Orchard Outlook Newsletter Vol. 22, No 9

Tuesday, June 7, 2022

Fruitlet growth is chugging along! Today's newsletter announces the risk of blossom blight on blossoming young trees in the near future. We discuss that black rot risk should be considered soon. We discuss that chemical thinning is ongoing and consider weather conditions this week. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Note: Codling moth predictions were added half an hour after original publication.

Table of Contents:

  • 2022 Degree Day Accumulations
  • Winter Injury to Apple Trees
  • Weather Station Communications

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple & Pear - Fire Blight Blossom Blight
  • Fire Blight - Shoot Blight Management
  • Apple - Black Rot
  • Apple Insects
  • Stone Fruit Insects
  • Pear Insects
  • Weather conditions for thinning
  • Apple fruitlet thinning
  • Nibble thinning
  • Defruiting Young Trees
  • Pear thinning
  • Calcium Nutrition
  • Weed Management
  • Grafting
  • Mowing
  • Training
  • Planting
  • On-farm Nursery

Pest Management Guides 2022

Events and Notices



2022 Degree Day Accumulations

The cumulative degree days are just slightly above the 5 and 10-year averages for base 5°C and 10°C heat units (Figure 1). The cool weather reduced accumulations and led to a lower accumulations than in 2021. Next week is expected to have average temperatures and the summer is expected to be warmer than average.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 6 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 12% more plant development heat units compared to the 5-year average, and 6% more compared to the 10-year average.
  • Approximately 8% less plant development heat units compared to 2021, and 22% more compared with 2020.
  • Approximately 14% more insect development heat units compared to the 5-year average, and 3% more compared to the 10-year average.

Winter Injury to Apple Trees

It is becoming apparent after trees expended energy during bloom that some trees are lagging in development or collapsing. Varieties like Gravenstein and Northern Spy are reportedly showing the most damage. It appears as though winter injury is responsible. Young trees, weakened trees, and fall pruned trees were at greatest risk of injury.

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): There is an issue with the battery in the Grand Pre (NSFGA) weather station that we are in the process of fixing. The solar panel is powering the station by day but by night the station is powering down. Although we have a spare battery on hand, we are waiting on a battery adaptor. Please do not rely on minimum temperatures being reported by the Grand Pre NSFGA weather station. Other nearby stations that are publicly accessible from the WeatherLink app are Grand Pre (NSW014) and Avonport (Luckett's). Grand Pre (NSW014) is being used for fire blight Maryblyt alerts. 
  • NORTH MEDFORD (NSFGA): The leaf wetness sensor is not functioning. The issue appears to be with the entire node but we are hoping to test the sensor on its own before replacing the node.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on June 6, I measured ten king fruitlets of each of the following varieties to get a rough average. The Idared buds measured 12.9 mm, Honeycrisp measured 9.2 mm, and Ambrosia measured 7.7 mm (Figure 2). Keep in mind that fruitlets grow about 1 mm each day.

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on June 6. Shown from left to right: Idared, Honeycrisp, Ambrosia.


Apple – Scab

Table 1: Apple scab infection events in Kentville from May 31 to June 7, 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 Sunday, April 17th. 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.


  • Currently, cumulative ascospore maturity is theoretically at about 99.8%. According to the model by June 10, the total seasonal ascospore maturity is expected to reach 100%.
  • Primary ascospores are still available for release. There is still some time before it is safe to reduce fungicide spray intervals.
  • Do not use folpan until 30 days after petal fall to avoid fruit russeting. 
  • 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


  • 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

  • Last week the cool temperatures produced a low bacterial population (represented as EIP) on open flowers. Therefore, the risk of blossom infection was not concerning. Currently the EIP is low.
  • Relatively warmer temperatures this week are more concerning. Currently it appears as though the EIP will approach or exceed the 100 threshold around June 10.
  • When concerning EIP values are imminent, alerts will be sent for the purpose of protecting late blossoms on new plantings.
Figure 3: The Maryblyt model output as calculated on the morning of June 7 and using the Environment Canada forecast for Kentville. Note how EIP values are expected to climb and reach concerning levels around June 10 for situations with open blossoms.

Please note: The Epiphytic Infection Potential (EIP) is a representation of the bacterial population that is growing on only the floral stigma that is relevant to blossom infection risk. EIP is not a representation of bacterial population in the orchard during a trauma event. Trauma events are always cause for concern because bacteria are transported from anywhere to open wounds. Water that accompanies the trauma in a hail or windy rainstorm are very effective at distributing bacteria.



  • Consider the ongoing risk of blossom blight infection on flowering apples.
  • If you are not receiving email alerts and you wish to, please let me know at mcortens@perennia.ca or sign up online. Alerts will be delivered on weekends and holidays. I also post daily screenshots in a folder online to make model predictions easily accessible. Predictions are updated daily. Access apple predictions and click on the images to expand.


  • 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.
  • Streptomycin 17 will provide excellent efficacy on blossom blight and should not be used more than 24 hours prior to an infection event. If necessary, it may be used after infection and is best used within 12-18 hours but can still be helpful if delayed longer. 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.
  • 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. When Apogee/Kudos 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:
    • A 10 hr wetting period at 16°C to 32°C allows infection. 
    • The optimum temperature for infection is 20°C to 24°C. 
    • CORRECTION: I had previously explained that the highest risk of black rot infection is 4-6 weeks after bloom but in fact the risk period is continuous from petal fall up until 4 to 6 weeks after bloom. 
    • There are few management options to cover such a long risk period. Merivon has activity but this group 7 + 11 product should not be used more than 4 times each year. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.
  • Black rot can survive on prunings. Flail mow prunings in row middles where they will degrade more quickly.
  • Minimize lenticel cracking by:
    • Avoiding drought stress with irrigation - inspect soil at your own site. Sandy soil will be at risk first.
    • 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.


  • Choose insecticides by considering what you are targeting and what the products control. Often your hardest to control pest will determine what you need to use, then check the label of that product for all pests that are also controlled by the product. 
  • All 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

Pesticide options and efficacy are listed in the May 31 newsletter. All registered insecticide options and label rates for calyx stage of apples are listed in the Pome Fruit Management Guide.
  • Monitor for white apple leafhopper. Sevin XLR applications for thinning in 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. If leaves are curling high, high water volumes are needed for effectiveness.
  • Dr. Blatt reports that in Kentville the peak European apple sawfly activity was last week.

Codling Moth: Degree Day and Treatment Timing Predictions

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 to predict when degree day thresholds will be met for treatments.

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 by June 17 for early regions and June 19 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 22 for early regions and June 24 for late regions.
The models were run on Tuesday, June 7 with a degree day threshold of 10 degrees (C). Stay tuned for updates.

Stone Fruit Insects

  • Healthy peach trees that do not have a crop this year due to winter injury should still be protected from direct pests. This would include the diseases peach leaf curl, brown rot, and powdery mildew. For insects, monitor for aphids and mites and especially plum curculio if apple trees are nearby. Inspect trees for injury to limbs and trunks in case trees may not recover.  
  • A second application for plum curculio is usually needed about 10 days later.

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.
  • If Agri-Mek is applied close to MaxCel then it can drastically increase thinning activity.

Chemical Fruitlet 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.
  • Expect fruitlets to grow about 1 mm each day in average temperatures. This growth rate is especially true after fruitlets are 6 mm in size.
  • 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). 

It is difficult to make specific predictions in this newsletter with such an actively changing forecast. However, here are a few thoughts:

    • Conditions last week were cool and may result in less thinner activity but there was no time to wait. 
    • Daytime temperatures are expected to warm to ideal conditions in the near future. Nighttime temperatures will still be somewhat cool. Cloudy conditions will cause some added stress. Taken altogether the conditions should be close to ideal. Thinning effectiveness should be relatively familiar unlike heat waves of the recent past. Rainy periods may complicate application. 

Apple Fruitlet Thinning


  • Pollination conditions and resulting fruit set seem good but evaluate your fruit set to inform thinning decisions.
  • 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.
    • Sevin is a thinner but it is also an insecticide. Do not spray Sevin with beehives still in the orchard.
    • 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.
  • 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!
  • Be careful when comparing our product rates to other regions by ensuring that rates are being expressed in equivalent formats. It is most reliable to thin based on local experience.

Nibble Thinning

  • A second thinner application is risky if the effects of the first application are unclear. To apply multiple thinners, the first should be applied just after petal fall and then wait 7-10 days to evaluate the outcome. Then there is still a short opportunity at the end of the window to thin again before 18 mm is reached.
  • If you would like to try the nibble/precision thinning approach, consider using the Predicting Fruitset Model to receive feedback on how many fruit will drop or persist in response to a chemical thinner application. Tracking the fruit growth rate in real-time will buy time and confidence to thin again before the chemical thinning window closes.
  • Select high value blocks to monitor fruitlet diameter using a digital caliper on a recommended 75 fruitlet clusters. Flag 15 clusters across 5 representative trees and number the fruitlets (1 to 5). Take the first measurements four days after a thinning application or no earlier than the 6 mm stage. Measure size every 4 days and input results into the model. Measurements taken 4 and 8 days after thinners are required to conclude growth rate. Contact me for guidance and questions.
  • If you don't want to commit this year, then try a sample to become familiar with the process. Monitor 5 clusters using a digital caliper on 4 and 8 days after a chemical thinner.
  • The Orchard Tools app by Perennia helps with data collection and it is available for iPhones, iPods and iPads. Available for download from the App Store.

Defruiting Young Trees

  • ATS is NOT recommended for defruiting young trees. The question of using ATS to defruit young trees comes up every year. 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.
  • 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.
  • Using currently available products, the amount of product that would be needed to completely defruit trees in our climate would likely negatively affect tree growth. Therefore, expect that hand thinning will still be required.

Pear Thinning

  • The MaxCel thinning window is 8-14 mm and early treatments are most effective.
  • If Agri-Mek is applied close to MaxCel then it can drastically increase thinning activity.


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

  • 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. Timely herbicide application will ensure you make the most of the weed free window.
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees.


  • The practice is most successful as long as bark is slipping, which may extend into summer.


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


  • Train and support young trees as soon as possible. This year is expected to be an active hurricane season.
  • 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.


  • A good soaking rain might not have occurred after planting. Pruning trees after planting can bring top growth in balance with the root mass to avoid root dieback under conditions of moisture stress.
  • Warm soil temperatures mean that roots will grow immediately. Start fertilizer programs as soon as possible after planting.
  • Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Under currently dry conditions, watering with drip tape if possible especially under sandier situations is recommended. Keith Fuller also notes that M26 wilts very easily and that water provided in replant situations can reduce stress from replant disease. A dry season compounds replant disease symptoms.
  • 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.
  • 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).

On-Farm Nursery

  • Strip leaves from rootstock for budding. Strip non-varietal buds from last year's rootstock soon.
  • 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.
  • Consider staking soon to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
  • 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!

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, Dr. Suzanne Blatt, Dr. Mathew Vankoughnett, Joan Hebb, Larry Lutz, Jeff Franklin, Crystal MacRae, Danny Davison, Dustin MacLean, Dr. Ian Willick, Keith Fuller, Jill MacDonald, Dr. Vicky Levesque, and Dr. Shawkat Ali.

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

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