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Biocontrols for Common Mullein
Gymnetron tetrum, the Mullein Seed-Eating Weevil, attacks Common and Moth Mullein.
The larvae of the Mullein Seed-Eating Weevil, Gymnetron
tetrum, eats the seed in the developing seed-capsules of Common Mullein and Moth Mullein. Where you find these larvae
in a seed-capsule, 100 percent of the seed will be destroyed.
Gymnetron tetrum is the only North American seed predator for Common and Moth Mullein. The insect attacks no
other plants or crops.
While neither mullein is a noxious weed, both are pests and
nuisances. In Lincoln County, Common Mullein infests pastures, roadsides, abandoned fields
and railroad rights-of-way.
Common Mullein can often be found just outside cultivated areas and
irrigation circles, especially in the western half of the county near
Odessa, Wilbur, Almira and outside Grand Coulee.
Common Mullein produces 136,000 to
175,000 seeds per plant. Each seed is
viable for 100 years. Seeds don’t spread
far away. About 93 percent of seeds
grow within 16 feet of the parent plant.
No wonder Common Mullein is among
the first plants to become established in
an area recently disturbed.
History of Common Mullein
• In Greek mythology, Ulysses
was given a common mullein
stalk by the Gods for protection against the enchantress
Circe.
• Ancient Greeks and Romans
dipped the stalks in tallow
and used them as torches.
Common Mullein
• In the Middle Ages, people
believed possession of mullein
protected the bearer from evil.
• In Europe, it has been a medicinal
herb for centuries. It was also
smoked like tobacco.
• The Puritans may have brought mul- Common Mullein with its tall
lein seeds to North America for me- seed-bearing inflorescence
dicinal purposes.
• Herb gardens often include mullein
for the plant’s medicinal properties.
• The plant followed settlers moving
West across North America.
Biology of Common Mullein
A colony of Common Mullein
• Common Mullein has a range • Common Mullein must reach a critithroughout most of Europe,
cal rosette size before it will flower.
including Britain, east
• The plant over-winters in the Flowering inflorescence
into Russia to the westrosette stage.
ern Himalayan Moun• During the second or later
tains; plus most of
seasons, the rosette produces a
North America.
stout, erect flowering stem, 1 to
• Common Mullein is
6.5 feet tall.
typically a biennial, or
• On average, there are 184 to
rarely an annual or
268 seed capsules per plant.
short-lived perennial.
Each capsule contains 566 to
• The size of the rosette
626 seeds.
is related to the fate of the
plant for the following season. • Each plant can produce from
136,000 to 175,000 seeds.
Seeds about to fall from pods
First-year rosette
Adult Mullein Seed-Eating
Weevil, Gymnetron tetrum.
Mechanical & Chemical Control of Mullein
• Severing the rosette from the • Chemical control is possible when
root will lead to plant mortality.
the plant is in the rosette stage.
• Continual mowing inhibits
flowering, but the plant will
increase in size and flower if
mowing is ever stopped.
• Use Weedmaster, Telar or Milestone. A good surfactant is essential
with all the hairs on the weed. Consider an MSO or silicone surfactant.
Pupa inside the seed head
How Effective Are Biocontrols?
• Gymnetron tetrum is the only seed
predator for Common and Moth
Mullein found in North America.
• Adults feed on leaves and seed capsules. Seed capsules, when present,
are the preferred food.
• Up to 100 percent of the seeds may
be eaten by larvae when larvae are
in a seed capsule.
• Weevils prefer Common Mullein
over moth mullein. The weevils do
not attack any other plants.
• Overall, the weevils destroy 48 to 57
percent of mullein seeds.
Common Mullein
• Weevils destroy 64 percent of
the bottom-third of an inflorescence, 68 percent of the
middle-third, but just 25 percent of the top-third.
• Origin: Europe and western Asia.
• Found in eastern Washington: 1932
• Generations: One per year.
• Description: Oval, robust adults,
usually 4.0-4.8 mm in length, densely
clothed with pubescent, yellowgrayish hairs.
• The rate of seed destruction
may increase as more insects
are present.
• The best control strategy for
Common Mullein may be
chemical and mechanical
controls for first-year rosettes,
and bio-controls for flowering
plants with an inflorescence.
Seed heads on stalk
• Egg incubation lasts 7 to 11
days. The viability of eggs in
the field is only 40 percent.
• Larvae: The creamy-white, Cshaped larvae feed on the seeds
within the capsule. By the second instar, larvae are typically
in separate halves of the seed
capsule. The 3rd-instar larvae
eat all seeds on their side, leaving only frass. The larvae are
cannibalistic, and no more
than two adults will eventually
exit from a seed capsule.
• Spring Activity: Adults emerge from
mid-May to early June. Populations
peak three weeks after first emergence. Adults are first found near leaf
axils or in the central bud area until • Pupae: Pupae are 3.5 to 5 mm
long and develop for 11-16
bolt formation. After the infloresmore days.
cence starts to bolt with warmer temperatures, the adults will congregate • Once mature, adults will exit
around the buds and flowers.
the seed capsule by chewing
holes, often inflicting mortal
• Mating: Typically on the infloresdamage to the seeds affected.
cence, near or in a flower.
• Eggs: Females typically lay 1 to 3 eggs
in a seed capsule. The eggs are translucent to creamy-white, 0.2-0.3 mm
long. Their shape varies depending
on placement in the seed capsule.
Seedhead eaten out
by larvae
Larva in seedhead
Number of viable
seedheads reduced
• After mid-September: Adults
are not seen any more as they
prepare to over-winter.
• Over-Wintering: In hollowedout seed capsules.
Hairy leaves require a good
surfactant. MSO, silicone surfactants, like SYL-TAC, DyneAmic, or HASTEN, work best.
Page 2
405 Ross Street
Davenport, Wash. 99122
509-725-3646
Biology of Gymnetron tetrum
• Common Name: Mullein SeedEating Weevil.
Flowers on inflorescence
Lincoln County
Noxious Weed
Control Board
Photos courtesy of Gary L. Piper, NAZ Flora, James H. Miller, Dave Powell, Ted Bodner, Steve Dewey,
Mary Ellen Harte, John D. Byrd, Mimi Kamp and Diana Northrup. Special Thanks to Jake Marquess.
Group of adult
Mullein SeedEating Weevils,
Gymentron tetrum
Biocontrols for
Common Mullein