Orchard Outlook Newsletter Vol 21, No 6

Tuesday, May 18, 2021


Note: Updated post-publication on May 18th at 2:45 PM to include moldy core comment under calyx/blossom end rot section.

Table of Contents:

  • 2021 Degree Day Accumulations
  • Cool nights but not freezing

  • Blossoms
  • Terminal Shoots

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Calyx or Blossom End Rot
  • Stone Fruit - Brown Rot Blossom Blight
  • Pre-Bloom Insecticides
  • Pome and Stone Fruit - Plum Curculio post-bloom
  • Other Insects

Weed Management

  • Pruning
  • Fertilizing
  • Pollination
  • Grafting
  • Planting Trees
  • On-Farm Nursery Trees
  • Mowing
  • Wild Apple Trees

Pest Management Guides 2021

Events and Notices

  • NSFGA Research Survey



2021 Degree Day Accumulations

The above-average trend continues, contributing to this year's early bloom. In terms of growing degree days for plant development, this year compares to 2017 and 2006. Even soil temperatures are warm compared to average.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to May 17th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 30% more plant development heat units compared to the 5-year average, and 20% more compared to the 10-year average.
  • Approximately 91% more plant development heat units compared to 2020, and 42% more compared with 2019.
  • Approximately 32% more insect development heat units compared to the 5-year average, and 14% more compared to the 10-year average.

Cool nights but not freezing

A frost warning throughout the province was issued for Saturday morning but thankfully damaging temperatures were not recorded. Buds at the stage of full pink to first bloom are vulnerable to freezing temperatures at -2.2℃ that causes 10% injury after a brief period of time. Overnight temperatures dipped down on May 15th but they were not low enough to cause concern. None of the NSFGA weather stations recorded temperatures below zero but a few low lying areas might have been slightly cooler.

Bud Development


An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. On May 17th, the Idared buds were at about 25-50% bloom. Honeycrisp was at full pink, and Ambrosia was at bud separation. Pears are in full bloom. In early regions, plums are still in bloom depending on the variety, sweet cherries are nearing the end of bloom, and peaches are at petal fall.

Figure 2: Bud development in early regions on May 17th. Middle Dyke Road in Kentville from left to right: Idared, Honeycrisp, Ambrosia.

Terminal Shoots

Trees on Middle Dyke Road in the Kentville area have measurable terminal shoot growth. The Idared trees have about 2 to 3.5 cm of shoot growth and Honeycrisp have about 3.5 to 4.5 cm of shoot growth. 

This growth is of interest if you are considering the use of prohexadione calcium (Apogee or Kudos) for vegetative growth control or suppression of fire blight. Label directions say to apply first at 2.5 to 7.5 cm of new shoot growth. The timing of the first application is critical to success. More information is included in the section below on fire blight.

Figure 3: Terminal shoot growth in an early region on May 17th. From left to right: Idared and Honeycrisp.


Apple – Scab

Table 1: Apple scab infection events at the Kentville Research Station from May 11th to May 18th, 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.

Significant ascospore release - pending

Note that we are in the development stage around pink to bloom that results in the greatest ascospore release. Significant tissue growth and ascospore maturity have developed since the last infection period. A wetting event on the weekend could release about 50% of the total seasonal ascospores that matured during the warm and dry weather.


  • Ensure that tissues are covered with a protectant fungicide prior to an infection event and reapply on a 7-day interval, with a shorter 5-day interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
  • Vigilant protection of primary scab will prevent the challenges that come with chasing secondary scab. Secondary scab will be increasingly challenging with upcoming product discontinuations.
  • 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


  • Apply two sprays targeting powdery mildew prior to bloom on the re-application schedule noted on the product being used (usually 7-14 days). Coverage during the pink to bloom stage prevents fruit infection.
  • Do not apply a product for powdery mildew before a heavy rain is expected. The product will wash off, plus powdery mildew spores will not germinate on a wet leaf surface anyway. As opposed to scab, powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected.
  • 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

Fire Blight Biology

Open blossoms must be present for a blossom blight risk. Fire blight bacteria are transported from overwintering canker sites to open flowers by the action of insects and rain. These bacteria then reproduce on the stigma of flowers and are washed down into the base of the flower by a wetting event – a minimum of just 0.25 mm of rain or heavy dew – which then initiates an infection if adequate bacterial populations are present. An average daily temperature of at least 15.6°C is needed to establish infections and the infection potential rises with consecutive hours above 18.3°C. Blossom blight risk increases with warm temperatures between 23°C and 27°C, especially when occurring over consecutive days because this temperature range is ideal for bacterial reproduction.

Monitoring Regions for Maryblyt Alerts

This year, all NSFGA-owned weather stations will be used for industry alerts. Those weather stations are located in the following communities: Atlanta, Aylesford, Grafton, Grand Pre, Melvern Square, Morristown, Moschelle, North Medford, Windsor, and Woodville.

Prepare for short notice Maryblyt alerts to be delivered directly to your email inbox. Periods with high fire blight bacterial populations are defined by Maryblyt as having an Epiphytic Infection Potential (EIP) greater than 100. Notifications will be sent as soon as it is evident that the EIP will approach 100 for apples and pears. 

To verify that you are receiving the Maryblyt email alerts, I will send a test email today. If you do not receive a test email from me by the end of the day today, please let me know. Maryblyt alerts will be delivered separately because they are more time-sensitive than the weekly newsletter.

Current and Forecast Maryblyt Risk

Open blossoms must be present for a blossom blight risk to exist. The first wave of blossoms opened in the Valley on May 14th so modelling began. According to today's forecast, EIPs will stay low for the foreseeable future. For apples, EIP will peak at 61 on May 21st and then decrease. For pears, EIP will peak at 69 on May 21st and then decrease. The current forecast does not predict an EIP that exceeds the threshold of 100. However, predictions can change on short notice.

Figure 4: Graphical outlook of the epiphytic infection potential (EIP) in red and the average temperature in black for the forecast period from May 18th to May 23rd. At the 100 EIP value, a horizontal line marks the risk threshold for bacterial populations that could cause infection. Currently, EIP is not expected to reach or exceed 100. Predictions can change on short notice depending on the forecast. (Click on image to expand).


  • Consider the ongoing risk of blossom blight infection on flowering apples and pears.
  • 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.
  • 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 12-18 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.
  • If interested in pinching buds on young trees the practice can begin around the bud separation stage when it's possible to avoid removing the terminal shoot. Pinching buds becomes risky as bloom begins because fire blight bacteria grow on the flower stigma and are expected to be present in high numbers in warm weather. Do not pinch flowers when tissues are wet. This practice is time-consuming.
  • 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. 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)!
  • 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.

Calyx or Blossom End Rot

Infections develop toward the end of bloom and appear about one month after petal fall as a brown discolouration surrounded by red on the calyx end of the fruit. The lesion is usually sunken and a corky rot develops in the flesh. When in storage, blossom end rot can lead to moldy core. 

Blossom end rot is more likely in years when the weather is warm (15 to 25°C)  and wet during and shortly after bloom. The disease is most common on Paulared, Delicious, Cortland, Honeycrisp and McIntosh.


  • Captan is a good product for blossom end rot and black rot management. Note the new WSP formulation changes to REI and maximum number of applications if using the product.
  • If blossom end rot has been an issue in the past, consider using a captan product during full bloom. Fungicides during bloom may also reduce the incidence of moldy core.
  • Black rot infections are believed to occur 4-6 weeks after bloom. Stay tuned if we find otherwise as we monitor spore production this year. With the limited number of captan applications, attempting to target blossom end rot and black rot is one approach.
  • If applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.

Stone Fruit – Brown Rot Blossom Blight

Brown rot infection of the flowers during bloom provides secondary inoculum for fruit infections later on.


  • Fungicide protection from brown rot should begin just prior to bloom and be maintained during periods of warm, wet weather. 
  • Rotating classes of brown rot fungicides is key to slow resistance development. There are many options in the management guide.
  • The new formulation of Captan limits the number of applications to one per year on stone fruit.



  • 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.

Pre-bloom Insecticides

Some regions might still have an opportunity to treat for insects if blossoms have not opened. 


  • In orchards with a history of damage and high numbers of EAS catches, an application of Altacor, Assail, Calypso, or Exirel at full pink is recommended to control the adults prior to egg laying.
  • If history of tarnished plant bug damage indicates that pressure is moderate to high, an application of insecticide at full pink can be beneficial.

Pome and Stone Fruit - Plum Curculio

Plum curculio is a weevil that begins laying eggs in stone fruit at shuck fall. Mated females will deposit their eggs in the developing fruit leaving the characteristic crescent-shaped scar. Activity of PC is increased in temperatures above 16°C.


  • 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.

Other Insects

  • For stone fruit, monitor for green peach aphids and black cherry aphid.
  • For pears, if needed treat for apple curculio as soon as possible at petal fall.

Weed Management

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.


  • Temperatures above 16°C are a good time to apply post-emerge products. 
  • Take time to allow concentrated products like Roundup to mix into the solution before adding other products.
  • Glyphosate formulations without the surfactants may be safer to trees than those with surfactants.
  • Be careful with tank mixing herbicides. At the Orchard Outlook committee, there was a report that the mixture of Roundup Transorb and 2,4-D Amine herbicide can form a white precipitate. New formulations may behave unexpectedly. If in doubt, consider performing a jar test to test compatibility. The jar test is described in a post by Sprayers 101.

Blossom Thinning

The caustic thinner ammonium thiosulphate (ATS) is the first chemical thinning opportunity of the growing season. ATS reduces pollen germination, interfering with fertilization. 


  • The advantages of blossom thinning with ATS are possibly increased fruit size and return bloom compared to later fruitlet thinning. ATS would be a good consideration for early thinning of small fruited varieties (e.g. Ambrosia and Gala). 
  • The caustic activity of ATS does not depend on the temperature at application. Consider ATS as a useful tool, especially in an environment that experiences cool nights and sunny days. Such low-stress weather conditions make it difficult to thin using plant growth regulators. 


  • Beware that if the fire blight risk is high (infection pending a wetting event) an antibiotic is needed prior to ATS or wait until the risk has decreased.
  • Note that the challenges of ATS are thinning with an unknown crop load and the potential for foliar spray injury. If ATS is applied to dry leaves then there is less chance of injury. Some foliar and petal burn is normal and suggests the concentration is effective for thinning. 
  • It can increase fruit russet so avoid sensitive varieties as a precaution.


  • ATS can be applied towards the later part of full bloom (80-100% FB), at which point adequate pollination of king flowers has occurred. This strategy can produce variable results by being too late if it gives most flowers the time needed for fertilization.
  • The goal is to apply ATS when the king flower has had enough time to become fertilized but prior to the lateral flowers becoming fertilized. For more accurate timing, consider that in order to become fertilized, a pollen grain must germinate on the stigma and grow a pollen tube to the base of the style to reach the ovary. In cool temperatures of 13°C, fertilization of open flowers takes 5 days and in warm temperatures of 24°C, fertilization takes 2.5 days. Therefore, time the ATS application for several days after the desired percentage of bloom has opened. Please ask me for more information if interested (and if you want to measure stigmas).
  • In Nova Scotia, ATS has been used at 5.5 L in 100 gal/acre (13.6 L ATS in 935 L/ha). The concentration is what matters for its activity so don’t concentrate it by spraying a lower volume. Keep records to learn from your results. If you are not familiar with the product, be conservative with the rates, use it on a small area first, and talk to someone with experience about rates.



  • Avoid heavy pruning now in order to avoid weakening trees.
  • Ensure that youngest blocks are pruned first so growth is directed into desirable leader and terminal extension.
  • In blocks with historically high fire blight pressure, prune only when the forecast calls for at least 2 days of sunny, dry weather. As an extra precaution, disinfect tools after working in a block with fire blight pressure.


  • Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.


  • Monitor bee activity around 6-9 PM to understand pollination conditions and to help you predict
  • flower set. This information will be helpful during thinning.


  • Bark typically slips from pink to bloom so grafting is underway.

Planting Trees

  • Remember the risk of dipping roots in a shared water solution. Widespread disease can affect the planting stock that is dipped in the same batch of solution. Microscopic organisms that cause plant diseases spread freely in water. Yes, we usually get away with root dipping unscathed, but not always. A guest presentation by a nursery grower a few years ago advised against root dipping because the practice is not worth the risk.
  • 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).
  • Remember to document the quality of your nursery trees with pictures and notes. Did trees dry out? Any signs of disease (cankers, crown gall)? How do the roots look (rinse and take a photo)? Notify the appropriate people of issues you notice. Record the date of planting. An issue that shows up after planting is much easier to diagnose or prevent given this information.
  • If fumigating in the spring, observe the warnings on the label prior to planting to avoid crop injury. Leave the soil undisturbed for 10 to 14 days or longer in wet weather. To verify plant safety, follow the safety germination test described on the label for PicPlus.

On-Farm Nursery Trees

  • 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!


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

Wild Apple Trees

  • Wild apple trees harbour pests, in particular apple maggot, that can then spread to nearby orchards. Now that wild apple trees are in bloom, it’s a good time to flag trees on your own property so that you can find them later in the season for removal.

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.

NSFGA Research Survey

Before time and energy is put into considering research proposals or applying to funding programs, direct input from members is needed to establish research priorities and propose research interests.

The NSFGA Research Committee is asking for your input on this survey to explain what you need or would like to see in terms of research so that we engage in research that is of benefit to growers, packers, and processors. It is important that we get your opinion on what information would benefit you and/or the apple industry. The survey is expected to take less than 5 minutes to complete. Please complete by end of day today on Tuesday, May 18th. 

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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