Orchard Outlook Newsletter Vol 21, No 7

Tuesday, May 25, 2021


Table of Contents:

  • 2021 Degree Day Accumulations
  • 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
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects

Weed Management

  • Apple - Blossom Thinning
  • Apple - Fruitlet Thinning
  • Pear Thinning

  • Pruning and Training
  • Pollination
  • Grafting
  • Planting Trees
  • Mowing
  • Wild Apple Trees

Pest Management Guides 2021

Events and Notices



2021 Degree Day Accumulations

The above-average trend continues. In terms of growing degree days for plant development, this year continues to match up with 2017 and 2006.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to May 24th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 27% more plant development heat units compared to the 5-year average, and 18% more compared to the 10-year average.
  • Approximately 67% more plant development heat units compared to 2020, and 50% more compared with 2019.
  • Approximately 30% more insect development heat units compared to the 5-year average, and 14% 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. On May 24th, the Idared buds were at about king bloom petal fall or later. Honeycrisp was at full bloom to early petal fall, and Ambrosia was not quite at full bloom. Pears are beginning petal fall. Plums, sweet cherries, and peaches are at petal fall/calyx.

Figure 2: Bud development in early regions on May 24th. Middle Dyke Road in Kentville from left to right: Idared, Honeycrisp, Ambrosia.

Terminal Shoots

The Honeycrisp trees on Middle Dyke Road have about 6.5 cm or more of shoot growth. They are nearing the end of the best treatment application window for 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 on Honeycrisp in an early region on May 24th.


Apple – Scab

Table 1: Apple scab infection events at the Kentville Research Station from May 18th to May 25th, 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 May 26th to 27th. With the forecast temperatures at an average of +13.0°C, it would take around 11 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills Table. Ascospores are expected to mature to 95%.
  • 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.
  • 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

An alert was sent to subscribers by email on May 24th and May 25th. An infection is in the forecast for all regions on apples and pears on May 26th. Please check the alerts 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.

How Bacterial Growth on May 26th relates to Spray Timing

The alerts sent by email show a scenario that an antibiotic applied today on May 25th would not provide protection against the bacterial growth that is expected on May 26th. Flowers that open on May 26th are only protected from bacterial growth if they are sprayed after they open. If the antibiotic is applied on May 25th then it has not protected flowers that open when the new day begins.

Myth busting: Water does not wash away bacteria

An excerpt from the Orchard Outlook Podcast with Dr. George Sundin in 2019: "Bacteria require rainfall to help them swim from the tips of the stigmas and down to the base of the flower where they infect. If we get quite a bit of rain they don't even have to swim... that will just splash them into the base of the flower. Bacteria are quite (small) - there is not much weight there. I think of (rain) more like you're releasing a cloud of cells that can move and colonize new flowers and sites on the tree. Rain is one of the mechanisms the pathogen uses to move.

The Maryblyt model doesn't reset after a rain because there is still a lot of bacteria present. If a rain corresponds with cooler temperatures then the cool temperatures are responsible for less bacterial growth.


  • 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. Pinching buds is not advised on May 26th.
  • 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


  • 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.


  • With the upcoming risk of fire blight infection, note that if applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.
  • 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.

Stone Fruit – Brown Rot Blossom Blight


  • Fungicide protection from brown rot should 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.

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).

Stone Fruit Insects

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.
  • For stone fruit, monitor for green peach aphids and black cherry aphid.
  • 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

  • Petal fall is the ideal treatment timing for winter moth and fruit worm in pear. Treatment should be based on need determined by monitoring. 
  • Apple curculio is difficult to monitor for and its presence often is not observed until damage on fruitlets shows up. Treatments for this pest should go on when pears have reached calyx. Use of one of the products registered for plum curculio should also control apple curculio.
  • 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.

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.


  • 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.
  • 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.

Chemical Thinning

Blossom Thinning

Beware of fire blight risk and high temperatures

The window for applying the caustic thinner ammonium thiosulphate (ATS) is coming to an end, depending on the orchard and variety in question. Beware that with the impending fire blight risk on May 26th, an antibiotic is needed prior to ATS or wait until the risk has decreased or rely instead on fruitlet thinners.

In Ontario, there is a recommendation to avoid application if the temperatures will exceed 27C within 24 hours. Such conditions will increase the risk of leaf injury and fruit russet.

Pollen tube growth model example

In earlier newsletters I explained that in cool average temperatures of 13°C, fertilization of open flowers takes 5 days and in warm temperatures of 24°C, fertilization takes 2.5 days. Out of curiosity, you might be interested to know how this panned out. On Gala with a stigma length of 12 mm, when the pollen tube growth model was started on May 20th the cool temperatures did result in a prediction of 4.5 days to fertilization. Flowers open on May 20th would set and then the ATS would prevent fertilization of flowers that opened afterward.

ATS not recommended for defruiting young trees

The question of using ATS to defruit young trees has come up a few times now. 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.

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).
  • 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.
  • 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!
  • 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. 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.

Pear Thinning

  • The Maxcel thinning window is 8-14 mm and early treatments are most effective.


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.


  • 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

  • Ensure that deer fencing is installed as soon as possible to protect new growth on young 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.


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

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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