Orchard Outlook Newsletter Vol. 21, No 2

Tuesday, April 20, 2021


Table of Contents:

  • 2021 Degree Day Accumulations
  • Seasonal Precipitation
  • UPDATE on Weather Stations in the Valley

  • Apple - Scab
  • Apple - Fire Blight Prevention

Weed Management

  • Pruning
  • Fertilizing
  • Liming
  • Planting and Nursery Trees

Pest Management Guides 2021

Events and Notices

  • Presentation on Weather Stations and Tools
  • Launch of Perennia's Field Research Services webpage



2021 Degree Day Accumulations

This year's growing degree day accumulations are still leading over the 5- and 10-year averages but the cool temperatures over the last week have diminished the lead. 

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to April 19th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 76% more plant development heat units compared to the 5-year average, and 58% more compared to the 10-year average.
  • Approximately 138% more plant development heat units compared to 2020, and 54% more compared with 2019.
  • Approximately 102% more insect development heat units compared to the 5-year average, and 52% more compared to the 10-year average.

Seasonal Precipitation

Figure 2 is a graph of cumulative precipitation over the last ten years including rainfall and the rainfall equivalent from snow. Follow the red line to see how 2021 compares to previous seasons. So far, the precipitation totals are tracking very similar to last year at below average. This likely doesn't come as a surprise because the soils have been workable over the last few weeks. 
Figure 2: Both rainfall and the rainfall equivalent from snow at the Kentville Research Station from 2012 to 2021. Provided by Jeff Franklin (AAFC).

UPDATE on Weather Stations in the Valley

As I mentioned last week, the Nova Scotia Fruit Growers’ Association through federal and provincial funding with the Nova Scotia Department of Agriculture has embarked on a smart farm demonstration project to install and maintain weather stations. 

Five of the ten weather stations are now operational. They include the locations: Atlanta, Aylesford, Grafton, Mochelle, and MorristownThe live weather data will be accessible in several formats, for example it is on a quick ‘weather’ tab on the NS Tree Fruit Blog. For more information about accessing the weather stations, tune in to the upcoming event mentioned at the bottom of this newsletter.

Bud Development

Buds have grown slowly over the last week in the cool weather. In an early region on Middle Dyke Road in the Kentville area, the Idared buds are at the stage of green tip to 1/4 inch green. Honeycrisp is at green tip. The bud scales on Ambrosia are still just beginning to separate. Later regions are around early green tip and late varieties are typically around scale separation to green tip.

Figure 3: Bud development in an early region on Middle Dyke Road in Kentville on April 19th. Shown from left to right: Idared, Honeycrisp, Ambrosia.


Apple – Scab

Beginning at green tip, apple tissues are susceptible to infection from the fungus that causes apple scab, Venturia inaequalis.  

Table 1: Apple scab infection events at the Kentville Research Station from April 13th to April 20th, based on the Modified Mills Table. 
*Assuming a green tip date of Tuesday, April 14th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
** 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.

Frequently Asked Questions about apple scab:

For how long do leaves need to stay dry to end an infection event?
Rainfall discharges spores from the leaf litter and onto the leaf surface.Whether or not the spore germinates to produce an infection depends on the temperature and duration of leaf wetness. A germinating spore can survive on a dry leaf for up to 10 hours (or roughly 8-12 hrs) and if the leaf is rewetted before the end of 10 hours then the spore continues to germinate. If leaves become completely dry and remain dry for 10 hours, there is no infection from the ascospores released in that rainfall event.

How does snow affect the infection period?
Snow does not discharge spores from the leaf litter. If snow melts and the precipitation transitions to rain then the spore release can occur. If rainfall happens prior to snowfall, then rain causes ascospores to discharge from the leaf litter. Even if rain turns to snow the ascospores are already developing.

Are ascospores released in the nighttime and are they a concern?
Yes, ascospores are released at nighttime but much fewer are released in the dark than after sunrise. The discharge is largely suppressed at night. Light is believed to activate the discharge mechanism for this fungal organism. But the risk of nighttime wetting isn't nonexistent, especially for high inoculum orchards. Even a small proportion of the total spores in a high-pressure orchard could be a significant risk.


  • Precipitation during the wetting event on the weekend varied throughout the Valley and would have influenced total leaf wetness periods: Kentville 20.7 mm, Atlanta 17 mm, Morristown 15 mm, Grafton 12.6 mm, Mochelle 8.8 mm, and Aylesford 8.2 mm.
  • Light infection events were possible but whether or not a farm experienced an apple scab infection period would depend on farm-specific conditions. If the first infection period hasn't happened on your farm yet, it is a signal that the scab season is near.
  • A period of rainfall is currently forecast for Thursday, April 22nd. With the currently forecast temperatures being a high of +12°C and a low of 0°C, it would take around 21 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills Table.
  • Apply a protectant fungicide to green tissue prior to the first infection event 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 upcoming 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.
  • Note that the new captan containing product 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 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

Last week I mentioned that in 2020, the Nova Scotia Department of Agriculture conducted a detailed survey of the weeds in orchard blocks. Those weeds are most vulnerable to herbicides early in the season when they've got only a few leaves, but they're also difficult to identify. In the following figure, I've featured a couple of weeds from the list of top 10 that are most abundant in local orchards. 

Common groundsel: First leaves have toothed margins, they are oval, and glossy like a succulent. The stalk might also have hairs. 

Lamb's-quarters: The seedling is powdery looking on new leaves. New leaves are triangular-oval. Often the underside is pink or purple.

Vetch: The young plants are often the shoots that arise from underground rhizomes. The leaflets attached to a middle vein create compound leaves that end in a tendril.

Figure 4: Young weeds in orchards at the first leaf stage. From left to right: common groundsel, lamb's-quarters, and vetch.


  • Lontrel is effective on vetch and clovers. Chateau and Devrinol work well on groundsel.
  • 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 such as Ignite, Gramoxone, and Glyphosate. Chateau should not be applied after budbreak unless application equipment is shielded to prevent crop injury. 
  • Always follow label directions. Note that residual herbicides can damage single tree replacements. 
  • Weeds are emerging. If weeds are already present, consider adding a post-emerge to a residual herbicide to achieve control.



  • If pruning is delayed, plan a strategy to get the most value for your time. Prioritize young blocks and high value varieties and return to low value areas. This strategy is especially important considering the new captan limitations.
  • 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

  • Remember to document the quality of your nursery trees with pictures and notes. Did trees dry out? Any signs of disease (cankers, crown gall)? How do the roots look (rinse and take a photo)? Notify the appropriate people of issues you notice. Record the date of planting. An issue that shows up after planting is much easier to diagnose or prevent given this information.
  • If fumigating in the spring, observe the warnings on the label prior to planting to avoid crop injury. Leave the soil undisturbed for 10 to 14 days or longer in wet weather. To verify plant safety, follow the safety germination test described on the label for PicPlus.
  • 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 2021

The pest management guides are now available online for download. All changes new to 2021 are made in red text. The information on all expected changes was summarized in a blog post on April 9th.

Events and Notices

For upcoming events, visit the ‘Events’ tab on the NS Tree Fruit Blog. Specific events will be described here when available.

Presentation on Weather Stations and Tools

Join the NSFGA on a rainy day on Thursday, April 22nd at noon for an update on their weather network project. Candy O'Connor will describe the project, Jonathan Bent with Perennia will introduce the technical components of the project, and Michelle Cortens will share advisory information about accessing the data, Maryblyt alerts, and a smart tools project in development. We encourage your questions. This meeting will be recorded and made available along with a handout of the presentation slide deck for future reference. If you are not already on the mailing list for the NSFGA, please register for the event by emailing coconnor@nsapples.com.

Launch of Perennia's Field Research Services webpage

We are excited to share with you the launch of our new Field Research Services webpage! Our new site fully showcases our team and the services available to support agriculture research in Nova Scotia. Our team's knowledge and skillset ensures we are fully equipped to deliver on-farm extension and small plot research. We pride ourselves on performing quality research to ensure accurate results and client satisfaction. Learn more about the services we offer and take a look at our projects page to see some of our previous work. Feel free to reach out to us anytime. We would be happy to discuss your research needs.

Edited by Michelle Cortens, Tree Fruit Specialist

Perennia Food and Agriculture Inc.

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