevant to blossom infection risk. EIP is not a representation of bacterial population in the orchard during a trauma event. Trauma events are always cause for concern because bacteria are transported from anywhere to open wounds. Water that accompanies the trauma in a hail or windy rainstorm are very effective at distributing bacteria.



  • The symptoms of blossom infections were reported on June 12 likely from early infections (around May 22). Start monitoring for signs of blossom infection.
  • Consider the ongoing risk of blossom blight infection on flowering apple trees.
  • If you are not receiving email alerts and you wish to, please let me know at mcortens@perennia.ca or sign up online. Alerts will be delivered on weekends and holidays. I also post daily screenshots in a folder online to make model predictions easily accessible. Predictions are updated daily. Access apple predictions and click on the images to expand.


  • Remove fire blight strikes at least 2-4 ft below active infections to remove the leading edge of the bacteria. Being aggressive at the first sign of symptoms will help prevent the re-occurrence of symptoms and the need for continuous cutting back.
  • 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. 
  • If pinching buds on young trees, leave at least 1-2 warm days for the wounds to heal prior to rain. Do not pinch flowers when tissues are wet, even in a morning dew.

Fire Blight - Shoot Blight Management


  • If a blossom blight infection occurred, prohexadione calcium is a tool known to slow down bacterial spread in the tree and may buy some time before bacteria reach the leader.
  • When Apogee/Kudos (prohexadione calcium) are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still slow fire blight progression.
  • Follow up with a second application applied around 14 days later.
  • 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

  • The black rot fungus infects fruit during warm rains from petal fall to harvest. The highest risk is from petal fall up until 4 to 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. Merivon has activity but group 7 + 11 products 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.
    • Captan is an effective protectant for high density orchards that have a history of black rot. However, consider Captan where practical in terms of label restrictions for re-entry intervals.
    • Check for nearby brush or wood piles because they serve as a major source of inoculum. Remove the brush pile to reduce the chance of infection.
    • Frog eye leaf spot infections on leaves tell you that you have black rot inoculum present. Oftentimes, the frog eye leaf spot will be in close proximity to fruitlet mummies (Figure 4).
  • Minimize lenticel cracking by:
    • Avoiding drought stress with irrigation.
    • Being cautious with spray mixtures (folpet, calcium, foliar nutrients). For comments on calcium, see the section below on horticulture.
    • Be especially cautious with spray mixtures 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.

Figure 4: Frog eye leaf spot indicates that black rot inoculum is present. Fruitlet mummies are often sources of inoculum so frog eye leaf spot is in close proximity.


Apple Insects

  • Stinging bugs: Assess the efficacy of earlier insecticides that targeted stinging bugs such as apple brown bug and mullein bug and whether or not re-treatment is warranted. Use limb taps to determine recent pressure. Pyrethroids are best used at moderate temperatures (20C or less). Ambrosia and Red Delicious are particularly susceptible to damage by stinging bugs.
  • White apple leafhopper: Monitor for white apple leafhopper. Sevin XLR applications on 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 and also pick up aphids.
  • Aphids: Monitor for rosy apple aphid and green aphid. There are plenty of aphids in young trees if you look up close (leaves may not be curling yet). In young trees the aphids can disrupt shoot growth. Monitor nursery plantings as well. If leaves are curling high, high water volumes are needed for effectiveness.

Codling Moth: Degree Day and Treatment Timing Predictions (Update)

The biofix dates for this season are May 31 for early and June 5 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
Products: Assail, Calypso, Delegate, Confirm, 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 18 for early regions and June 20 for late regions.

Codling Moth Treatment with Organophosphate
Product: 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 24 for early regions and June 27 for late regions.

The models were run on Tuesday, June 13 with a degree day threshold of 10 degrees (C). Stay tuned for updates as the model will be run again this week. Dr. Suzanne Blatt reports sustained trap captures at Kentville.

Stone Fruit Insects

  • Mites and aphids: Monitor mite and aphid populations. Prolonged feeding especially in early- to mid-summer can affect next year’s fruit set.
  • Plum curculio: A second application for plum curculio is usually needed about 10 days later.

Pear Insects

  • Pear Psylla: 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 apply Agri-Mek with any bloom around as this product is highly toxic to bees. Do not use Captan/Maestro as a fungicide for pear scab within 14 days of Agri-Mek + Oil. If Agri-Mek is applied close to MaxCel then it can drastically increase thinning activity.
  • 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.

Chemical Fruitlet Thinning

Apple Fruitlet Thinning

  • 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). 

Where are we at?

  • Most thinning has occurred already but there may still be an opportunity in late regions on late varieties. 
    • When the average king fruit diameter reaches 15 to 18 mm, fruitlets are still receptive to thinners but less receptive than earlier timings. 
    • By 20 mm king fruit diameter, thinning activity is highly unlikely. 
    • Measurements are made on king fruitlets to standardize the timing of thinning treatments so even if side fruitlets are smaller, it does not mean that they are still receptive to thinners.
  • This year I took fruit growth rate measurements on mature Honeycrisp trees and I'm sharing the results for your curiosity. I marked 20 clusters on untreated trees and 20 clusters on trees treated on June 3 at 7 mm with 3.2 L/ha Sevin and 390 mL/ha Fruitone L in 950 L of water. I measured the fruit size on June 8 and June 13 (Figure 5) to determine the fruit growth rate and used the Predicting Fruit Set Model to calculate fruit set:
    • 57% of the measured untreated fruit are expected to set
    • 23% of the measured Sevin + Fruitone treated fruit are expected to set
    • By June 13, average king fruit diameter at the site was 15 mm. The opportunity for re-application is very narrow but this fruit growth rate practice might help in some situations.

Figure 5: Fruit growth rate measurements taken on Honeycrisp this year to evaluate how many fruit will drop or persist in response to a chemical thinner. On untreated and chemically thinned trees, 20 clusters were marked and fruitlets were numbered from 1 to 5.


  • 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.
    • 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. For a comparison between products, review the Thinning and Growth Regulation Guide.
  • Please note that the label for MaxCel was, in fact, updated last year and now reads a PHI of 28 days which is equal to the PHI of Cilis Plus. 
  • Be careful when comparing our product rates to other regions by ensuring that rates are being expressed in equivalent formats. It is most reliable to thin based on local experience.

Defruiting Young Trees

  • ATS is NOT recommended for defruiting young trees. 
  • The thinner combination intended for defruiting young trees is 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.


Calcium Nutrition

  • The goal of foliar Ca sprays is to increase the concentration of Ca in the fruit and reduce bitter bit incidence. 
  • Early calcium application has been recommended in Washington State but research has not been done locally. Fruitlets are most sensitive to injury at petal fall and first cover so calcium at this time poses a risk. The risk is highest if humid weather follows application and creates slow drying conditions. Damage caused by calcium could also aggravate black rot infection.
  • Avoid calcium chloride for early applications. Formulated calcium products have less risk but they also have lower concentrations of calcium.
  • As fruit grow and increase in surface area, a greater total amount of the calcium applied is taken up by the fruit. If bitter pit has not been a significant issue, then continue as normal which means calcium beginning at 4 to 6 weeks after petal fall.

Weed Management

  • Due to herbicide shortages, it seems that weed management in young plantings will be reliant on consistent and vigilant use of burnoff products. Note the risk of frequent use of Agral 90 for bark blistering on Delicious varieties.
  • 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.
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees.


  • Mowing will help to conserve moisture so that it is not transpired by the large surface area of tall weeds and grasses. Mowing and blowing the clippings into the tree row can also help to conserve moisture.
  • Mowing and herbicide strips help to prevent issues with two-spotted spider mite (John Michael Hardman).
  • Keeping the orchard floor cover mowed will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.


  • Select strong terminals on young trees and remove competing terminals to single the tops.
  • Training practices should be done on dry and sunny days, especially in high risk fire blight blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
  • 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). This year is expected to be an active hurricane season.


  • 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.

On-Farm Nursery

  • Consider staking to prevent blowouts. Stakes should be placed on the side opposite from the bud so it pulls the bud toward the rootstock rather than away. Shoots are over 6 inches tall so they can also be tied. 
  • Monitor for aphids.
  • 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!
  • Although Aim is registered for use in nurseries, damage has been reported several times in the past. It is a contact herbicide so it kills tissue on contact.

Pest Management Guides 2022

All changes new to 2022 are made in red text directly on the guides. The information on all changes was summarized in a blog post on April 8th.

Events and Notices

For upcoming events, visit the ‘Events’ tab on the NS Tree Fruit Blog. Specific events will be described here when available.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Jeff Wentzell, Danny Davison, Jill MacDonald, Crystal MacRae, Dr. Suzanne Blatt, Joan Hebb, Larry Lutz, Dr. Vicky Levesque, Jeff Franklin, and Keith Fuller.

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

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