Orchard Outlook Newsletter Vol. 22, No 8

Tuesday, May 31, 2022

Another week later and petal fall is the predominant stage! Today's newsletter discusses the usual diseases. We move into post-bloom insect management. With some measurable fruit size now, the fruitlet thinning window begins. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2022 Degree Day Accumulations

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot (Advance Notice)
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects
  • Weather conditions for thinning
  • Apple fruitlet thinning
  • Nibble thinning
  • Defruiting Young Trees
  • Pear thinning
  • Weed Management
  • Grafting
  • Mowing
  • Pruning and training
  • Planting
  • On-farm Nursery

Pest Management Guides 2022

Events and Notices

  • Webinar Recording Available for Weather Station Training
  • Nova Scotia Programs
  • 2022 Virtual orchard meetup series



2022 Degree Day Accumulations

Currently the cumulative degree days are above the 5 and 10-year averages for base 5°C and 10°C heat units (Figure 1). However, the forecast cool weather may result in a return to average.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 30 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 19% more plant development heat units compared to the 5-year average, and 13% more compared to the 10-year average.
  • Approximately 3% more plant development heat units compared to 2021, and 36% more compared with 2020.
  • Approximately 28% more insect development heat units compared to the 5-year average, and 15% more compared to the 10-year average.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 30, I measured ten king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 7.1 mm, Honeycrisp measured 5.2 mm, and Ambrosia measured 5.1 mm (Figure 2). Keep in mind that fruitlets grow about 1 mm each day.

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on May 30. Shown from left to right: Idared, Honeycrisp, Ambrosia.

The fairly compacted bloom has led to relatively similar fruit size in different regions. In the Morristown area that is considered a later region, an average of 50 king Honeycrisp fruitlets measured 5.3 mm today on May 31. Some blossoms were still present.


Apple – Scab

Where primary lesions are present, secondary infections have been occurring and will continue during wetting events of sufficient duration. The minimum wetting required for secondary infections is 3 hours less than the wetting required for primary infections.

Table 1: Apple scab infection events in Kentville from May 24 to May 31, 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.


  • If spray intervals were stretched to the limit for the past week's infection event, there may be a risk of infection. During bloom the petals interfere with coverage and much leaf expansion has happened over the week. If infection occurred, the time to lesion appearance is about 12 to 17 days according to the Modified Mills Table. 
  • Currently, cumulative ascospore maturity is theoretically at about 97.9%. By the weekend, the total seasonal ascospore maturity is expected to reach 99.7%.
  • Primary ascospores are still available for release. There is still some time before it is safe to reduce fungicide spray intervals.
  • Do not use folpan until 30 days after petal fall to avoid fruit russeting. 
  • 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

Several alerts were sent for the risk of high bacterial populations on May 29 (some regions) and May 30 (all regions).

  • Wetting could have produced infections on open blossoms that were not protected. Wetting on May 28 was enough to keep flowers wet for May 29. The May 30 risk was followed by an early rain on May 31 that could have caused an infection.
  • Applying protection on May 29 or 30 reduced bacterial populations (EIP) and then populations are not expected to grow for the next few days. Antibiotic application was a juggle with winds, changing temperatures, and changing rain risk.
  • The alerts will continue to be sent for the purpose of protecting late blossoms on new plantings.



  • Consider the ongoing risk of blossom blight infection on flowering apples.
  • 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.


  • 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.
  • Streptomycin 17 will provide excellent efficacy on blossom blight and should not be used more than 24 hours prior to an infection event. If necessary, it may be used after infection and is best used within 12-18 hours but can still be helpful if delayed longer. It is recommended that you keep Strep on the farm at this time of year to respond quickly. Streptomycin 17 may be used up to 3 times each year.
  • Kasumin also has excellent efficacy and may be used up to 4 times each year during bloom. Consider using Kasumin if you need to re-enter a block because it has a short REI of 12 hours. However, the PHI for Kasumin is 90 days, which can be challenging for early varieties like Paula Red. Note that Kasumin is not partially systemic and should not be used for post-infection control or after a trauma event.
  • For on-farm nurseries, consider applying a copper product at the lowest labeled rate prior to training trees and follow the labeled REI. Make cuts on only dry and sunny days. 

Fire Blight - Shoot Blight Management


  • Apogee/Kudos (prohexadione calcium) supress shoot blight. The timing of the first application at 2.5-7.5 cm of new shoot growth is critical to success. Honeycrisp shoots are now measuring 8.5-11.0 cm so efficacy will be lower with late applications. 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.
  • 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 (Advance Notice)

  • Black rot can survive on prunings. Flail mow prunings in row middles where they will degrade more quickly.
  • Minimize lenticel cracking by:
    • Avoiding drought stress with irrigation - inspect soil at your own site. Sandy soil will be at risk first.
    • Being cautious with spray mixtures (folpet, 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 black rot fungus infects fruit during warm rains from petal fall to harvest:
    • A 10 hr wetting period at 16°C to 32°C allows infection. 
    • The optimum temperature for infection is 20°C to 24°C. 
    • Based on our limited knowledge, the highest risk of infections is theoretically around 4-6 weeks after bloom.


  • Choose insecticides by considering what you are targeting and what the products control. Often your worst pest (ex. mullein bug) will determine what you need to use, then check the label of that product for all pests that are also controlled by the product. 
  • Fungicide, antibiotic, and growth regulator sprays are best applied early morning or late evening when bees are not actively foraging. Be aware that dandelion blooms are open until about dusk.

Apple Insects

Pesticide options and efficacy are listed in Table 2. All registered insecticide options and label rates for calyx stage of apples are listed in the Pome Fruit Management Guide.

Table 2: Pesticides options for calyx stage of apples in Nova Scotia (revised May 2022) with input at original publication from Erika Bent (APM). Products are rated from 1 (poor) to 4 (excellent).

Stone Fruit Insects


  • Healthy peach trees that do not have a crop this year due to winter injury should still be protected from direct pests. This would include the diseases peach leaf curl, brown rot, and powdery mildew. For insects, monitor for aphids and mites and especially plum curculio and tarnished plant bug if apple trees are nearby. Inspect trees for injury to limbs and trunks in case trees may not recover.  
  • Treatment for plum curculio should be applied at petal fall before shuck split to obtain optimal control. Treat between petal fall and shuck split. A second application is usually needed about 10 days later.

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. Rapid penetration into young leaf tissue is essential because AgriMek on the leaf surface is rapidly degraded by UV light. After the product is absorbed however, for several weeks or months a rust mite, red mite, or two-spotted spider mite that feeds on treated leaf tissue is killed. Local trials by John Michael Hardman showed that Agri-Mek + oil had minimal adverse effects on typhs.
  • 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. Minecto Pro (Abamectin and Cyantraniliprole) is a new formulation that is registered for control of pear psylla with the same recommended application time.
  • If Agri-Mek is applied close to MaxCel then it can drastically increase thinning activity.

Chemical Fruitlet Thinning

Weather Conditions for Thinning

Weather influences tree sensitivity to chemical thinners. The weather 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.
  • Expect fruitlets to grow about 1 mm each day in average temperatures.
  • 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


  • Pollination conditions seemed good but evaluate your fruit set to inform thinning decisions.
  • It is difficult to make specific predictions in this newsletter with such an actively changing forecast. However, here are a few thoughts:
    • The moderate daytime temperatures and cool nighttime temperatures being shown suggest familiar thinning conditions unlike the heat waves of recent years. Last year some overthinning occurred because of the heat that followed application, especially on Honeycrisp. 
    • This week also seems to offer a rain-free period and it would be good to thin early in case the future brings rainy periods.
  • Sevin is a mild thinner, and for this reason it is a good option for early thinning with the opportunity to thin again later when fruit set is more clear. 
    • Even though Sevin applied with Fruitone is more aggressive than either product used alone, there is a good argument for applying Sevin alone. If a fungicide is combined with Sevin, covering the whole orchard should not be overcomplicated. Fruitone or MaxCel/Cilis Plus on specific varieties could be followed up later. Whatever approach is taken, have a strategy and plan before starting.
    • 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.
    • 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.
  • MaxCel can be applied up to 15 mm but note the PHI of 86 days. Cilis Plus has a PHI of 28 days.
  • 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!
  • 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.

Nibble Thinning

  • If you would like to try the nibble/precision thinning approach, consider using the Predicting Fruitset Model to receive feedback on how many fruit will drop or persist in response to a chemical thinner application. Tracking the fruit growth rate in real-time will buy time and confidence to thin again before the chemical thinning window closes.
  • Select high value blocks to monitor fruitlet diameter using a digital caliper on 75 fruitlets. Flag 15 clusters across 5 representative trees and number the fruitlets (1 to 5). Take the first measurements four days after a thinning application or no earlier than the 6 mm stage. Continually measure size over time every 4 days and input results into the model. Contact me for guidance and questions.
  • If you don't want to commit this year, then try a sample to become familiar with the process. Monitor 5 clusters using a digital caliper every 4 days.
  • The Orchard Tools app by Perennia is available for iPhones, iPods and iPads. Available for download from the App Store.

Defruiting Young Trees

  • ATS is NOT recommended for defruiting young trees. The question of using ATS to defruit young trees comes up every year. I do not recommend the practice because of concern about foliar spray injury to young trees. In order to eliminate all blossoms, the ATS would need to be applied multiple times to target flowers that open at successive times. The frequent number of applications would increase the risk of foliar spray injury. The leaves of young trees are also very tender.
  • 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 Thinning

  • The MaxCel thinning window is 8-14 mm and early treatments are most effective.
  • If Agri-Mek is applied close to MaxCel then it can drastically increase thinning activity.


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.
  • Note that residual herbicides can damage single tree replacements. 
  • Residuals need an activating rain of 0.5 inches within 7-10 days of application.
  • When mixing residual herbicides, agitation is important to keep the product in solution. If the herbicide settles in the tank then it can be delivered in a high concentration and possibly result in crop injury.
  • If weeds are already present, add a post-emerge to a residual herbicide to achieve control. 
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees.


  • The practice is most successful as long as bark is slipping, which may extend into summer.


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

Pruning and Training

  • Summer pruning is the next best opportunity if pruning is not complete by bloom.
  • Train and support young trees as soon as possible. Work in dry weather especially if the block has historically high risk of fire blight. This year is expected to be an active hurricane season.
  • 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.


  • A good soaking rain might not have occurred after planting. Pruning trees after planting can bring top growth in balance with the root mass to avoid root dieback under conditions of moisture stress.
  • Warm soil temperatures mean that roots will grow immediately. Start fertilizer programs as soon as possible after planting.
  • Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Under currently dry conditions, watering with drip tape if possible especially under sandier situations is recommended. Keith Fuller also notes that M26 wilts very easily and that water provided in replant situations can reduce stress from replant disease. A dry season compounds replant disease symptoms.
  • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees.
  • 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

  • Strip leaves from rootstock soon for budding. Strip non-varietal buds from last year's rootstock soon.
  • 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.
  • Consider staking soon to prevent blowouts.
  • Monitor for green 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!

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.

Webinar Recording Available for Weather Station Training

The webinar recording for the Weather Station Apps and Website Training Session is now available on the Perennia YouTube channel. You can find the link here: https://www.youtube.com/watch?v=-ujYsZ88kAk

Nova Scotia Programs

Nova Scotia Department of Agriculture Programs and Business Risk Management have released all programs for the 2022-23 program year and are available on the website: https://novascotia.ca/programs/. If you have questions on the programs and applications please connect with your local Agriculture Extension Coordinator or Business Development Officer. It is important to note changes in application, activity periods and claim dates.

2022 Virtual Orchard Meetup Series

Last year various extension specialists across the United States put together a virtual apple meetup series, focusing on ‘Honeycrisp’ apples. This year, the series will focus on labour and technology in the orchard with representation from across the U.S. and Ontario. Register at bit.ly/orchardmeetups.

Orchard Efficiency: Labour and Technology (4PM PST, 7PM EST)
June 2. Labour – Grower Experiences
June 16. Labour – Specialist Panel
June 30. Technology – Growers Experiences
July 14. Technology – Specialist Panel

These meetups will provide an opportunity to review challenges, best practices, and new recommendations for orchard labor and technology. Led by a panel of scientists, growers, and other experts in labor and technology across North America.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Jeff Wentzell, Colin Hirtle, Danny Davison, Jeff Franklin, Dustin MacLean, Dr. Vicky Levesque, Larry Lutz, Joan Hebb, Dr. Ian Willick, Keith Fuller, Dr. Suzanne Blatt, Dr. Mathew Vankoughnett, and Dr. Shawkat Ali.

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

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