Junipers With ‘Strange Fruit’ Can Harm Apple, Crabapple Trees

Released April 8, 2010

MANHATTAN, Kan. – Some junipers – including Kansas’ native Eastern red cedars – are now developing what appears to be strange fruit.

The structures are actually brown, brain-shaped galls. In spring, these galls produce orange “horns,” poking out in every direction. When finished, they look like a ball of orange, almost jelly-like tendrils.

“Many people think they’re part of the tree’s life cycle, but they’re not. They’re dramatic-looking fungal structures that don’t harm junipers. Instead, they produce the airborne spores of a rust disease that’s best known for affecting apple and crabapple trees, typically in April and May,” said Megan Kennelly, plant pathologist with Kansas State University Research and Extension.

The disease’s common name — cedar-apple rust — reflects its two-plant life cycle, she said. Closely-related fungi that cause similar diseases are cedar-hawthorn rust and cedar-quince rust.

“This fungus is why choosing rust-resistant varieties is so important when you first buy apples, crabapples and such — even if you select one that flowers, but doesn’t produce fruit,” Kennelly said. “It’s also one reason why you need to prune any potential host trees you already have, to allow for good air movement through the canopy. That reduces the damp conditions that promote this rust disease.”

Wind or rain carry the disease’s fungus spores from a juniper’s galls to a deciduous host tree. Upon arrival, the spores require leaf wetness to complete their task. That’s why the disease tends to be more severe during wet spring weather. If they meet those conditions on a susceptible tree, in about one to three weeks its leaves will start to develop spots.

A light infection isn’t likely to affect the tree’s long-term health, Kennelly said. But, repeated infections, year after year, warrant attention. And, if they lead to severe defoliation that affects the tree’s food-making ability, they may justify a series of preventative fungicide sprays from April through May (i.e., as long as the juniper’s orange-looking galls are actively releasing spores).

“You’ll need to read fungicide labels carefully to find the right product and apply it correctly,” she warned. “In this case, for example, some products are safe to use on trees that flower and produce usable fruit. Others aren’t — they’re just for ornamental varieties.”

More facts about cedar-apple rust are available at any local K-State Research and Extension office, plus on the Web at http://www.plantpath.ksu.edu/DesktopModules/ViewDocument.aspx?DocumentID=1154.

http://www.ksre.ksu.edu/news/story/briefs040810.aspx

Editor: Elaine Edwards, elainee@ksu.ed

Original article at: extension.org