When the Juniper Gets Covered in Orange Goo—the Cedar-Apple Rust

Cedar-apple rust fungal ‘rosettes’ amid juniper berries, ON (photo by Nina Munteanu)

In early June, after a gentle warm rain the previous night, I did my daily morning walk along the river through the local forest and meadow thickets. The day was already warming and an invisible mist steamed off the moist earth, carrying the scent of wet vegetation and loam. When I emerged from a small stand of mixed trees into a meadow, I had to stop walking at what I saw:

The large juniper shrub by the river was covered in huge bright orange flower-like growths! It was as though I’d entered “Area X” in Jeff VanderMeer’s science fiction thriller ‘Annihilation‘.

Cedar-apple rust covers a juniper (Juniperus virginiana), ON (photo by Nina Munteanu)
Juniper by the river hosts cedar-apple rust with profuse jelly-like telia horns that carry fungal spores, ON (photo by Nina Munteanu)

These orange profusions resembled exotic jungle ‘flowers’ with multiple tapered ‘tentacles’ that reached out like a sci-fi creature or Tentacruel from Pokemon. On closer inspection, I recognized them as fungal growths with a gelatinous texture. I later identified the fungus as Gymnosporangium juniper-virginianae, commonly known as cedar-apple rust. The orange fungus consists of ‘flowers’ that commonly locate at the ends of the juniper branches and soft slimy ‘carpets’ of oozing ‘goo’ along stems and branches. They have a gel-like consistency and upon squeezing, disintegrate to water and an orange paste. By the time I returned later that day with naturalist friend Merridy to have another look, the growth had already dried up noticeably. Braver than I, Merridy had a taste and announced that they even tasted of water. A day after, the rosettes had shrivelled into lank powdery tendrils and the slime into smudges of dried ‘paint.’  The exotic magic had already faded. But the magic had just transferred elsewhere… 

Squeezing the jelly-like fungal tendrils, leaving orange residue on finger (photo by Nina Munteanu)
Juniper by the river hosts a profusion of cedar-apple rust growths concentrated at the ends of its branches. Upper: extent of growths; Lower: closer view, ON (photo by Nina Munteanu)

Cedar-apple rust gets its name from the two main alternate hosts, the Eastern Red Cedar (not a cedar but a juniper, Juniperus virginiana) and the apple tree (also the hawthorn and apparently the buckthorn). The rust doesn’t infect or cause significant damage to the juniper, where it lives half of its life. I did, however, notice that the juniper was putting out an extraordinary amount of berries. Note to self: forage later for use in a tea or in a chicken sauce. Did you know that junipers contain the potent antiviral compound deoxypodophyllotoxin (DPT) which has been shown to be effective against viruses that cause the flu and herpes? DPT is found in the berries of the juniper—and might be part of what gives gin—flavoured with juniper—its distinctive taste. 

In early spring rust gall shows indentations where ‘pores’ will develop to exude jelly telia horns (photo by Nina Munteanu)
Dimpled rust gall developing pores in April, ON (photo by Nina Munteanu)

The cedar-apple rust starts out as a brown-greenish gall on the juniper in spring (after overwintering). The galls develop indentations that turn into ‘pimples’ with ‘pores’ from which exude orange jelly protuberances. The jelly ‘flowers’—called telia horns—exude from the galls in a burst of show in early June or late May (after a warm rain), and quickly dry up within days, waiting for the next wetting period.

Various stages in the rust gall on the juniper, from ‘pimpled’ to extending jellied telial horns (photo by Nina Munteanu)
Developing rust gall on juniper, wet (left) and dried (right), both with extended telia horns (photos by Nina Munteanu)

This wet and dry stage can occur over several weeks depending on the rains. The ‘blooms’ contain fungal teliospores which give rise to basidiospores that are ejected as the horns dehydrate and collapse. According to the experts, the spores are then carried by the wind to the next host, an apple, crab apple or hawthorn, where they germinate to complete their life cycle later in the summer. The spores discharge with the rain, travelling as far as 8 km, with most infections occurring on the apple or hawthorn host within a few hundred metres. Later in the summer, the rust on the apple or hawthorn develops cup-like structures on the underside of the leaf. These release spores carried on the wind back to the juniper, where greenish galls are produced the next spring (but do not mature and release spores until the following spring, according to Ontario Agriculture.) I noticed some nearby apple trees, which affirmed this co-evolutionary adaptation. By July, the apples showed signs of rust infestation.

Apple tree showing rust infestation on leaves in July, ON (photo by Nina Munteanu)

Rebecca Finneran of Michigan State University tells us that, “leaves [of the second host] will show a classic spot that typically is bright orange to yellow with a lighter, outer ring. The underside of the leaf may show light coloured, cup-shaped structures.” A few days after the big ‘flowering’, I checked the nearby apple and hawthorn trees. While I spotted some rust spotting on one apple, most were unaffected. But the nearby buckthorn was covered in tangerine mats with donut structures.

Upper: typical orange spot on buckthorn leaf; Lower: curling buckthorn leaf with orange cedar-apple rust growth. Both show donut growths, ON (photo by Nina Munteanu)
Cedar-apple rust on stem of buckthorn showing cup-like growths (photo by Nina Munteanu)
Cedar-apple rust on the underside of buckthorn leaf. Upper: showing both sides of the leaf and flowers; Lower: close up of rust growth showing cup-shaped apparatus (photos by Nina Munteanu)
Cedar-apple rust actively colonizing juniper twigs in late spring (photo by Nina Munteanu)

Every story has a conclusion, and that is true for this strange interactive fungal-plant association. For several weeks I observed the orange goo ‘flowers’ on the juniper ‘bloom’ after a warm rain then shrink back to the original gal with shrivelled ‘fingers’ ready to develop into jelly telia horns in the next rain. Then, after several weeks of this shrinking and extending, I noticed that even during a great rain, the telia horns no longer extended; on some gals, orange wet ‘pimples’ remained, like weeping sores. This stage of the rust had done its job of dispersing basidiospores. Now, with the dry weather, the outer part of the gall, no longer producing spores, turned brittle and friable. I noticed dried up blackened telia horns on several. Up to then, the juniper had looked slightly beleaguered by the extensive fungal infestation; some of its leaves seemed to be choking beneath the strangling galls. But, like shedding a disease that had run its course, the juniper was discarding the galls. They fell off easily in my hands. At the slightest nudge, the gall dislodged, as if just hanging on by a thread. The juniper was left totally unscathed underneath; it had lost a few of its leaves, but otherwise looked as green and healthy as ever. It was remarkable.

End-stage cedar-apple rust gall on juniper, friable and brittle, showing shrivelled and dried telia horns, ON (photo by Nina Munteanu)
End-stage of cedar-apple rust gall on juniper, showing strings of dried up telia horns and orange ‘sores’ from where they had extended, ON (photo by Nina Munteanu)
End-stage of cedar-apple rust gall on juniper, showing strings of dried telia horns, and orange ‘sores’ beneath friable shell, ON (photo by Nina Munteanu)

Medicinal Uses & Eating Juniper Berries

According to Earthweeds, juniper berries help treat diabetes and are used to flavour gin and the French liqueur Chartreuse. The berries take two to three years to ripen; mature blue berries are often used to flavour game, stuffing, marinades and stews. Authentic European sauerbraten or sauerkraut is made with juniper berries. 

Berry-laden Juniper (Juniperus virginiana), ON (photo by Nina Munteanu)

Indigenous peoples have many medical uses for the Easter Red Cedar. They use it to treat cold symptoms, swollen joints, stiff neck or back, swollen legs, eye diseases, fever, headache, dizziness and diarrhea.

Green Deane of Earthweeds tells us that, “the Cedar Waxwing likes the ‘berries’ of the Eastern Red Cedar so much it was named after it. The J. virginiana also has one species of butterfly, the Juniper Hairstreak, that always lays its eggs only on the Eastern Red Cedar.”

Cedar Waxwing perches on a mulberry tree, ON (photo by Merridy Cox)
Juniperus virginiana shrub by the river, showing a profusion of cedar-apple rust ‘flowers’, ON (photo by Nina Munteanu)

(This article was updated with information and images in June 2022)

Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press(Vancouver) was selected by Margaret Atwood in the New York Times‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.

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