Orchard Outlook Newsletter Vol 21, No 12

Tuesday, June 29, 2021


Table of Contents:

  • 2021 Degree Day Accumulations

  • Apple - Scab
  • Apple - Powdery Mildew
  • Fire Blight - Orchard Management
  • Apple - Black Rot/Frog-Eye Leaf Spot
  • Apple - Brooks Spot
  • Apple - Flyspeck and Sooty Blotch
  • Stone Fruit - Brown Rot
  • Apple Insects (Leafhopper, aphids, codling moth, mites, leaf roller, apple maggot)
  • Summer Hedging
  • Honeycrisp Leaf Chlorosis
  • Solstice Reminders
  • Pruning and Training
  • Young Trees
  • Calcium Nutrition
  • Weed Management
  • Nursery Trees
  • Mowing
Pest Management Guides 2021

Events and Notices
  • Bitter rot and apple scab samples for AAFC
  • Perennia has moved to downtown Kentville!



2021 Degree Day Accumulations

The above-average trend continues and this year is one of the warmest, if not the warmest year, in recent history.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to June 28th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 20% more plant development heat units compared to the 5-year average, and 18% more compared to the 10-year average.
  • Approximately 18% more plant development heat units compared to 2020, and 35% more compared with 2019.
  • Approximately 30% more insect development heat units compared to the 5-year average, and 28% more compared to the 10-year average.

Fruit Set

Compared with last week, fruit set is becoming more clear. In many cases, trees this year do not appear to have a heavy set loaded with five-fruit clusters. Two-fruit per cluster is certainly possible though and hand thinning will be needed. Preliminary observations suggest that the heat promoted fruit drop and thinning products. Fruit set on varieties between regions seems to differ based on the weather conditions at bloom. In other words, it's difficult to generalize!

Figure 2: The orchard floor in the tree row showing the progression of fruit drop last week (left) and this week (right).


Apple – Scab


  • According to the Modified Mills table, lesions from the final primary infection event should be visible. 
  • Where primary lesions are present, secondary infections have been occurring and will continue during wetting events of sufficient duration. The minimum wetting required for secondary infections is 3 hours less than the wetting required for primary infections.
  • This year we experienced relatively light pressure from primary ascospores. During the month of May, about 71% of the ascospores were released prior to short wetting periods and light infection events. But these are observations that we can make only in hindsight and be glad that pressure was manageable. Fungicide protection is needed whether or not an infection is light or heavy.


  • Plugged sprayers warning - You are already aware that water soluble packaging should not be tank mixed with boron and the tank should be rinsed well before and after boron. Sometimes boron is not the target nutrient in a product but it is included. Please carefully review nutrient formulations that might contain boron in small quantities.
  • Folpan cautions - Folpan is not a new product but it is new for use in the industry. It is considered a cousin to Captan and is similarly a hot product that has the potential to cause fruit russetting. Do not use Folpan close to oil sprays or products containing surfactants. Also, be wary of tank mixes with liquid nutrients that are formulated to maximize uptake.
  • Hand thinning REI reminder - Be very aware of the re-entry periods on the new captan-containing product Maestro 80 WSP for planning ahead to hand thinning. High-density plantings with a maximum canopy width of 2 m have an REI for hand thinning of 15 days. Otherwise, low-density plantings have an REI of 24 days for hand thinning. 
  • Do not reduce fungicide spray intervals until you can identify your pressure from secondary scab lesions. Also note the risk of summer diseases if spray programs are stretched to the limit.
  • The pre-harvest interval for EBDC fungicides (e.g. Manzate, Dithane, Polyram) for fruit destined for the United States is 77 days versus 45 days for the domestic market. An application of EBDC on June 29th would require until September 14th to meet pre-harvest requirements for the United States.
  • Always tank mix single site fungicides with a group M for resistance management.

Apple – Powdery Mildew


  • Powdery mildew pressure is high this year. On young trees, monitor for active mildew to determine the need to protect new terminal growth. Only group 3, 7, and 11 fungicides have activity and resistance is a concern in group 11. This issue of not having enough groups is widespread across apple growing regions.
  • Remember that late summer sprays are protectants and not eradicants. Flag shoot symptoms from overwintering infections will be visible for the rest of the season.
  • Pay particular attention to susceptible and high-value varieties such as Honeycrisp and Gala.

Fire Blight - Orchard Management


  • Continue to monitor for signs of fire blight blossom infections, especially in young blocks.
  • Canker blight and shoot blight symptoms should also be visible by now.
  • In blocks with historically high pressure, prune only when the forecast calls for at least 2 days of sunny, dry weather. As an extra precaution, disinfect tools after working in a block with fire blight pressure.
  • When pruning, remove fire blight strikes at least 2-4 ft below active infections to remove the leading edge of the bacteria. Being aggressive at the first sign of symptoms will help prevent the re-occurrence of symptoms and the need for continuous cutting back. Leave prunings in orchard alleyways to dry thoroughly for several weeks. 
  • Monitor for shoot blight on suckers that can infect the rootstock.
  • For on-farm nurseries, consider applying a copper product at the lowest labeled rate prior to training trees and follow the labeled REI. Make cuts on only dry and sunny days.

Apple - Black Rot/Frog-Eye Leaf Spot

This disease has been an issue in certain orchard blocks. Varieties most prone to infection include Honeycrisp, Northern Spy, Delicious, Sunrise, and Ginger Gold. Infection can develop on fruit after about a 9-hour wetness period at an average temperature around 20-24C.

Dr. Sajid Rehman and Dr. Paul Hildebrand have been exploring the black rot disease. Research they reviewed from North Carolina (Sutton 1980) suggests the following:
    • The total spore load is highest for a period from petal fall to 4-6 weeks later. Spores are likely active beginning at green tip.
    • Spores are produced for at least 6 years in dead wood that researchers tied to trees.
    • As little as 0.25 mm of rainfall triggered spore discharge.
    • Spores are detected during the first hour of rainfall.
    • Spore concentration increased as the rain continued.


    • The heaviest spore release is believed to occur for a four to six week period following petal fall. If considering when to apply the second and final Captan on a low-density block, we are currently in the assumed high risk period and rainfall would release spores. Be cognizant of the REI for hand thinning activities.
    • Fungicides are protectants because they prevent spore germination on plant tissues so for protection from this disease the fungicides would need to be applied prior to the wetting event. 
    • Do not reduce rates of Captan after bloom in high density orchards that have a history of black rot. Consider this recommendation where practical in terms of new label restrictions. Pristine and Merivon would also have good protective activity but these chemistries should not be overused.
    • Check for nearby brush or wood piles because they serve as a major source of inoculum. Remove the brush pile to reduce the chance of infection.

    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 and Aprovia Top.

    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. Include a product for cover sprays that is labelled for flyspeck and sooty blotch such as Captan, Maestro, Inspire Super, Aprovia Top, Allegro, Pristine, and Merivon.

    Stone Fruit - Brown Rot

    As sweet cherries begin to ripen they become more susceptible to brown rot infection. The interval between fungicide applications will need to be shortened as the fruit softens. Check the Stone Fruit Management Guide for fungicide options and always check the pre-harvest spray intervals when selecting the fungicide.


    Apple Insects

    • White apple leafhopper: Monitor for white apple leafhopper that has been enjoying this heat. Sevin XLR applications will control leafhopper but monitor untreated plants for leafhopper. The first generation is nearing the end when there will be only adults on trees. The nymphs will start to appear again and cause feeding damage in early August so the second generation is the next treatment opportunity. If treatment is required, a neonicotinoid, Sivanto Prime, or Exirel would control leafhopper and also pick up aphids. 

    • Aphids: Monitor for rosy apple aphid and green aphid. 
      • Winged adults are present for the rosy aphids so monitor the presence of nymphs and whether predators are taking care of the issue before they move from trees to weedy hosts. 
      • In young trees the aphids can disrupt shoot growth. Monitor nursery plantings as well. Now that leaves are curling high water volumes are needed for effectiveness. Green aphid will move back into orchards that were treated previously so continue to monitor. Assail and Calypso also have activity on codling moth, apple maggot and leafhoppers. Be cognizant of REIs if installing trellis.

    • Codling moth: Approximately a week after application of an OP insecticide, clean out the trap and start monitoring the trap. The capture of an additional 10 or more moths would indicate that a second treatment is required.

    • 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.
      • Scout your orchards or check your scouting reports to see if there is a treatable population.
      • Both European red mite and two-spotted spider mite are controlled by the products Acramite, Apollo, Kanemite, and Nealta. All three mite species are controlled by Nexter and Envidor.
      • This is the time of year to get rust mite under control instead of mid to late August when the foliage has become bronzed.
      • 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. The use of dormant oil applications will also help to delay resistance selection for European Red Mite.

    • Obliquebanded leafroller: Monitor or check scouting reports for larval populations soon.

    • Apple Maggot: In 2012 that had similar heat to this year, the first capture of apple maggot in a heavily infested orchard was reported on June 29th. Captures in commercial orchards were more common around July 10th. In blocks that are still being treated for codling moth, the control is extended to early maggot flies. No captures have been noted yet for this year by Dr. Suzanne Blatt at the research station.
      • The economic threshold is 1 maggot fly per orchard on a yellow sticky board. Apply a treatment 7-10 days after the first fly is captured on a yellow sticky board or immediately after a female is captured on a red sphere.


    Summer Hedging

    • You might recall a local study by Perennia in 2013 that evaluated summer hedging using Ambrosia on M.9 and Gala. Treatments were applied at 6, 8, and 10-leaves of new growth corresponding to June 25, July 5, and July 11, respectively. 
      • Table 1. Summary of regrowth from summer hedging cuts to ‘Ambrosia’ and ‘Gala’ apple trees in the Annapolis Valley.


        Frequency of Regrowth (%)

        Length of Regrowth (cm)

        25 June

        5 July

        11 July

        25 June

        5 July

        11 July















      • Regrowth occurred most frequently on cuts to the current year’s growth, and hedging cuts into 1-year-old and older wood also often generated regrowth. 
      • Note that more vigorous rootstocks would be expected to have greater re-growth response.
    • For more information, there is a good article from Cornell that concludes: first week of June hedging = 8 inches regrowth with a terminal flower bud, first week of July = 5 inches regrowth, and first week of August = no regrowth. Note that in the Cornell study they evaluated M.9 with several varieties.

    Honeycrisp Leaf Chlorosis

    • The committee discussed leaf chlorosis because symptoms are just beginning to appear. There is the potential for early and noticeable symptoms this year. 
    • Leaves start out chlorotic and by the end of the season they turn brown and dry. The symptoms commonly form on the edges of the leaf and progress inwards. Not to worry though, this genetic trait of Honeycrisp shows up at the end of every season, and severe symptoms do not appear to negatively affect the health of the trees.
    • It’s tempting to think the discolouration is related to a nutrient deficiency because the resemblance is strikingly similar, but the scientific consensus is that a nutrient deficiency is not involved. Honeycrisp leaves become discoloured when export of carbohydrates from the leaf becomes partially disabled. Carbohydrates accumulate and interfere with chloroplast function. As a result, the chloroplasts break down and the green pigment is lost.
    • Symptoms tend to appear after shoot growth is complete. Growing points like shoot tips, and storage organs like roots and fruit all attract carbohydrates for their own use. When shoot tips stop growing, there is less demand for carbohydrates... allowing it to accumulate to excess levels in Honeycrisp leaves.
    • Years that are sunny and warm encourage excess carbohydrate production and may cause more severe symptoms. Also, light crop loads will show more symptoms.

    Solstice Reminders

    • If granular fertilizer is applied now, the risk is that any dry weather in July will slow the release. Late release will prevent trees from hardening off before the winter. Top dressing is not recommended after the end of June.
    • 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.

    Pruning and Training

    • If bamboo is limited because of COVID delays, we recommend looking at other options in the meantime. As young trees grow more foliage they are more susceptible to sailing in the wind. Consider running wire supports or new solutions to support trees. The hurricane season has begun and even the risk of high wind events is cause for concern.
    • 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).
    • Train and support young trees as soon as possible. Remove competing terminals. Work in dry weather especially if the block has historically high risk of fire blight.

    Young Trees

    • Broadcasting grass seed is not recommended for establishing grass in the alleyway. Direct seeding is recommended to confine the grass seed to the alleyway and avoid spread to the tree row. The herbicide gramoxone used to provide good control of bluegrass species but post-emerge products for grass control are now limited.
    • Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Deer are browsing young plantings and causing damage. Thiram is no longer an option to deter feeding while the fence is being installed. Another deterrent product called Bobbex is available for nonbearing trees.
    • Remove root suckers. Suckers compete with the main tree for water and nutrients. They harbour pests, and they are an entry point for fire blight. Pull or break off suckers because otherwise cutting them would let them rebound. If necessary, AIM herbicide is registered for control of suckers but avoid drift onto young trees and apply only near mature brown bark.

    Calcium Nutrition

    • Note that nutrient product formulations with calcium may contain boron that would interact poorly with water soluble packaging.
    • The goal of Ca sprays is to increase the concentration of Ca in the fruit and reduce bitter bit incidence. 
    • Calcium applied at two-week intervals is better than occasional, high-rate applications. 
    • The recommended rate is 4 to 14 pounds of elemental calcium per acre in a season spread over six to eight cover sprays. The percentage of elemental calcium will be listed on the label.
    • Ca has very low movement within the tree and needs to be applied directly to the fruit surface to be absorbed. Therefore, thorough coverage is important to cover developing fruit.
    • Calcium chloride flake (77% Ca) is the most economical Ca material to use but also the highest risk for foliar burn. Apply calcium chloride flake at no more than 4.5 kg per 1000 L of spray solution. The risk of leaf or fruit damage from calcium is highest in hot and dry weather. Susceptible varieties can develop lenticel spotting if damaged. 
    • Risk of leaf injury may be enhanced by Captan. Incompatibility has been observed with Epsom salts, and liquid or emulsifiable pesticide formulations in some cases. Do not apply calcium with apogee.

    Weed Management

    • Note that 2,4-D has an 80-day PHI. Eighty days from now is September 17th. 
    • Prevent herbicide drift by avoiding sprays during wind gusts, periods of dead calm, wind speeds above 16 km/hr, and temperatures above 25°C.
    • Remember the importance of weed control in nurseries and young plantings. Management practices now will impact the outcome of the final tree. Encourage the growing point to be successful.

    Nursery Trees

    • Scion leaders will need support.
    • Aim is registered for nurseries but it is a hot product and caution is recommended around green tissue. The product is not volatile but green tissue is very sensitive on contact.
    • Monitor for aphids, leafhoppers, and tarnished plant bug.
    • Strip the lower leaves on nursery rootstock before they become woody.


    • As grass becomes long the extra surface area increases transpiration. Keep grass mowed to conserve moisture.
    • Keeping the orchard floor cover mowed will minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.

    Pest Management Guides 2021

    The pest management guides are available online for download. All changes new to 2021 are made in red text.

    Events and Notices

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

    Bitter Rot and Apple Scab Samples for AAFC

    The Plant Pathology Lab of Kentville’s Agriculture and Agri-Food Canada is looking for apple growers who will participate in a province-wide study of the fungal pathogens responsible for bitter rot and apple scab disease in apple. One of the goals of the research is to look at the fungicide resistance profile to find out which fungicides are still effective or not. This is an industry and AAFC funded project. 

    Growers who notice either bitter rot or apple scab appearing in their orchard are invited to contact Dr. Shawkat Ali (shawkat.ali@canada.ca) or Shayne McLaughlin (mc615708@dal.ca). Researchers will then monitor the orchard to collect diseased leaves or fruit from the orchard for further study. Samples cannot be collected from the orchard floor due to rapid deterioration. The industry needs your help in identifying sites where samples can be taken.

    Perennia office has moved to downtown Kentville!

    We are now located at 28 Aberdeen Street in downtown Kentville. Our office phone number stays the same: (902) 678-7722. Please note, we are not open for visitors until July 5th. You can access the building from Aberdeen Street and walk through to the back parking lot where our entrance is or enter the back parking lot (turn left beside the Independent grocery store off Webster Street) where we have designated parking and our own separate entrance. For those of you familiar with Kentville over the years, we are in the old Access Nova Scotia space.

    This Orchard Outlook has been published with the input of the Orchard Outlook Committee
    Edited by Michelle Cortens, Tree Fruit Specialist
    Perennia Food and Agriculture Inc.

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