Last March, Gary Chastagner was driving around southwest Oregon scouting test plots for a study of madrone, the gnarly, reddish-brown tree found up and down the West Coast. A variety of diseases had been hitting the trees in recent years, and Chastagner, a plant pathologist in WSU’s Puyallup Research and Extension Center, was undertaking a study to see if some varieties might be more disease resistant than others.
Driving between Roseburg and Medford, he started seeing entire slopes of trees that looked decidedly disease prone.
“It just looked like someone went through with a blowtorch,” Chastagner recalls.
County extension agents and natural resource officials soon reported similar devastation in British Columbia, the San Juan Islands, and the Olympic Peninsula. Puget Sound residents echoed them on a special madrone research web page.
“As we drive along side roads and down the Key Peninsula Hwy towards Purdy it looks like all the Madrone trees are dying or dead,” said one writer. “All the leaves are dried up and brown. We don’t see any new growth at all on most trees. They just don’t look like they’re going to come back.”
The madrone leaf blight, as it is called, brings to mind tree-ravaging epidemics of gypsy moths, Dutch elm disease, and chestnut blight. And while the tree has limited commercial value, it’s good for drought-tolerant native landscaping and plays an important ecological role as wildlife habitat and food. It has been a recorded Northwest feature at least as far back as 1792, when the Vancouver expedition’s naturalist, Archibald Menzies, mistook it for an oriental strawberry tree.
“It’s sort of an iconic tree with a lot of passion attached to it,” says Chastagner. “When things happen to it, people pay a lot of attention.”
Leaf blight had been seen before but not investigated thoroughly. WSU researchers started looking at it in earnest in 2009, when Rita Hummel, a WSU Puyallup horticulturist, noticed several sickly madrones at the research station. Marianne Elliott, a plant pathologist, collected samples and found nearly half had a fungus, Phacidiopycnis washingtonensis, that was first isolated in apples by Chang-Lin Xiao, a plant pathologist at the WSU Tree Fruit Research and Extension Center in Wenatchee.
The fungus causes cankers and kills twigs in crabapples, a pollen source in commercial apple orchards, says Xiao. It also lies dormant on apples themselves, rotting fruit after it is harvested.
In the madrone—often called madrona in Washington state—it concentrates on the leaves and appears to be particularly active after colder-than-normal winters, says Elliott.
“I think it kills the tissue,” she says. “It tends to sort of dry it out. We think that’s because this fungus can somehow grow in cold temperatures and that somehow the plant has to have been cold-stressed before infection can occur. So we’re trying to understand that better.”
Walking around the research center, Elliott points out the madrones that Hummel saw afflicted two years earlier. The leaves are wilting and covered by gray-brown blotches and spots.
But while the trees look awful and foregone in early spring, they bounce back in fine order in late spring as new growth emerges.
“It looks really bad,” says Elliott, “but wait ’til June, and it might even look like it didn’t happen.”
Afflictions like branch dieback and canker are worse because they kill leaf buds and roots, preventing the tree from regenerating. The leaf blight can be a serious problem if it strikes several years in a row, starving the tree by limiting its photosynthesis, but probably won’t kill the tree unless it’s already compromised. Homeowners can help by raking up dead leaves, reducing the amount of fungus that can carry over from one winter to the next.
Meanwhile, Elliott and Chastagner are using a $50,000 U.S. Forest Service grant to look for disease-resistant madrones among 18,000 seedlings gathered from as far away as Arizona and Texas and as close as the 400-year-old champion tree in Port Angeles. Plans call for planting them in various ecoregions, places with different climate and soil, and seeing which fare best.