In this edition of the newsletter, we shift toward bloom-time activities and risks. We review the current powdery mildew disease risk during warm and dry weather and report that, given the prevailing hot temperatures, the risk of fire blight blossom infection remains high. Apple scab infections have not happened recently but the next infection will release a very large spore load. Apple terminal shoots are entering the early window for Apogee/Kudos applications. We invite you to join us for a discussion on blossom thinning approaches at the Growing Good Growers tailgate meeting tomorrow at 11:00 AM (Cancelled). As always, I extend my sincere thanks to the Orchard Outlook Committee members for their ongoing dedication and valuable contributions.
Table of Contents:
- 2026 Degree Day Accumulations
- Precipitation
- Apple Buds
- Pear and Stone Fruit Buds
- Apple - Scab
- Apple - Powdery Mildew
- Fire Blight Prevention and Shoot Blight Management
- Apple and Pear - Fire Blight Blossom Blight
- Apple - Calyx/Blossom End Rot
- Grafting
- Pollination
- Mowing
- Root Pruning
- Pruning and Training
- Weed Management
- Fertilizing
- Wild Apple Trees
- Nursery Trees
- Growing Good Growers - Wednesday, May 20 at 11 AM (Blossom Thinning)
- NSFGA Webinar Tree Fruit Herbicides and Weeds - Thursday, May 21 at 12 PM
Weather
2026 Degree Day Accumulations
The cumulative degree days remain ahead of the 5- and 10-year averages (Figure 1). Development stages are slightly behind last year so far but may soon catch up. Of course, as you have noticed the rapid heat accumulation in a few short weeks has led to compressed management stages.
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 18 for the past 17 seasons. Provided by Harrison Wright (AAFC Plant Physiology).
- Approximately 7% more plant development heat units compared to the 5-year average, and 18% more compared to the 10-year average.
- Approximately 10% less plant development heat units compared to 2025, and 19% more compared with 2024.
- Approximately 12% more insect development heat units compared to the 5-year average, and 25% more compared to the 10-year average.
Precipitation
Precipitation this month is now above-average but this is due to the heavy rainfall event at the beginning of the month. Weekly rainfall has been below average at around approximately 10 mm/week. Soil moisture conditions in the upper soil layers appear dryer than normal.
Bud Development
Apple Buds
An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. In this heat, bud stages are expected to move quickly. Since last week, buds have moved forward about 1.5 to 2 growth stages. These photos were taken on the morning of Monday, May 18 when the Idared buds were at full pink to first bloom, and both Honeycrisp and Ambrosia were at early pink with no bud separation (Figure 2). Some bud separation may have occurred later on the day on Monday.
Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on May 18. Shown from left to right: Idared, Honeycrisp, Ambrosia.
If you want to target the early timing for Apogee/Kudos of 2.5 cm, the stage has been reached for early varieties like Gravenstein that are in bloom. The length of Honeycrisp shoots varied on the tree from 1.2 cm to 2.5 cm. Please note that as soon as terminal growth begins it progresses quickly.
Figure 3: Terminal shoot growth in an early region in Greenwich on May 18. Shown from left to right: Gravenstein (2.5 cm) and Honeycrisp (1.2 cm).
Pear and Stone Fruit Buds
Figure 4: Bud development on May 18. Shown from left to right: An early region in Greenwich with pear, peach/nectarine, and European plum.
Diseases
Apple – Scab
No new infections were recorded over the past week. The environmental conditions for an infection are listed in the Modified Mills Table.
Recommendations:
- The next wetting event will release a very large spore load. Reapply a protectant fungicide on a 5-7 day interval, using the shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
- By the end of the week, ascospore maturity is forecast to reach 90.7%. Since the last rainfall event on May 15, our model says that 42.1% of spores have matured in the meantime and are available for discharge at the next rainfall.
- Ascospores are maturing at a rate of 2-7% per day, where higher rates occur on warm days.
- Folpan/Follow should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting.
- Pears: For pear scab, Allegro and mancozeb are not registered uses. Captan may be used 2 times for low density and 10 times for high density. Note that for pears, Scala and Luna Tranquility have a 72 day preharvest interval. Products are listed in the Pear Pest Management Guide.
Apple – Powdery Mildew
Typically, conidia are released around the tight cluster stage. Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.
Recommendations:
- Conditions are currently ideal for powdery mildew infection of new leaves.
- Our research has suggested that post bloom applications have protective value. If one of the typical pre bloom applications was missed, the powdery mildew products may be applied starting again at petal fall and 10-14 days later.
- Fungicide options with reminders:
- Group 3 products Nova and Fullback are very effective. However, do not use them more than two times consecutively to avoid resistance development. They are ineffective on scab due to resistance, so use in conjunction with a fungicide that manages apple scab. Fullback and Nova are systemic and given a long drying period of 24 hrs they should be well-absorbed into the plant before a rain event.
- Group 7 containing products are Luna Tranquility, Inspire Super, Sercadis, Excalia, Fontelis. For Luna Tranquility, activity for scab control is only provided at the high label rate. Fontelis contains a mineral oil in the formulation so do not use near captan or folpet products.
- Aprovia Top is a combination group 3 + 7 product, therefore, be careful that you do not make more than two consecutive applications of group 3 or group 7 containing products.
- Migiwa is a new chemical group 52 that may be incorporated into the program to strengthen resistance management. Migiwa also has control of apple scab and it should always be used at the high label rate.
- Gatten is a new group U13. The product does not have activity on apple scab.
- Property is a new group 50. The product does not have activity on apple scab.
- There is industry resistance to group 11 products such as Flint so it should NOT be used for powdery mildew management.
- Other products are listed in the pest management guide.
- 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.
Fire Blight Prevention and Shoot Blight Management
Recommendations:
- Pruning practices should be done on dry and sunny days, especially in high risk blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
- Even if bacterial EIP populations are low, do not pinch flowers on young trees in wet weather. Pinching causes open wounds like a trauma event and bacteria are transported to wounds in wet weather. Preferably, allow 2 days of dry weather for the wounds to heal.
- Apogee/Kudos (prohexadione calcium) suppress shoot blight. Apogee/Kudos is first applied at 2.5-7.5 cm of shoot growth, which has been reached on early varieties and will be reached soon on later varieties.
- Please note that the product Apogee is discontinued by BASF. Kudos is another product with the same active ingredient and will remain available.
- The product takes 10 days to become active so for the maximum effect on fire blight suppression it should be applied before fire blight symptoms appear. Early application might even thicken cell walls of the flower pedicels giving some added protection from blossom 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.
- The product is not systemic so good coverage with high water volume is required.
- 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)!
- Use low rates on young apple trees to avoid delaying growth too much.
- Some disadvantages of using prohexadione calcium for consecutive years are shortened fruiting branches and when used repeatedly on Gala the retention of fruit set can contribute to smaller fruit size.
Apple and Pear – Fire Blight Blossom Blight
Bacteria multiply rapidly in warm temperatures, especially when occurring over consecutive days. The Maryblyt model criteria is used to predict blossom blight infections. Periods with high fire blight bacterial populations are defined by Maryblyt as having an Epiphytic Infection Potential (EIP) greater than 100.
Blossom Blight Risk
- Currently, the temperature is conducive to rapid bacterial growth.
- Email alerts began on the weekend to warn about the infection risk that would start today on Tuesday and last into Wednesday. Notifications will continue while the EIP is near or above 100 for apples and pears.
- Pears:
- Are in full bloom so there are many flowers that could be colonized by bacteria during this heat wave.
- Wetting would trigger infection on open pear flowers on Tuesday or Wednesday.
- Apples:
- Only blossoms open by Sunday, May 17 are at risk on Tuesday.
- All blossoms are at risk on Wednesday, even if flowers open on Wednesday.
- If you would like to join the alert contact list, please let me know or sign up online.
- Ideally, you will monitor your own farm-specific situation with PomeBlight using a selected weather station. The user account and PomeBlight tool are free. Follow my 17-minute Quickstart video or Quickstart PDF document.
- Contact me if you have ANY questions!
Apple – Calyx/Blossom End Rot
Recommendations:
- Infections occur when weather conditions are warm (15 to 25°C) and moist during bloom and shortly after bloom.
- The only product with activity on calyx/blossom end rot is captan applied during full bloom. If applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.
- Infections can occur in problem blocks as the pathogen can last in the soil for several years. The disease is most common on Paulared, Delicious, Cortland, Honeycrisp and McIntosh.
- Keeping grass and dandelions mowed will allow the soil to dry and reduce the environmental conditions for spore ejection. Other broadleaf weeds are also a host of this disease so weed control prevents the build up of this pathogen.
Insects
- The opportunity for pre-bloom insecticides was a narrow window!
BE RESPONSIBLE FOR POLLINATORS – DO NOT SPRAY INSECTICIDES DURING BLOOM!
- Fungicide, antibiotic, and growth regulator 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 - Postbloom Insects (Advance Notice)
Choose post-bloom insecticides according to the pest complex on your scouting report. Insects might include the caterpillar complex, stinging bugs (mullein bug), green and rosy apple aphids, and curculio.Refer to the Apple Efficacy Guide for product selection. You may begin by determining the product and rate for your most difficult to control pest and then note the other pests that will be managed by your product selection and whether or not additional products are required. Take note of the higher rate required for some pests.
Stone Fruit - Postbloom Insects
Plum curculio is a weevil that begins laying eggs in stone fruit at shuck fall. Mated females will deposit their eggs in the developing fruit leaving the characteristic crescent-shaped scar. Activity of PC is increased in temperatures above 16°C so low temperatures in the forecast for later this week might decrease their activity.Recommendations:
- Be aware of bee toxicity warnings on pesticide labels and take precautions while nearby crops are in bloom.
- Note that pyrethroids are best used at moderate temperatures (20°C or less) and lose efficacy at around 25°C.
- Plum Curculio
- Treatment for PC should be applied at petal fall before shuck split to obtain optimal control. A second application is usually needed about 10 days later.
- The insecticides available for managing plum curculio include Malathion, Pounce, 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 they are nearby.
- Monitor for green peach aphids and black cherry aphid.
- Tarnished plant bug and stinging bugs cause catfacing of peaches.
- This stinging takes place around shuck split/fall. Apply one to two applications of one of the pyrethroids Up-cyde, Ambush, or Pounce listed in the Stone Fruit Pest Guide for peaches. Repeat treatment in 5-7 days if additional stings are detected. (Matador was cancelled from registration in peaches.)
Pear - Postbloom Insects (Advance Notice)
- 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 young tissues because of rapid penetration.
- 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.
- Do not use MaxCel in close proximity to AgriMek because the oil will increase thinning activity.
- Minecto Pro (Abamectin and Cyantraniliprole) is registered for control of pear psylla with the same recommended application time.
- Petal fall is the ideal treatment timing for winter moth and fruit worm in pear. Treatment should be based on need determined by monitoring.
- Apple curculio is difficult to monitor for and its presence often is not observed until damage on fruitlets shows up. Treatments for this pest should go on when pears have reached petal fall. Use of one of the products registered for plum curculio should also control apple curculio.
Thinning
Apple Blossom Thinning
See the Events section for information about the Growing Good Growers tailgate meeting happening tomorrow on Wednesday, May 20 on the topic of blossom thinning. (Cancelled)
The greatest benefits of blossom thinning are on small fruited varieties like Gala and Ambrosia where there is an opportunity to increase fruit size through early crop load reduction. Do not apply ammonium thiosulphate (ATS) to varieties that are prone to russet. Remember, unopened flowers are unaffected by the ATS so ideally target when a block is at 80% to just reaching 100% bloom.
Advantages this year:
- A pollen grain that lands on the flower stigma then germinates and a pollen tube grows toward the ovary at a rate determined by temperature. In this hot weather, newly opening king blossoms are forecast to become fertilized within 2 days of being pollinated. Later in the week, lateral flowers may be present during cooler temperatures and they could be susceptible to blossom thinners for about 3-4 days. This weather pattern works well to keep king blossoms and remove lateral blossoms.
- Product efficacy is not temperature-dependent. ATS will thin blossoms even with the cool temperatures later this week.
- The lack of rain means quick drying conditions will reduce the risk of foliar injury.
- Blossom thinning is an early opportunity to reduce the crop load on trees that were severely drought stressed last year.
Disadvantages this year:
- Do not apply ATS during this heat wave because of the risk of fire blight.
- Need to assess the effect of the drought on the abundance and uniformity of blossoms in a block.
- The effect of last year's drought on the strength of flower buds is unknown.
Apple Fruitlet Thinning (Advance Notice)
General Comments:
- The timing of chemical thinning is based on the average size of the king fruitlet. The size of the side fruitlets is irrelevant. After petal fall, fruitlets typically grow about 1 mm each day in average temperatures. Chemical thinning occurs when king fruit are 5 to 18 mm in diameter and is most effective from 7-12 mm.
Product Overviews:
Sevin XLR
- Does not overthin so it is mild and reliable.
- Undissolved Sevin remains active. Damp and drizzly weather that keeps tissue wet but does not wash off product results in more thinning.
- Often combined with Fruitone for a synergistic effect resulting in more thinning than either product used alone.
- Temperatures at application should be above 17°C.
- 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.
- 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 note that it is also an insecticide and care should be taken to avoid contact with bees.
Fruitone L
- Strong thinner that is very effective in Nova Scotia and is rate-responsive. Higher rates thin more.
- Unabsorbed residue on leaves is inactivated by sunlight. Slow drying conditions cause more absorption. Therefore, nighttime applications are usually more effective.
- Temperatures at application should be above 16°C.
MaxCel/Cilis Plus
- Product is most likely effective when weather conditions cause a carbohydrate deficit. The thinning effectiveness has been limited in Nova Scotia and it may be because in many years the trees are not stressed during chemical thinner application.
- This product can be used to increase fruit size (20g/fruit) beyond the influence of thinning by stimulating cell division but the timing matters. When applied at 10-15 mm, it increases fruit weight 80% of the time. Earlier timings are less reliable.
- Temperatures at application should be above 18°C.
Brevis (NEW)
- Temporarily reduces carbohydrate production that leads to carbohydrate stress and causes the tree to drop fruit during resource competition.
- It is a strong thinner that is rate-responsive. Adjust rates up or down depending on carbohydrate status (warm and cloudy thins easier than cool and sunny),
- Apply when air temperatures are between 10°C and 29°C and delay application if temperature will exceed 29°C within five days of application.
- Young trees experience more aggressive thinning.
- Combining Brevis with other fruit thinners creates a risk of overthinning.
- High humidity before and after Brevis will improve uptake and efficacy.
Accede
- Product has activity at up to 25 mm fruitlet diameter but should be targeted at 18 mm.
- Do not apply if temperatures will exceed 30°C on the day of application and for the following three days due to inactivity.
- Direct 80% of the spray into the upper 2/3 of the tree canopy.
- Use the adjuvant Agral 90 at 0.125% v/v.
Recommendations:
- During the thinning window I will comment on the suspected carbohydrate status of the trees.
- The optimal temperature for thinner activity is between 21-24°C. In cooler temperatures the thinning activity is less and in warmer temperatures the thinning activity is more.
- Have a block with trees on and off? Thin according to trees with the heaviest fruit set. Trees with less flowers are less likely to thin anyway because holding onto well-supplied fruitlets.
- 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).
Pear Fruitlet Thinning (Advance Notice)
- The Maxcel thinning window is 8-14 mm and early treatments are most effective.
- Brevis is a new thinner that is registered for use from late petal fall until 16-18 mm.
- Avoid applying to trees less than 4 years old.
- Do not add any adjuvants that increase droplet spreading or penetration.
- Do not spray on wet leaves.
- Apply when air temperatures are between 10°C and 29°C and delay application if temperature will exceed 29°C within five days of application.
- Avoid drift to plum and cherry trees.
Horticulture
Grafting
- Bark is slipping and grafting has begun.
- The local business Maple Grove Nursery made a video about top working young trees. The video is available on their website called, “Reworking Young Orchard Trees (slow motion)” https://www.maplegrovenursery.ca/grafting-supplies
- Our region benefits from leaving a nurse limb but there is no consensus on how long to leave the limb. More vigorous rootstocks likely need the nurse limb for longer.
Pollination
- Move honeybees into the orchard for pollination when king flowers open.
- Remember last year when poor weather conditions restricted the opportunity for pollination to a few short days. Also, solid variety blocks rely on plenty of bee activity.
Mowing
- Keeping the orchard floor cover mowed pre-bloom will minimize dandelion flowers that attract bees, which increases the safety of pre-bloom and post-bloom insecticide applications.
Root Pruning
- If you are considering root pruning to reduce excessive vigour, the window of timing is from bloom and up to two weeks later. An article from Michigan State was recommended by a local grower.
- Consider the effect of the drought last year and whether the treatment would be too aggressive on trees.
Pruning and Training
- Ensure that deer fencing is installed as soon as possible to protect new growth on young trees.
- 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).
Weed Management
- When burndown products are needed:
- Reglone works in cool and cloudy conditions.
- Ignite requires warm and sunny conditions. Also, applying Ignite when leaves are wet is ineffective.
- Glyphosate and 2,4-D require daytime highs of 10°C-15°C. Activity of glyphosate is best when applied from noon to 6 PM.
- In young plantings, weed control is essential.
- Local research showed that by year 4, a weedy planting was 39% the trunk cross sectional area of a hoed comparison.
- Trees planted this year would have received a good settling rain by now and you may consider a residual herbicide before the next rain.
- Most residual herbicides need about 1/2" of rainfall within 7 to 14 days of application to deliver product to the germination zone and to activate the chemical by putting it in solution.
- Note that residual herbicides can damage single tree replacements of young trees if the product is not registered for use on young trees. Keep this in mind if you are considering planting single tree replacements after the drought.
- Damage may occur by planting into soil with herbicide residue or by mistakenly applying new residual herbicide.
- The following residual herbicides can persist longer than usual in extreme circumstances like drought: Authority, Chateau, and Alion.
Fertilizing
- Foliar nutrients to correct nutrient deficiencies:
- Boron: Applied pre-pink. Do not use water soluble pesticide bags in a tank mix with boron and rinse the tank well before and after boron. Do not use boron with oil or Epsom salts.
- Magnesium: Epsom salts are applied starting at pink. Do not use with oil or boron.
- Nitrogen: Urea may be used from pre-pink to mid-June as a nitrogen supplement. Sprays near bloom give a boost of nitrogen when it is needed most. Urea used from tight cluster to mid-July can remedy a nitrogen shortage.
- When foliar nutrients are applied in slow drying conditions, about 40% is absorbed in 6 hours. When applied in dry conditions, about 75% can be lost in 48 hours. Foliar nutrients are not well-absorbed at below 10°C.
- Finish fertilizer applications soon. Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth. A new resource written by Keith Fuller is now available, "Managing Nitrogen Supply in Mature, High-Density Apple Orchards in Nova Scotia." We are pleased to introduce this resource that includes a guide for estimating nitrogen fertilizer rate using soil organic matter content and cropping potential!
- Apply granular fertilizer to newly planted trees now that soil has settled from rain.
Wild Apple Trees
- Wild apple trees harbour pests, in particular apple maggot, that can then spread to nearby orchards. Now that wild apple trees are in bloom, it’s a good time to flag trees on your own property so that you can find them later in the season for removal.
Nursery Trees
- Treat for tarnished plant bug and green aphids.
- Consider staking soon to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
- Remove rootstock leaves when they are tender and before shoots become woody.
- 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.
- 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!
Events and Notices
CANCELLED Growing Good Growers - Wednesday, May 20 at 11 AM
Unfortunately, due to fire blight management activities we are cancelling the meeting.
The Growing Good Growers tailgate session will be held with Harrison Van Meekeren at Van Meekeren Farm on Wednesday, May 20 at 11 AM. Join us for an engaging discussion focused on blossom thinning. We’ll be in an orchard block featuring Gala, Ambrosia, Honeycrisp, Gingergold, Pazazz, and McIntosh varieties. Whether you have experience with blossom thinning or are considering trying it for the first time, this is an excellent opportunity to explore the practice together. As a group, we’ll evaluate whether this season presents favorable conditions and consider the recent drought. We’ll discuss optimal timing and practical considerations. Please bring your thoughts, experiences, and questions on thinning and join us for this discussion. Feel free to bring your fire blight questions too.
Meet us in Lakeville off Lamont Rd. Take the orchard road next to the multi-leader block and travel east toward the meeting location.
There is no need to RVSP, and we encourage you to bring your own coffee and snacks. Everyone is welcome to attend! It’s a good chance to catch up with friends.
NSFGA Webinar Tree Fruit Herbicides and Weeds - Thursday, May 21 at 12 PM
Zoom Meeting Details
When: May 21, 2026, from 12:00 PM to 1:30 PM
Registration:
Please register in advance.
After registering, you will receive a confirmation email with details on how to join the meeting. Looking forward to seeing you online!
Pest Management Guide
We offer printable PDFs of the guides from our website:
Online pest guides are also available without login (https://www.perennia.ca/pest-guides/) and with login on your Perennia account (https://www.farmdatatools.perennia.ca/). Using the online tool you can filter for organic and conventional options, search for key information, and sort based on information of interest.
This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Harrison Wright, Danny Davison, Joan Hebb, Ian Willick, Keith Fuller, Colin Hirtle, Mathew Vankoughnett, and Bob Prange.
Written by Michelle Cortens, Tree Fruit Specialist
Perennia Food and Agriculture Corp.
Perennia Food and Agriculture Corp.
