Refuge Notebook • Vol. 4, No. 23 • June 28, 2002

Scent of witches’-broom not for the tender-nosed by Ed Berg

If you have walked through a forest re- broom on a spruce tree cannot infect other spruce cently, you may have noticed a rather potent sweet trees; it has to first infect a bearberry vine. The bear- smell in the air, quite unlike the fragrant flowers of berry has to produce its spores to infect more spruce. your garden. Likewise, one bearberry vine cannot infect an- A bit of searching will reveal that the odor is com- other bearberry vine; it has to go through the spruce ing from a “witches’-broom” on a spruce tree. These stage. This is called an “obligate” relationship because brooms are one to three feet in diameter, and are a the cycle only works when both partners are available. thick wad of tangled branches. Right now they are There are many examples of these obligate part- displaying new needles, which are light green in color, nerships in nature. I remember as a teenage applying and stand out in contrast with the normal dark green (unsuccessfully) for a job with the Forest Service in needles of the rest of the tree. If you are working in the Idaho fighting the white pine blister , which kills woods at this time of year, you have probably learned a lot of white pine in the western states. to not sit down and eat your lunch beside a tree with The alternate hosts of the blister rust are currants one of these smelly brooms. and gooseberry bushes (all of the Ribes), and When I first noticed the smell of the witches’- for years crews of strong young backs were hired to broom, it reminded me of an animal cage overdue for go though the woods and chop out the currants and cleaning. When my daughter Tanya was little, we had gooseberries. I think this program has long since been hamsters, gerbils, and guinea pigs, and Tanya was gen- abandoned because it was simply impossible to get rid erally a bit slow on the cage cleaning detail. of all the bushes. If we were concerned about witches’- My first thought was that animals (such as squir- brooms, we could be sending kids out in the woods to rels) were nesting in the witches’-broom and that is chop out the bearberry. why they smelled so bad. After inspecting a few of Fortunately, witches’-brooms are not a major them, however, I noticed that even the new brooms threat in Alaska. If you don’t like looking at them, it is with too few branches for a nest smelled equally bad, fine to saw off the branches with the brooms. Idon’t so I eliminated the dirty nest hypothesis. After watch- recall ever seeing a tree so loaded with brooms that its ing the brooms for several years I found that they only life was threatened. smell bad for a few weeks in the spring. Spruce needle rust ( ledicola) is an- Witches brooms are cancer-like growths caused by other example of an obligate partnership. You may a rust (called or Chrysomyxa have seen twigs on spruce trees whose new needles arctostaphyli) which has a remarkable two-phase life- turn bright yellow-orange in the summer. If you flick cycle. If you look at the needles of broom rust with a the twig, a cloud of yellow “smoke” (spores) will ap- magnifying glass, you will see yellow dots. These dots pear. This rust has Labrador tea(Ledum) as an alter- will turn dark, and then release tiny spores, just like a nate host. mushroom. The spores will be dispersed by the wind, There were localized occurrences of needle rust and some will land on kinnikinnick (bearberry, Arc- around Kenai several years ago. Again, this is worri- tostaphylos uva-ursi), whose dark berries on sprawling some to see on your trees, but it doesn’t generally kill vines are well-known to fall berry pickers. the trees. The outbreaks usually occur for only one The spores will infect the bearberry leaves, al- year, especially with cool damp weather, so the trees though you would never notice this unless you were are not affected from year to year. looking for it. Infected leaves have an orange-brown If you really wanted to get rid of it, it would prob- powder on the underside, which is the second type of ably be necessary to remove all Labrador tea bushes spores in the rust life cycle. within 1,000 feet of your spruce trees, according to The remarkable aspect of this life cycle is that both Forest Service plant pathologists. hosts are required to complete the cycle. A witches’- I am still puzzling about the weird smell of the

40 USFWS Kenai National Wildlife Refuge Refuge Notebook • Vol. 4, No. 23 • June 28, 2002 witches’-broom. Some smells in nature have impor- parently, some volatile compound is involved in the tant adaptive value: flowers attract pollinators to aid spore production process, but it’s probably just an ac- fertilization, and plants with good-smelling fruits get cident of the way our noses work that we find it so their seeds dispersed by whoever eats the fruit. smelly. Spruce bark beetles emit attracting and repelling Ed Berg has been the ecologist at the Kenai National odors (pheromones) to regulate the numbers of bee- Wildlife Refuge since 1993. For more information about tles attacking a tree. So, what does the witches’-broom the Refuge, visit the headquarters in Soldotna, call (907) accomplish with its aroma? 262-7021. Previous Refuge Notebook columns can be Probably nothing, as best I can tell. Its spores are viewed on the Web at http://kenai.fws.gov. distributed by the wind—no critters are required. Ap-

USFWS Kenai National Wildlife Refuge 41