As long-term snow melts, an intricate web creeps across Sisters and our surrounding forest. It looks like filaments of cobweb or tufts of dog hair, etched across lawns, leaves, and pine needles.

For some, it’s a lawn maintenance nuisance. For others, it’s a source of misery: snow mold.

“Often times people will think, ‘I get a cold every spring.’ It is actually more their allergies,” Dr. Stephanie Fox told CBS News. The Minnesota-based allergy and asthma clinician said it’s possible to develop allergies even if you’ve never had them before.

Snow mold causes typical respiratory symptoms like sniffing, sneezing, throat-clearing, and runny nose, according to Lilly Byrtus of the Allergy Asthma Information Association.

“Some people will get itchy, watery eyes or ears, or a sore throat. Then it goes into the lower respiratory system and causes wheezing or asthma.”

Indoor molds are commonly linked to asthma and other problems. Many people don’t realize that outdoor molds can also cause hay fever. Some doctors say they can trigger headaches, deep fatigue, even depression.

If you develop sensitivities or allergies to mold, there are practices to help reduce exposure (see story, page 7).

Snow mold’s filaments are called mycelia — the vegetative part of a fungus.

“We often see mycelia that resemble spider web on plants just after snowmelt,” Japanese researcher Naoyuki Matsumoto, Ph.D., told The Nugget.

When Matsumoto talks about “snow mold,” he means fungal diseases (pathogens) that kill plants under snow. He said the gray stuff we call snow mold might just be an innocent saphrophyte, doing the important work of consuming dead plant matter.

“Snow cover creates a unique habitat with constant low temperatures, darkness and high moisture,” Matsumoto said. “Snow cover acts as an insulator and protects plants from freezing, but plants deteriorate in the darkness, consuming reserve materials through respiration.”

This opens the door to various fungi. Local observations suggest our gray snow mold tends to appear in late winter or spring, after a deep snow that sticks around a while.

“Prolonged snow cover is essential for most snow molds; in areas like Hokkaido, Japan, snow cover lasts for four months or more,” Matsumoto said. “However, gray snow mold fungus can readily attack plants such as bent-grass soon after the occurrence of snow cover.”

Folks often remark that the air smells crisp and clean when it’s snowing out. Later, some notice a stale or acrid smell as the streets turn to slush. Is that smell related to snow mold?

It’s possible. Humans sense smells by perceiving chemicals in the air, called volatile organic compounds (VOCs).

Recent research at McGill University showed that snow takes up air pollution and changes its tiniest particles, many of which are carcinogenic.

Once in the snowpack, they undergo chemical transformations, creating a new array of toxic nanoparticles. Some volatilize back into the air; others are “released” with meltwater.

Science Daily reported, “Unexpectedly, colder temperatures and interaction with snow increased the relative presence of smaller nanoparticles in the polluted air above the snow.” Such VOCs could indeed cause an unpleasant smell — and cancer.

Matsumoto said he didn’t know whether snow molds emit or decompose VOCs, but he suspects “their involvement under natural conditions. I think no one has ever worked on the decomposition of chemicals by snow mold fungi.”

As local lawn maintainers and golf course owners know, snow mold can kill plants. Matsumoto recommends “resistance breeding of crops and cultural practices to improve winter hardiness of plants. This is the most practical method.”

Fungicide can also be effective, but costly annual applications add up. Fungi also build immunity — similar to how “superbugs” became resistant to medicines after humans overused antibiotics in healthcare and in animal feed.

“One should always be aware of environmental concerns” using fungicides, Matsumoto added. Fungicides are linked to health problems in humans and animals, notably bees.

Molds are commonly used for industrial production. For example, the food preservative citric acid is no longer squeezed from lemons.

Vats of the black mold Aspergillus niger are fed sugar and corn syrup; the results are processed using sulfuric acid.

So far, there’s no similar gold to be found in mining snow mold.

“Some of snow mold fungi have antifreeze protein which enables them to survive extreme low temperatures,” Matsumoto explained. But commercial producers would rather cultivate a mushroom that contains the same protein.

Research on snow mold is limited. What brought Dr. Matsumoto to the study?

“We had a serious outbreak of snow mold on forage crops in the spring 1975 when I was assigned to Hokkaido National Agricultural Research Center, Sapporo,” Matsumoto said.

Dr. Takao Araki assigned the subject to him, and Matsumoto went on to become one of the world’s few experts on snow mold.