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Plant Disease Update

Artillery Fungus

October 2016 Plant Disease Advisory

The artillery fungus is common in home and urban landscapes where it decays organic debris and is

most commonly associated with wood mulch. The genus of this fungus is Sphaerobolus, which translates

to “sphere thrower”, and gives a clue regarding its unique adaptation. If not for the production of the

sticky spore masses that it discharges forcibly about 15’ high and 20’ distant, this fungus would likely be

overlooked because its fruiting body or spore-producing structure is less than 1/20 of an inch in

diameter. 

   

artillery fungus The tiny dark objects on this rhododendron leaf are the spore masses or peridioles of the artillery fungus. (Photo credit: Bruce Watt, University of Maine, Bugwood.org)

 

Each year the Virginia Tech Plant Disease Clinic receives inquiries from clients anxious about

numerous, tiny, dark dots that adhere to the siding of homes, vehicles or plants. These strongly adhesive

“peridioles” are the spore masses of the artillery fungus (Fig. 1), which are most often projected toward

light surfaces. The sticky peridioles do not harm plants. At best, they are a cosmetic problem on plants,

houses, and vehicles and, at worst, when peridioles cannot easily be removed, they cause a stain or

damage to the finish upon removal. Last year a diagnostician in the Plant Clinic experienced

repercussions from the artillery fungus when a stump near her driveway was ground up and used for

mulching a bed near her driveway. Subsequently the wood mulch became an ideal habitat for the

artillery fungi. She easily identified the tiny, dark dots on her car, but removing them was another

matter. 

There are no fungicides registered to control this fungus. The best approach for the artillery

fungus is avoidance: locate any wood mulch away from objects that you do not want subjected to

“sphere throwing”. If you must mulch, you may want to use synthetic mulch, which is not subject to

habitation by the artillery fungus. Mulch containing mostly bark (e.g. 85%) vs. wood deters colonization

by the artillery fungus, but does not guarantee the artillery fungus will not appear. The internet is full of

information on this fungus, along with lots of anecdotal approaches for peridiole-removal; however, try

them at your own risk!