Orchard Outlook Newsletter Vol 21, No 16

Tuesday, July 27, 2021


Table of Contents:

  • 2021 Degree Day Accumulations
  • Review of Apple Scab
  • Review of Fire Blight
  • Review of Powdery Mildew
  • Apple Storage/Pinpoint Scab
  • Apple Storage Rots and Fungi

  • Preparing for Fumigation
Harvest Fruit Quality
  • Summer Pruning for Red Colour
  • ReTain and Harvista: Preharvest Management Strategies
  • Reducing Bruising
  • Considering Watercore
  • Avoiding Internal Browning
  • Harvesting Too Early
  • NSFGA Virtual Summer Tour Sneak Peek
  • Agriculture Weather Station Assistance Program
  • Perennia Virtual Field Days!
  • Bitter rot and apple scab samples for AAFC

*** Please note that this will be the last weekly issue of Orchard Outlook for 2021. Orchard Outlook will continue to be produced occasionally for the remainder of the season. In this issue, I begin to wrap up with a review of disease pressure, however, the full end of season summary will be published in November. I also look ahead to preharvest management strategies. It seems early but I'd rather the information be out there in good time! I wish everyone a smooth harvest season when it arrives. ~ Michelle ***


2021 Degree Day Accumulations

The gap between 2021 and the 5- and 10-year averages has been gradually narrowing. Degree days may not directly translate to a change in harvest dates but monitor blocks earlier than usual as more heat might lead to earlier maturity. We are currently tracking similar to the degree day accumulation in the years 2010, 2012, and 2013.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to July 26th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 10% more plant development heat units compared to the 5-year average, and 8% more compared to the 10-year average.
  • Approximately 9% more plant development heat units compared to 2020, and 19% more compared with 2019.
  • Approximately 11% more insect development heat units compared to the 5-year average, and 9% more compared to the 10-year average.

2021 Review of Disease Pressure

Review of Apple Scab

The infection periods for the 2021 season are summarized in Table 1. Above-average temperatures in early spring led to early maturing ascospores along with consistent wetting that produced repeated infection events. By May, four infection events had already been recorded... resulting in a very early start to the fungicide season.

Throughout the month of May, consistent rain continued to produce regular infection events. Although, the rain was not long-lasting so at most the events were light infections, depending on microclimates. Prolonged wetting on May 22-24 resulted in a heavy infection and it was a notable risk period because 15.9% of total spore load had matured since the last infection and new tissue had developed in the meantime. This season there were relatively few heavy infection events but a total of 13 primary infection events were still recorded.

Secondary scab infection events were also ongoing and can occur up until harvest time, therefore any orchards with scab should continue regular fungicide sprays until preharvest intervals no longer allow their application. August fungicide applications are also used to prevent summer fruit rot diseases from showing up at harvest.

Table 1: Summary of apple scab primary infection periods recorded in Kentville in 2021, based on the Modified Mills Table and assuming a green tip date of Tuesday, April 14th.

Review of Fire Blight

The first blossoms in the Valley opened around May 14th with early regions in full bloom around the last week of May. A heat wave created a high risk of fire blight blossom infection during a critical period of bloom throughout the Valley. 

According to the Maryblyt model, high EIP values were first noted on May 23rd for Windsor and May 26th through to May 27th for all regions. The EIP was again high on open blossoms from June 3rd through to June 11th. Wetting events including rainfall and dew during high EIP periods were conducive to bacterial infection, unless antibiotic protection was applied. Blossom infections developed where protection was not achieved.

This year’s new orchards that were planted late were vulnerable as they bloomed during the summer heat. It was a very high-risk period when antibiotics provided only one day of control given bacteria growth in the heat.

The risk of trauma blight was recorded from isolated hail events on May 18th and July 21st, and during winds from post-tropical storm Elsa on July 10th. Elsa caused wind gusts up to 80-106 km/hr. Damaged tissues were widespread from Elsa even though winds in most regions gusted to only 50-60 km/hr.

This year, the NSFGA weather stations have been a new tool to inform decision making and to record microclimate conditions that impacted fire blight infection risk.

Review of Powdery Mildew

Conditions this year were favourable for powdery mildew to spread and pressure was high throughout the Valley. Susceptible varieties like Cortland are heavily infected and relatively heavy infection is showing on Honeycrisp as well. Warm, humid, and dry weather during shoot growth in June and July contributed to secondary infections on new leaf tissue. The pressure this year might be related to carry over from high pressure last year, limited fungicide products, and a mild winter that allowed the fungi to survive. Stay tuned for our upcoming podcast that is all about powdery mildew!

Where pressure was high this year, powdery mildew inoculum will overwinter and next spring the risk of new infections will be best controlled with well-timed fungicide applications. Continue to watch for powdery mildew in nurseries and young plantings if terminal buds have not set.

Late Season Diseases

Refer to the July 13th Orchard Outlook for earlier management information about apple scab, powdery mildew, fire blight management, and summer diseases.

Apple Storage/Pinpoint Scab

Pinpoint scab results from infections that occur late in the growing season. Small black dots appear as infections on the skin of the apple. In some cases, the fruit infections don’t appear until after the fruit has been placed in storage, however, the infections do occur prior to harvest.


  • Fungicide protection maintained through to early September can help to prevent these late season scab infections and provide some protection against storage rots.
  • Late season fungicide treatment is highly recommended in blocks that have leaf and/or fruit scab. Scab lesions that appear to be inactive at this time of the year can become active again in the fall under cool wet weather conditions.
  • When selecting a late season fungicide, consider the days to harvest. For apples and pears, captan has a 7-day PHI but the REI for hand harvesting in high-density production is 15 days and in low-density production is 19 days. Always check both the REI and PHI because in some cases the REI for hand harvesting is longer than the pre-harvest interval. In that case, respect the longer of the two intervals.
  • Allegro has been a good option with the short 3-day REI but keep in mind the 28-day PHI.

Apple Storage Rots and Fungi

A well-timed preharvest chemical control can go a long way to prevent storage rots. Black rot, flyspeck, sooty blotch and brooks spot are preharvest issues that can infect fruit in the orchard. Fungal spores that land on unprotected fruit can germinate and show up as infections in storage. Fruit with bruises and punctures are even more susceptible to rot, especially when fruit are harvested during a wet period. Blue and gray moulds can invade only damaged fruit. Sooty blotch won’t cause decay but it does shorten fruit storage life by increasing water loss.


  • Monitor precipitation during harvest, especially for late-season varieties. Cumulative rainfall of 25-50 mm washes off fungicide protection.
  • The group 7 & 11 products Pristine and Merivon can be applied up to 5 days before harvest. They are labelled for the control of scab, black rot, flyspeck, and sooty blotch. The short PHI and good activity are especially helpful for protecting apples being placed in long-term storage.
  • Of course, avoid bruising or wounding to prevent infections of blue and gray moulds. Take the time to educate staff on the proper way to handle fruit.


Insect management programs should be based on grower monitoring and/or scouting reports. Refer to the July 13th Orchard Outlook and July 20th Orchard Outlook for information regarding white apple leafhopper, potato leafhopper, apple maggot, spotted wing drosophila, aphids, obliquebanded leafroller, and mites.


Refer to the July 13th Orchard Outlook and July 20th Orchard Outlook for information about summer pruning/hedging, pruning & training, young trees, calcium nutrition, weed management, nursery trees, mowing, leaf tissue sampling for nutrient analysis, soil sampling for nutrient analysis, and nursery practices for propagation. In addition:

Preparing for Fumigation

Sites that will be fumigated early this fall need to have the soil prepared to where it is in a seed bed condition. A poorly prepared site could result in the fumigant being ineffective. This means that there should be no large clumps of soil or vegetative matter that will hinder the sealing of the soil surface. Preferably, the fumigation strip should also be deep ripped to bring up roots or stones that may damage the fumigator.

Harvest Fruit Quality

Summer Pruning for Red Colour

Vigorous shoot growth in orchards could present a fruit shading problem. Summer pruning could be used to expose the fruit to more sunlight to improve fruit colour. Also, summer pruning controls vigour so it could divert more calcium to fruit. The practice might help reduce the risk of bitter pit. 


  • Summer pruning should be a simple process of making the pruning cuts to one- and two-year old wood. Remove vigorous shoots in the entire canopy but especially at the top.
  • Leave the weaker side laterals to supply the fruit with carbohydrates. If you over prune you could end up reducing fruit size.
  • Avoid leaving short stubs as they will produce two or more shoots next spring.

ReTain and Harvista: Preharvest Management Strategies


  • As even more new plantings come into bearing, consider the advantages of harvest management tools to help slow fruit maturity as you manage labour resources. 
  • Both ReTain and Harvista can help reduce the incidence of watercore and internal browning by delaying maturity. 
  • The economic return for these products is expected to be greatest with good crop loads, high-value varieties, and good fruit quality.
  • Consider testing ReTain or Harvista on a small block and talk to others who have experience using them.


ReTain’s active ingredient (aviglycine hydrochloride) inhibits the production of ethylene in plant tissues, delaying fruit maturity. Potential benefits of ReTain include harvest management to delay the maturity in blocks of a single variety, improved fruit size (as fruit hangs longer on the tree), maintenance of firmness, and reduced greasiness and cracking. ReTain can also offer additional benefits including improved storage quality. However, Retain can also slow red colour development. Delays to fruit colour development can be minimized by lowering the rate of application or by delaying the harvest period.


  • Note that the amount of ethylene produced differs by apple variety and so the variety’s response to ReTain will also differ. McIntosh is a high ethylene-producing variety and the full rate is often needed 3 weeks before harvest to slow its maturity. Sensitive varieties like Gala, Jonagold and Honeycrisp produce low ethylene and are more sensitive and thus greatly delayed by ReTain.
  • ReTain applied 3-4 weeks before harvest will delay the harvest period up to 7 to 10 days.
  • The effectiveness of ReTain is dose-dependent and time-dependent. Later applications and smaller doses have less effect on maturity and colour development.
  • For a multi-pick harvest, ReTain applied 7 to 14 days prior to the anticipated start of harvest can improve the quality and storage potential of 2nd and later picked apples. First picks will not be affected but later picks will be delayed. Note the PHI of 7 days.
  • Xiameter surfactant is recommended at a concentration of 0.05 to 0.1% (v/v) in the spray tank. To prevent possible spotting on fruit, use the 0.05% (v/v) concentration.


Harvista (1-methylcyclopropene) is another product for preharvest management that was registered in 2017. The mode of action is different from Retain because Harvista blocks ethylene action in fruit, even after ethylene has been produced by fruit. Therefore, Harvista can act quickly to slow maturity whereas ReTain requires a timely application to fruit before ethylene production escalates.


  • Harvista can be applied 3 to 21 days before the anticipated harvest and at a higher rate for fruit that are more advanced in maturity and producing plenty of ethylene.
  • Harvista will delay the harvest period up to 7 to 14 days.
  • Typically the product will reduce the number of harvest picks because it helps synchronize the maturation rate.
  • Lower rates are recommended for biocoloured apple varieties to allow colour development to progress. It can delay red colour development on Gala and Ambrosia so apply after colour has developed at close to 3 days before harvest. It also reduces stem splits on Gala.
  • A customized sprayer system is required for Harvista applications.

Reducing Bruising


  • Apples picked after significant rain will bruise more easily than if they’re picked when the soil has a lower moisture capacity. This information might be helpful for varieties especially sensitive to bruising.
  • Let fruit warm up before harvesting. Apples picked in the cool weather of early morning bruise more easily than those picked in the day’s warmth. Generally, susceptibility to bruising decreases gradually from 0 to 15°C.
  • Take the time to educate staff about the proper way to perform harvest activities that reduce bruising. For example, pick the bottom of the tree first, don’t overfill the picking bag, avoid long harnesses that let the bag bump against knees when walking, explain the difference between varieties etc.
  • Re-grade orchard roads prior to harvest to lessen bumps that would jostle fruit being transported in bins.
  • Have an inspector sample fruit from various positions in the bin two times each week and leave at room temperature for 24 hours to check for signs of bruise development.
  • If bins of fruit will sit in the orchard during overnight freezing temperatures, place the bins where they will be shaded from direct morning sun. Direct sun will warm the fruit too quickly and can lead to deep and lasting bruises.

Considering Watercore

Watercore is a fruit disorder closely associated with over-mature apples along with several other factors. It happens most frequently in years with high sunshine and lack of cloudy, rainy days. Also, highly coloured and large fruit are most prone to the disorder. Fruit with the disorder have an appearance of water-soaked flesh because the spaces between the cells become concentrated with sugars instead of air. Small signs of watercore can disappear in storage and add sweetness to fruit. However, more serious watercore can reduce gas exchange in the fruit and lead to internal breakdown.


  • Mature fruit are more likely to develop the disorder because as fruit mature the starches are converted to sugars. The sugar solution builds up in the fruit. Harvest blocks that have a history of watercore before other blocks.
  • Consider products to delay harvest maturity. Both ReTain and Harvista labels state delayed onset and incidence of watercore.
Figure 1: An example of watercore symptoms in Honeycrisp from 2018. Note the areas of water-soaked flesh.

Avoiding Internal Browning

Internal browning is likely related to carbon dioxide injury. The disorder frequently occurs in overmature and large fruit that have high carbon dioxide concentrations. In particular, fruit harvested late in the harvest window are most susceptible because as fruit mature their ability to diffuse internal carbon dioxide concentrations decreases. The internal carbon dioxide builds up and increases the chance of injury. Consider products that delay harvest maturity.

Harvesting too Early

While trying to avoid overmature fruit, avoid the other extreme as well – immature fruit. Picking fruit too early has penalties. Fruit continue to grow as they mature so a 1/4 inch increase in size from 2 3/8 to 2 5/8 can translate into a 35% increase in fruit volume. It takes just as long to pick one large (88 count) apple as it does to pick one small apple (160 count). But it will take half as long to make up a bushel of large apples than small. So picking cost and time required are less for larger fruit. Picking too early can also sacrifice fruit colour and reduce pack out. Immature fruit bruises easily and is subject to scald, shriveling in storage, and poor flavour.

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 Virtual Summer Tour Sneak Peek

Here's a sneak peek into the Nova Scotia Fruit Growers' Association summer tour in 2021. Visit farms with your host Michelle Cortens, Tree Fruit Specialist at Perennia to hear from local growers about weather stations, root pruning, mechanical weed control and more. Plus, see new perspectives like a bird’s eye view of a 2D planting. Stay tuned for a series of videos in early August of 2021. The bus is leaving soon. Watch the video here: https://youtu.be/PbxAxVymv6s

Agriculture Weather Station Assistance Program

The Nova Scotia Department of Agriculture and Perennia have launched the Weather Station Assistance Program. The objective of the Farm Weather Station Program is two-fold: to encourage producers to install weather stations and adopt new technology tools; and fully utilize the data to make proactive management decisions to mitigate the impacts of climate change and adverse weather conditions. The application is due July 30th. For more information, view the webpage. For questions, please contact Jody Wipp.

Perennia's Virtual Field Days!

Join us for this year's Virtual Field Days taking place throughout the month of August! Each week, Perennia specialists will host a 30 minute virtual field day, followed by a question and answer period. For more details, click on the link to register.

Refining Horticulture - August 3, 2021, at Noon (Register)
Technology in Agriculture - August 10, 2021 at Noon (Register)
Optimizing Production - August 17, 2021, at Noon (Register)
Livestock Management - August 24, 2021 at NOON (Register)

Bitter Rot and Apple Scab Samples for AAFC

The Plant Pathology Lab of Kentville’s Agriculture and Agri-Food Canada is looking for apple growers who will participate in a province-wide study of the fungal pathogens responsible for bitter rot and apple scab disease in apple. One of the goals of the research is to look at the fungicide resistance profile to find out which fungicides are still effective or not. This is an industry and AAFC funded project. 

Growers who notice either bitter rot or apple scab appearing in their orchard are invited to contact Dr. Shawkat Ali (shawkat.ali@canada.ca) or Shayne McLaughlin (mc615708@dal.ca). Researchers will then monitor the orchard to collect diseased leaves or fruit from the orchard for further study. Samples cannot be collected from the orchard floor due to rapid deterioration. 

View a research update from past work hereParticipants who provide a site for collection of bitter rot samples will have the species in their orchard identified and they will be informed of the fungicide sensitivity profile for that species.

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

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