Cold Weather Follow Up and More

Tuesday, February 7, 2023

Comments and Observations from February 4 Cold Snap

Minimum Temperatures Recorded on the NSFGA Davis Weather Station Network

Critical cold temperature events were recorded on the local network of Davis weather stations throughout the Valley on February 4, 2023. In all locations, temperatures dipped from near 0°C to approximately -25°C within about 20 hours. Extreme minimum temperatures were recorded that would be expected to damage stone fruit buds and possibly peach trees.

Last year's cold weather event was an inversion that brought incredible variation between regions by concentrating cold in frost prone areas. This year's event was a cold air mass that settled over the province and resulted in very little variation in temperature between regions. Strong winds also helped to distribute the cold temperatures evenly.

Table 1: The lowest temperatures and highest wind gusts recorded on the NSFGA network of weather stations on February 4, 2023, ranked from coldest to warmest temperature. Note there is less than 1 degree of difference between all locations.
Weather StationLowest Recorded Temperature (°C)Highest Recorded Wind Gust (km/hr)
Melvern Square-25.468
Grand Pre-25.377
North Medford-24.969

Typical Bud and Tree Hardiness Thresholds

Full winter hardiness is usually achieved in mid-February for our region. However, this winter has been warmer than average and the warmth might have delayed the acquisition of cold hardiness. The following values are for guidance only and can vary a lot depending on the situation.

Peach buds that have acquired their full winter hardiness typically start to become damaged at -23°C (see actual measurements below). Shoot death and tree damage is possible at temperatures below -25°C but may not be severe given that temperatures did not approach -29°C. 

Cherry buds at their full winter hardiness become damaged at -26°C. 

Apple and pear buds are able to withstand relatively colder winter temperatures up until about -32°C. Varieties like Gravenstein and Northern Spy are more susceptible and may be damaged much sooner.

Trees are even more susceptible if they were pruned or hedged. Take note of what was pruned before February 4 because you are more likely to see damage to trees if pruning was done prior to the event. Trees are also more susceptible if they had limited photosynthesis due to nematode pressure, diseases, mites or psylla injury, and poorly drained sites. Also, trees with relatively low available resources from an excessive crop load are more at risk.

Peach Bud Hardiness Determined by AAFC

The AAFC Plant Physiology Program (Harrison Wright and Jeff Franklin) collected peach buds prior to the cold snap to determine their cold hardiness. In Table 2, LTE is the Low Temperature Exotherm meaning the temperature at which you'd see 10% bud mortality, 50% bud mortality, and 90% bud mortality. Each number is the average of 100 buds (10 buds selected from 10 randomly selected trees for each variety) that were collected on January 31.

Table 2: Local Annapolis Valley peach hardiness data collected by the AAFC Plant Physiology Program (Harrison Wright and Jeff Franklin). 
VarietyLTE10 (°C) (10% bud mortality)LTE50  (°C) (50% bud mortality)LTE90   (°C) (90% bud mortality)Standard Deviation  (°C)
Harrow Beauty-16.5-19.7-21.41.9
Harrow Diamond-18.5-20.9-22.31.8
Redhaven Early-19.3-21.4-23.62.2
Redhaven -18.2-21.5-22.82.3

The results show that, in fact, peach buds did not achieve their full winter hardiness and that 90% of buds would be damaged at around -23°C. Therefore, the critical temperature for peach injury was exceeded in all regions being monitored. 

Ian Willick at AAFC sampled Honeycrisp, Gala, and Ambrosia apple shoots prior to the cold snap as part of a preliminary study on the influence of the pneumatic leaf defoliator on tree cold hardiness. The information should give us even more inferences. Stay tuned.

Many thanks to AAFC for this work!

How can you evaluate buds for damage?

It has been good to see that some of you have been checking buds and asking what to look for. The full extent of the bud injury and potential tree injury will not become clear until bloom but in the meantime, evaluating a sample of buds could start to guide your decision making. 

Dormant buds are easiest to cut horizontally in a cross section through the ovary. The ovary should be green if it is healthy. The ovary will be brown if it is damaged because ice crystals punctured cell walls, releasing their contents. Focus on cutting floral and not vegetative buds for your evaluations. Assessing 100 flower buds reportedly gives a good estimate of percentage crop loss. A factsheet by Colorado State is a great resource for evaluating tree fruit buds.

Remember to take pictures and contact crop insurance.

For more examples of cross sections, refer to images from 2022:

Don't hesitate to contact me if you have questions, need help interpreting, or want to send photos for a second opinion. 

What is being observed so far?

In a very limited number of cross sections, I'm not immediately seeing damage to Honeycrisp and Ambrosia buds. I have observed damage in cherry buds.

Figure 1: Damaged cherry buds evaluated on February 6, 2023.

Events and Resources

Custom No Till Drill Seeding

Great for cover crops! Service provided by Chester Friesen 902-321-1436. Great Plains 10 foot, no till seed drill. Regular large grain seed box. Grass seed box option. 7.5 inch row spacing. Tractor equipped with GPS guidance auto steer for precision planting.  

Marbicon Pesticide Exam Preparation or Points Workshop

Marbicon Inc / Jim Jotcham will be offering in-person full-day exam preparation courses (T2237) AND points workshops (T2236) this spring. The following locations are confirmed, with additional courses and locations being planned. The full course, preparing for the exam, is $125. Doors open at 8:30, finishing by 5:00 at the latest. Five recertification points (T2237) are available. $110 for points only, and out by 3:15.

Feb 24 – Oxford, Cumberland Co.
Feb 27 – Heatherton, Antigonish Co.
Mar 2 – Millville, Victoria Co.
Mar 6 – Little Brook, Digby Co.
Mar 7 – Berwick, Kings Co.
Mar 10 – Truro, Colchester Co.
Mar 15 – New Germany, Lunenburg Co.

Pesticide exams are normally only written online. Contact NS Environment for details and the 2023 exam schedule. A course is not required before challenging the pesticide exam, but it usually helps. Recertification workshop (5.0 points T2236), $110 taxes in. This workshop is for people holding valid NS pesticide applicator certificates needing points to renew. Doors open at 8:30, finishing around 3:15.

Feb 16 – Berwick, Kings Co.
Feb 23 – Bible Hill, Colchester Co.
Mar 3 – Millville, Victoria Co.
Mar 17 – New Germany, Lunenburg Co.

HST is included in the price. Cash or cheques (payable to Marbicon Inc) or e-transfer. Pay at the door or by corporate/government purchase order. Contact Jim Jotcham at or at 902-538-7101 for more details and to pre-register.

Calling All Fruit and Vegetable Suppliers!

CanadaGAP is a GFSI-recognized food safety program developed to promote Good Agricultural Practices (GAPs), for Fresh Fruit and Vegetable suppliers who produce, pack and store as well as Good Manufacturing Practices and HACCP programs for repackers and wholesalers. CanadaGAP has released version 10.0 of the Food Safety Manuals which take effect on April 1, 2023, for certification purposes.

Perennia is partnering with Kim Best from Prospect Agri-Services to offer three virtual CanadaGAP training workshops outlining these new updates. 

Advanced CanadaGAP: February 13th, 2023 (half day).
CanadaGAP an Introduction: 2 half day sessions: February 23rd & 24th and February 27th & 28th, 2023.
Click here to register you and your team today!

Register Now: Perennia Product Registration Changes Webinar

Every year, crop production is impacted when pesticide products are cancelled or when labels are updated to include amendments to use patterns. Join us on Tuesday, February 28 from 10 AM to 11 AM to learn updates from our team of Perennia specialists who are here to support you in the horticulture and field crops sectors.

The focal crops during the session are apples, wild blueberries, cranberries, vegetables, berries, cannabis and field crops. Each specialist will bring information on products that are relevant to their sector. In this conversational-style webinar, we’ll answer frequently asked questions and live questions that you submit.

Pesticide points will be available for this session! Product Registration Changes Impacting Horticulture and Field Crops is NS Environment course T2253 and is worth 1.0 points in General Information. You must attend the entire session to receive points.

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