Orchard Outlook Newsletter Vol 21, No 5

Tuesday, May 11, 2021


Updated with addendums on May 18, 2020: 
  • The negative symbol was added to correctly read: "With many buds now at the tight cluster stage they become vulnerable to freezing temperatures at or below -2.8℃."
  • The temperature factor for fire blight was inaccurately explained. The average daily temperature factor for fire blight infections to occur is 15.6°C. The value 18.3°C is a separate factor for determining the epiphytic infection potential. Below in the fire blight explanation, 18.3°C has been replaced with 15.6°C. 

Table of Contents:

  • 2021 Degree Day Accumulations
  • Weather

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple - Fire Blight Prevention
  • Apple - Calyx or Blossom End Rot
  • Stone Fruit - Brown Rot Blossom Blight
  • Spring Caterpillar Complex
  • European Apple Sawfly
  • Tarnished Plant Bug
  • Pre-Bloom Insecticides

Weed Management

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

Pest Management Guides 2021

Events and Notices

  • NSFGA Research Survey



2021 Degree Day Accumulations

The above-average trend continues but the lead in degree day accumulations has diminished after recently cool temperatures. For comparison, consider that in the year 2010 the bloom started around May 10th for early apple varieties and pears. In 2012, early apple varieties were at pink to full bloom by May 16th depending on location. In this newsletter, you will notice that we are already thinking ahead to bloom.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to May 10th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 29% more plant development heat units compared to the 5-year average, and 24% more compared to the 10-year average.
  • Approximately 94% more plant development heat units compared to 2020, and 29% more compared with 2019.
  • Approximately 25% more insect development heat units compared to the 5-year average, and 14% more compared to the 10-year average.


Seasonal Precipitation

Figure 2 is a graph of cumulative precipitation over the last ten years including rainfall and the rainfall equivalent from snow. Follow the red line to see how 2021 compares to previous seasons. Cumulative precipitation totals were behind average in late winter and early spring but recent rainfall events have brought it up to the 10-year average. Some regions saw significant rainfall on May8/9th seeing up to 59 mm of rain with the most around Atlanta, Aylesford, and Melvern Square.

Jeff also commented that the rainy weather is a major factor in the slight cooling we have seen in the soil and lower air temperatures.
Figure 2: Both rainfall and the rainfall equivalent from snow at the Kentville Research Station from 2012 to 2021. Provided by Jeff Franklin (AAFC).

Cool nights but not freezing

With many buds now at the tight cluster stage they become vulnerable to freezing temperatures at or below -2.8℃. Overnight temperatures dipped down on May 8th but they were not low enough to cause concern. Only the Windsor area dropped below zero at -0.2℃.

Weather Station Update

All ten weather stations that were purchased and installed through the NSFGA project with federal and provincial funding are now up and running!

Refer to previous posts for more information about accessing weather stations. At the very least, I highly recommend you download the Davis WeatherLink application for smartphones to access the current weather. Use the NSFGA account or create a free account. Any weather stations on the Davis WeatherLink network that do not have "NSFGA" in the name are not being maintained under this project. 

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Over the last week pink buds have become visible as the bud clusters separate. On May 10th, the Idared buds were at the stage of bud separation, Honeycrisp was at tight cluster, and Ambrosia was at early tight cluster. Stone fruit in Greenwich including sweet cherries, plums and peaches are in full bloom. Pears are at the green cluster stage.

Figure 3: Bud development in early regions on May 10th. (Top) Middle Dyke Road in Kentville from left to right: Idared, Honeycrisp, Ambrosia. (Bottom) Sweet cherries from KRDC, and from Greenwich plum and peach.


Apple – Scab

Table 1: Apple scab infection events at the Kentville Research Station from May 5th to May 11th, 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.


  • A period of rainfall is currently forecast for today. With the forecast temperatures at an average of +11.0°C, it would take around 12 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills TableNote that we are nearing the development stages around pink to bloom that result in the greatest ascospore release. 
  • 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.

Special notes on products containing Captan and water soluble packaging:

  • The product formulations Maestro 80 DF and Supra Captan 80 WDG are phased-out. There are new registrations for the formulations Supra Captan 80 WSP and Maestro 80 WSP.
  • Water soluble packaging has been used in the past but now we are looking at more frequent use. Consider these best practices:
    • Make sure packets fully dissolve and disperse before adding other products. Packets dissolve faster in warm water than cold water, like dishwasher pods. 
    • Check the filter after the first use and every couple of uses.
    • Be careful mixing. 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

Typically, conidia are released around the tight cluster stage. Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.


  • 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 – Fire Blight Prevention

Bloom and Maryblyt Alert Period Approaching

Open blossoms must be present for a blossom blight risk. When the first blossoms open in the Valley, I will begin running the Maryblyt model predictions for industry alerts. As blossoms open in your orchard and temperatures average above 15.6°C along with other factors, prepare for short notice Maryblyt alerts to be delivered to your email inbox. Notifications will be sent as soon as it is evident that the Epiphytic Infection Potential (EIP) will approach 100 for apples and pears. Everyone who subscribes to the newsletter will receive the alerts. 

Figure 4: When bloom begins, prepare for short notice Maryblyt alerts to be delivered directly to your email inbox. Email alerts will now look like this image so they are clearly visible.

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.


  • 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. 
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees. 
  • In blocks with historically high 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.
  • 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.

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 it has been an issue in the past, consider using a captan product during full bloom. 
  • 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 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.


Depending on the heat in the forecast, your region, and monitoring reports, action may be needed during the pink stage.

Spring Caterpillar Complex

(winter moth, green pug moth, eyespotted bud moth, speckled green fruitworm, obliquebanded leafroller)


    • Treatments for spring caterpillars should not be applied too early because product must enter the developing flower clusters where the larvae like to feed to be effective. Treatments should be applied pre-bloom so target the full pink stage. 
    • Evidence of feeding includes tiny holes in new leaves and flower buds, and black specks of frass. Begin scouting procedures described in Perennia’s Best Management Practices. Check your scouting reports for notes on WM, GPM, and other caterpillars for those with scouting services. Dr. Suzanne Blatt reports from KRDC that the pug moth stripe is becoming visible.
    • Note that there is a lower tolerance for WM than GPM. Green Pug Moth do not feed directly on developing fruitlets.
    • If a treatment for just WM is required, then a Bt product (e.g. Dipel or Bioprotec) with Mako applied at bud separation is effective with a minimum impact on beneficial insects.

    European Apple Sawfly


    • 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.
    • In blocks with low to moderate pressure, control of EAS can occur at petal fall.

    Tarnished Plant Bug


    • If history of tarnished plant bug damage indicates that pressure is moderate to high, an application of insecticide at full pink can be beneficial.
    • Pyrethroids (group 3) and the sulfoximine product Closer (group 4), are registered for control.

    Pre-bloom Insecticides


    • Monitor for rosy apple aphid populations that exceed thresholds when aphid stem mothers start producing offspring.
    • If treatments for OBLR are required at pink, the treatments should also have some activity on WM and GPM. 
    • If a pyrethroid is applied for tarnished plant bug at pink, it will also have activity on WM and GPM. Similarly, pyrethroids are expected to have some activity on EAS if being applied for other pests.
    • As a reminder, pyrethroids are best used at moderate temperatures (20°C or less) and are harsh on beneficial insects and predator mites. They should only be used where potential losses justify their application.

    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). It can increase fruit russet so avoid sensitive varieties as a precaution.
    • 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. 


    • ATS could 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. Prune early to encourage vigour or delay pruning to remove vigour.


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


    • Consider that it is near the time that honeybees should be moved into the orchard for pollination when king flowers open.


    • Bark typically slips from pink to bloom but can be checked early if you plan to get a head start.

    Planting 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).
    • 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

    • Rootstock tops should be cut so the rootstock does not overpower the bud.
    • 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!
    • If growing your own trees, criticize their quality and don't plan to plant 100% of the trees. Planting small (<4 ft), weak trees will delay production. Trees are typically small for a reason and will continue to be weak trees. Commercial nurseries grade their trees and build in the cost of discarded trees so the same approach is recommended for on-farm nurseries. Tree losses of at least 10% are common.


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

    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 Tuesday, May 18th. 

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