Prevention of Nara Disease

Due to the confirmation of oak wilt in the city, we are implementing measures to prevent its rapid spread.

What is Nara-kare?

Nara dieback is a tree infectious disease that causes the death of Quercus species and Fagaceae, mediated by the Kashi-naga beetle (hereinafter referred to as "Kashi-naga") and the Nara fungus. It particularly causes collective dieback in Mizunara and Konara, with a high mortality rate and a tendency for damage to spread to surrounding areas.
Kashi-naga is less likely to breed in Quercus species with a diameter of 10 centimeters or less, and breeding efficiency is said to be better in larger trees. In recent years, the lack of tree renewal in satoyama has led to the growth of larger Quercus species, which has been cited as one of the factors contributing to nationwide damage due to the increase of forests and woodlands suitable for Kashi-naga breeding.

Mechanism of Nara Dieback

New adult woodborers will fly to healthy trees to lay eggs around June to July. Many woodborers will gather intensively due to the aggregation pheromones released by males. Additionally, egg-laying will occur within the tunnels.
When the oak fungus carried by females enters the tree, the tree will lose its water transport function around July to September, and the leaves will begin to wither as if they have turned red, rapidly wilting within 1 to 2 weeks (though this may not always happen).
The larvae of the woodborer grow by feeding on yeasts cultivated within the tunnels and will fly to new healthy trees around June of the following year.

Characteristics of Nara dieback

The following are characteristics of Narakare.

1. It includes oak species such as Mizunara and Konara, as well as evergreen oaks like Arakashi and Sudajii.
2. From June to September, the leaves rapidly change color to reddish-brown and wither.
3. There are many small holes with a diameter of 1.4 to 1.9 mm created by the Kashinaga.
4. There is a large amount of frass near the base

Damage Situation in the City

Until now, no damage from oak wilt had been confirmed, but in August of 2020, oak wilt was confirmed in the trees of the city park. Additionally, damage has been confirmed in private forests, such as in the natural environment conservation area located south of Inagi Station.

The damage situation on land managed by the city, such as parks and green spaces (as of October 2020), is as follows.

• Parks and Green Spaces
  Inagi Central Park 6, Shiroyama Park 71, Hirao Neighborhood Park 4
  Omaru Nature Park 1, Yatoyama Green Space 28
• Others
  Inagi Fureai Forest 31 trees

Total 141

Methods for Preventing Nara Disease

As measures for trees affected by Nara dieback, there are broadly the following methods.

1. How to fell trees and dispose of them properly
2. Method of injecting insecticide while keeping the tree standing
3. Method of covering trees with sheets, etc. to prevent Kashinaga escape

In city-managed areas such as parks and green spaces where there is a high number of visitors, it is not appropriate to leave dead trees that pose a high risk of falling, so the basic approach is to cut them down and dispose of them properly.