- Fruits: apples, cherries, general tree fruits
- Production Systems: general crop production
In contrast to the majority of the world’s major food crops in which the primary climatological production constraint is the amount and timing of precipitation during the growing season, the primary weather-related constraint for most temperate tree fruit crops is the frequency and severity of spring freeze events. In the Great Lakes region, the frequency of freeze events following initial phenological development during the spring season has increased during the past few decades, with profound impacts on regional fruit production. For example, Michigan’s tart cherry and apple production in 2012 was reduced by about 90% and 88%, respectively, compared to the previous year’s production due to a series of spring freeze events that followed the warmest March on record. The timing of the onset of phenological development in the spring is a key factor in determining potential cold damage risk, as the vulnerability of vegetation to freeze injury increases rapidly with the stage of development. One technique that shows some potential for reducing overall cold damage risk is the application of water to cool vegetative tissue by latent evaporation and delay phenological development. Evaporative cooling with water has been used in the past (mid 70’s and early 80’s) prior to bud break to delay early development of flowers, with one to three weeks of observed delay. However, related problems (greater disease risk, poor fruit set, and high water demand) reduced its potential for commercial use. This study re-examines the approach with the use mist-cooling to delay bloom through a solid set canopy delivery system (SSCD), and evaporative cooling application based on changes in temperature and humidity. In our study, bloom was delayed by 6-11days in apple with the mist application of 14-15 cm/ha and bloom was delayed by 9 days in sweet cherry with the mist application of 10.8cm/ha.
Abbreviations- Solid set canopy delivery (SSCD), Growing degree days (GDD), Relative Humidity (RH), South west Michigan research and extension centre (SWMREC), Horticulture Teaching and Research Centre (HTRC).
The production of the majority of the world’s major food crops is constrained by climatic variables such as the amount and timing of precipitation during the growing season. However, the primary weather-related constraint for most temperate tree fruit crops such as apple and cherry is the frequency and severity of spring freeze events (Flore, 1994). Unfortunately, for tree fruit producers in the Great Lakes region, the frequency of spring freeze events following initial phenological development has increased during the past few decades, resulting in relatively greater risk of production losses with time (Andresen et al., 2012). These trends have had significant impacts on regional fruit production in recent years. An unprecedented heat wave in March, 2012 brought fruit crops out of their dormant state more than 1 month earlier than normal. A subsequent series of 15-20 freeze events during April and May resulted in catastrophic freeze damage, with tart cherry and apple yields reduced by 90% and 88% respectively relative to the previous year’s production (USDA, 2013). A similar early warm up and freeze event in Michigan reduced the cherry yields by more than half during the 2002 season compared to that in 2001(Michigan Agriculture Statistics, 2003).
Given the increasing trend in spring freeze events, new technology or strategy is needed to reduce climate-related risks for fruit producers. Development of new, more freeze-resistant varieties may be a long term solution, but they will not likely be available in the foreseeable future. Conventional frost protection methodologies such as wind machines and overhead sprinklers offers some defense, although they may not be effective in all freeze situations (e.g. wind machines in an advective freeze situation) or may require large amounts of water which result in flooding, leaching of fertilizer or pesticides, or collateral tree damage from ice formation (e.g. overhead sprinklers).
One potential approach to reduce the vulnerability of tree fruit to freeze events is the application of water during the late stages of dormancy and early vegetative stages to cool the plant tissue and delay the rate of growth and development. Plant vulnerability to cold damage decreases rapidly from the end of dormancy through bloom. So, any delay in phenological development potentially increases chance of the bud tissue survival in early spring freeze events. This method has been shown to effectively delay the onset of vegetative growth by one to as many as three weeks, although the conventional overhead sprinkler system used in the research consumed very large amounts of water (Andersen et al., 1975; Hewitt and Young, 1980). A promising new variant of this approach is the application of water mist through solid set canopy delivery system (SSCD), which is increasingly being used in high density orchards for application of fertilizer and other spray applications (Agnello and Landers, 2006). The SSCD can theoretically provide the water necessary for cooling at a tiny fraction of rates consumed by a conventional sprinkler. This system comprises of micro-emitters attached to the main or lateral pipe lines and dropped partially into the canopy using drop-tubing. This research examines the use of water mist as an adaptive strategy to delay the bloom and reduce the risk of frost damage to tree fruit buds. The successful application of such technology could sustainably increase production efficiency and grower profitability.
Our long term goal is to develop an effective, environmentally friendly method to protect fruit tree buds and flowers from spring frost damage through the delay of phenological development by cooling the buds once dormancy has been broken.
Specific short term goals include:
1) Determining the potential delay in early vegetative development of cherry and apple buds by evaporative cooling using the solid set canopy delivery system.
Further ahead, intermediate term goals include:
2) Identification of optimal water application rates and timing based on ambient temperature and humidity relative to the effective rate of cooling and associated delay in phenological development.
3) Development of improved methods to estimate tree growth and development based on internal tissue temperatures.