Fungus attacking street trees

Publication Date: Wednesday Jun 3, 1998

PALO ALTO: Fungus attacking street trees

El Nino rains bring out arboreal pest, leaving thousands of trees bare

From Barron Park to Louis Road and along University Avenue, a fungus thriving because of the long rainy season is attacking thousands of Palo Alto trees, causing their leaves to crinkle and fall off.

The fungus, known as anthracnose, thrives in moist environments and lives on new tree leaves, filling them with brown spots. When raindrops hit the tree, they spread the spores from the twigs, where they have spent the winter, onto the new foliage.

Hardest hit are Modesto ash trees, native to the Central Valley and planted as street trees throughout Palo Alto about 50 years ago.

Normally, these trees have a "beautiful green leafy canopy," said Debbie Mytels, executive director of Canopy: Trees for Palo Alto. "But most of them right now are quite bare. The leaves are falling off."

Once the first round of leaves fall off, the trees can often push out a second round of new leaves. If the weather turns dry and warm, killing the spores, the second set of leaves will thrive. If not, some trees will probably die.

The areas most seriously affected are Ross and Louis roads south of Oregon Expressway, Ash Street in Evergreen Park, parts of Barron Park and areas of north Palo Alto, where London plane trees (also known as sycamore) are also affected by the fungus.

City Arborist David Sandage said all of the approximately 2,000 Modesto ash trees in Palo Alto are affected by the fungus, as are sycamores, Chinese elm and some oaks.

While he sees the fungus in action every year, "it's a lot worse this year. We won't know the final impact until the weather dries out and heats up."

Weakened trees with low reserves will show a lot of dead twigs. The city will evaluate each of these trees to determine which should be removed or merely cut back. Sandage said the sycamores, which are heartier trees, should be just fine but that the ash may be damaged.

"I think it's going to cull out the weaker ones," Sandage said.

He noted that most plants have their own versions of the same fungus, and he has seen evidence of damage to other tree species as well as rose bushes this year.

For more information on this problem or other tree information, call Canopy at 964-6110.

--Elizabeth Lorenz 

Back up to the Table of Contents Page