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Production and pest update brought to you by the OMAFRA Apple Team: Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

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Questions have arisen regarding potential early bud break due to the mild winter, along with the recent and upcoming warm temperatures. We encourage you to keep an eye on your trees, taking note of bud swell and any movement into silver and potential green tip.

Chilling Units

Chill units usually aren’t much of concern for Ontario because our winter temperatures usually don’t rise much more than a few degrees above zero which will keep buds dormant until spring. This winter the number of chill units that have accumulated can be of concern because warm temperatures may signal trees to start coming out of dormancy. Although this is a concern, we have not seen bud break in Ontario as of the release of this article, but parts of Michigan are seeing this. Chill units are usually met in late January and early February. This year, requirements were met in early February.

If you would like to check your own chill units, please utilize either of the models below.

Various chilling models:

1. Chilling Hour Model: more of a rule of thumb then a model.
   • 1 chilling unit for every hour that the temperatures are between 0 and 7.2 ﹾC.  
2. Utah Model: assigns partial, while and negative chilling units depending on the temperature:
   • 1 hour below 1.4 ˚C = 0 chill units
   • 1 hour 1.4 to 2.4 ˚C = 0.5 chill units
   • 1 hour 2.5 to 9.1 ˚C = 1 chill unit
   • 1 hour 9.2 to 12.4 ˚C = 0.5 chill units
   • 1 hour 12.5 to 15.9 ˚C = 0 chill units
   • 1 hour 16 to 18 ˚C = – 0.5 chill units
   • 1 hour above 18 ˚C = -1 chill units

Growing Degree Days & Forecast

Looking at 8 locations across Ontario, the accumulation of Growing Degree Days (GDD) is shown in the graphs below. All GDD started January 1 of each year with a baseline of 5ﹾC. The 2024 line is forecast (AccuWeather) between Julian Days 64 to 97 at each location.

It is very early to tell what may happen this spring and as we all know, weather can change drastically. These graphs are for your awareness.

Takeaways:

• The 2024 season seems to follow 2016 (most locations)
• Delhi, Goderich, Harrow and Vineland are the most advanced for GDD
• If the weather stays cool over the next few weeks, we could be set for a ‘typical’ year

Comprehensive Outlook

This graph may look like a lot, but it lends us a lot of important information when looking at all of the datasets together. This graph averages 8 locations across Ontario for GDD at last frost, last frost date, last frost temperature and average fall/winter temperature. All GDD started January 1 of each year with a baseline of 5ﹾC.

Takeaways

• Last frost temperature is sporadic
  • The warmest temperature being -1.3 in 2016
  • The coolest temperature being -3.4 in 2019
• Last frost date remains stable averaging at Julian day 118 (April 28)
  • The latest being 131 in 2020
  • The earliest being 107 in 2017
• Average bud break occurs at Julian day 102 (April 12)
  • The latest being 120 in 2018 & 2019
  • The earliest being 79 in 2012
• Average fall/winter temperature fluctuates dramatically
  • The mildest fall/winter being 2016
  • The coldest fall/winter being 2015
• Crop production has been stable in the past 5 years (106%)
  • The highest yielding year being 2022 & 2023
  • The lowest yielding year being 2012
• GDD at the last frost date fluctuates dramatically
  • Peaks include 2012 and 2021
  • Valleys include 2018 and 2019
• Honeycrisp production plays a large role in crop production and is reflected in certain years
  • In 2022 and 2023 Honeycrisp trees were ‘on’ which consisted of 15% and 16.5% of total apple production
• In 2021 Honeycrisp trees were ‘off’ where the variety consisted of 12% of total apple production

Comparison

• Bud break has a strong correlation to GDD at last frost date
  • This is to be expected as a high GDD at last frost date would coincide with earlier growth staging of trees
• Crop production relates to GDD at last frost date
  • This is shown in 2012, 2015, 2017 and 2021, where GDD was high and crop production was lower (20%, 65%, 76% and 89%)
  • This is also shown in years where a lower GDD at last frost date were accumulated and crop production was high (2016, 2018, 2019, 2022 and 2023)
• When analyzing low crop production (<90%) data together we see:
  • 2012, 2015 and 2021 have bud break occurring before the high GDD at last frost
  • 2017 is an anomaly where the GDD at last frost was lower than the bud break day, although the fall/winter was mild and the last frost temperature was very low
• When analyzing high crop production (>100%) data together we see:
  • 2016, 2018, 2019, 2022 and 2023 all have GDD at last frost that are lower than bud break and the last frost date

Conclusions

• A mild fall/winter doesn’t necessarily mean low crop production
• Early bud break doesn’t necessarily mean low crop production
• GDD at last frost date plays a role in crop production
• Reasons for low crop production in previous years:
  • 2012 – combination of a late last frost date, early bud break, high GDD at last frost, and low last frost temperature
  • 2015 – combination of an extremely cold fall/winter, high GDD at last frost, and a late last frost date
  • 2017 – combination of a mild fall/winter, high GDD at last frost, and low last frost temperature
  • 2021 – combination of mild fall/winter, high GDD at last frost and early bud break

Data was collected from the following sources: OAG Annual Reports, Norfolk Fruit Growers Association, Ontario Ministry of Agriculture, Food & Rural Affairs Datasets and Environment Canada

Never Too Early To Start Thinking About Pests!

With the season on our doorstep, are you prepared for early pest management? Let’s go through the checklist of things to consider:

Orchard sanitation – your first line of defense

The first line of defense for pest management in an orchard is prevention. There is no silver bullet to eradicate something like disease once it becomes well established. Instead, management is about reducing inoculum and preventing spread to healthy trees or fruit.

• Prune out dead or diseased limbs, trees or signs of cankers as well as rotten or mummified fruit. These can harbour overwintering pests, such as fire blight, black rot or bitter rot.
• Get rid of wood or cull piles and stumps that may have been in or near the orchard over the winter. These often provide overwintering sites for insects, such as codling moth and plum curculio.
• If the ground is dry enough to get the tractor through, flail mow the orchard floor to mulch up leaves, branches and fruit.
• If you haven’t already done so last fall or earlier this spring, apply 45 kg of agricultural urea per 1,000 L of water/ha to the orchard floor for scab or apple blotch (Marssonina) inoculum reduction.

Dormant copper for fire blight and scab management

Dormant copper such as Copper Spray, Copper 53W, Cueva, Parasol and Kocide can safely be applied up to ¼” green (possibly ½” green) without risk of phytotoxicity. However, the use of a softer copper registered for season-long control such as Cueva could be extended in those early spray timings to ½” green or tight cluster in blocks with low scab inoculum (ie., free of scab last year) to provide some scab protection.

Residual activity typically last about 7-10 days under ideal spring conditions. However, once rainfall exceeds 2” from last copper application, it should be assumed all residue has been washed off. For some copper formulations, using a dormant oil will act as a sticker/spreader as well as provide efficacy on scale, European red mite and suppression of powdery mildew. This is not the case for all registered coppers. Always refer to precautions listed on the product label prior to use.

Dormant oil – the earlier, the better for scale control

Depending on the target pest, the term “dormant” oil can be rather misleading as sprays can be applied from the true dormant state prior to bud break up until pink. Unfortunately, optimal dormant timing for scale is not necessarily the same for mites.

If monitoring indicates scale is a bigger issue in the orchard, oils need to be applied before or shortly after bud break. This efficacy against scale is significantly reduced with later oil applications for European red mite as they develop a waxy protective layer that impedes the oil from effectively penetrating and preventing respiration.

However, if European red mite populations are the problem, sprays can be delayed. Ideal timing is half-inch green to tight cluster but can be delayed to pink; however, blossoms can be quite sensitive to oil under adverse conditions so consider using a lower rate at this timing.