Orchard Outlook Newsletter Vol. 22, No 2

Tuesday, April 19, 2022

There it is! Green tissue is starting to show up in some regions. This newsletter focuses on bud development and early season disease management. We also revisit winter temperatures and bud injury. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • Revisiting Winter Temperatures and Bud Injury
  • 2022 Degree Day Accumulations

  • Apple - Scab
  • Apple - Fire Blight Prevention

Weed Management

  • Pruning
  • Fertilizing
  • Liming
  • Planting and Nursery Trees

Pest Management Guides 2022

Events and Notices



Revisiting Winter Temperature and Bud Injury

In last week's newsletter I posted a table showing extreme cold temperatures at two specific points in time. In the meantime, I have put together a summary table of the recorded extreme winter low temperatures from all of the NSFGA Davis stations and the dates on which the temperatures were recorded (Figure 1). In all locations, temperatures dipped below -20°C at some point in time this past winter. In some locations, temperatures reached below -20°C several times between late January and early February (not shown). 

Figure 1: A summary of extreme winter low temperatures recorded on the NSFGA network of Davis weather stations.

Injury to peach buds from several regions was reported in the previous newsletter. Peach buds that have acquired their full winter hardiness become damaged at -23°C. Therefore, the critical temperature for peach injury was exceeded in most regions being monitored.

This past week I also observed some damage to cherry buds in a location that did not exceed the threshold temperature for cherry buds of -26°CCherry flower buds have multiple flowers within a single bud. The injury varied between buds and throughout flowers within buds (Figure 2 and 3)

This observation of injury to cherry buds is likely related to the tree's state of cold hardiness when the cold temperature occurred. Usually, full winter hardiness of tree fruit is reached in mid-February, so the cold temperature events in late January to early February are considered early. The injury occurred in cherries prior to the expected state of full winter hardiness to -26°C.

Figure 2: Cherry buds cut horizontally to show healthy green tissue or dead brown tissue indicative of winter injury.

Figure 3: Cherry buds cut vertically to show healthy green tissue or dead brown tissue indicative of winter injury.

2021 Degree Day Accumulations

The past week's accumulation of degree days was relatively seasonal. The cumulative degree day accumulations are tracking slightly above average. 

Figure 4: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to April 18th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 36% more plant development heat units compared to the 5-year average, and 26% more compared to the 10-year average.
  • Approximately 19% less plant development heat units compared to 2021, and 92% more compared with 2020.
  • Approximately 21% more insect development heat units compared to the 5-year average, and 8% less compared to the 10-year average.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on April 18th, the Idared buds were at green tip, Honeycrisp was at scale separation, and in Ambrosia a small percentage were beginning scale separation but most were still at silver tip (Figure 5).

Figure 5: Bud development in an early region on Middle Dyke Road in Kentville on April 18th. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Orchard Outlook committee members reported green tip in the Windsor area on Idared, Russet, and Gravenstein. Also, in the Lakeville area there is green tip on Gravenstein. 


Apple – Scab

Beginning at green tip, apple tissues are susceptible to infection from the fungus that causes apple scab, Venturia inaequalis. The environmental conditions for an infection are listed in the Modified Mills Table.

Ongoing precipitation started late morning today in Kentville and is forecast to end overnight. 
  • Whether this is an infection event relevant to you depends on the presence of green tissue on your individual farms.
  • At the forecast average temperature of 7.5°C, it would take 17 hours of leaf wetness for a light infection event to be caused by mature ascospores. Leaf wetness from late morning today to late morning tomorrow makes a light infection event possible.
  • According to the Gadoury model and using Kentville temperatures, ascospores have matured to 1.1% of the seasonal load.
  • Rain, at times heavy, could bring totals of 20 to 30 mm.


  • The current 7-day forecast with dry and sunny days should hopefully be conducive to getting protection on before the next infection event when green tissue will be more widespread. Apply a protectant fungicide to green tissue prior to infection events and reapply on a 7-day interval, with a shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
  • Vigilant protection of primary scab will prevent the challenges that come with chasing secondary scab. Secondary scab will be increasingly challenging with product discontinuations.
  • Always tank mix single site fungicides with a group M for resistance management.
  • 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.
  • If you plan to use oil for European Red Mite control, Captan should be avoided within 7-14 days of an oil application.
  • Remember that Maestro 80 WSP has re-entry periods that differ depending on the orchard density and activity (anywhere from 2-24 days).

Apple – Fire Blight Prevention

The goal of copper application is to cover the bark with copper to reduce the population of bacteria on plant surfaces that arise from bacterial ooze around the pink stage. The copper treatment will reduce the initial inoculum and limit the spread of fire blight bacteria to blossoms or wounded tissue on the tree. This strategy is most effective in blocks that had fire blight cankers in the previous two seasons.


  • If possible, apply copper to the entire orchard block including non-susceptible varieties because they can serve as reservoirs of randomly dispersed bacteria. However, if limited by time, prioritize high risk blocks.
  • A copper application is recommended when buds have reached green tip. A fixed copper product such as Copper Spray Fungicide (50% copper oxychloride) is recommended because it is resistant to being washed off by rain. Cumulative rainfall of 100 mm will wash away most of the product, which is why it is applied no earlier than green tip. If applied later than green tip, residues that persist on fruitlets can cause russetting.
  • 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. A half rate of an EBDC can be included as extra protection for apple scab.

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. 


  • Residual herbicides such as Chateau, Alion and others offer a much longer weed control period than post-emergent products including Ignite, Gramoxone, 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.
  • Note that residual herbicides can damage single tree replacements. 
  • 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. Also, some residual herbicides need rainfall for activation so it is a good idea to tank mix with a herbicide that works immediately without rainfall.
  • Unfortunately, this year there are widespread shortages of herbicides, in particular glyphosate and glufosinate. Reduce the reliance on post-emerge products by starting clean with residual herbicides.  Treat emerged weeds when they are small and succulent.



  • If pruning is delayed, plan a strategy to get the most value for your time. Prioritize young blocks and high value varieties and then return to low value areas.
  • Ensure that youngest blocks are pruned first so growth is directed into desirable leader and terminal extension. Prune early to encourage vigour or delay pruning to remove vigour.
  • 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.


  • 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 as pH can change over the growing season. 
  • The provincial limestone trucking assistance program is open.

Planting & Nursery Trees

  • If fumigating in the spring, remember the importance of soil preparation to get the most out of the fumigant. Remove old roots and work to get a good soil tilth without sods and clods.
  • 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.

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.
As we look to the future, we really want your feedback on how you access the guides, as well as some things we are considering when sharing the information to make it easier for you to use. If you can please take 2 minutes to complete this short survey for us that would be very helpful and much appreciated.

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: Dr. Suzanne Blatt, Dr. Bob Prange, Jeff Wentzell, Colin Hirtle, Joan Hebb, Danny Davison, Dr. Shawkat Ali, Dustin McLean, Jeff Franklin, Dr. Vicky Levesque, and Dr. Mathew Vankoughnett.

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

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