Fly Specks on the Window or the Cannon Fungus Strikes Again
General Principles Information Note 1 (GPIN-001)
L.F. Grand, Plant Pathologist
R.K. Jones, (Retired) Extension Plant Pathologist
In recent years there have been an increasing number of complaints aobut
small (less than 1/10 inch), dark brown to black, "flyspeck-like" objects
that stick tenaciously to house siding, windows, cars and a variety of
other surfaces. Removal of these sticky objects has proven quite difficult,
especially from light-colored cars where attempts to remove the spots
have resulted in a marring of the paint finish. Speculation on the identity
and source of these structures has implicated insects, fungi and even
tar splashed from road resurfacing activities.
dark "eggs" stick to the surface of this house.
The culprit is a fungus, aptly described as the cannon fungus, Sphaerobolus
stellatus. The fruiting bodies of this fungus are 1-3 mm (0.04-0.12
inches) broad, roundish in shape and off-white to a buff or orange-buff
color. At maturity the fruiting body splits in a star-like pattern exposing
a dark brown, roundish "cannon" or "egg" (termed a peridiole) that is
1-2 mm (0.04-0.08 inches) broad and contains the spores of the fungus.
This structure is forcibly ejected or shot from the fruiting body, hence
the name "cannon" fungus. This fungus is also called the "sphere thrower"
and the "artillery fungus". The "egg" which may be ejected up to 14 feet
from the fruiting body has an oily or sticky surface that enables it to
adhere to most surfaces it encounters. Once stuck to a surface the "egg"
dries to a disk shape and adheres tenaciously. Removal of the "egg" often
leaves an oily stain or discoloration on the surface. Fruiting body development
is correlated with high moisture and temperatures in the 70s and low 80s
degrees F (10-20 degrees C). A change in temperature to 90 degrees F will
stimulate ejection of the "egg" from the fruting body. The fungus also
is phototrophic and the "egg" is shot toward a light source.
you see distinct, small brown/black, hard structures that are hard
to pick off from the surface.
The fungus is not picky on where the "eggs" land.
Sphaerobolus stellatus grows primarily on decaying woody substrates
(especially wood chips), twigs, corn cobs, and dung. The fungus can also
be found on rotted wood in greenhouses and on wood chip mulch and some
bark mulch in potted indoor plants. The apparent increase in occurrence
of this fungus is attributed to the increased use of wood chips as mulch
in landscapes. Under the proper environmental factors large numbers of
fruting bodies can develop over a substantial area of wood chip mulch
in a landscape. Conditons of high moisture and temperatures in the 70-80
degrees F range that favor fruting body development (growth) occur in
the spring and fall.
Avoid using wood chips as mulch when this problem occurs; pine or hardwood
bark mulch does not seem to harbor the fungus as much and can be used
as an alternative. Spores are known to survive up to 11 years so covering
mulch which contains fruiting bodies with fresh wood chips may only solve
the problem temporarily. No fungicides are recommended nor labeled for
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Carolina Insect Notes
Carolina Agricultural Chemicals Manual
with a specific problem, contact your local North
Carolina Cooperative Extension Service
of specific chemicals are based upon information on the manufacturer's
label and performance in a limited number of trials. Because environmental
conditions and methods of application by growers may vary widely, performance
of the chemical will not always conform to the safety and pest control
standards indicated by experimental data. All recommendations for pesticide
use were legal at the time of publication, but the status of registration
and use patterns are subject to change by actions of state and federal
regulatory agencies. Last printed: 06/96
Published by North Carolina Cooperative Extension Service Distributed
in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment
and program opportunities are offered to all people regardless of race,
color, national origin, sex, age, or disability. North Carolina State
University at Raleigh, North Carolina A&T State University, U.S. Department
of Agriculture, and local governments cooperating.
Reformatted Nov. 2000 by Plant
Disease and Insect Clinic