Climate change and the peach
In 1751, Franciscan monks brought the first peaches to Georgia. However, as soon as the second half of this century, climate change could bring an end to the entire industry. Agricultural climatologists are closely monitoring the situation. And scientists are working to ensure the Georgia peach never disappears.
(Prunus persica 'Red Baron')
Peaches like to chill out
Since 1960, the average winter temperature in Georgia and the entire Southeastern United States has risen by 5°F. The warming trend is expected to continue. However, peach trees must have a certain number of cold hours in order to produce fruit.
Each winter when temperatures fall below 45°F, peach trees produce hormones that signal dormancy. The average Georgia peach requires between 650-850 cold chill hours each year. 'Elberta', one of the most popular varieties, needs at least 800 hours of cold weather, a trait developed in its native country of China. By going dormant, trees reserve energy during unfavorable conditions and emerge from dormancy at the proper time.
Dormancy and survival
Nothing can wake a dormant peach until its internal thermostat is triggered. Once it has enough chill hours above 45°F, sap begins to flow, signaling it's time to produce peaches. If exposed to sufficient warm weather, flowers will develop and produce small fruitlets.
However, continued warming is necessary. If a spring frost suddenly occurs, it can damage the growing fruit. Developing fruit is full of water. When frost occurs, the water freezes and ruptures the cells, killing the fruit. Apples, peaches, and apricots are most affected by chill hours.
In 2017, an especially warm winter destroyed 85% of Georgia's peach crop due to the lack of chill hours needed to bloom. Between 1980 and 2010, central Georgia saw an average of 1,100 chill hours every year. In 2016, the average number of hours dropped to around 600. In 2017, it struggled to reach 400. Growers who had feared their trees wouldn't emerge from dormancy and bloom began wondering if the trees could even survive.
Most peach varieties in central Georgia need 600–900 hours of cold weather. As temperatures rise, agricultural zones can shift. Additionally, the increase in greenhouse gas emissions has resulted in less sunlight and fewer chill hours.
A hardier peach
A study indicated 2017 would have been a warm year even without global warming. It also found that climate change exacerbated conditions, increasing their probability.
This presents a challenge for Southern peaches needing a delicate balance of cold winter weather followed by a mild spring.
Some varieties require as little as 50 chill hours, and can grow in Florida. In Georgia, peaches incur routine frosts throughout the spring. Climate change means warmer winter weather with no difference in the last frost date.
The dilemma for growers
This has created an enigma for peach farmers. Should they plant a variety that needs only a few hundred hours below 45°F and blooms earlier, exposing fruit to frost damage? Or choose a frost-resilient peach tree that blooms later but risks failing to emerge from dormancy because the weather doesn't provide the necessary chill hours?
(used with permission of Fruitland Augusta)
Searching for solutions
An ideal peach would need 500-700 chill hours along with more days of hot weather in order to bloom. It would get the required chilling and be able to wait for warm weather to produce fruit.
Researchers must first determine if the gene for chill hours and the gene that detects warm days are different. If so, that difference could possibly result in a new peach variety with medium chill requirements that's also tolerant of spring frosts.
Southern researchers are looking for quicker fixes by cross-breeding peaches for climate hardiness, pest resistance, drought tolerance, and taste. However, creating a new variety can take 7-14 years.
In addition to resilience, there are technical fixes that could help. A cellulose and water mixture with the consistency of thick mayonnaise could potentially help insulate peach trees from cold weather. It can safely be sprayed on the trees a few days prior to a temperature drop without resulting in chemical contamination. Large wind machines similar to those used in California orchards could help stave off frosts by moving warmer air closer to the ground.
Unfortunately, these solutions present big hurdles. Wind machines are expensive, and the cellulose spray is still in the research stage. However, similar Washington State University trials with cherries and apples have shown promising results.
(used with permission)
Georgia’s agricultural future
Chill hours aren’t the only problem. Climate change means the Southeast is also likely to experience changes in precipitation. Farmers who haven't needed to irrigate their trees may face periods of drought along with short, intermittent periods of heavy rainfall. Increased humidity could promote more bacterial and fungal diseases.
Georgia will continue to remain an agricultural hub. The soil is fertile, and current rainfall is still more reliable compared to other states. As the West experiences worsening droughts, heatwaves, and wildfires, some agricultural production could possibly shift to the Southern states. Olives and other new crops are now being grown in Georgia. Cold-hardy citrus is another possibility.
In comparison to the rest of the country, Georgia has been warming at a slower rate. But that may soon end. The Southeast has been in a warming hole where warmer temperatures are less prevalent. However, scientists have found evidence the warming hole resulted from increased tree growth after the post-Civil War South ceased cotton production. Also, increasing air pollution has resulted in less sunlight.
But that effect could be waning. A 2018 Dartmouth College study of the warming hole found early evidence suggesting the anomaly may lose its race with climate change.
(Elberta clingstone peach)
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