Orchard Outlook Newsletter Vol 21, No 8

Tuesday, June 1, 2021


Table of Contents:

  • 2021 Degree Day Accumulations

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Stone Fruit - Brown Rot, peach scab, and powdery mildew

  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects

  • Weather Conditions for Thinning
  • Apple - Fruitlet Thinning
  • Apple - Nibble/Precision Thinning
  • Track Measurements with Orchard Tools App for iOS
  • Apple - Defruiting Young Trees
  • Pear - Fruitlet Thinning

  • Weed Management
  • Pruning and Training
  • Grafting
  • Planting Trees
  • Nursery Trees
  • Mowing

Pest Management Guides 2021

Events and Notices



2021 Degree Day Accumulations

The above-average trend continues. Jeff Franklin observes that, "The above-average days have offset the below-average days and we are still 5-7 days above the five and ten year averages."

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to May 31st for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 24% more plant development heat units compared to the 5-year average, and 15% more compared to the 10-year average.
  • Approximately 35% more plant development heat units compared to 2020, and 52% more compared with 2019.
  • Approximately 27% more insect development heat units compared to the 5-year average, and 11% 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. There is still plenty of bloom throughout the Valley. The following observations are from May 31st: 
  • Idared buds were at petal fall and measuring an average of 8 to 8.5 mm
  • Honeycrisp was at petal fall and measuring an average of 6.5 mm with still the odd blossom cluster
  • Ambrosia was at about 75% petal fall and measuring 4.5 mm
  • Pears are well into petal fall and measuring 7.5 mm with still some rattail bloom
  • Peaches, and plums are at shuck split
  • Nectarines are at shuck split to 1.5 cm length
  • Cherries are at 1.5 cm length 
Other observations: On late varieties, the cool weather has delayed the progression of bloom. 

Figure 2: Bud development in early regions on May 31st. From left to right: Honeycrisp, pear, and peach.


Apple – Scab

For the past week, regions of the Valley have had variable and scattered showers with generally minimal rain until yesterday's event. 

Table 1: Apple scab infection events at the Kentville Research Station from May 25th to June 1st, 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 Tuesday, April 14th. 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.


  • Wetting is forecast for June 3rd and 4th. With the forecast temperatures at an average of +19.0°C, it would take around 10 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills Table. Ascospores are expected to mature to 99.3%.
  • Ensure that tissues are covered with a protectant fungicide prior to an infection event by reapplying on a 7-day interval, with a shorter 5-day interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
  • Primary ascospores are available for release. There is still some time before it is safe to reduce fungicide spray intervals.
  • Always tank mix single site fungicides with a group M for resistance management.
  • Note that Polyram is being phased-out due to the cancellation of the active ingredient. The last date of use is June 21, 2021.
  • 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.
  • Note that the new captan containing product Maestro 80 WSP has re-entry periods that differ depending on the orchard density and activity (anywhere from 2-24 days).

Apple – Powdery Mildew


  • Where powdery mildew pressure is historically high, a third application is often recommended by petal fall. 
  • 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

Current and Forecast Maryblyt Risk

Alerts have been sent to subscribers by email over the last few days. The most recent alert was sent today on June 1st. An infection is in the forecast for all regions on apples and pears on June 3rd and some regions are at risk sooner on June 2nd. Please check the alert for more details.

This year, all NSFGA-owned weather stations are used for industry alerts. I post screenshots in a folder online to make model predictions easily accessible. Predictions are updated each morning. Access apple and pear predictions and click on the images to expand.


  • The current forecast predicts that antibiotics will provide two to three days worth of protection.
  • There is plenty of work to do with young trees. Kasumin has only a 12-hour REI and it MUST be applied before the rain in an infection event. Streptomycin has a 7 day REI at minimum.
  • 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 and Agral 90 are best applied with little else in the tank to prevent incompatibility issues that would reduce efficacy. However, if manzate is applied it has a spreader-sticker so reduce the use of Agral 90 by at least half to avoid strep burn.
  • Streptomycin 17 will provide excellent efficacy on blossom blight and is best used up to 24 hours prior to an infection event. If necessary, it may be used 20 hours after infection. 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.
  • At bloom, to run the Maryblyt model using your own temperature, rainfall, bloom and spray dates, download the Maryblyt desktop software
    • Need a refresher on how to use Maryblyt? Watch the 2020 Perennia Maryblyt video tutorial
    • This year you can use the daily max and min temperature data from the NSFGA weather stations to run Maryblyt. Do so by logging in to the NSFGA account on www.weatherlink.com, choose the weather station, select the tab "data" and then choose the view "Monthly Summary". Enter the given values into Maryblyt.
  • 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

The material prohexadione calcium is not an antibiotic, has no direct activity on the fire blight organism, and has no effect on blossom blight incidence. However, application of Apogee thickens the cell walls of treated shoots. This effect makes it difficult for the fire blight pathogen to invade shoots, and treated shoots become much more resistant to the spread of fire blight infection. In addition to shoot blight suppression, the application of Apogee at the correct timing also results in a reduction of terminal growth in apples by 30-40%.


  • At least one infection event was already possible during bloom and another infection approaches. If a blossom blight infection occurred on unprotected flowers, prohexadione calcium is a tool known to slow down bacterial spread in the tree and may buy some time before bacteria reach the leader.
  • The timing of the first application at 2.5-7.5 cm of new shoot growth is critical to success. Follow up with a second application applied around 14 days later. When Apogee/Kudos are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still provide fire blight suppression.
  • 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)!
  • Apogee/Kudos inhibit the biosynthesis of the plant growth regulator gibberellin. When gibberellic acid sprays such as Promalin or Accel are applied in the same season, loss of efficacy may occur for either product.

Stone Fruit – Brown rot, peach scab, and powdery mildew


  • Fungicide protection from brown rot should be maintained during periods of warm, wet weather. 
  • The new formulation of Captan limits the number of applications to one per year on stone fruit.
  • Peaches are susceptible to peach scab infections from shuck fall to 4-6 weeks before harvest. Symptoms are visible on the bark. The shuck fall application is particularly important for disease control. Periods of wet weather will require additional applications until 4-6 weeks before harvest.
  • Monitor for signs of powdery mildew on fruit at 1⁄4 inch size and refer to the Stone Fruit Management Guide.



  • If you were unable to treat tarnished plant bug, spring caterpillars, rosy apple aphid, and European apple sawfly prior to bloom you will have another opportunity at petal fall/calyx.
  • 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

In anticipation of upcoming petal fall, pesticide options are listed in Table 2. 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 2021) with input at original publication from Erika Bent (APM). Products are rated from 1 (poor) to 4 (excellent).

  • 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.
  • Monitor for rosy apple aphid and green aphid. In young trees the aphids can disrupt shoot growth. Monitor nursery plantings as well.
  • Stay tuned for the codling moth biofix date and degree day model predictions for treatment. Dr. Suzanne Blatt reports that forecast nighttime temperatures above 12°C will encourage moth flight.

Stone Fruit Insects


  • Treatment for PC should be applied before shuck split to obtain optimal control. Treat between petal fall and shuck split. A second application is usually needed about 10 days later.
  • The insecticides available for managing plum curculio include 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.
  • Plum curculio will target apples if stone fruit are nearby.
  • Be aware of bee toxicity warnings on pesticide labels and take precautions while nearby crops are in bloom.
  • Monitor mite and aphid populations. Prolonged feeding especially in early- to mid-summer can affect next year’s fruit set.
  • Tarnished plant bug and stinging bugs cause catfacing of peaches. This stinging takes place around shuck split/fall and one to two insecticide applications may be required to reduce the incidence of catfacing if pressure is high. Apply one to two applications of one of the pyrethroids listed in the Stone Fruit Management Guide. Repeat treatment in 5-7 days if additional stings are detected.

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 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.
    • 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.
    • Stay tuned for codling moth biofix and degree day model predictions for treatment timing.

    Chemical 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.

    This week's outlook for thinner activity:

    This week weather conditions are not expected to have a significant influence on chemical thinner performance based on the current Environment Canada weather forecast (Figure 3). Some observations are listed for more detail:
    • Daytime temperatures are mostly in the range of 21-24°C for several days meaning that chemical thinners should work predictably in these ideal temperatures. Temperatures are expected to increase by week end so stress could increase thinner activity.
    • If we experience the rainy periods, the slow drying conditions will increase absorption of chemical thinners and result in added thinning activity.
    • Mainly cloudy conditions are expected to reduce photosynthesis. 
    • Cool nights below 18°C will slow respiration and reduce the stress. 
    • Overall, weather conditions suggest applying the standard chemical thinner rate but by the week end re-evaluate if conditions are hot because thinners become more active during warm trends. Note that Fruitone, MaxCel, and Sevin product labels warn against application in hot conditions.
    • These observations are based on weather only. Adjust based on other factors on your farm and use in the context of your own experiences.

    Figure 3: The Environment Canada 7-day forecast at the time of publication used to provide some predictions for thinning activity. Consider this an example and adjust practices based on the most recent forecast weather conditions.

    Apple - Fruitlet Thinning

    • Weather conditions have not been consistent for pollination between varieties and regions. Conditions were cool when late varieties achieved full bloom at the end of last week. Evaluate your fruit set on different varieties early to inform thinning decisions.
    • 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). Note this week's outlook for chemical thinner activity in the above section.
    • Focus your chemical thinner in the top 2/3rds of the tree.
    • In the US apple production regions, the carbohydrate model recommends adjusting the usual chemical thinner program by plus or minus 30% depending on the carbohydrate status of the tree (explained in the above section). Adding a surfactant or PureSpray Green oil at 1% is also considered a way to increase the aggressiveness of a thinner on hard-to-thin varieties. Take caution using PureSpray Green oil on varieties that are easy-to-thin like Ambrosia.
    • 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.
    • 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!

    Apple - Nibble/Precision Thinning

    • 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 in cases where fruit set is low, consider applying Sevin to take off the weak fruit that would not set good fruit. 
    • 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 at least 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.

    Track Measurements with Orchard Tools App for iOS

    The Orchard Tools by Perennia is available for iPhones, iPods and iPads. It is a tool to help record measurements that will inform your thinning decisions! Easily track the diameter of king fruit. Also, enter the fruit diameter for each fruit in the cluster over time. The data can be exported and then pasted into the Predicting Fruitset Model. There is no need for cellular data or internet while recording. Available for download from the App Store.

    Tutorials will get you up and running:

    Apple - 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.

    Pear - Fruitlet Thinning

    • The Maxcel thinning window is 8-14 mm and early treatments are most effective. Note that pears are within or quickly approaching this opportunity.


    Weed Management

    • Remember the importance of weed control in nurseries and young plantings. Management practices now will impact the outcome of the final tree. Encourage the growing point to be successful.

    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. Consider using Kasumin for fire blight protection if a short 12-hour REI is needed.
    • 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).


    • The practice can be done as long as bark is slipping, which may extend into summer.

    Planting Trees

    • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Deer are browsing young plantings and causing damage. Thiram is no longer an option to deter feeding while the fence is being installed. Another deterrent product called Bobbex is available for nonbearing trees.

    Nursery Trees

    • 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.


    • Keeping the orchard floor cover mowed pre-bloom will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.

    Pest Management Guides 2021

    The pest management guides are available online for download. All changes new to 2021 are made in red text.

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

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