Protecting Fruit Trees from Climate Change-related Frost Damage, High Summer Temperatures, and Pests
| Date of interview | July 11 & 12, 2022 |
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| Interviewees |
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Please tell us about the regional characteristics of Iwate Prefecture and your fruit tree production efforts up to now.
Ono: Iwate Prefecture is located in the northeastern part of Honshu, and most of the inland regions consist of mountainous and hilly terrain. The Kitakami River flows south through the central part of the prefecture, nestled between two mountain ranges, and its lower basin broadens into an expansive plain, while in the northern part of the prefecture, the Mabechi River flows through hilly country.
Moreover, Iwate has an inland climate characterized by cold winters and hot summers. Most of the prefecture’s fruit trees are cultivated in the plains close to the mountains and on the hillsides along either side of the Mabechi River. We are working to establish high-quality and highly profitable fruit tree cultivation by taking advantage of Iwate’s extensive land resources and its cool diurnal temperature range, and by making the most of each district’s specific geographical conditions.
In the case of apples, we have been promoting high-quality and labor-saving production through dwarf cultivation, for which Iwate has achieved the highest penetration rate of any prefecture in Japan, while in the case of grapes, we have been shifting to varieties for which there is high consumer demand, such as Shine Muscat. We are also trying to introduce cherries, peaches, pears, and blueberries that take advantage of Iwate’s regional characteristics.
What kind of cultivation method is “dwarf cultivation”?
Ono: Basically, apples are cultivated by grafting the rootstock, which is the base of the tree, onto the scion, which is the upper part that bears fruit, but the size of the tree can be controlled by changing the rootstock. Making the trees smaller saves labor during harvesting and also ensures that the fruits receive good sunlight, which greatly affects the coloring and results in higher-quality apples. The penetration rate of dwarf cultivation for apples in Iwate Prefecture is 90%, which is the highest in Japan.
What precisely is the “frost damage” that Iwate Prefecture’s apples have been suffering from in recent years as a result of climate change? Can you please elaborate on why this has occurred?
Ono: According to continuous surveys conducted at nine observation sites throughout the prefecture, the record high temperatures in March 2021 brought forward the cultivation of apples in the prefecture by more than 10 days when compared to an average year. This caused the apple trees to reach the leaf-expansion stage by early April, which is earlier than usual. At this time of year, the trees are susceptible to the effects of low temperatures, and frost on the mornings of April 11 and 15 resulted in significant damage to the year’s apple production, with losses totaling more than 1 billion yen. Similar damage has been observed in cherries grown in the northern part of the prefecture and in Japanese pears in the southern part.
Nakazato: When frost damage occurs, the surface of the fruit becomes rough and distorted, which makes it impossible to ship.
Mr. Nakazato, as a fruit grower, what kind of measures do you take to prevent frost damage?
Nakazato: On my farm we use the water sprinkling icing method. Approximately 50 sprinklers are installed in the orchard area, which are designed to release water when the temperature drops below 2ºC. This utilizes the principle that when ice and water are present in the same space, an energy exchange takes place, and the temperature does not fall below 0ºC.
Ishikawa: In addition to the water sprinkling icing method using sprinklers, there are also frost protection fans that use air blowers, and a burning method in which a fire is kindled in the field to heat the area. However, the burning method is a little more difficult because the larger the area, the more kerosene is consumed, and permission from the fire department must be obtained in advance. In addition to these methods, we are currently verifying the effectiveness of foliar spray materials by applying special materials before and after frost damage occurs to increase the cold tolerance of the plant body, or by coating the plant body itself to make it more resistant to the cold.
Have you seen other effects of climate change besides frost damage?
Ono: Black star disease of apples, which had almost disappeared after the year 2000 due to the development of highly effective fungicides, began to re-emerge around 2015, mainly in the central and northern parts of the prefecture. Black star disease is a disease that forms lesions on apple leaves and fruit, and when it occurs frequently, it is very damaging to growers as they are unable to ship their apples.
Nekoduka: As a result of various research studies carried out by the Agricultural Research Center on the cause of the black star disease outbreak, it has become clear that higher spring temperatures are allowing the black star pathogen to infect apples earlier in the season than was the case in past years.
Although conventionally, highly effective fungicides have been applied just before flowering to control black star disease, it was discovered that the infection was occurring more than a week before the time of application. In response to this finding, we decided to take additional control measures during the flower bud coloring period (7 to 10 days before flowering) and have been providing guidance in the field since 2021. The results of these efforts have gradually become evident since 2022, and the area of infestation also began to decrease in 2022.
Ishikawa: There have also been cases of “sunburned fruit” caused by high summer temperatures. When the surface of an apple faces towards the sun so that the same spot is exposed to direct sunlight for an extended period of time, the surface temperature rises, causing sunburn to occur. If an apple is only lightly sunburned, this may not be a problem in some cases even if the fruit eventually changes color, but if the apple is severely sunburned, it will begin to rot from the sunburned surface. This could cause the product to lose its commercial value, which would in turn reduce the fruit grower’s income.
Another major concern is that apples are usually harvested in the autumn, and high temperatures prior to the harvest can affect their coloring. The lower the temperature, the redder the fruit becomes, but in recent years September temperatures have remained extraordinarily high, and probably as a result of this there have been noticeable cases where coloration has been delayed or apples have ended up only lightly colored.
Also, if temperatures remain high, the sugar content tends to increase resulting in apples that are merely sweet but with diminished acidity, or that are softer, which results in a loss of crispness, or that are less juicy due to loss of moisture caused by the high temperature, all of which has a substantial impact on the overall quality of the apples.
In this regard, we are working to cultivate new varieties that can be grown consistently, such as apples that develop their color even under high-temperature conditions. Different varieties are bred in each municipality, but there are many varieties that may or may not be suitable for Iwate Prefecture. So, while we continue to look at whether there are varieties that are well-suited to the changing climate in Iwate, we would like to maintain and develop the prefecture as an apple production area.
Regarding sunburn prevention, we are conducting tests with a focus on avoiding direct sunlight by covering the fruit with bags, and we are also in the process of applying a special material to the fruit that prevents sunburn before it becomes a serious concern, thereby reducing the occurrence of sunburned fruit.
While you are undertaking various adaptation measures, what are your thoughts on the positive impacts of higher temperatures?
Sato: It may become possible to cultivate new fruit tree varieties. However, we believe that frost damage due to earlier flowering and poor coloration in the case of apples and the occurrence of moist or pulpy fruit in the case of cherries will outweigh any positive impacts.
Ishikawa: Having said that, we still want to try to view climate change in as positive a light as possible. According to data from the National Agricultural Research Organization, tree fruit production zones are expected to shift northward due to global warming in future, and Iwate Prefecture appears to lie within the zone of suitable areas. As the consistent production of apples becomes more difficult, we will continue to support the prefecture so that it can survive as a tree fruit production region by focusing on technological development adapted to climate change and also focusing on the potential of cultivating different kinds of tree fruit that we have been unable to produce up to now.
Please tell us what you find most rewarding about your job.
Ono: One of my main tasks is to help organizations such as agricultural research centers, regional agricultural extension centers, and pest control centers to strengthen their partnerships. We are proceeding with discussions with local communities on how they can use the varieties bred in the Fruit Tree Research Section and the technology developed in the Plant Disease & Entomology Research Section in the field. I think that being involved in agriculture in a comprehensive fashion is an interesting job in the sense that it encompasses not only technology, but also human resource development.
Ishikawa: I am currently conducting experimental research at the Fruit Tree Research Section of the IWATE Agricultural Research Center, but the varieties and technologies we develop will only become useful when they are adopted and used by the fruit growers. When I see fruit that was produced as a result of actually using these things lined up in supermarkets, for instance, I feel glad that we did this research. We are involved with the fruit growers, but beyond that, I think it is very rewarding to be able to work in ways that connect us with consumers as well.
Nekoduka: I am investigating the causes of diseases that attack fruit trees and blossoms, and researching possible measures to control these diseases. I provide pest control guidance while talking directly with growers who are having trouble due to disease damage, and I find it rewarding when I realize that I have helped them solve their problems by finally eliminating damage.
Haruyama: I am working to broaden awareness of climate change adaptation among the people of the prefecture, and it is very rewarding to think that this will eventually contribute to protecting people’s lives and property. The situation surrounding fruit tree cultivation in the prefecture is also a major resource to help people understand climate change. I believe that making people aware of disease prevention measures, changes in varieties, and other adaptation measures is a major step that will lead to a better life for all of us.
Sato: As someone who provides support to producers in the field, I find it very rewarding when people are grateful to me, saying things like, “Thank you for telling me that.” On the other hand, I often learn things from growers in the field who have a clear view of the issues. Even though we are in different positions, we all want to continue to do our best and we all share the same desire to make the production area more prosperous.
As a fruit grower, is there anything in particular that you would like national institutions, government agencies, or consumers to do?
Nakazato: I would like to see more research and development of varieties and technologies adapted to climate change, and greater popularization of measures that we, as growers, can make use of. As these measures are implemented, I think people will change their impression of farming, thinking of it as a job that is easy to work in.
Moreover, our work is not over when the fruit is grown; it is complete only when consumers eat the fruit. All the growers put a lot of effort into fruit production, and so I want to encourage as many people as possible to eat a lot of fruit.
(Posted on February 15, 2023）
