Orchard Outlook Newsletter Vol 21, No 10

Tuesday, June 15, 2021


Table of Contents:

  • 2021 Degree Day Accumulations

  • Apple - Scab
  • Apple - Powdery Mildew
  • Fire Blight - Orchard Management
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Stone Fruit - Brown Rot, peach scab, and powdery mildew

  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects

  • Chemical Thinning
  • Pruning and Training
  • Calcium Nutrition
  • Young Trees
  • Weed Management
  • Grafting
  • Nursery Trees
  • Mowing
  • Irrigation
Pest Management Guides 2021

Events and Notices



2021 Degree Day Accumulations

The above-average trend continues. In general, growth in the Valley is 5-10 days ahead of the five and ten year averages.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to June 14th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 22% more plant development heat units compared to the 5-year average, and 16% more compared to the 10-year average.
  • Approximately 29% more plant development heat units compared to 2020, and 39% more compared with 2019.
  • Approximately 31% more insect development heat units compared to the 5-year average, and 22% 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. Note that fruitlets grow an average of 1 mm each day at average temperatures. The following measurements are from June 14th for an average of 10 king fruitlets for each varieties, which are shown with a representative photo: 

Figure 2: Fruitlet diameters on representative king fruitlets from Middle Dyke Rd on June 14th.

Peaches and nectarines are about 2.5 to 3.0 cm in length.


Apple – Scab

Table 1: Apple scab infection events at the Kentville Research Station from May 25th to June 14th, 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.


  • The last infection event was recorded on June 3rd when ascospore maturity was 99.3%. There are viable and mature ascospores available for the current infection event.
  • Do not reduce fungicide spray intervals until you can identify your pressure from secondary scab lesions.
  • The pre-harvest interval for EBDC fungicides (e.g. Manzate, Dithane, Polyram) for fruit destined for the United States is 77 days versus 45 days for the domestic market. An application of EBDC on June 15th would require until August 31st to meet pre-harvest requirements for the United States.
  • 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

Flag shoots are the primary infections that produce inoculum for secondary infections on leaves, blossoms and fruit. Secondary infections occur in warm and dry weather when spores land on young leaves. As leaves age they become more resistant to infection.


  • This year the powdery mildew pressure is high throughout the Valley, and susceptible varieties like Cortland are heavily infected. Symptoms of heavy infection are also showing up on Honeycrisp. 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. We may need to revisit our approach to powdery mildew through discussions this winter.


  • On young trees, monitor for active mildew to determine the need to protect new terminal growth. Only group 3, 7, and 11 fungicides have activity and resistance is a concern in group 11. This issue of not having enough groups is widespread across apple growing regions.
  • Remember that late summer sprays are protectants and not eradicants. Flag shoot symptoms from overwintering infections will be visible for the rest of the season.
  • Pay particular attention to susceptible and high-value varieties such as Honeycrisp and Gala.

Fire Blight - Orchard Management


  • The final blossom blight alert for the season was sent on June 13th. If you still have new plantings in bloom please let me know and I can continue running the model for relevant stations.
  • Monitor for signs of early fire blight blossom infections that are now becoming visible.
  • 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.
  • When pruning, remove fire blight strikes at least 2-4 ft below active infections then leave them in orchard alleyways to dry thoroughly for several weeks.

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 are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still provide fire blight suppression.
  • 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.

Apple - Black Rot

  • The heaviest spore release is believed to occur for a four to six week period following petal fall. Rain is required for spore release. Infection can develop on fruit after about a 9-hour wetness period at an average temperature around 20-24C. Fungicides are protectants because they prevent spore germination on plant tissues so for protection they would need to be applied prior to the wetting event.
  • Do not reduce rates of Captan after bloom in high density orchards that have a history of black rot. Consider this recommendation where practical in terms of new label restrictions.
  • 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.

Stone Fruit – Brown rot, peach scab, and powdery mildew


  • Fungicide protection from brown rot should be maintained during periods of warm, wet weather. 
  • The new formulation of Captan limits the number of applications to one per year on stone fruit.
  • Peaches are susceptible to peach scab infections from shuck fall to 4-6 weeks before harvest. Symptoms are visible on the bark. The shuck fall application is particularly important for disease control. Periods of wet weather will require additional applications until 4-6 weeks before harvest.
  • Monitor for signs of powdery mildew on fruit and refer to the Stone Fruit Management Guide.


Apple Insects

  • Stinging bugs: Assess the efficacy of earlier insecticides that targeted stinging bugs such as apple brown bug and mullein bug and whether or not re-treatment is warranted. Use limb taps to determine recent pressure. If required, treatments should be targeted this week. Pyrethroids are best used at moderate temperatures (20C or less) and may be ineffective in the heat. Ambrosia and Red Delicious are particularly susceptible to damage by stinging bugs.

  • 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.

  • Codling moth: The biofix dates for this season are June 3rd and 4th for early regions and June 6th for later regions determined by Erika Bent, APM. Jeff Franklin, AAFC, ran the degree day model to predict degree day thresholds for treatments. The models were run on Monday, June 14th with a degree day threshold of 10 degrees (C). The models are run using Kentville temperatures for predictions and actual timing may vary based on observed temperatures throughout the Valley.

    Codling Moth Treatment with Egg Hatch Products 
    • Products: Assail, Calypso, Delegate, TwinGuard, Confirm, Intrepid, Altacor, and Exirel
    • Timing: The treatment timing for egg hatch products is 100-degree days Celsius from biofix.
    • Prediction: According to the current forecast, the 100-degree day threshold is expected to occur today on June 15th for early regions and June 18th for late regions.

          Codling Moth Treatment with Organophosphate 
    • Product: Imidan
    • Timing: Control of codling moth with Imidan is typically slightly later at 140-degree days after biofix. 
    • Prediction: According to the current forecast, the 140-degree day threshold is expected to occur by June 20th for early regions and June 23rd for late regions.
    • New changes to Imidan as a result of re-evaluation do not come into force until October 2022. Use of the product can continue according to the current label until then.

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.

  • Stinging bugs: 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


    • Pear Psylla: 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.

    • 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.


    Chemical Thinning

    • Most thinning has occurred already but there may still be an opportunity in late regions on late varieties. Average king fruit diameters of 15 to 18 mm are still receptive to thinners but less receptive than earlier timings.
    • A second application of chemical thinners for defruiting young trees can be done before 18 mm if additional thinning is needed. A second application will likely still miss some fruit so consider that hand thinning may still be required.
    • Peaches and nectarines can be hand thinned to 6-7 inches apart.

    Pruning and Training

    • If bamboo is limited because of COVID delays, we recommend looking at other options in the meantime. As young trees grow more foliage they are more susceptible to sailing in the wind. Consider running wire supports or new solutions to support trees. The hurricane season has begun and even the risk of high wind events is cause for concern.
    • 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).
    • Train and support young trees as soon as possible. Work in dry weather especially if the block has historically high risk of fire blight.

    Calcium Nutrition

    • The goal of Ca sprays is to increase the concentration of Ca in the fruit and reduce bitter bit incidence. 
      • Foliar calcium applications can begin early at 7-10 days after petal fall. Early in the season, the fruit are fuzzy so calcium uptake per unit area is improved over later stages when wax develops. 
      • However, note that fruit are most sensitive to injury at petal fall and first cover so avoid calcium chloride for early applications. Also weigh the risk of calcium sprays on young fruitlets. Even calcium nitrate sprayed before slow drying conditions can increase the chance of russet.
      • 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 been an issue, the early sprays might help and if not then continue as normal.
    • Calcium applied at two-week intervals is better than occasional, high-rate applications. 
    • The recommended rate is 4 to 14 pounds of elemental calcium per acre in a season spread over six to eight cover sprays. The percentage of elemental calcium will be listed on the label.
    • Ca has very low movement within the tree and needs to be applied directly to the fruit surface to be absorbed. Therefore, thorough coverage is important to cover developing fruit.
    • Calcium chloride flake (77% Ca) is the most economical Ca material to use but also the highest risk for foliar burn. Apply calcium chloride flake at no more than 4.5 kg per 1000 L of spray solution. The risk of leaf or fruit damage from calcium is highest in hot and dry weather. Susceptible varieties can develop lenticel spotting if damaged. 
    • Risk of leaf injury may be enhanced by Captan. Incompatibility has been observed with Epsom salts, and liquid or emulsifiable pesticide formulations in some cases. Do not apply calcium with apogee.

    Young Trees

    • 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.
    • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Deer are browsing young plantings and causing damage. Thiram is no longer an option to deter feeding while the fence is being installed. Another deterrent product called Bobbex is available for nonbearing trees.
    • 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.

    Weed Management

    • 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.


    • The practice can be done as long as bark is slipping, which may extend into summer.

    Nursery Trees

    • There are reports that T-buds are underperforming this year relative to chip buds with the same rootstocks and varieties. T-buds are reportedly more affected by plant water status and temperature extremes than chip buds. Last August, we had received minimal rain until the last week when we received 57 mm. September also had sporadic rain in limited heavy events.
    • There are anatomical reasons why chip budding is more reliable. The chip bud is a direct replacement, so the cambium of the scion lines up with the cambium of the rootstock. By comparison, in t-budding the cambium is tucked under the bark so callus tissue must fill all the air pockets and new cambium must develop. Refer to last year's newsletter on July 15th for more information.
    • The budding methods will be revisited closer to this year's budding timing.


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


    • Seasonal precipitation as of last week was slightly below average. This year's above-average heat has not been paired with above-average moisture.
    • Young plantings in particular look like they need water as they are limited by their small root systems. 
    • For those using irrigation, a handy relationship is that 1 litre of water on every square metre is equivalent to 1 mm of rainfall.

    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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