Highbush cranberry

a worthy berry…and a mysterious fungus

Autumn in Juneau can be a bit difficult—shortening days, lots of rain (in my neighborhood, there has been much more than the official numbers!—flowers on my deck actually got moldy), migrating songbirds flocking up and leaving us for the south, the end of the flowering season. But there is always (at least) one outdoor thing I look forward to—the ripening of highbush cranberries. And this year there was a bumper crop.

One thing should be made clear here at the beginning: high bush cranberries are not cranberries and they are not even related to true, bog cranberries. Bog cranberries (and domestic cranberries) are related to blueberries; they thrive in muskegs, their frail little vine-like stems crawl over the moss, and the seeds are tiny. The so-called highbush cranberries grow on whippy shrubs up to ten or more feet tall, have big, flat seeds, and are related to honeysuckles and elderberry. What the two kinds of ‘cranberries’ have in common is a tart flavor and a brilliant red color when ripe.

Bog cranberries are good-tasting and useful for making a holiday drink or sauce for turkey, but it’s a lot of stoop-labor to harvest them. I like the highbush cranberries for several reasons: the shrubs are decorative much of the year, from the showy clusters of white flowers in early summer to the scarlet leaves and berries in fall. Harvesting them is much easier—no stooping. The berries are reported to have high levels of vitamin C and antioxidants. And, although they too can be made into holiday drinks and jelly, even better, to my taste, is the pungent, savory ketchup that some of us like to make (and especially eat!). The ketchup is good on fish and other meats, potatoes, cheese sandwiches, and no doubt other things still to be tried.

The university extension service website has a list of publications, and one of these features highbush cranberries. Look for the article by Dinstel and Johnson in 2011, labeled as FNH-00112. You’ll find some good recipes there.

We are not the only ones who like highbush cranberries. We see evidence on the trails that bears have eaten good numbers of them, but, oddly, many of the berries pass through their digestive tract whole. Birds can eat them, but smaller birds would spit out the big seed. Being eaten by a vertebrate is how the seeds are moved around the landscape; the lucky ones germinate and grow into new shrubs. In some areas of Alaska, the twigs are sometimes an important source of browse for moose, too.

One day last year I walked the Herbert River trail with a friend, and we noticed something new to us. Some of the highbush cranberry bushes along the trail had strange, rough-surfaced, dark, lumpy cankers on the stem. One of the Forest Service forest pathologists at the Juneau Forestry Sciences Lab very kindly followed up on this observation, sending the specimens to a genetics lab for identification. It turns out to be a rust fungus (Puccinia linkii) that is also reported from highbush cranberry shrubs in western Canada and elsewhere. This rust can overwinter in infected stems or on infected leaves that have dropped to the forest floor, sending out spores that start new infections on leaves, flowers, stems, and berries in spring. Spores are can be produced on any of these infected plant parts, facilitating further disease spread throughout the growing season; some leaves become conspicuously dotted with numerous spore-bearing bodies. Spores spread when blown about by the wind or rain-splash. Interestingly, the common stem infections in the Juneau area are apparently rare or undocumented elsewhere, as this fungus normally only or primarily affects the foliage .

Photo by Robin Mulvey

Research in British Columbia has shown than this rust infection can affect the shrub in several ways. Berry production is reduced, and the berries that do develop contain less sugar than normal. Heavily infected leaves die off early, so the plant loses some ability to synthesize carbohydrates, and infected twigs are likely to die an early death too.

The FSL forest pathologist, Robin Mulvey, has so far mapped the occurrence of this fungus at several spots in the Juneau area from the Valley to Out the Road, but not south of the Valley. She is interested to learn of other sites with infected highbush cranberry shrubs. If you see signs of this rust fungus on highbush cranberries in Juneau or elsewhere in Southeast, please notify her at rlmulvey@fs.fed.us or 586-7971.

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