The Carlisle Mosquito Online

Friday, October 29, 2004


Biodiversity Corner Witches Broom

(Photo by Kay Fairweather)

Name: Witches Broom is the name given to the dense cluster of twigs or shoots arising from a common point, that can occur on a wide variety of woody plants and trees.

When and where seen: The three brooms in the photo are growing on a highbush blueberry in the back of my property on School Street. They have been there for at least a year.

Cause: The cause of witches brooms is different for different host plants and could be due to mites, fungi, viruses, insects, nematodes, or the Curse of the Bambino. Witches brooms are a well-documented disease of both highbush and lowbush blueberry. The organism responsible for the phenomenon in blueberries is a rust fungus called Pucciniastrum goeppertianum.

Life Cycle: The Pucciniastrum fungus spends part of its life cycle on the blueberry and part on fir trees (especially Balsam fir). Both plants need to be present in the general area for the disease to occur. The spores produced from infected blueberries germinate on the blueberry and produce a different kind of spore which is carried by the wind to infect firs. Spores from the fir-resident form of the fungus are also dispersed by the wind and go on to infect other blueberries. The blueberry witches brooms are perennial; they don't kill the plant but the brooms do not have berries and there can be many brooms on a single plant.

Control: Control is of concern to blueberry farmers. The fungus is systemic, so cutting off the brooms or even cutting the plants back to the ground does not get rid of the disease. There is no effective fungicide for it. Infected plants have to be dug up or eradicated with a herbicide. The rest of us non-blueberry-farmers can take comfort in knowing that if a few witches get stranded in the neighborhood on Halloween they will be able to find some transportation.

References: University of Connecticut, Department of Horticulture at; Nova Scotia Department of Agriculture and Fisheries at

Submissions and suggestions for the Biodiversity Corner are encouraged from everyone. What are you finding? Send a note to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to

2004 The Carlisle Mosquito