The Trend Is Your Friend, Weather You Like It or Not

Climate and Weather Data

Major climactic factors that affect any crop production include temperature, solar radiation and precipitation. Over time, these factors have been changing, causing unrest in crop production globally.

Spring has been moving quickly these past few weeks, yet a cold snap is upon us, analyzing past data could give light as to how the growing season could go and factors to consider in the future.

Below are charts representing the past few years of weather data, including monthly temperature averages, precipitation values and growing degree days from several locations across Ontario.

Growing Degree Days (GDD)

GDD are an important tool utilized in apple production, as it is can give growers an idea for pest and disease predictions, but also allows us to observe seasonal changes over time.

Figures include the ongoing 2021 season (to April 20th, 2021) with a five-year history, along with comparisons to the 2015 and 2012 season, as frost and advanced growth staging occurred.

Although this spring has advanced quickly, Figure 1 and 2 demonstrate that GDD aren’t as advanced as in 2012 but are similar. This can be concerning due to the earliness of growth staging. Apple staging across the province varies, but are generally a week or two ahead depending on the variety.

Figure 1. Growing degree days of apple growing regions in Ontario over multiple years
1 5ºC was used as the base temperature 2 Biofix date was January 1st of each year
 
Figure 2. Growing degree days of apple growing regions in Ontario over multiple years.
1 5ºC was used as the base temperature. 2 Biofix date was January 1st of each year. * Last date used for 2021 was April 20th

Monthly Temperatures

Weather is single handedly one of the most important measures to a fruit tree grower. Temperature impacts apple trees physiologically in many processes, including respiration, photosynthesis, dormancy, growth patterns, chilling requirements, root growth, pollination, fertilization and the list goes on. These processes have major implications as to apple production and that is why analyzing temperature data is important.

When observing the 2021 season temperature data (Figure 3), irregularities in the fall and spring stand out. May stood out as well, showing that 2020 had cooler temperatures by 2 degrees. Generally speaking, June through October of 2020 followed the 5-year average with some higher temperatures in July. Taking a closer look at the fall and winter, Figure 4 shows that the 2021/2020 season was more mild from November through January, along with March and April compared to the 5-year average (Figure 4). February was the only month where 2021 was cooler than the average. When comparing the 2021/2020 season to 2012, generally 2021/2020 has been more mild, but April has recently surpassed 2012. Given the lower temperatures in the past few days, the average in 2021/2020 will decrease.

Looking back at 2012, roughly 80% of Ontario apple crop was lost due to a frost event. The advancement of apple staging and a cold temperature drop for an extended period caused this devastation. Thus far, apples in 2021 aren’t as advanced as they were in 2012 and hopefully the weather doesn’t give us many more cool nights in the next month.

Figure 3. Average temperatures (ºC) of apple growing regions in Ontario over multiple years
*2021/2020 season consists of January through April (2021), May through December (2020)
Figure 4. Average fall, winter and spring temperatures (ºC) of apple growing regions in Ontario over multiple years
*2021/2020 season consists of January through April (2021), May through December (2020)

Monthly Precipitation

Rainfall is another measurement that is important for all crop production. Although some orchards have irrigation to mitigate drought stress within their orchard, timely rainfalls, especially before the beginning of irrigation season, are crucial to the success of the apple crop. Lack of rain has been associated with loss of production, delay in flower differentiation, spur death, decreased fruit size and other implications in tree health.

Overall, Ontario has had a dry season in 2021/2020 compared to the 5 year average (Figure 5) with a major increase in August. The only other month during the 2021/2020 season that showed a higher value in precipitation compared to the 5-year average was December. When observing the 5-year average compared to 2012 similarities in trend lines are shown, yet the 2012 year is more erratic in changes, showing peaks and valleys throughout the year. Looking more closely at the late fall to early spring (Figure 6), the 2021/2020 season has slightly lower precipitation in comparison to the 5-year average.

Figure 5. Average precipitation (mm) of apple growing regions in Ontario over multiple years
*2021/2020 season consists of January through April (2021), May through December (2020)
Figure 6. Average fall, winter and spring precipitation (mm) of apple growing regions in Ontario over multiple years
*2021/2020 season consists of January through April (2021), May through December (2020)

Summary

Overall, the 2021 spring season following the trend of the 2012 season in terms of GDD, but temperature and precipitation have been less erratic in comparison to 2012.

  • GDD continue to advance, but are not as far along as in 2012
  • Temperatures were cooler in the fall and early spring, but April has been warmer compared to 2012 and the last 5 years
  • The fall of 2020 and the spring of 2021 have been more dry in comparison to the past 5 years

GDD, temperature and precipitation are all important in having a successful apple season. And although these are aspects out of our control, data on temperature and precipitation assist growers in making decisions within their orchards, data could increase apple production through strategic planning over time and data based on new production techniques change the way we produce apples in the future through technological advancements.

References

Caprio, J.M. and Quamme, H.A. 1999. Weather conditions associated with apple production in the Okanagan Valley of British Columbia. Can. J. Plant. Sci. 79(1): 129-137.

Erika DeBrouwer
Erika DeBrouwer

Tree Fruit Specialist, OMAFRA