Introduction
and Impact
Impact
The
invasion of noxious weeds onto private and public lands causes substantial
economic loss and ecological damage.
Most noxious weeds are not native to the
United Stated and have no natural controls in this country. Some
were introduced through contaminated seed while others were intentionally
introduced without the knowledge of their future destructive nature.
Left to spread without control these
introduced plants can create severe problems for farmers, land managers,
home owners and recreation enthusiasts. The long term effects of
uncontrolled spread can result in higher crop and livestock production
costs, loss of native plants, degradation of wetlands and destruction of
wildlife habitat. At risk are agricultural lands, forests,
wilderness areas, parks and recreational sites.
Introduction
Common sources for the introduction and spread of weed seed include
the purchase, transportation and utilization of contaminated seed, forages
and plant materials. The use of clean materials is a grower/user
responsibility and an important step in limiting the spread of noxious
weeds. Additionally, with free access to large amounts of unfenced public
and private land in Alaska, the spread of weeds by human recreational
activities is a potentially serious problem.
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Photo courtesy of Victoria Naegele, AACD. |
Canada thistle
(Cirsium arvense)
Perennial, spread by seed and creeping roots; stems erect to 4
feet, branched near top; leaves alternate, irregularly lobed,
spiny, dark green on top, white-hairy underneath; flowers white,
rose or purple, diameter to 3/4 inch, grouped in small clusters.
|
 Perennial
sowthistle
( Sonchus arvensis )
Perennial, spread by seed and creeping roots; stems erect to 5
feet, hollow with milky sap, branched near top; leaves alternate,
crowded on lower half of stem and scarce near the top, more or
less lobed with mildly prickly margins, leaves clasp stem at base;
flowers bright yellow. diameter to 2 inches, grouped in small
loose clusters.
Michele Hebert, UAF |
 Quackgrass
(Agropyron repens)
Perennial, spread by seed and creeping roots; stems erect to 3
feet, upper portion smooth, lower sparsely hairy; leaves 1/4 to
1/2 inch wide, sparse hair on upper surface, underside glossy;
claw-like appendages where leaves clasp stem; flowers arranged on
slender 6-10 inch spike, flower clusters (spikelets) arranged in
two long rows, borne flat-wise to stem.
Photo courtesy of Weeds of the West |
 Field
bindweed
(Convolvulus arvensis)
Perennial, spread by seed and creeping roots; stems slender
vine-like and twining to 4 feet long; leaves alternate,
arrowhead-shaped, length to 2 inches; flowers white to pinkish,
funnel-shaped, diameter to 1 inch.
Photo courtesy of Weeds of the West |
Hoary cress
(Cardaria draba)
Perennial, spread by seed and creeping roots; stems erect to 2
feet, branched near top; leaves alternate, lance-shaped,
grayish-green, length to 3 inches, finely toothed edges, covered
with soft fine hairs; flowers white, 4 petaled, diameter to 1/4
inch, form dense flat-topped clusters.
Photo courtesy of Weeds of the West |
Russian knapweed
(Centaurea repens)
Perennial, spread by seed and creeping roots; stems erect to 3
feet, often branched from base, leaves alternate, length to 4
inches, lower leaves lobed or sharply toothed, upper leaves not
lobed but finely toothed; flowers borne singly at end of branches,
diameter to 1/2 inch, color-pink to lavender.
Photo courtesy of Weeds of the West |
Austrian fieldcress
(Rorippa austriaca)
Perennial, spread by seed and creeping roots; stems slender, erect
or sprawling to 3 feet, branched near top; leaves alternate,
smooth, length to 3 inches, lower leaves more distinctly toothed
than upper; flowers bright yellow, 4 petaled, diameter to 1/8
inch, in loose clusters at tips of branches.
Photo courtesy of Cindy RochÈ, Washington
State University |
Leafy spurge
( Euphorbia esula )
Perennial, spread by seed and creeping roots; stems thickly
clustered, erect to 3 feet; leaves alternate, narrow,
lance-shaped, length to 4 inches; flowers yellowish-green,
diameter 1/8 inch, in numerous small clusters, each cluster
surrounded by a pair of heart-shaped yellow-green bracts (leaves);
plant contains a milky sap.
Photo courtesy of Weeds of the West |
Blue lettuce
( Lactuca pulchella )
Perennial, spread by seed and creeping roots; stems erect to 4
feet; leaves alternate, smooth, bluish-green, lance-shaped on
upper stem, lower leaves deeply notched, length to 6 inches;
flowers blue to purple, diameter to 1 1/4 inch; plant contains a
milky sap.
Photo courtesy of USGS |
HorsenettleSolanum
( carolinense)
Perennial, spread by seed and creeping roots; stems erect to 4
feet, sometimes branched, covered with prickly hairs and spines;
leaves alternate, length to 7 inches, coarsely toothed, covered
with tiny hairs, long spines down the midrib and veins on the
lower leaf surface; flowers blue, violet or white, star-shaped, 5
petaled, diameter to 1 inch, look like potato flowers.
Photo courtesy of Jerry Doll, University of
Wisconsin |
Smallflower galinsoga
(Galinsoga parviflora)
Annual, spread by seed; stems erect or spreading, branched, to 2
1/2 feet; leaves opposite, oval, pointed at the tip with finely
toothed edges, surfaces mostly smooth, length to 3 inches; flowers
white, diameter to 1/2 inch, in small loose clusters at tips of
branches.
Photo courtesy of Jerry Doll, University of
Wisconsin |
Hempnettle
(Galeopsis tetrahit)
Annual, spread by seed; stems erect, hairy, branched, to 3 feet;
leaves opposite, lance-shaped, oval at leaf base, hairy above and
below, length to 4 inches, with rounded or pointed teeth; flowers
white or pink with purple markings, diameter to'/: inch, borne at
the juncture of the upper leaves and stems.
Photo courtesy of Saskatchewan Department of
Agriculture |
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Integrated
Pest Management (IPM)
The focus of IPM is on long-term prevention or suppression of pests. The
integrated approach to weed management incorporates the best suited
cultural, biological and chemical controls that have minimum impact on the
environment and on people.
It is important to understand that IPM is not pesticide-free management.
However, a successful IPM program should result in the most efficient use
of pesticides if and when they are needed.
Preventing Spread
Protecting land that is not presently weed infested is the single most
important management goal. The purchase of weed free seed, forages and
plant materials can help to prevent the introduction of unwanted plants.
Once noxious weeds are identified on agricultural land, their spread can
be slowed by limiting traffic through the infested area and by thoroughly
cleaning equipment and vehicles traveling between fields. Uncomposted
manures that are known to contain weed seed should not be spread as
fertilizer. New infestations should be treated immediately to minimize the
cost of cleanup.
Weed seed is often spread by human recreational activities. Suggestions
for limiting this type of spread include: not driving or camping in weed
infested areas. Weed seeds can easily attach to vehicles, tires and
camping gear. Before moving on, be sure to shake out tents, sleeping bags
and clean your vehicle if you have been in areas which contain noxious
weeds.
If pack animals or dogs are being used for transportation in the back
country, use clean, weed free bedding and feed. Seeds contained in feed or
bedding can be lost along the trail and start new populations in remote
areas where control measures are difficult to apply. Before returning home
from a backcountry trip remember to clean seed from your animals"
hooves and coats.
Don't pick the flowers of unknown plants or transplant wild flowers that
can't be identified. Noxious weeds can be spread by taking home bouquets
or plant materials for landscaping.
If a weed infested area is found, let the land owner or management agency
know so they can take steps to control the weeds.
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Control
In areas where prevention has failed, control may be necessary. There are
a number of questions that must be answered before the proper control
measures can be determined. What is the invading plant? Is its presence
threatening? What are the control options for the site as well as for the
weed? How effective are the available controls? What is the most cost
effective, low impact practice available?
For further information on the control of specific weeds please contact
your local Alaska Cooperative Extension district office.
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Introduction and Impact
Classification & Identification
Integrated Pest Management
Prevention
Control
Alaska Regulations
