Orchard Outlook Newsletter Vol 21, No 9

Tuesday, June 8, 2021


Table of Contents:

  • 2021 Degree Day Accumulations
  • Seasonal Precipitation

  • Fruitlet Size
  • Early Fruit Set from Fertilization
  • General Tree Health

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

  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects

  • Weather Conditions for Thinning
  • Apple - Fruitlet Thinning
  • Apple - Defruiting Young Trees
  • Pear - Fruitlet Thinning

  • Weed Management
  • Pruning and Training
  • Calcium Nutrition
  • Young Trees
  • 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. This season the nighttime low temperatures have been above-average, and when they are above the degree day threshold temperature they have had a big impact on the overall degree daysAt this point early in the season the growing degree days are tightly related to growth stage but the relationship becomes less clear as the season progresses toward maturity.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to June 6th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 25% more plant development heat units compared to the 5-year average, and 16% more compared to the 10-year average.
  • Approximately 32% more plant development heat units compared to 2020, and 49% more compared with 2019.
  • Approximately 35% more insect development heat units compared to the 5-year average, and 19% 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. The precipitation totals are tracking very similar to the 10-year average (black line).

Figure 2: Both rainfall and the rainfall equivalent from snow at the Kentville Research Station from 2012 to 2021. Provided by Jeff Franklin (AAFC).


Jeff Franklin also shared an observation about precipitation trends this season. Often in spring the precipitation arrives as sporadic showers and in summer the rain events become more widely consistent. Usually the sporadic showers resolve by now but it is unknown if this sporadic trend will continue. Last year, showers were sporadic for most of summer.

NS Precipitation Radar Maintenance

Nova Scotia's weather radar station is being replaced by a new tower this summer. The equipment has been experiencing issues since April so it will be shut down on June 11th for replacement. The equipment is responsible for short-term precipitation radar images, so during maintenance the gap will be filled by radar from nearby regions to form a composite image. Therefore, precipitation radar may be inaccurate until the new system is operating around the end of August. The upgrade is expected to improve the accuracy of the radar system in the long-term. There is more information in an article on CBC.

Bud Development

Fruitlet Size

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 observations are from June 7th for an average of 20 king fruitlets each: 
  • Idared: 14.7 mm
  • Honeycrisp: 12.7 mm
  • Ambrosia: 8.5 mm
Pears in Morristown are in the range of 16-17 mm.

Figure 3: Fruitlet diameters on representative king fruitlets from Middle Dyke Rd on June 7th. From left to right: Idared, Honeycrisp, Ambrosia.

Early Fruit Set from Fertilization

Last week we reported that weather conditions were not consistent for pollination between varieties and regions. In early regions, fruit set appears heaviest in the early varieties such as Idared that flowered during a stretch of good weather. Honeycrisp fruit set is variable with heavy fruit clusters in the tops of the trees and lighter clusters in the bottom. Conditions were cool when late varieties achieved full bloom so varieties like Ambrosia have less set but still require thinning.

Figure 4: Fruit set after fertilization on representative clusters from early regions on June 7th. From left to right: Idared, Honeycrisp, Ambrosia.

General Tree Health

A general comment this year is that trees are looking very healthy. The foliage is large, green, and shoots are elongating. The good tree health seems to be related to a combination of good early-season factors: mild winter, above-average temperatures, plenty of solar radiation, and generally good moisture levels in the ground. Young trees are growing nicely as well. Sun, heat and moisture have been the perfect conditions for shoot elongation.


Apple – Scab

Table 1: Apple scab infection events at the Kentville Research Station from May 25th to June 8th, 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 sample of the leaf litter on June 3rd revealed the presence of immature ascospores that were not yet mature by the June 3rd infection event. Therefore, viable ascospores are still present. 
  • Ascospore maturity was at 99.9% yesterday. In today's heat, ascospores are expected to reach 100% maturity according to the model. The final spores have not yet been released. There is still some time before it is safe to reduce fungicide spray intervals.
  • Ensure that tissues are covered with a protectant fungicide prior to an infection event by reapplying 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).

Figure 5: Microscopic observation of a leaf litter sample taken in the Morristown region on June 3rd. Left: Black pseudothecia. Right: Asci with viable ascospores. Viable ascospores are still present and will be monitored in conjunction with the ascospore maturity model. Photo by Dr. Sajid Rehman, plant pathologist at Perennia.

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.


  • On young trees, monitor for active mildew to determine the need to protect new tissue as terminal shoots continue to grow. Only group 3, 7, and 11 fungicides have activity and resistance was found 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.

Figure 6: Powdery mildew symptoms. Left to right: flag shoot symptoms from overwintering primary infection, secondary infection spread to a new leaf when it was young and susceptible, closeup of secondary infection with white felt-like patches on underside of leaf. Secondary infection photos taken June 2021.

Fire Blight - Blossom Blight

There is still bloom on this year's new plantings. Alerts have been sent to subscribers by email over the last few days. The most recent alert was sent today on June 8th. An infection is possible on open blossoms with a high EIP forecast now and over the next few days. Please check the alert for more details.

Information from my conversation with Dr. George Sundin and William Turechek was emailed on June 4th.

Fire Blight - Orchard Management


  • 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.
Figure 7: Fire blight blossom blight symptoms and ooze. Photos taken in June 2021.

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.

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 at 1⁄4 inch size and refer to the Stone Fruit Management Guide.


Apple Insects

Pesticide efficacy for calyx stage are listed in Table 2. More information is 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).

  • 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.
  • 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.
  • Stay tuned for the codling moth biofix date and degree day model predictions for treatment. Dr. Suzanne Blatt reports in Kentville that codling moth flight started on June 2nd and has since been steady. Communications with Erika Bent APM will soon determine biofix dates for the Valley.
  • Also, Dr. Blatt reports that in Kentville the peak European apple sawfly activity was last week.

Figure 8: Rosy apple aphid on the underside of leaves and curling leaves. High water volumes for insecticides are needed now for efficacy. Photos taken in June 2021.

Stone Fruit Insects


  • A second application for plum curculio is usually needed about 10 days after the first.
  • 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.
  • Monitor mite and aphid populations. Prolonged feeding especially in early- to mid-summer can affect next year’s fruit set.
  • 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


    • 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 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.
    • Stay tuned for codling moth biofix and degree day model predictions for treatment timing.

    Chemical Thinning

    Weather Conditions for Thinning

    Weather influences tree sensitivity to chemical thinners. The weather 2 days before and more importantly the 4 days after applying thinners determine thinner response. The relationship has been explained in terms of the carbohydrate status of the tree. During sunny days the tree is photosynthesizing unimpaired and when matched with cool nights (<18°C) it is respiring slowly, meaning carbohydrates are plentiful. Reversing the conditions, cloudy days impair photosynthesis and when coupled with warm nights the respiration uses many carbohydrates making them in short supply, causing stress to weak fruitlets.

    This week's outlook for thinner activity:

    Well, it seems like we're going to see many different weather situations for this thinning season.
    • During the heat wave, thinners are expected to be more active. Heat on the day of application or the following days has the most influence. Nighttime temperatures have been at the 18°C threshold so they have not been excessive.
    • There is no need for concern about rates that worked for you in the warmth last year. If however, you thinned too aggressively last year in the heat, you might want to reduce rates in those situations where you got overthinning.
    • After the heat wave the temperatures will move to the other extreme of being cool during the day and night. Sunny and cool conditions reduce thinner activity. 
    • Conditions return to relatively normal (moderate temperatures and wet) by the weekend that would suggest standard rates.
    • These observations are based on weather only. Adjust based on other factors on your farm and use in the context of your own experiences.

    Apple - Fruitlet Thinning

    • Trees treated with Fruitone in the heat are flagging.
    • 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). Many varieties appear to be in the window but quickly approaching the end.
    • Focus your chemical thinner in the top 2/3rds of the tree.
    • In the US apple production regions, the carbohydrate model recommends adjusting the usual chemical thinner program by plus or minus 30% depending on the carbohydrate status of the tree (explained in the above section). 
    • Adding a surfactant or PureSpray Green oil at 1% is considered a way to increase the aggressiveness of a thinner on hard-to-thin varieties. Take caution using PureSpray Green oil on varieties that are easy-to-thin like Ambrosia.
    • 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.
    • MaxCel can be applied up to 15 mm but note the PHI of 86 days. Cilis Plus has a PHI of 28 days.
    • When using Sevin in high density orchard do not exceed 3.22 L of product/ha/year. In low density orchard do not exceed 2.15 L of product/ha/year.
    • 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!

    Apple - Defruiting Young Trees

    • 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 (avoid Gala, Ambrosia, Golden Delicious, Red Delicious). 
      • 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. A second application will likely still miss some fruit so consider that hand thinning may still be required.
    • Choosing to use Fruitone (NAA) in this mixture instead of Maxcel will result in chemical pinch at the terminal bud that stunts growth. The flagging might also be concerning in this heat wave.

    Pear - Fruitlet Thinning

    • The Maxcel thinning window is 8-14 mm and early treatments are most effective. Note that pears might be outside of the treatment opportunity for effectiveness.


    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.

    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. Consider using Kasumin for fire blight protection if a short 12-hour REI is needed.
    • 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).

    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. Note that fruit are most sensitive to injury at petal fall and first cover so avoid calcium chloride for early applications. 
      • 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

    • 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.


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

    Nursery Trees

    • For bench grafts, leave some shoots on the rootstock to feed the scion as the callus tissue develops. Locally, rootstock leaves have been stripped when the scion has 8-10 leaves. Early in the season, leave at least an extra scion leader for insurance.


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


    • 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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