Orchard Outlook Newsletter Vol. 23, No 2

Tuesday, April 25, 2023

This newsletter focuses on early season disease management including the progression of apple scab and how to spot fire blight cankers. With the soil heating up we discuss root growth. Finally, we review horticulture practices including weed control and reminders for planting. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2023 Degree Day Accumulations
  • Apple Bud Growth
  • Apple Root Growth
  • Apple - Scab
  • Apple - Fire Blight Prevention
  • Apple - European Red Mite

Weed Management

  • Pruning
  • Fertilizing
  • Liming
  • Planting
  • On-farm Nursery

Events and Notices

  • NSDA Programs: Sustainable Canadian Agricultural Partnership
  • Season Extension Enhancement Program Presented by Horticulture Nova Scotia
  • Perennia Webinar: Understanding Fire Blight Biology while using PomeBlight (pesticide points available)

Pest Management Guides 2023



2023 Degree Day Accumulations

Cumulative degree days are closely following the 5- and 10-year averages for plant development (Figure 1). 

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

For the following comparisons, please note that early in the season only a few warm events contribute significantly to the accumulated degree days.
  • Approximately 3% less plant development heat units compared to the 5-year average, and 3% more compared to the 10-year average.
  • Approximately 21% less plant development heat units compared to 2022, and 35% less compared with 2021.
  • Approximately 18% more insect development heat units compared to the 5-year average, and 17% more compared to the 10-year average.

Tree Growth

Apple Bud Growth

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on April 24, the Idared buds were at 1/4 inch green, Honeycrisp was at late green tip and Ambrosia was at green tip (Figure 2). Orchard Outlook committee members also report that varieties range from green tip to 1/4 inch green in Falmouth and Melvern Square.

Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on April 24. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Apple Root Growth

Keith Fuller notes that root growth is beginning where soil temperatures have reached around 9 to 10°C (Figure 3). A site measuring 8.2°C did not have new root growth and a site measuring 12.1°C had about 2" to 3" of new root growth. New root growth is white or tan coloured and succulent.

Figure 3: State of root growth on April 20, 2023. Photos by Keith Fuller, AAFC.


Apple – Scab

Table 1: Apple scab infection events in Kentville from April 18 to April 25, 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 Saturday, April 15th. 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.

Wetting also occurred on April 18 but was unlikely to cause concern for a low pressure orchard because spore release in the dark is low. In a high pressure orchard, an estimated 11.5 hours of wetness at 8.3°C was close to causing an infection (minimum 15 hours under these conditions).


  • Currently there is no rain in the forecast but do not let it lure you into a false sense of safety because precipitation forecasts can change quickly. There has been more tissue exposed and spores are maturing so orchards should receive fungicide protection. According to the forecast, ascospores are expected to mature at a rate of 1% per day and within the next five days about 9.8% of total seasonal ascospores are expected to be mature.
  • Apply a protectant fungicide to green tissue prior to an infection event and reapply on a 7-day interval, with a shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
  • Early in the season, there is no need to control powdery mildew so products with activity on powdery mildew can be saved for application at half inch green.
  • Remember that there is a new label for Manzate (mancozeb). The product may be applied 4 times/ha/year, the re-treatment interval is 7 days, the REI for hand thinning is 35 days (12 hrs for all other activities), and the PHI is now 77 days.
  • If you plan to use oil for European Red Mite control, Captan should be avoided within 7-14 days of an oil application.

Apple – Fire Blight Prevention

Dormant fire blight cankers are a sunken area of bark that can be black to almost purple in colour. The bark might also be cracked or peeling but it does not encircle a branch like the ring-shaped cracks of European canker. The fire blight cankers are often associated with nearby branches that were killed last year (Figure 4). 

When temperatures warm up, the bacteria will begin to multiply and ooze from cankers. Initially the ooze is a watery light tan that darkens to amber. Typically the ooze begins to appear at the stage of tight cluster or early pink at which point pruning practices should be done on dry days, especially in high risk blocks. When the canker blight bacteria are active, water sprout shoots close to cankers will wilt. 

Figure 4: Fire blight canker showing purple to black bark, sunken tissue and cracks. Photos are from prior seasons.


  • Cankers are visible now before they become hidden by this year's foliage. Scout for cankers now.
  • If in doubt, take it out! No cankers are helpful and they harbour diseases. If you need a second opinion, I can take a look. Cankers are especially risky in young orchards because they harbour the bacteria for new blossom infections that give bacteria rapid access to the leader of the tree. Consider completely removing young trees that have cankers.
  • A fixed copper product such as Copper Spray Fungicide (50% copper oxychloride) is recommended because it is resistant to being washed off by rain. If copper is applied later than green tip, residues that persist on fruitlets can cause russetting which is a concern for fresh fruit varieties. Processing varieties where russet is tolerable can be treated later as well as nonbearing trees.
  • Copper can be applied as a tank mix with 0.5% by volume (5 L in 1000 L) dormant oil to increase adherence. Apply in a high water volume to cover plant surfaces. Do not use dormant oil within 14 days of Captan or within 48 hours of freezing temperature.


European Red Mite

A delayed dormant oil is effective at managing European red mite if monitoring indicates a treatable overwintering egg population. The oil is most effective when applied around egg hatch (typically around tight cluster and before pink) but if practical it may be applied earlier. European red mite eggs overwinter in the cracks on buds and spurs so adequate water volume is needed to reach all of the crevices. The oil treatment is not effective for rust mite or two-spotted spider mite.

For varieties with Delicious parentage (Ambrosia, Gala, Delicious), early applications of oil prior to tight cluster are less likely to result in bark blistering. Oil should not be applied to young trees.

Do not use dormant oil 48 hours before or after freezing temperature.

Weed Management

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. Weeds are still small and post-emerge and residuals should have good impact when applied in the right weather conditions.


Residual Herbicides
  • Most residual herbicides need about 1/2" of rainfall within 7 to 14 days of application for activation. Currently there is no rain to depend on in the short term forecast.
  • Residual herbicides such as Chateau, Alion and others offer a much longer weed control period than post-emergent products including Ignite and Glyphosate. Note the differences in the application directions for Chateau and Alion and refer to the labels for more detailed information:
    • Chateau can be applied to young trees. Chateau should not be applied after budbreak unless application equipment is shielded to prevent crop injury. 
    • On the other hand, Alion can be applied only to mature orchards with trees established for 3 growing seasons. Alion can be applied anytime throughout the growing season.
  • Authority is a good product but it does not have a lot of grass control so rotate with other products to avoid shifting toward more grass population. 
  • Note that residual herbicides can damage single tree replacements. The Alion label says that individual plants within an orchard may be replanted by removing all treated soil from the transplant hole and refilling with soil that has not been treated.
  • If you are taking out orchard within the next 2-3 years for replanting, avoid applying residual herbicides. The Alion label says to allow at least 12 months from last application to replanting an orchard.
  • When mixing residual herbicides, agitation is important to keep the product in solution. If the herbicide settles in the tank then it can be delivered in a high concentration and possibly result in crop injury.
  • If weeds are already present, add a post-emerge to a residual herbicide to achieve control. 

Post-Emerge Herbicides 
  • Applying 2,4-D in temperatures below 10°C has historically been ineffective. 
  • Applying Ignite when leaves are wet is also relatively ineffective.



  • Plan ahead and watch re-entry intervals for pruning activities now that fungicide programs are beginning. 
  • Ensure that youngest blocks are pruned first to ensure growth is directed into desirable leader and terminal extension. Prioritize high value trees and then return to low value areas.
  • Mature blocks can be pruned later and are best when pruned prior to bloom.


  • Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.
  • Target 10-16 inches of new growth each year. More is a sign of excessive nitrogen.


  • Lime especially if a site is being planted this year. When applied in spring the lime works best when applied as soon as possible to get the product working in the top layer of soil. 
  • Surface applied lime will take a number of years to adjust pH of the soil profile so it is best to apply annually or biannually where needed. If soil testing for pH, measure during the same time each year (August) as pH can change over the growing season. 
  • The provincial limestone trucking assistance program is open.


  • Remember the importance of soil preparation. Remove old roots and work to get a good soil tilth without sods and clods especially in the top 15 cm of soil.
  • When trees are first planted they need a high level of soil phosphorus because roots are too poorly developed to forage for it. If phosphate is needed, diammonium phosphate (DAP) can be banded in furrow. There is no need to apply phosphorus if a soil test shows P2O5 to be high, such as on land with a history of manure application.
  • The worst conditions for apple replant disease are on light soils where poor root growth is combined with moisture stress. Install irrigation where possible.
  • If growing your own trees, criticize their quality and don't plan to plant 100% of the trees. Planting small (<4 ft), weak trees will delay production. Trees are typically small for a reason and will continue to be weak trees. Commercial nurseries grade their trees and build in the cost of discarded trees so the same approach is recommended for on-farm nurseries. Tree losses of at least 10% are common.

On-Farm Nursery

  • Early application of granular fertilizer can minimize the risk of leaf burn. Otherwise, granules can get trapped and sit in new leaf tissue that is close to ground level. 

Events and Notices

NSDA Programs: Sustainable Canadian Agricultural Partnership

Programs have been released under the Sustainable Canadian Agricultural Partnership. Below is a brief description and links to the programs. Please connect with your regional NSDA office staff with any questions.
Please check the NSDA website for all programs under the Sustainable Agricultural Partnership: https://novascotia.ca/programs/. As this is a new 5-year agreement moving into the Sustainable Canadian Agricultural Partnership programs, producers will need to fill in a new Program Funding Registration Form

Season Extension Enhancement Program Presented by Horticulture Nova Scotia

The objective of the Season Extension Enhancement program is to help support fruit and vegetable growers who invest in innovative technologies to extend their growing season, adapt to a changing climate and open up new market opportunities.

The program encourages and supports Nova Scotia’s fruit and vegetable producers by providing financial assistance with the following on-farm infrastructure:
  • adopting season extension technologies; 
  • enhancing storage capacity; 
  • adopting and developing irrigation capacity for field operations.
For more information, visit Horticulture Nova Scotia

Perennia Webinar: Understanding Fire Blight Biology while using PomeBlight (Pesticide Points Available)

The most critical time of the fire blight disease cycle is the blossom blight phase. Flowers have open nectar pores where the disease-causing bacterium  Erwinia amylovora  gains entry during favourable weather. Properly timed management with antibiotics at bloom can prevent infection to protect the health of your trees. 

On Wednesday, May 3 from 12 PM to 1 PM join Tree Fruit Specialist Michelle Cortens to learn how PomeBlight – a responsive web-based tool – can help you monitor for fire blight infection risk. The focus of this webinar is to learn about the biology of the disease while exploring scenarios through the modeling program. 

The ‘Understanding Fire Blight Biology while using PomeBlight’ webinar is NS Environment and Climate Change (ECC) course T2337 and is worth 1.0 point in Pest Management for continuing certification points.

Pest Management Guides 2023

All changes new to 2023 are made in red text directly on the guides. The information on all expected changes was summarized in a blog post on March 7. 

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Larry Lutz, Bob Prange, Danny Davison, Jeff Wentzell, Mathew Vankoughnett, Suzanne Blatt, Dustin MacLean, Karen Burgher, Ian Willick, and Keith Fuller.

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

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