Orchard Outlook Newsletter Vol. 22, No 11

Tuesday, June 21, 2022

In today's newsletter you'll find information to help you consider the risk of spreading fire blight during wet weather. Also note the risk of summer diseases if spray programs are stretched to the limit. For insect management, updated codling moth treatment timing predictions are provided. Hardly believing that today is already the summer solstice, we offer reminders about the risk of granular fertilizer and glyphosate, and also approaching pre harvest intervals on certain products. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2022 Degree Day Accumulations
  • Weather Station Communications
  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Apple - Brooks Spot
  • Apple - Flyspeck and Sooty Blotch
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects
  • Solstice Reminders
  • Calcium Nutrition
  • Weed Management
  • Mowing
  • Training
  • Young Trees
  • On-farm Nursery

Pest Management Guides 2022

Events and Notices



2022 Degree Day Accumulations

The cumulative degree days remain slightly above the 5 and 10-year averages for base 5°C and 10°C heat units (Figure 1).

Recent precipitation has been sporadic. Kentville precipitation is running close to average for the month of June. Regions in Annapolis County were missed by recent precipitation events and seem to be running at half the average precipitation.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 20 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 8% more plant development heat units compared to the 5-year average, and 7% more compared to the 10-year average.
  • Approximately 7% less plant development heat units compared to 2021, and 16% more compared with 2020.
  • Approximately 7% more insect development heat units compared to the 5-year average, and 6% more compared to the 10-year average.

Weather Station Communications

Perennia is contracted to provide maintenance for the ten NSFGA weather stations. A couple of issues are currently being serviced outside of routine maintenance:
  • GRAND PRE (NSFGA): The station was fixed last week and is now operating normally.
  • NORTH MEDFORD (NSFGA): Leaf wetness data is not being reported. We determined that the leaf wetness sensor is functional so an issue is being investigated with the node.


Apple – Scab


  • As of June 10, cumulative ascospore maturity theoretically reached 100% according to the model. 
  • Do not reduce fungicide spray intervals until you can identify your pressure from scab lesions. This requires waiting at least 2 weeks after the last primary infection event that was theoretically on June 13. Also note the risk of summer diseases if spray programs are stretched to the limit.
  • Where primary lesions are present, secondary infections have been occurring and will continue during wetting events of sufficient duration. The minimum wetting required for secondary infections is 3 hours less than the wetting required for primary infections.
  • The pre-harvest interval for EBDC fungicides (e.g. Manzate, Dithane) for fruit destined for the United States is 77 days versus 45 days for the domestic market. An application of EBDC on June 21 would require until September 6 to meet pre-harvest requirements for the United States.
  • Do not use folpan until 30 days after petal fall to avoid fruit russeting, which is likely around early July. Also note that new to this year Folpan has a 6-day REI for hand thinning fruit.
  • Re-apply a protectant fungicide to green tissue prior to an infection event on a 7-day interval, with a shorter 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.
  • 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.

Apple – Powdery Mildew


  • Remember that summer sprays are protectants and not eradicants. Flag shoot symptoms from overwintering infections will be visible for the rest of the season.
  • Powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected, and not prior to heavy rain. 
  • Do not apply more than two consecutive applications of a group 3 or group 7 fungicide.
  • 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

Past and Forecast Blossom Blight Risk

  • Multiple alerts were sent for new plantings that were in bloom. Unprotected blossoms were under risk of infection on June 18 and 19.
  • In recently cool temperatures, bacterial growth is slow and does not currently pose a high risk of infection.
  • Warm temperatures beginning around June 23 are then forecast to increase the risk. Currently it appears as though the EIP on open blossoms will approach or exceed the 100 threshold around June 24.
  • When concerning EIP values are imminent, alerts will be sent for the purpose of protecting late blossoms on new plantings. Alerts will be provided for the risk at the end of this week. Alerts will likely then end for this season unless I am notified that blossoms are still present.

A Discussion on Trauma Blight Risk

A severe thunderstorm passed through regions of the Valley on Saturday, June 18 and I observed heavy rain and downbursts of wind in the Kentville region. I reached out to a network of colleagues and a few growers to find out if hail had been observed anywhere. At the time, I was not informed of hail in orchards so a trauma alert email was not sent. Recently, I have learned of minor hail damage that was managed on a case by case basis. 

Apart from hail, we also talk about the risk of spreading fire blight when working in wet trees. The recommendation is to avoid working with trees when they are wet and to work in high risk blocks when there are two days of sunny and dry weather ahead. What is the foundation for such a conservative recommendation? 
  • During the first few minutes of rain, bacteria present in dried ooze becomes rehydrated and is splash-dispersed.
  • During rain, the bacteria is present in the air collected near active infections. In dry weather the bacteria is much less likely to be airborne near infected tissues.
  • The bacteria is present at very high populations in water droplets on infected trees.
  • A wound allows the bacteria to surpass the tree's natural defence mechanisms.
  • The chance of a wound becoming infected rapidly diminishes with time from the injurious event. Infections are unlikely if bacteria are transported to the wound site at 48 hours after injury. 

Does the temperature matter at the time of a trauma event? Not as far as I am aware. I know there is a tendency in the industry to hope that cool temperatures will reduce the risk of trauma infections. However, trauma infections happen when the bacteria-laden ooze from an active infection is transported (usually in water) to an open wound. 

Temperature matters for blossom blight risk because bacteria rely on heat to grow on the floral stigma. For trauma blight, the source of the bacteria is active infections that already have excessive bacterial populations contained in ooze. Trauma events are always cause for concern because bacteria are transported from active infections to open wounds. 

Reference: Fire Blight: The disease and its causative agent, Erwinia amylovora (JL Vanneste, CAB International 2000)



  • Continue monitoring for signs of blossom infection.
  • Consider the ongoing risk of blossom blight infection on flowering apple trees.


  • Remove fire blight strikes at least 2-4 ft below active infections to remove the leading edge of the bacteria. Being aggressive at the first sign of symptoms will help prevent the re-occurrence of symptoms and the need for continuous cutting back.
  • Cut out infections when a period of 2 dry days are in the forecast. Leave prunings in orchard laneways to let dry thoroughly for several weeks. If cutting a whole tree consider letting it dry while attached to the trellis. Don’t make piles that will prevent the wood from drying. 
  • 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.

Fire Blight - Shoot Blight Management


  • If a blossom blight infection occurred, prohexadione calcium is a tool known to slow down bacterial spread in the tree and may buy some time before bacteria reach the leader.
  • When Apogee/Kudos (prohexadione calcium) are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still slow fire blight progression.
  • 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)!

Apple  Black Rot

  • The black rot fungus infects fruit during warm rains from petal fall to harvest. The highest risk is from petal fall up until 4 to 6 weeks after bloom.
    • A 10 hr wetting period at 16°C to 32°C allows infection. 
    • The optimum temperature for infection is 20°C to 24°C. 
    • There are few management options to cover such a long risk period. Merivon has activity but group 7 + 11 products should not be used more than 4 times each year. 
    • Fungicides are protectants because they prevent spore germination on plant tissues so for protection from this disease the fungicides would need to be applied prior to the wetting event. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.
    • Captan is an effective protectant for high density orchards that have a history of black rot. However, consider Captan where practical in terms of label restrictions for re-entry intervals.
    • Check for nearby brush or wood piles because they serve as a major source of inoculum. Remove the brush pile to reduce the chance of infection.
    • Frog eye leaf spot infections on leaves tell you that you have black rot inoculum present. Oftentimes, the frog eye leaf spot will be in close proximity to fruitlet mummies.
  • Minimize lenticel cracking by:
    • Avoiding drought stress with irrigation.
    • Being cautious with spray mixtures (folpet, calcium, foliar nutrients). For comments on calcium, see the section below on horticulture.
    • Be especially cautious with spray mixtures when heavy rains follow drought conditions because rapid fruit expansion can break lenticels and allow product to cause more damage than usual, making it susceptible to fungal infection.

Apple - Brooks Spot

Brooks spot is caused by a fungus that creates sunken, dark green lesions on the fruit. It is a minor disease that has been an issue on Honeycrisp in the past. The symptoms of Brooks Spot can resemble lenticel breakdown and bitter pit which are also common on Honeycrisp. Include a product for cover sprays that is labelled for brooks spot such as Inspire Super and Aprovia Top (or Folpan 30 days after petal fall).

Apple - Flyspeck and Sooty Blotch

These summer diseases develop on the surface of the fruit in midsummer until harvest. They are caused by fungi that overwinter in dead twigs and the fungi tend to cause more infections under conditions of moderate temperature, high humidity and rainfall. Include a product for cover sprays that is labelled for flyspeck and sooty blotch such as Captan, Maestro, Inspire Super, Aprovia Top, Allegro, Pristine, and Merivon (or Folpan 30 days after petal fall).


Apple Insects

  • White apple leafhopper: 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.

  • Aphids: Monitor for rosy apple aphid and green aphid. In young trees the aphids can disrupt shoot growth. Monitor nursery plantings as well. Now that leaves are curling high water volumes are needed for effectiveness. Green aphid will move back into orchards that were treated previously so continue to monitor. Assail and Calypso also have activity on codling moth, apple maggot and leafhoppers. Be cognizant of REIs if installing trellis.

  • Codling moth: The biofix dates for this season are May 31 for early and June 5 for late regions determined by Erika Bent, APM. Jeff Franklin, AAFC, ran the degree day model again on June 21 to predict when degree day thresholds will be met for treatments.
    • The treatment timing of 100 DD for egg hatch products was met on June 18 for early biofix and today on June 21 for late biofix dates. 
    • The treatment timing for organophosphate (Imidan) is slightly later at 140-degree days after biofix. Based on current forecasts, the projected treatment date for the early biofix is June 26 and late biofix timing is June 28.
    • If trap captures are below the treatment threshold but continue to build over time then treatment should be applied once a threshold is reached. 

    • These are approximate dates. The North Medford region is typically cooler by a day or two. 
    • Codling moth lay eggs and hatch over a period of time. Late application may miss the first egg hatch and could result in a few codling moth entries. 
    • A heavy rain just after application is more concerning than a late application because heavy rain would wash off and reduce the residual life of the insecticide. 
    • Approximately a week after application of an OP insecticide, clean out the trap and start monitoring the trap. The capture of an additional 10 or more moths would indicate that a second treatment is required.

  • Mites: European red mite, two spotted spider mite and apple rust mite are the prominent species that affect apple trees. Although not directly damaging to the fruit, these mites in all their motile life stages can drain the nutrients from the trees and dramatically degrade fruit quality. 
    • Scout your orchards or check your scouting reports to see if there is a treatable population.
    • Both European red mite and two-spotted spider mite are controlled by the products Acramite, Apollo, Kanemite, and Nealta. All three mite species are controlled by Nexter and Envidor.
    • Mites have many generations per year and therefore have a high potential to develop resistance. For resistance management, it is critical to rotate miticide classes. The use of dormant oil applications will also help to delay resistance selection for European Red Mite.

  • Obliquebanded leafroller: Second generation egg hatch may occur in about a week. Monitor or check scouting reports for larval populations soon.

  • Apple Maggot: In early years, captures in commercial orchards can occur around July 10th. In blocks that are still being treated for codling moth, the control is extended to early maggot flies. 

Stone Fruit Insects

  • Mites and aphids: Monitor mite and aphid populations. Prolonged feeding especially in early- to mid-summer can affect next year’s fruit set.

Pear Insects

  • Pear Psylla: Refer to the management guide for product options.
  • Pear rust mite: 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.
  • Codling moth: Refer to the above degree day timing given for apples.


Solstice Reminders

  • If granular fertilizer is applied now, the risk is that any dry weather in July will slow the release. Late release will prevent trees from hardening off before the winter. Top dressing is not recommended after the end of June.
  • Around July the trees are storing reserves in the roots for next year’s growth. When they are storing reserves, late glyphosate applications can be damaging if taken up by root suckers and transported to the root system. Avoid the risk by avoiding glyphosate applications after the end of June.

Calcium Nutrition

  • The goal of foliar Ca sprays is to increase the concentration of Ca in the fruit and reduce bitter bit incidence. 
  • Early calcium application has been recommended in Washington State but research has not been done locally. Fruitlets are most sensitive to injury at petal fall and first cover so calcium at this time poses a risk. The risk is highest if humid weather follows application and creates slow drying conditions. Damage caused by calcium could also aggravate black rot infection.
  • Avoid calcium chloride for early applications. Formulated calcium products have less risk but they also have lower concentrations of calcium.
  • As fruit grow and increase in surface area, a greater total amount of the calcium applied is taken up by the fruit. If bitter pit has not been a significant issue, then continue as normal which means calcium beginning at 4 to 6 weeks after petal fall.

Weed Management

  • Note that 2,4-D has an 80-day PHI. Eighty days from now is September 9. 
  • Due to herbicide shortages, it seems that weed management in young plantings will be reliant on consistent and vigilant use of burnoff products. Note the risk of frequent use of Agral 90 for bark blistering on Delicious varieties.
  • 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.
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees.


  • Mowing will help to conserve moisture so that it is not transpired by the large surface area of tall weeds and grasses. Mowing and blowing the clippings into the tree row can also help to conserve moisture.
  • Mowing and herbicide strips help to prevent issues with two-spotted spider mite (John Michael Hardman).
  • Keeping the orchard floor cover mowed will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.


  • Select strong terminals on young trees and remove competing terminals to single the tops.
  • Training practices should be done on dry and sunny days, especially in high risk fire blight blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
  • 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). This year is expected to be an active hurricane season.

Young Trees

  • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Prior to deer fencing, the product Bobbex may be used as a deer repellent but it requires frequent application to new growth and after rainfall.
  • Broadcasting grass seed is not recommended for establishing grass in the alleyway. Direct seeding is recommended to confine the grass seed to the alleyway and avoid spread to the tree row. The herbicide gramoxone used to provide good control of bluegrass species but post-emerge products for grass control are now limited.
  • Remove root suckers. Suckers compete with the main tree for water and nutrients. They harbour pests, and they are an entry point for fire blight. Pull or break off suckers because otherwise cutting them would let them rebound. If necessary, AIM herbicide is registered for control of suckers but avoid drift onto young trees and apply only near mature brown bark.

On-Farm Nursery

  • Consider staking to prevent blowouts. Stakes should be placed on the side opposite from the bud so it pulls the bud toward the rootstock rather than away.
  • Monitor for aphids.
  • 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!
  • Although Aim is registered for use in nurseries, damage has been reported several times in the past. It is a contact herbicide so it kills tissue on contact.

Pest Management Guides 2022

All changes new to 2022 are made in red text directly on the guides. The information on all changes was summarized in a blog post on April 8th.

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 including this week's participants: Jeff Wentzell, Danny Davison, Dr. Suzanne Blatt, Dr. Ian Willick, and Jeff Franklin.

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

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