Aspen stands in Southwest suffering from fungal disease

October 4, 2015 byFelicia Fonseca

Visitors marveling at the fall foliage in national forests might find that some of the aspen leaves are brown and blotchy or gone already.

Spores released from leaves and twigs that were infected by a fungus last summer were carried to new leaves by splashing rain and wind this year. The result is that instead of presenting golden yellow colors, leaves in some aspen stands across the Southwest have brown spots and blotches.

U.S. Forest Service officials say visitors shouldn't fret because the discoloring isn't widespread enough to ruin leaf-peeping trips.

"It can be really patchy, depending on some of the moisture," forest entomologist John Ahold said.

Arizona cities near national forests where aspen are found at higher elevations got above-normal precipitation this monsoon season, including Alpine and Heber, in the Apache-Sit greaves National Forest, and Flagstaff, surrounded by the Coconino National Forest.

Grayish areas in the center of the brown and blotchy spots indicate a presence of spores that could perpetuate the infection of aspen leaves if weather conditions are favorable for the disease.

"It's really about the timing of the moisture and having enough of that," Ahold said.

Forest officials say they're not expecting a die-off of aspen or significant loss in growth. However, successive annual epidemics of the disease can weaken or kill the root systems of aspens.

Pam Baltimore, a spokeswoman for the Apache-Sit greaves , said she figured some of the aspen leaves just fell off trees early until a silviculturist mentioned the fungus.

"It made me take pause and look," Baltimore said. "To think that a whole stand could be infected and possibly lost over time is a bit startling after you find out the facts."

In the spring, aspen stands in New Mexico and Arizona were hit by hungry Western tent caterpillars that ate leaves off entire stands. As leaves regrow and fall sets in, the colors are subdued—more bronze than gold. The new, smaller leaves can hang on longer, but late summer moisture and cold temperatures can cause wrinkles in the regrowing process.

The caterpillars have been blamed for defoliating tens of thousands of acres of aspen trees in the past. They damaged at least 8,000 acres of aspen on the Santa Fe National Forest in New Mexico in 2014.

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