Today's newsletter announces the appearance of green tissue and focuses on early season disease management including apple scab and copper for fire blight sanitation. We review a full season weed control strategy that was discussed at the most recent Growing Good Growers tailgate meeting. Finally, we review horticultural interests like lingering injury to scaffold limbs from the 2023 polar vortex and review what we know about the practice of initiating branches on blind wood. Thanks to the ongoing commitment of the Orchard Outlook Committee members.
Table of Contents:
- 2025 Degree Day Accumulations
- Apple Buds
- Pear and Stone Fruit Buds
- Apple - Scab
- Fire Blight Sanitation
- Delayed Dormant Oil - Cautions and Considerations
- European Red Mite
- The Strategy
- Efficacy of Herbicides
- Crop Safety of Common Herbicides
- General
- Lingering Injury from 2023 Polar Vortex?
- Treatments for Blind Wood
- Pruning
- Fertilizing
- Liming
- On-Farm Nursery
Weather
2025 Degree Day Accumulations
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to April 21 for the past 17 seasons. Provided by Jeff Franklin (AAFC Plant Physiology).
- Approximately 9% more plant development heat units compared to the 5-year average, and 29% more compared to the 10-year average.
- Approximately 1% less plant development heat units compared to 2024, and 27% less compared with 2023.
- Approximately 24% more insect development heat units compared to the 5-year average, and 42% more compared to the 10-year average.
Bud Development
Apple Buds
The warmer than forecast conditions meant that the degree day requirement for bud burst was fulfilled on April 21. The date was a close predictor of field observations of green tip this year, when cumulative degree days are close to average. The average date of bud break is April 20 so this year has been close to average.
Figure 2: Bud development in an early region on Middle Dyke Road in Kentville on April 21. Shown from left to right: Idared, Honeycrisp, Ambrosia.
Pear and Stone Fruit Buds
Yesterday on April 21 at an early region in Greenwich, the pear buds were at scale separation, peach was at calyx green, and European plum was at bud burst (Figure 3). Orchard Outlook committee members also report that sweet cherry in Kentville is at early swollen bud.
Figure 3: Bud development in an early region in Greenwich on April 21. Shown from left to right: pear, peach/nectarine, and European plum.
Diseases
Apple – Scab
For industry monitoring purposes, a green tip date of April 20 will be used for predictions of ascospore maturity this year. An apple scab infection event has not yet been recorded. Rain today at an average temperature of 5°C would need to wet leaves for 26 hrs to cause infection. The environmental conditions for an infection are listed in the Modified Mills Table.Recommendations:
- Green tissue should be protected with fungicide prior to the first predicted infection event. In the forecast there is heavy and prolonged rain expected near the end of this week. At relatively warm forecast temperatures averaging 9.5-11.5°C, an infection will occur if green tissue is wet for 12 hrs to 14.5 hrs. An infection event is likely and the next few days are a great opportunity to get that brand new tissue protected ahead of time.
- According to the forecast, ascospores are expected to mature at a rate of 0.4% per day and by Friday about 2.2-3.3% of ascospores are expected to mature and available for release.
- 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.
- There is some good news for the registration of Manzate! I have been told that a modified label for Manzate has been approved and published to allow more total applications at half rates. The label is not yet posted on the PMRA public online database but I expect it will be posted soon. This is great news for fungicide resistance management programs!
- 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.
Fire Blight Sanitation
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 but does not replace the need for blossom blight management. The copper sanitation strategy is most effective in blocks that had fire blight cankers in the previous two seasons.
Recommendations:
- Please note that leaf tissue injury could occur when copper is used alone or combined with oil when hard frosts/freezing temperatures occur so proper timing is key. The active ingredient in copper products is the copper ion that is fungicidal and bactericidal but at effective rates the copper is also toxic to plant life.
- A copper application is recommended when buds are at the green tip stage and no later than 1/4 inch green for fresh market varieties, after which phytotoxicity becomes a problem. Processing varieties where russet is tolerable can be treated later as well as nonbearing trees.
- This week may be a good opportunity for applying copper. Copper will provide some fungicidal activity on apple scab but does not redistribute in rain so use a mancozeb fungicide as well if possible (considering the possible heavy rain in forecast).
- A fixed copper product such as Copper Spray Fungicide (50% copper oxychloride) is recommended because it is resistant to being washed off bark surfaces by rain.
- 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. In other words, coverage is very important and a concentrate volume applied to every other tree row would not provide enough coverage.
- Do not use dormant oil within 14 days of Captan or within 48 hours of freezing temperature.
- 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.
Insects
Delayed Dormant Oil - Cautions and Considerations
CAUTIONS: DELAYED DORMANT OIL
- When green tissue is present, do not use dormant oil 48 hours before or after freezing temperature. Oil that is applied before freezing temperatures breaks down and adheres to the plant tissues unevenly instead of the target insects. Also if the oil and water mixture freezes before it dries then the green tissue can be injured.
- 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.
- Coverage is important because the oil acts by smothering mite eggs. Consider that greater water volumes are needed for large canopy trees that have not been pruned yet versus trees that have been pruned.
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 with slightly less effective results. European red mite eggs overwinter in the cracks on buds and spurs so high water volume is needed to reach all of the crevices. The oil treatment is not effective for rust mite or two-spotted spider mite.Weed Management
The Strategy
Over time I hope to contribute more information about the opportunities for different herbicide options. As you know, there are many factors and complicating layers of pre- or post-emergence activity, planting age, target weeds and ideal timing. We had a great group discussion last week at the Growing Good Growers tailgate meeting with guest Sonny Murray about the overall strategy.
The group consensus was that there is a need for 3-4 herbicide treatments per season. To get out of the cycle of trying to manage large weeds with post-emergent herbicides, think about pre-emergent/residual herbicides as filling windows of time. Most residual products will give about 6 weeks of weed control. Use residual herbicides through periods of high weed germination like in spring. Post-emergent herbicides help with clean up when weeds are small. The risk of crop damage by using burndown products is minimized by practicing prevention and keeping weeds small.
Recommendations:
Young Trees (1-2 yrs):
- PREPLANT: Treat tough perennials preplant with glyphosate.
- TREATMENT 1: After planting trees, allow the soil to settle in a rain and then apply a registered residual herbicide ahead of the next notable rain. Sinbar has shown good efficacy or Chateau (broadleaf) + Prowl H2O (grass).
- TREATMENT 2: At 6-8 weeks later, apply another residual treatment before rain. The remaining options for residual control are simazine products (broadleaf) and Dual II Magnum (grass). Use burndown if needed.
- TREATMENT 3: At preharvest, use burndown products Reglone or Ignite. In new plantings, there is an opportunity to try Basagran.
Established trees (>3 yrs):
One approach is to respond to weed growth and continual clean up with glyphosate and 2,4-D.
An alternative approach is to prevent weed growth with residual herbicides:
- TREATMENT 1: Apply a residual herbicide before rain with a burndown like glyphosate to target some tough perennials.
- TREATMENT 2: At 6-8 weeks later, use a residual herbicide before rain with a burndown like Ignite.
- TREATMENT 3: At preharvest, consider a burndown like Reglone + adjuvant.
- TREATMENT 4 (?): Perform a dormant fall cleanup of perennials in late November or December if needed. Take caution for tree health and contact Michelle if you have questions about fall cleanup.
Efficacy of Herbicides:
- Most residual herbicides need about 1/2" of rainfall within 7 to 14 days of application to deliver product to the germination zone and to activate the chemical by putting it in solution.
- When burndown products are needed, consider that Reglone works in cool and cloudy conditions whereas Ignite requires warm and sunny conditions. Also, applying Ignite when leaves are wet is ineffective.
- Glyphosate and 2,4-D require daytime highs of 10°C-15°C after a night above 3°C to have good activity and weeds must be actively growing.
- Perennial weeds may be targeted in spring when new perennial plants are at the seedling stage. Other timings are spot sprays at the early flowering stage or during fall re-growth after a minor frost. Glyphosate and group 4 products are systemic and work on certain perennial plants.
- If weeds are already present, add a post-emerge to a residual herbicide to achieve control.
Crop Safety of Common Herbicides:
- In the USA, there are concerns about Ignite causing bark cracking. The specific risks are yet to be defined but just be cautious that Ignite is not sprayed onto or drifts onto young tree bark.
- Chateau should not be applied after budbreak unless application equipment is shielded to prevent crop injury.
- 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.
- Note that residual herbicides can damage single tree replacements because the trees are not yet established for longer than 3 years.
- 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.
Horticulture
General
- Remove tree guards to prevent trunk diseases.
Lingering Injury from 2023 Polar Vortex?
- We may continue to observe the impact of the polar vortex on trees. It can take several years for all trees injured by a winter cold snap to succumb to their injuries.
- Some trees might have experienced sublethal injury during the 2023 cold snap that did not command our attention. In such cases, some trees might have been able to heal vascular tissue. In other cases, wood rotting fungi that live in the trees might have taken advantage of a weakened tree and expanded the area of injury and the size of the canker.
- This spring it was noticed that a block of Honeycrisp on MM106 had dead tissue around crotches on scaffold limbs. In this situation, there was no disease concern and the field pattern suggested a widespread weather event.
- Looking closely, the cankers (dead tissue) were on the crotches and lower scaffolds which are the last to harden off in winter. The scaffold limbs are especially susceptible to low temperature killing when they are closely arranged, effectively exhausting the area of resources.
- Previous winter injury in Nova Scotia in 1980-81 damaged lower scaffold limbs and the crotches of the main scaffolds.
Figure 4: Suspected injury as a result of extremely cold temperatures in February 2023 on Honeycrisp MM106. The cankers are concentrated around crotches on lower scaffold limbs where winter protection is weakest. It is likely that wood rot fungi have expanded the area of injury.
Treatments for Blind Wood
- In general, scoring and notching is best done from green tip and up until bloom time. The ideal time is at the stage of half-inch green.
- An excellent local on-farm trial done by Walsh Farms was shared during a previous Growing Good Growers tailgate meeting. They tried different treatments of notching, scoring, and growth regulators around May 5, 2024 on young Ambrosia trees. Their results and some of the discussion is referenced here:
- Success ranged from 7% to 25% branch induction. Only buds with shoot extension were counted in the trial so some instances of bud induction might eventually form into shoots and increase the success rate. We will have to follow up!
- In this situation, scoring worked better than notching. Scoring resulted in more branch elongation (Figure 5). The growth regulators did not improve success.
- Most people concluded that the practice of notching and scoring was time consuming, especially during the narrow opportunity in spring.
- Treating blind wood is likely only worthwhile if the success rate is 20% or higher.
Figure 5: Scoring trees above a paradormant bud removes the cambium and disrupts the flow of auxin. Doing so allows the buds to break dormancy. Note the top bud initiated by scoring and the bottom shoot initiated by scoring. Photo by Courtney Walsh, Walsh Farms.
- The plant growth regulators work in cooler temperatures but warm temperatures at the time of application increase the response. For more information, see an article by MSU Extension.
- Please note that the success rate of inducing a branch depends on the age of the planting. Applying a mist of plant growth regulators to the notched area can increase the success rate, namely for older plantings of up to 7 years of age.
Pruning
- Watch re-entry intervals for pruning activities when fungicide programs begin.
- Ensure that youngest blocks are pruned first so growth is directed into desirable leader and terminal extension. Prioritize high value trees and then return to low value areas.
- Remember that if bud counts are occurring on young trees that the bud count for a full crop load cannot be cropped on young trees. Consider pruning enough buds to prevent runting out trees.
- Consider prioritizing pruning in fire blight blocks to finish prior to tight cluster when cankers begin oozing. Cut out cankers, whether fire blight or other diseases.
- Pruning may be delayed closer to bloom for vigorous Ambrosia to reduce its vigour.
- Mature blocks can be pruned later and are best when pruned prior to bloom.
- A handout for farm workers 'The Fundamentals of Pruning' is available in English and Spanish.
Fertilizing
- Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.
- If leaf and soil samples show that phosphorus and potassium are adequate there is no need to apply phosphorus and potash. Granular formulations with 0.3 boron are encouraged for sandy soils.
- If Honeycrisp is on the rootstock G.41 then potassium additions are discouraged.
- Target 10-16 inches of new growth each year. More growth is a sign of excessive nitrogen. Keith Fuller and Michelle are working on an updated factsheet for nitrogen fertilizer recommendations to be available next year!
Liming
- Lime soils prior to planting an orchard with rates according to your soil report. Early spring is an option but fall can be a more practical time to apply lime to a new site and lengthen the time for acidity to become neutralized.
- Orchard maintenance with surface applied lime twill 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 will be open soon. A summary of the programs was released last week but they are not yet open for application. When the program opens, early applications will be considered first in line for available funds.
On-Farm Nursery
- Consider colour coding varieties in the nursery for easy reference. Write the colour code somewhere and use the same code every year.
- If planting bench grafts, outside expertise has advised that it is best to wait for the soil temperature to be warm enough for bench grafts to grow. It is better to wait for warm soil than to let the grafts sit. Currently, the soil temperature at 35 cm depth is near average at about 6°C. Also, keep in mind that the new callus is susceptible to damage from freezing temperatures.
- Rootstocks that were chip or t-budded last year may have buds pushing. Cutting rootstock tops early can help to prevent the rootstock from overpowering the new buds. Rods may also be put into place early to avoid knocking off buds if done at a later timing.
- 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
Nothing that I'm currently aware of!
Pest Management Guide
We offer printable PDFs of the guides from our website:
Online pest guides are also available without login (https://www.perennia.ca/pest-guides/) and with login on your Perennia account (https://www.farmdatatools.perennia.ca/). Using the online tool you can filter for organic and conventional options, search for key information, and sort based on information of interest.
This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Larry Lutz, Jeff Franklin, Ian Willick, Ariana Willick, Suzanne Blatt, Harrison Wright, Danny Davison, Colin Hirtle, Joan Hebb, Kari Brown, Heather Rand, and Shawkat Ali.
Edited by Michelle Cortens, Tree Fruit Specialist
Perennia Food and Agriculture Corp.
Perennia Food and Agriculture Corp.
