Weather risks: strategies to mitigate the risk of cool growing Season
Information for apple and tender fruit growers to assess and mitigate damage caused by cool weather.
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This in the 8th in a series to help apple and tender fruit growers in Ontario assess the weather risks that can damage their trees and crops. It is important to recognize the weather risks at each location, and develop strategies to reduce or eliminate the impact on your business operation.
What it is
Cool temperatures may delay tree and fruit growth, which can ultimately limit yields and delay fruit maturation. Low temperatures slow down photosynthesis, which may limit cell division, and production of carbohydrates needed to produce fruit sugars. Cool temperatures can be especially damaging if they occur during pollination and fruit set, in the critical period of fruit size determination after calyx or shuck, and when fruit is in the final stages of fruit sizing and maturation.
When it occurs
Cool temperatures result when weather patterns force cooler air from northern Canada to flow into our area. Cool temperatures may also result when cloud cover is extended due to stalled rainy patterns, or if upper air disturbances such as volcanic eruptions cause excessive cloudiness.
Where it occurs
Although the trend is to warmer summers, Ontario has occasionally experienced a cooler than normal season. In the cooler growing areas of Ontario, tree fruit growers may deal with some consequences of cool temperatures every year.
What can you do
Some of these potential mitigation strategies may help reduce or eliminate damage due to winter injury:
- Production insurance (PI): Production insurance can cover yield loss from reduced fruit size from poor pollination or reduced fruit size. Your premiums will depend on the coverage you choose, your claim history, and the yield potentials of your orchards. Over time, your premiums can be reduced if you are lucky enough not to have claims. However, some growers struggle with the premium costs (especially in their start-up years or if they have claims) and the fact that PI is not intended to fully cover your loss, either in yield or price. There is also the problem of reduced coverage levels in the years after your crop is reduced, due to the effect of the loss on your long-term average yields. Also, spot loss insurance is not available, so growers with multiple orchard sites may be penalized when good yields occur on the non-damaged sites.
- Choice of cultivars: Some easy-to-colour cultivars naturally finish well with good colour, without much sunshine before harvest, and some actually prefer cooler night-time temperatures. Early-ripening cultivars may avoid late summer cool temperatures. Green or yellow apples do not require as much heat and sunshine to finish, but may be too winter-tender for some areas. Cool temperatures and/or lack of sunshine may cause storage life may be affected, and the incidence of internal browning may increase under cool pre-harvest conditions. It is important to identify this risk, and monitor fruit in storage to market it before losses occur.
- Reflective mulch: Placing reflective material under trees before harvest will help maximize fruit colour and enhance harvest efficiency. Using these mulches requires attention to orchard floor management eg. Mowing, levelling. A system is needed to install and anchor them, and remove them afterwards. Mulches may be moved to later-ripening cultivars after use, and re-used for several years, which enhances the cost-benefit analysis.
- Nitrogen management: Because excessive N will delay fruit colouring and maturity, it is prudent to apply only the minimum rate (as indicated by leaf analysis) early in the spring, especially in cool climates. Avoiding later soil-applied applications or excessive levels of foliar feeding, and encouraging sod middle or cover crop growth will scavenge excess N and encourage fruit maturity. However, attention to rodent management is necessary if orchard covers are allowed to grow.
- Tunnels: High tunnels will enhance temperatures and tree growth, and advance harvest dates earlier. Sweet cherries seem particularly suited to tunnel production, because of the high cost of structures and management. Tunnels also help reduce cracking in sweet cherries enhancing the the cost-benefit analysis. High winds or heavy snow loads may damage tunnels so covers may need adjustment in bad weather.
Reducing the effects of cool weather is an occasional challenge for fruit growers, although orchards in colder districts may always benefit from some of these strategies. If erratic weather patterns continue, some seasons will be cooler than normal, so fruit quality and markets may suffer. Investing in intensive orchards and high-valued varieties may encourage more investment in cold mitigation strategies in the future.