Orchard Outlook Newsletter Vol. 22, No 4

Tuesday, May 3, 2022

Today's newsletter focuses on early season disease management including staying on top of apple scab and considerations about powdery mildew. Weed management is a hot topic this week with luscious growth following the rainy period. With trees arriving, we review all of Dr. A.D. Crowe's reasons why trees fail to grow rapidly in the first year... so you can avoid them! Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

  • 2022 Degree Day Accumulations
  • Soil Temperature

  • Apple - Scab
  • Apple - Powdery Mildew
  • Apple - Fire Blight Prevention
  • European Red Mite
  • Nematode (Pre-plant samples)

Weed Management

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

Pest Management Guides 2022

Events and Notices

  • Rapid tests for temporary foreign workers



2022 Degree Day Accumulations

The past week's accumulation of degree days was below seasonal and now we have lost our lead so cumulative totals are similar to average (Figure 1). Very few base 5°C degree days were accumulated in April so development has been progressing slowly.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 2 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

  • Approximately 5% less plant development heat units compared to the 5-year average, and 3% less compared to the 10-year average.
  • Approximately 31% less plant development heat units compared to 2021, and 56% more compared with 2020.
  • Approximately 37% less insect development heat units compared to the 5-year average, and 38% less compared to the 10-year average.

Soil Temperature

Soil temperature has declined by about 1
°C over the recent rainy and cool period as expected. Currently, the temperature at 35 cm deep is around 7.5°C (Figure 2, red line). For those of you waiting for spring fumigation or spring nematode sampling, the temperature of interest is 10°C. Typically 10°C is reached in early to mid-May.
Figure 2: Soil temperatures at 35 cm depth at the Kentville Research Station from 2017 to 2022. Provided by Jeff Franklin (AAFC).

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 2, the Idared buds were at early tight cluster, and Honeycrisp and Ambrosia were at half-inch green (Figure 2).

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

Also in North Medford, Jonagold and Marshall Mac were at half-inch green. Orchard Outlook committee members reported that Honeycrisp, Jonagold, and Ambrosia in the Melvern Square area were around half-inch green.


Apple – Scab

Over the string of rainy days, there was hardly any noticeable break in leaf wetness. A heavy infection with available ascospores was easily possible, even in cold conditions.

Table 1: Apple scab infection events in Kentville from April 26 to May 2, 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 Sunday, April 17th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
3 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.


  • A period of rainfall is currently forecast for the evening of Wednesday, May 4 and into the day on Thursday. With the forecast temperatures being an average of +9.5°C, it would take around 14.5 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills TableNote that ascospores are now maturing more rapidly and 5% of the total spore load is expected to mature since the last infection event. 
  • Re-apply a protectant fungicide to green tissue prior to an infection event 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 recent product restrictions.
  • Always tank mix single site fungicides with a group M for resistance management.

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.


  • As opposed to scab, powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected. Do not apply a product for powdery mildew before a heavy rain is expected because:
    • The product will wash off.
    • Powdery mildew spores will not germinate on a wet leaf surface. 
    • Rain removes powdery mildew spores in the air and destroys spore-producing structures.
  • Application of a protectant mildew fungicide at tight cluster prevents primary infections of leaf clusters. Timely application early in the season will reduce the risk of secondary infections later. 
  • 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.
  • Practice resistance management:
    • Powdery mildew: Group Ms do not have activity on powdery mildew so they will not help prevent powdery mildew resistance development. Products in the groups 3, 7 and 11 are registered for control of PM. Resistance to group 11 products was reported in a survey in 2013. Therefore, whenever the remaining groups 3 & 7 are used, careful consideration must be given to rotating the groups to slow resistance development. Avoid more than two consecutive applications of a single group.
    • Scab: The Group M fungicides (mancozeb and captan) provide scab control so tank mixing them with single-site fungicides is a great strategy to slow resistance development in the apple scab population. Although Group 3 fungicides Nova and Fullback are labeled for apple scab, they are not expected to provide control because of resistance in the scab population.

Apple – Fire Blight Prevention

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. When the canker blight bacteria are active, water sprout shoots close to cankers will wilt. 


  • I have not observed ooze at confirmed cankers. Typically the ooze begins to appear between tight cluster and early pink at which point 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.
  • Not sure if it's fire blight? 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.
  • Be cautious when applying post-emergent herbicides to prevent injury to young trees. 
  • Copper can be applied to nonbearing trees where fruit russet is not a concern. Note that copper may even have a suppressive effect on powdery mildew that could help with resistance management.


European Red Mite

To be most effective, oil application for European red mite should be targeted close to egg hatch – around tight cluster and before pink. Erika Bent (APM) notes that egg hatch has not yet begun but next week is a possibility.

Avoid oil if freezing temperatures will occur within 48 hrs and no captan within 7-14 days. Oil should not be applied to young trees at less than 3 years old, and the risk on varieties with Delicious parentage (Ambrosia, Gala) increases after tight cluster.

Nematode (pre-plant samples)

Root and soil samples are best collected in the spring (May-June) or during the fall (September-October), both of which avoid the heat or drought conditions in summer. Soil temperatures at sampling should be above 10°C for adequate nematode presence in the upper soil levels. Soil temperatures are not yet warm enough but they should be soon.

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.

If a particular weed issue is giving you trouble, have you identified the weed species to make sure that your herbicide selections have activity on it? For a quick identification, download the free smartphone app called 'Seek by iNaturalist'. No account is required. Simply select the camera function in the app and hover over the plant species of interest. The app will offer an identification, and in my experience it has been surprisingly accurate except for grass species and very young broadleaf stages. Try different angles such as the whole plant, leaves, or flowers (Figure 3). 

If you take a picture, the identification will be saved as long as you don't delete the app. You can also upload pictures that you've taken in the past. Notice that the background can be busy and it doesn't interrupt the identification.

Figure 3: Screenshots while using the live camera in the smartphone app 'Seek by iNaturalist'. From left to right, the app identified broad-leaved dock, common chickweed, and red deadnettle. What a cool tool!


Weeds are now more luscious after the rain. Management as soon as conditions allow will help to improve efficacy by targeting small and susceptible weeds early in the season.

Residual Herbicides
  • The residual product newly registered for tree fruit called Prowl H2O is a better formulation that doesn't stain like the old formulation. Based on experience with other crops, Prowl H2O is good for grass control but for broadleaf control another product should be included.
  • 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. 

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.
  • 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.
  • Foliar nutrients to correct nutrient deficiencies:
    • Zinc: Zinc chelate can be applied early in the season. The timing for zinc sulphate is at petal fall, first and second cover. Do not apply zinc sulphate to russet-prone varieties during the growing season.
    • 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 and winter conditions, about 75% can be lost in 48 hours.
    • Foliar nutrients are not well-absorbed at below 10°C.


  • Be cautious because a lime spreader intended for fields with tall beaters at high speeds can damage the leaf tissue and buds on tree fruit.
  • 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.


This past winter I shared past research from Dr. A. D. Crowe on the question of why trees fail to grow rapidly in the first year. I've included some of the recommendations below as a reminder.

Nursery tree health:
  • 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 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.

Handling from nursery to planting:
  • Avoid letting trees dry out. About 40% of trees can die from drying out, and surviving trees grow slowly. Survivors of 15-minute dry winds recover by year 3. Survivors of 45-minute drying winds still don't grow well by year 3.
  • Bundles of trees sitting in water awaiting planting can asphyxiate, especially in stagnant water and/or warmish water.

Site and Preparation:
  • Trees should not be planted in waterlogged soil. Wait for the ground to dry after the recent rain. Planting in heavy, wet soil can create a cemented layer around roots.
  • Tilth should be friable enough to avoid air pockets for good root to soil contact.
  • In some rigid subsoils, the major barrier to root growth is acidity. Subsoiling without deep lime placement would be ineffective.
  • By using tile drainage on a poorly drained site, for every 20 cm decrease in the water table from 45 cm to 85 cm depth (May 1-15) there is about an 18% increase in yield.
  • Fumigation:
    • If you fumigated last fall, remember to practice tillage within the same direction as fumigated rows and not across. Tillage across rows would mix fumigated soil in the tree row with non-fumigated soil in the laneway.
    • 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 especially in the top 15 cm of soil.

  • Remember the risk of dipping roots in a shared water solution. Widespread disease can affect the planting stock that is dipped in the same batch of solution.
  • Pruning roots reduces growth in the first year, but roots can be pruned if they are damaged.
  • Rootstock effects are magnified the longer the length of the rootstock that remains above-ground.
  • Budding M7 high followed by deep planting (if soil depth supports it) can reduce the amount of root suckers.

  • Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Watering-in or rainfall soon after planting can help to fill air gaps.
  • Be vigilant in spraying for key insect and disease pests. 
  • 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.

On-Farm Nursery

  • 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!
  • Early application of broadcast 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. 

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.

Events and Notices

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

Rapid Tests for Temporary Foreign Workers

You are now able to access Rapid Test Kits for your Temporary Foreign Workers at our regional offices across the province and at the Perennia office in the Annapolis Valley region. These rapid tests are to be used as recommended by Nova Scotia Public Health in certain situations only, not as a widespread asymptomatic screening tool (we do not have the quantity of tests to support this use - so please only request the number you need on an as needed basis throughout the season).

Rapid tests should be used if:
  • you have symptoms.
  • someone in your household has tested positive for COVID-19.
  • you are at risk of severe disease (even with no symptoms).
  • you spend time with others at risk of severe disease.
Please reach out to your AEC (or Sara Marceau at the Perennia office) in advance of dropping by so they know you are coming and how many tests you might require.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Larry Lutz, Dr. Suzanne Blatt, Colin Hirtle, Jeff Wentzell, Dr. Mathew Vankoughnett, Danny Davison, Dr. Vicky Levesque, Dustin MacLean, Dr. Ian Willick, Jeff Franklin, Joan Hebb, and Keith Fuller.

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

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