Photo/Illutration Red leaves on a withered tree indicate fungal infection at Suwa No. 3 Park in Tama, western Tokyo, in September. (Provided by Tama city)

A withering disease has killed more than 500 broad-leaved trees and infected hundreds of others at parks throughout Tokyo this fiscal year, according to the Tokyo Metropolitan Park Association.

In comparison, the disease killed 44 trees the previous fiscal year, the association said.

The wilt condition is caused by a fungus transmitted by ambrosia beetles measuring 4 to 5 millimeters long. Broad-leaved trees bearing acorns are targeted.

The disease spread rapidly likely because the bug was more active in the higher-than-average summer temperatures that followed a prolonged rainy season around June, the association said.

The leaves of infected trees wither and turn brown or reddish brown even though they are not part of autumn foliage.

Once trees wilt due to the condition, they never recover.

The association, responsible for around 60 parks in the capital, confirmed at least 500 trees died at 21 parks as of August last year. More than 1,700 trees, including partially withered ones, were infected.

The disease has also spread among park and roadside trees managed by municipalities.

The beetle is not active in winter after it lays eggs inside trees. Unless the larvae are removed from the trees during winter, imagoes would emerge again in summer and cause further damage.

The association plans to cut down the 500 trees in phases to eliminate the larvae. The wood will be broken into tiny pieces for use in woody biomass power production and papermaking.

Tama and Inagi cities in western Tokyo for the first time included costs for countermeasures against the wilt condition in their supplementary budgets late last year.

Under their plans, affected trees will be chopped down or agents will be injected to prevent the disease from spreading.

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