Due to the recent severe temperatures throughout the Okanagan, some growers are understandably concerned about damages to their cherries and want to assess their dormant cherry bud mortality. Having this information allows to you modify your pruning strategy and give you some preliminary insights on what to expect as far as crop volume for the year. The following factors have an impact on the winter hardiness of cherries:
- When the low temperatures occur (early vs. mid/late winter)
- Rate at which the temperature drops
- Temperatures prior to the cold temperatures
- Time and duration of cold temperatures
- Predisposition factors; such as how well the plants went into dormancy and variety
Sweet cherry dormant bud can be hardy to the point of approximately -26°C. Trees that have been impacted by some kind of stress such as drought or over cropping, however, can sustain damage at higher temperatures. The same is true for healthy blocks; trees might come through healthy at some degrees above their hardiness levels.
After a freeze event, you should be able to notice any damage within 48 to 72 hours. Below is a brief discussion on how to assess bud mortality in cherries in your own orchards, at the dormant stage.
Sample Collection and Assessment
- Collect 20 random spurs (or 100 buds) in the orchard per variety: avoid frost pockets, unless you aim to collect information from them. Sample from the top and bottom of the trees and use a lopper to extend your reach if you need to
- Keep the spurs at room temperature: for 12-24 hours. If you cannot process the buds in a timely manner, place them in plastic bag and in the fridge to prevent desiccation
- Detach all fruit buds from the spur and examine all primordia within a bud for signs of injury. Generally, fruiting buds can have 2 to 5 primordia (flowers). Use a very sharp single blade such as a utility knife blade (Exacto) or a razor blade to cut through the bud. Start by making a cut across the very tip of the bud, making several cuts proceeding towards the base of the buds until you can see all the primordia
- Note the information in an Excel spreadsheet. Record brown or black primordium as “dead”. Information related to vascular tissue damage can be valuable. Make a longitudinal cut through the spur and note discoloration of the tissues below where the buds are attached
Finding some levels of damage is not necessarily negative. Some growers often hope for a little damage which results in some natural thinning in a normal or high crop load year. It is said that you can still have a normal crop with up to 50% damage, depending on the damage (from the bottom to the top of the tree) as well as the crop load. It is good to remember that each bud contains multiple cherries so an added benefit of recording the bud damage assessment is comparing the number of primordia and buds across years. This will give you further insights on next year’s crop.
This blog gives you a brief idea of how to assess your own orchards and assess dormant bud mortality in your cherries, but should you have any questions or need assistance with the assessment, please reach out to your Growers Supply Co. Grower Support Team; Scott and Christine for the South and Matt, Sara and Taylor for the North.