Download HOARY ALYSSUM

HOARY ALYSSUM
(Berteroa incana)
¾ Hoary alyssum is an annual in the
mustard family that grows 1½ to 2
feet tall.
¾ Leaves, which grow alternately, and
stems, are covered with hairs that
give a grayish green appearance.
¾ Flowers are white, with four deeply
divided petals.
¾ The distinctive seed pods are grayish
green, slightly oval, hairy and flat
with a short beak on the end.
¾ Basal rosettes appear, then the plant
flowers and seeds in early spring,
summer and fall.
¾ Plants spread by seed and root
crowns.
WHY BE CONCERNED?
¾ Dried or green, hoary alyssum can be toxic to livestock.
¾ Death has been observed in horses eating hay infested with
30 to 70% hoary alyssum.
¾ Hoary alyssum can retain its toxicity for up to nine months.
¾ Hoary alyssum out competes natives and desirable forage plants,
especially when habitat is stressed.
¾ Hoary alyssum is a highly invasive noxious weed.
¾ Hoary alyssum seeds can easily spread to hay fields, pastures or
roadsides, through contaminated equipment, soil or human
activity.
Hoary alyssum is a Class B designate weed
in Clallam County.
Control and preventing the spread of hoary alyssum is
required county-wide.
DISTRIBUTION: As of August 2008, there are only two known infestations, documented in Clallam
County. Hoary alyssum appears to thrive in dry disturbed areas, with poor grass competition. When
mowed, the plant continues to survive and flower. Plants flower and set seed continuously during the
growing season. In Okanogan County the plant has spread to almost 5,000 acres in just a few years.
Sequim is the perfect habitat for this plant.
Poisoning Symptoms:
¾ Signs of severe intoxication include stiffness, fever, diarrhea, intravascular
¾
hemolysis, and hypovolemic shock.
Premature birth or abortion may occur in pregnant animals.
Ecology:
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Hoary alyssum is generally an annual, but in our mild climate, can become a biennial or
even a perennial.
It spreads by seed or by root crowns.
Plants are found in waste places, overgrazed pastures or stressed meadows.
It adapts well to dry habitats.
CONTROL
¾ Practice good pasture management; avoid overgrazing, irrigate and fertilize as needed and
reseed bare ground. Hoary alyssum is sufficiently suppressed in well maintained pastures.
¾ Small patches can be pulled or dug. Watch for any returning plants and remove those as
well. Larger infestations may need to be controlled with herbicides.
¾ Replant newly weeded areas with desirable plant species that will discourage reinfestation.
¾ Use weed free hay and seed.
¾ Avoid introducing soil or gravel from areas known to have hoary alyssum.
¾ Clean equipment that has been used in infested areas.
¾ Dispose of weeds properly; bag or burn seed heads or fragments that may resprout.
¾ Continue to monitor site for several years; promptly remove new seedlings.
HANDPULLING/DIGGING:
Works best when the soil is moist. Because this method can be time consuming, it may only be
effective for new or small infestations. Plants can spread by root crowns, so make sure you get
the entire root.
MOWING:
May slow, but will not stop the spread of hoary alyssum. In fact, if you do not clean the
equipment used in the mowing, you will most likely spread the plant to any other site where the
equipment is used. Equipment easily carries seeds to new locations!
HERBICIDES:
Can be effective, but should always be applied with care. Do not apply herbicides over or near
bodies of water. Always read the label to check that you are applying an herbicide;
1) in the right place, 2) to the right plant, 3) at the right time and 4) in the right amount.
Several herbicides can be used effectively on hoary alyssum; a surfactant will aid in
effectiveness and repeated applications may be necessary. Plants are most susceptible when
young and growing rapidly. Be sure to contact your local noxious weed office or extension
agent for current herbicide recommendations.
Prepared by the Clallam county Noxious Weed Control Board; 3/2009
For more information call: (360) 417-2442
Or see www.clallam.net/weed