Codling Moth: Degree Day and Treatment Timing Predictions (June 18, 2026 Update)

Thursday, June 18, 2026

The codling moth biofix dates for this season are June 13 for most regions and June 15 for late regions determined by Erika Bent, APM.

Suzanne Blatt, AAFC, has run the degree day model today to predict when degree day thresholds will be met for treatments. The models were run on Thursday, June 18 with a degree day threshold of 10 degrees (C) using Kentville weather station data.

Codling Moth Treatment with Rimon
Timing: The treatment timing for Rimon is 80 degree days Celsius from biofix to target eggs before they hatch.

Prediction: According to the current forecast, the 80 degree day threshold is expected to occur by June 23 for early regions. Late regions are not yet included in the forecast.

Codling Moth Treatment with Egg Hatch Products
Products: Assail, Delegate, Intrepid, Altacor, and Exirel
Timing: The treatment timing for egg hatch products is 100 degree days Celsius from biofix.

Prediction: Not yet forecast.

Codling Moth Treatment with Organophosphate
Product: Imidan

Caution: All hand thinning activities must be completed prior to application. No hand thinning can occur on trees treated with Imidan.
Timing: Control of codling moth with Imidan is typically slightly later at 140 degree days after biofix.

Prediction: Not yet forecast.

Recommendations:

Monitor the forecast for rain and do not apply treatment before heavy rain. Codling moth lay eggs that hatch over a period of time. Late application may miss the first egg hatch and could result in a few codling moth entries but will still provide residual activity for future egg hatches.
If trap captures are below the treatment threshold but continue to build over time then treatment should be applied once a threshold is reached.

Orchard Outlook Newsletter Vol. 26, No 10

Tuesday, June 16, 2026

This week’s Orchard Outlook shows king fruit sizes around 11–17 mm, which means the optimal thinning window is wrapping up. There’s still a short opportunity for rescue thinning, but time is limited. You may start to see early signs of fire blight blossom infection, although nothing has been confirmed yet. We’ve also included an early estimate on codling moth treatment timing and a few notes on summer miticides. With the summer solstice approaching, remember cautions about nitrogen application and glyphosate use. Don’t forget to protect young trees—tie up leaders and take steps to keep deer out. For nurseries, it’s best to start irrigation sooner rather than later to avoid stress. Thanks, as always, to the Orchard Outlook Committee for their continued efforts.

Weather

2026 Degree Day Accumulations

The cumulative degree days have crept up again during the warm, double-digit nights (Figure 1). Harrison Wright says, "We are now well above the 10-year average and are sitting just below the 5-year average. Keep in mind that the last 5 years (2021 – 2025) are all amongst our top 10 warmest growing seasons on record (out of 112 years)."

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to June 15 for the past 17 seasons. Provided by Harrison Wright (AAFC Plant Physiology).

Approximately 2% less plant development heat units compared to the 5-year average, and 7% more compared to the 10-year average.
Approximately 5% less plant development heat units compared to 2025, and 4% less compared with 2024.
Approximately 2% less insect development heat units compared to the 5-year average, and 9% more compared to the 10-year average.

Precipitation

The past week was a dry week. Harrison Wright summarizes, "A dry week in which we only added an additional 2 mm of rain. While May, at 110 mm, trended well above the average (despite having a dry period in there), we are so far trending below the norm for June."

Bud Development

Apple Buds

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on Monday the average diameter of ten king fruitlets on Idared was 17.3 mm, Honeycrisp was 14.6 mm, and Ambrosia was 11.3 mm (Figure 2). In South Berwick at a thinning trial on Sunday, the Honeycrisp measured 13.2 mm and Gala 11.3 mm.

Over the past week, Idared grew 1.1 mm/day, Honeycrisp grew 0.9 mm/day, and Ambrosia grew 0.7 mm/day. Typically fruitlets grow about 1 mm each day in average temperatures. Compared with last year, fruitlets are about 4 mm smaller so they are about 4 days behind.

The results of chemical thinning are still under evaluation. Likely the only chemical thinning that may be possible now is rescue thinning. Refer to the thinning section later in the newsletter for more information.

There are reports of some frost rings on pears in low lying areas. This injury could be related to the cold event that recorded -1.5°C to -2.0°C on May 23 when pears were around the petal fall to early fruit sizing stage.

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on June 15. Shown from left to right: Idared 17.3 mm, Honeycrisp 14.6 mm, and Ambrosia 11.3 mm.

Current measurements of extension shoots indicate that Idared averages 30 cm (doubled), Honeycrisp 20 cm (doubled), and Ambrosia 15 cm (+5 cm) (Figure 3). Idared now has 9-10 fully expanded leaves (+2 leaves), Honeycrisp 7-8 fully expanded leaves (+2 leaves), and Ambrosia 7 fully expanded leaves (+ 2 leaves).

Figure 3: Terminal shoot growth in an early region in Greenwich on June 15. Shown from left to right: Idared 30 cm, Honeycrisp 20 cm, and Ambrosia 15 cm.

Diseases

Apple – Scab

Table 1: Apple scab infection events in Kentville from June 10 to June 16, based on the Modified Mills Table.

- 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.
-Assuming a green tip date of April 19. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
Note: The environmental conditions for an infection are listed in the Modified Mills Table.

Recommendations:

According to the model, total seasonal ascospores matured to 100% on Wednesday, June 10 and the wetting event on June 13 would have released the final primary spores. Models are not completely accurate so wait 2 weeks after ascospores are depleted and when you can assess your incidence of primary apple scab infections. Decisions about whether to lengthen fungicide intervals can be made on June 27.
Fungicide options can be limited this time of year... so let's review some options:

Captan may be used as long as it is not applied within 7-14 days of an oil such as Agral 90 (worse if applied after oil that preconditions leaves). The REI for hand thinning fruit in high-density systems is 15 days and in low-density systems it is 24 days. The product has activity on summer diseases and is ideal. For high density, do not use more than 10 applications per year and for low density do not use more than 2 applications per year.

Remember, if using SHARDA CAPTAN 48 the rate equivalent to other captan products is 5 L/ha (2.4 kg of active ingredient).

Allegro/Vantana/Downforce may be applied as long as oil has not been applied within 3 days (including Fontelis and Agral 90). The REI is short at 24 hrs.
Migiwa is registered for scab control and it has a short REI of 12 hours. Just be sure to use the high rate of 220 mL/ha so that the powdery mildew that is present isn't exposed to a sublethal dose at the low rate. We want to preserve this product efficacy for powdery mildew.
Do not apply: Folpan/Follow and Syllit should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting.
Buran may be considered. But remember that the product is registered for only suppression of apple scab and must be used post-infection only. Summer disease control is not likely strong.
Note that single site products in group 3 are not expected to provide control of apple scab due to resistance. For other products, check the label for rates required for apple scab control because for Luna Tranquility the high rate is needed unless it is tank mixed with another product for scab control.
Several of the single site products do not have activity on scab after petal fall (fruit scab). Such products include Fullback, Nova, Cevya, Aprovia, Sercadis, Excalia, Scala, and Vangard.

Apple – Powdery Mildew

Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.

Figure 4: Left: An overwintering flagshoot in the background was infected with powdery mildew last year and provides inoculum for infection this year on new leaves shown on the leaf being held in the foreground. Right: A closeup of white to silver-grey fungal growth on the underside of newer leaves that causes the leaf to crinkle and curl.

Recommendations:

Individual apple leaves are most susceptible to powdery mildew infection when they are new and not yet fully expanded. Infections found in Figure 4 on Idared on new leaves #7 through #10 would suggest conditions were conducive to infection when those leaves were newly emerged at around June 2 to June 9.
Last year's drought conditions might have been conducive to powdery mildew infections that would have infected buds. An increased number of flagshoots carrying primary spores would increase the spore pressure this year.
Protection may continue on 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. Product reapplication intervals can vary from 7-14 days.
Do not use any products with powdery mildew activity more than two times consecutively to avoid resistance development.

Fire Blight Prevention and Shoot Blight Management

Recommendations:

If a blossom blight infection occurred on May 20, the symptoms may be visible now according to the model, but I do not yet have confirmed reports. A blossom blight infection occurring around June 6 to June 10 may become visible by June 17 to June 20.

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.

A second application of Apogee/Kudos is made around 14-21 days after the first. Successive applications ensure no gap in activity until you can assess blossom blight infection pressure.

As soon as you find fire blight infections, an application of Apogee/Kudos (prohexadione calcium) can help to suppress the progression of infection that buys you time for cutting it out. Use a lower rate if trees have not filled their space or the full rate if tree growth is not an issue.

Do not break off branches with fire blight infections as you navigate the orchard. Research shows that the bacteria becomes systemic in the tree because branches are not adequately removed. There are then a high number of new infections and significantly more canker tissue and cankers on structural wood.

Prune out fire blight infections on young trees in the current year, don't wait for winter.

Remove fire blight strikes at least 2-4 ft below active infections to remove the leading edge of the bacteria. The younger the tree, the deeper the cut. Being aggressive at the first sign of symptoms will help prevent the re-occurrence of symptoms and the need for continuous cutting back. Repeat tree inspections.

If you feel confident that you can monitor the formation of a canker on a stub cut for later removal, then a stub cut may be appropriate. A 4-inch stub cut causes a canker to form on the stub before reaching structural wood like the leader of the tree. However, do not forget to remove the stub because otherwise the canker will serve as a source of bacteria. Mark the tree for revisiting.

Apple – 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 - representing 100% of the bacteria load needed to cause infection.

Blossom Blight Risk

Bacterial growth on open flowers is increasing to near or above-threshold values in the current warmth. The risk is forecast to be high throughout this week. Refer to the blossom blight alert email from this morning for more details.

Recommendations:

Do not spray high water volume on trees in bloom unless an antibiotic has been applied.
Do not underestimate the risk of infections on late flowers. By the time of late flowers there is already plenty of bacteria established throughout the environment.
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 – Black Rot

Recommendations:

Based on our limited knowledge, the highest risk of infections is theoretically between petal fall and 4-6 weeks later.

A 10 hr wetting period at 16°C to 32°C allows infection.
The optimum temperature for infection is 20°C to 24°C.
There are few management options to cover such a long risk period. Captan has activity but note the REI for orchard activities. Merivon has activity but this group 7 + 11 product should not be used more than 4 times each year. Folpan has activity but should not be applied until 30 days after petal fall to avoid russet. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.

The fruit cuticle is sensitive to damage at this stage. Be cautious with spray mixtures (calcium, foliar nutrients) that could create an entry point for the pathogen.

Apple - Brooks Spot

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

Apple - Flyspeck and Sooty Blotch

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

Insects

Apple and Pear: Codling Moth

Degree Day and Treatment Timing Predictions

We are very grateful for the regional biofix dates set by Erika Bent, APM. The biofix dates for this season are June 13 for most regions and June 15 for late regions. An even later region might be considered.

Suzanne Blatt, AAFC, has run the degree day model today to predict when degree day thresholds will be met for treatments. The models were run on Tuesday, June 16 with a degree day threshold of 10 degrees (C) using Kentville weather station data.

PREDICTION

The forecast to the end of Sunday, June 21 is only 60 degree days Celsius. Stay tuned for updates and for treatment timing options see below.

Codling Moth Treatment with Rimon
Timing: The treatment timing for Rimon is 80 degree days Celsius from biofix to target eggs before they hatch.

Codling Moth Treatment with Organophosphate
Product: Imidan

Apple - Sucking Insects

Aphids: Monitor in young trees and nursery plantings where feeding can disrupt shoot growth. If leaves are curling high water volumes are needed for effectiveness.
Mites: European red mite, two spotted spider mite and apple rust mite are the prominent species that affect apple trees. Although not directly damaging to the fruit, these mites in all their motile life stages can drain the nutrients from the trees and dramatically degrade fruit quality.

Mite counts are most accurate by using a specialized machine for brushing. Growers without a crop consultant can use the process of determining the presence or absence of mites on 5 leaves of 4 trees per block. The threshold depends on the sample time and number of leaves so contact me for more details.
In a hot and dry year, mite populations can double in 7-10 days.
Good spray coverage is critical.
Mites have many generations per year and therefore have a high potential to develop resistance. For resistance management, it is critical to rotate miticide classes.

European red mite: Red mite populations can increase and cause damage in the summer.

Mid-June is the first sampling period. New eggs hatch in June and nymphs are present at a relatively uniform life stage. By mid-July there is an overlap of generations and all life stages (eggs, nymphs and adults) are present.
If eggs are numerous then products with ovicidal activity should be used such as Nealta or Envidor.
If mites are motile/active then products with motile activity should be used such as Acramite, Magister, Nexter, Nealta, Envidor or Kanemite.
AgriMek and Minecto Pro are applied early for early absorption and they have long residual activity (8-12 weeks) to control motile stages after they hatch.
Envidor is slow acting so it requires early intervention.
Acramite, Kanemite, Nealta, and Nexter provide quick knockdown.

Two-spotted spider mite: Are expected to be present in mid-June as well and may be included in the red mite count for threshold levels.
Rust mite: Typically present in mid-July. A microscope is needed for identification. Contact me for thresholds. All miticides are effective on European red mite and two-spotted spider mite but only products Nexter, Envidor, and Magister provide control of rust mite.

Pear Insects

Pear Psylla: Refer to the management guide for product options.
Pear rust mite: Pear rust mite can go unnoticed until heavy russeting extending from the base to the top of the fruit. Growers that apply Agri-mek for pear psylla control would also obtain pear rust mite control. Nexter or Envidor would be other options for pear rust mite control.

Thinning

Apple Fruit Set - Revisited

Assessing fruit set is a challenge every year. Let's revisit this year's main concerns to follow up with what was observed for: 1) variable flowering and pollination and 2) unpredictable bud strength.

1) Variable flowering and pollination

Influenced by cold weather during pollination that extended the effective pollination period. There are concerns that there wasn't enough bee activity for good set or alternatively the long exposure to pollination could result in heavy set. Update: Generally more set than expected but variable.
Fruit on 1-year-old wood is excessive and developmentally behind the rest of the tree. Update: Certainly a prolonged bloom.
Missing kings make the lateral flowers stronger. Update: Yes, strong side fruitlets where applicable.

2) Unpredictable bud strength

Tree reserves influence bud health, not fruit set directly. Where trees appear healthy I'm inclined to think there is a good potential for fruit set. Update: Yes, fruit buds are still looking healthy.
Research would suggest that in the year following a drought, the June drop depends largely on weather during the thinning window, like business as usual. Update: Warm weather during thinning would have promoted thinning activity. Excess heat at or slightly above 29°C was observed in some but not all regions. This year's weather was warmer than usual during thinning but not as warm as what was observed in the year 2021.

Figure 5: Left: Honeycrisp fruit set is variable but generally plentiful unless it is in an 'off' bearing year. Right: Gala fruit set is generally heavy, except maybe in regions that bloomed later during poor weather.

Apple - Rescue Fruitlet Thinning

Please note that the timing of chemical thinning is based on the average size of the king fruitlet and that all varieties are likely now beyond the typical thinning window of 7 to 12 mm. It is still early to assess thinners that were applied last week. The associated fruit drop is not yet apparent.

Product Recommendations:

This week is likely a last-chance at thinning for most regions, known as rescue thinning.
Local research with Brevis suggests:

Application can be made up to 14 mm king fruitlet diameter. Higher rates should be used at the late timing.

Local research with Accede suggests:

It may be applied to high value varieties at 15 to 18 mm and ideally before 20 mm. Earlier treatments are expected to be most effective.
Remember that you can adjust your spray pattern based on fruit set on the top versus bottom of the tree. Usually late in the thinning window the target is excess fruit set in the top of the tree so you may direct your spray.
In the past, temperatures above 30°C seemed to decrease activity of this product. The forecast this week looks reasonable for use of Accede.

Defruiting Young Trees

Some of the fruit on young trees can be removed using a combination of Sevin XLR at 2.5 L plus Maxcel/Cilis Plus 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 the economics if hand thinning may still be required anyway.

Choosing to use Fruitone (NAA) in this mixture instead of MaxCel/Cilis Plus will likely result in chemical pinch at the terminal bud that stunts growth.

Pear Hand Thinning

On mature trees, if the total crop load is high then reduce the number of fruit per cluster to 1 or 2. During years of light fruit set, leaving 2-3 fruit per cluster will still produce good sized fruit. Space clusters 12-15 cm apart.

Peach Hand Thinning

Hand thin early-maturing varieties first for increasing the chances of fruit sizing.
Start thinning after natural drop is clear.
Space fruit clusters about 15 cm apart.

Horticulture

Solstice Reminders

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

Tree Decline

So far decline has been reported on Gravenstein G.41, Gravenstein B.9, Honeycrisp G.41, and Honeycrisp G.11.
The causes are being explored and most likely relate to extreme environmental conditions in recent history. Trees with root systems or graft unions that were already weakened are particularly susceptible.
Please report to Michelle if you have tree collapse to help us discern patterns and develop best practices for our local region.

Suckers

Remove woody suckers by cutting or ripping to avoid resource competition, the risk of systemic herbicide uptake, harbouring pests like fire blight shoot blight.
If suckers are more prevalent because of exposed roots due to frost heaving, try to hill the soil to cover the roots.

Mowing

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

Pruning and Training

Select strong terminals on young trees and remove competing terminals to single the tops if there are no re-entry intervals active and before the shoots get woody.
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

If you applied a residual herbicide about 6-8 weeks ago (end of April) then you are likely due for reapplication.

For young trees (1-2 yrs), a good option could be Simazine and Dual II Magnum with Reglone for burndown.
In established trees (>3 years), a good option is Alion and Ignite when conditions are dry and hot before an upcoming rain.

If using glyphosate alone, consider coarse droplets and low pressure to reduce drift. By the approaching summer solstice, glyphosate applications become more risky.
When burndown products are needed, consider that Reglone works in cool and cloudy conditions whereas Ignite requires warm and sunny conditions. Also, applying Ignite when leaves are wet is ineffective.
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.
The following residual herbicides can persist longer than usual in extreme circumstances like drought: Authority, Chateau, and Alion.

Nursery Trees

New trees have limited root systems and are likely to benefit from irrigation early during establishment.
Treat for tarnished plant bug and green aphids.
Remove rootstock leaves when they are tender and before shoots become woody. Single and tie tops.
For bench grafts, 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!

Cover Crops

Perennia has a series of videos about cover crops that can be accessed from our website.
Summer grasses such as pearl millet and sorghum-sudangrass that have been a popular choice can be planted from mid-June until early August.

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: Larry Lutz, Danny Davison, Ian Willick, Joan Hebb, Heather Rand, Suzanne Blatt, and Colin Hirtle.

Written by Michelle Cortens, Tree Fruit Specialist
Perennia Food and Agriculture Corp.

Orchard Outlook Newsletter Vol. 26, No 9

Tuesday, June 9, 2026

This week’s Orchard Outlook shows varieties measuring approximately 7 mm to 10 mm king fruit diameter that signals the window for fruitlet thinning in some regions. Warm temperatures will promote thinning activity. Be mindful of the fire blight risk on open blossoms in this heat as well. Note that blossom blight infections resulting from the May 20 infection event may be visible within the next week. This newsletter also covers more about fruit set than you probably ever wanted to read and offers considerations for chemical thinning programs. Many thanks to the Orchard Outlook Committee for their continued contributions.