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Thursday - June 20, 2013

From: Buckley, WA
Region: Northwest
Topic: Pests, Shrubs
Title: Spots on calycanthus petals from Buckley WA
Answered by: Barbara Medford

QUESTION:

Petals on calycanthus develop black spots the turn into holes. Problem appears shortly after buds open. Occurs every year. Foliage is healthy. Plant growing well and doubles or triples size every year. Has been in present location about four years.

ANSWER:

There are two members of the Calycanthus genus native to North America. This USDA Plant Profile of Calycanthus floridus (Eastern sweetshrub) shows it growing nowhere in western North America. According to our webpage on Calycanthus occidentalis (Western sweetshrub) it is endemic to California. The USDA Plant Profile shows it growing only in Klickitat County of Washington, a couple counties away from you in Pierce Co., but we assume the climate, rainfall and soils are nearly enough alike that it will do all right in your garden.

From our webpage, here are the growing conditions for Calycanthus occidentalis (Western sweetshrub):

"Growing Conditions

Light Requirement: Sun , Part Shade
Soil Moisture: Moist
Soil Description: Moist soils.
Conditions Comments: Calycanthus occidentalis will develop leaf burn if planting site is too dry."

Please note the comment on leaf burn, if the site is too dry, as well as the need for sun (6 hours or more of sun a day) or part shade (2 to 6 hours of sun), but that is referring to leaves, and we assume you are finding the spots on the petals of the flowers. So, we will look further and see if we can find an explanation of the spots on blossoms.

Here is more information and pictures from Las Pilitas Nursery in California. From that, we learned that pollination is by members of the Nitidulidae family of beetles. Further research said that these are sap sucking beetles, and we could not find any indication that they did damage to flowers they were pollinating.

All the references we searched said that the plant was relatively pest and disease free. Since, as you say, the plants are healthy, we would not be too worried about it. We are native plant gardeners, not entomologists, but if you are concerned, you might contact the Washington State University Extension Office for Pierce County to see if other similar occurrences have been reported in your area.

From the Image Gallery

Western sweetshrub
Calycanthus occidentalis