Weeds on the Move

Most land managers are familiar with the many species of thistle and knapweed that continue to nag pastures, natural areas, and our own backyards. Although not new to the United States, the following invasives are on the move and are capable of showing up on your roadside. Be on the look out to stop the spread of these weeds that are gaining momentum and mass.

Cogongrass, Imperata cylindrical

Cogongrass, Imperata cylindrical

(excerpted from USDA fact sheet No. 1999.01 by John D. Byrd, Jr. of Mississippi State University and Charles T. Bryson of the Agricultural Research Service.)

Background:
Cogongrass was introduced accidentally in a shipment to Mobile, and intentionally through agricultural plantings for forage and erosion control in the early 1900's. Cogongrass with reddish to maroon foliage is still sold by nurseries as an ornamental grass called Japanese bloodgrass. Cogongrass occurs as a weed in Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. Because of its aggressive, weedy habit in other countries, cogongrass is included on the Federal Noxious Weed List.

Characteristics:

• Spreads by seed and rhizomes.
• Now 7th worst weed in world.
• Although native to tropical and subtropical, appears to be adapting.
• Tolerates sand and other soils.
• Matures at 6-47 inches in height.
• Dense stems and rooting system chokes out existing.
• Flowers early and after frost, fire, mowing, and/or tillage.
• Identified by silvery, whitish flowers that create a feathery plume.
• Confused with native silver beardgrass, Andropogon saccharoides.

Impacts:

• Outcompetes native plants.
• Spreads easily in disturbed sites.
• Produces dense flammable biomass.
• Threatens wildlife habitat.
• Not good forage or erosion control.

Management:
Currently there is no single treatment that effectively eliminates cogongrass infestations. This fact makes it imperative to identify it before it establishes.

Giant Hogweed, Heracleum mantegazzianum

Giant Hogweed, Heracleum mantegazzianum

(Excerpted from the Pennsylvania Dept of Agriculture and USDA/APHIS collaborative brochure. Hotline = 1-877-HOGWEED.

Background:
Giant hogweed is a member of the carrot or parsley family that was introduced into North America in the early 1900's. Its huge size made it desirable for arboretums and gardens. It establishes easily in disturbed soils. Hogweed is found in much of the Northeast and now the Northwest.

Characteristics:

• A biennial or perennial herb growing from a forked or branched taproot.
• Hogweed sprouts from roots or seed in early spring
• Stems are hollow, and ridged with purple blotches and coarse white hairs
• Leaves are lobed and deeply incised an up to 5 feet across.
• Flowers are many small white clustered in a flat-topped umbel to 2.5' across.
• Except for size, resembles cow parsnip, angelica, and poison hemlock. Learn other differences before treatment.

Impacts:

• Hazardous to human health, skin irritation with blisters after contact

Management:
Since Hogweed seeds are able to remain viable in the soil for at least 5 years, eradication will require a long term commitment. Mowing or cutting are not recommended because of the plant's large perennial root system. Also these methods increase the opportunity to come in contact with the plant's sap. Seed is moved by wind, water and people. In Pennsylvania, Agricultural staff visits the newly reported location of Hogweed to recommend treatment. Their toll free hotline is: 1-877-464-9333

Garlic Mustard, Alliaria petiolata

Garlic Mustard, Alliaria petiolata

(Information excerpted from "Garlic Mustard, A Major Threat to Wisconsin's Woodlands" written by Paul Hartman and Sharon Morrisey as part of the UW-Extension Urban Horticulture Team, Extension Office Publication 2000.)

Background:

• Native to Europe, introduced during settlement for medicinal and cooking properties.
• It now spreads rapidly, dominating a forest floor within 10 years of arrival.

Characteristics:

• Garlic mustard is a biennial that produces hundreds of seeds per plant.
• Seeds can remain viable for seven years or more
• First year plants appear as basal rosettes, scalloped edges of heart shaped leaves which remain green throughout winter.
• A white flowering stalk (4 petals each) bolts and blooms from late April to early June.
• Seeds become viable quickly. Plants die after seeds are dispersed.
• Seed is carried by deer, squirrels, horses, birds, water and human activities.
• Grows in complete shad and forest edge, often along roadsides.

Impacts:

• This quickly spreading invader is found from the east coast to Utah, north to lower Canada and south to the Carolinas. Its greatest impact is the displacement of native ground layer vegetation and/or woodland natural habitat.

Management:
Preventing the spread is the first line of defense. Clean your clothing and shoes when walking along or in woodland. Monitor vulnerable sites each spring. Alert neighbors and/or adjacent land managers when discovered. Any control method selected must be repeated for several years until the garlic mustard seed bank is depleted. At this time, no one control method appears completely successful. Biological controls are being studied and could be available soon. In the meantime, treat small edge infestations as soon as you see them.

Yellow Starthistle, Centaurea solstitialis

Yellow Starthistle, Centaurea solstitialis

(Information excerpted from FICMNEW's "Invasive Plants, Changing the Landscape of America" and facts developed by the Wyoming Weed and Pest Council.)

Background:
Introduced from Europe and the Mediterranean region, this annual moves easily into disturbed soils. This annual was likely introduced accidentally from alfalfa seed contaminant in the early 1900's. It already covers more than 9 million acres in Idaho, California and much of the Northwest. Untreated, it has covered mountainsides. The State of Montana believes it has eradicated starthistle invasions thus far.

Characteristics:

• Growth habit is erect with rigid, branching stems.
• Appears to move easily along highway corridors.
• Seedling basal leaves in early spring are similar to dandelions.
• 2-3 foot with yellow flowers and thorn-like bracts.

Impacts:

• A serious rangeland weed throughout the West.
• It causes chewing disease in horses.
• It forms monocultures that reduce forage production.
• The plant displaces native plant communities.

Management:
Prevention is paramount. Hand-pulling an individual plant before it goes to seed will be a valuable use of time. Once starthistle is established you will likely need a combination of mechanical and chemical control, plus a well-timed grazing and/or burning event. Because Once in the soil seed bank, starthistle seeds can remain viable for 10 years. Therefore, management must include long term monitoring.

Saltcedar, Tamarix Sp

Saltcedar, Tamarix Sp

(Excerpted from publications by: the North Dakota Department of Agriculture, United States Fish and Wildlife Service, and the Weed Research & Information Center at UCDavis.)

Background:
Saltcedar was introduced in the late 1800's for stream bank stabilization, windbreaks, and ornamental landscaping. Native to Europe, and Asia, saltcedar can rapidly take over, forming a monoculture. It is still being planted in horticultural settings.

Characteristics:

• Gray-green leaves that turn yellow and drop in the winter
• Produce thousands of white to dark pink flowers in spring and summer.
• Small seeds are dispersed by wind, water, and animals.
• One mature plant can easily produce 500,000 seeds annually.
• Hardy from Mexico to Canada.
• Develops a taproot to reach existing water table.
• Can germinate in moist soil and/or water.
• Tolerates drought, heat, cold, salinity, fire, and flooding.

Impacts:

• Currently infests 1.5+ million acres in the Western United States.
• One plant can transpire up to 200 gallons of water per day.
• Fallen saltcedar exude salt causing oils too saline for other plants to grow.
• Displaces existing native plants.
• Saltcedar infests all river systems in the Southwest.
• It invades open water sources including: desert springs, water holes and oases.

Management:
Avoid planting it for it is difficult and expensive to control. After applying herbicides, do not remove the top growth for three years, or resprouting might occur. Small plants can be pulled by hand and incinerated. However, the use of fire and mechanical methods to control large plants often causes extensive regrowth from the plant's root crown, located 8 to 14 inches below ground. A biological control is on the horizon.

Common Crupina, Crupina vulgaris

Common Crupina, Crupina vulgaris

(Information in part taken from "Idaho's Noxious Weeds" Bulletin 816, University of Idaho Extension and Roger L. Sheley and Janet K. Petroff's recent book, Biology and Management of Noxious Rangeland Weeds.)

Background:
Crupina comes to us from the eastern Mediterranean region. It is considered a relatively new weed in the United States, discovered in Idaho in 1968. It is commonly found on dry south-facing slopes. This annual is now found in the Pacific Northwest . In 1980 APHIS did an economic analysis of potential impacts to agriculture and determined that it would cost $2.6 million to eradicate Crupina at that time. Already the loss in forage dollars would now exceed $19 million.. Impacts to natural areas are unknown. Wildlife will also be affected.

Characteristics:

• A winter annual up to 3 feet in height.
• First rosettes have entire leaves with toothed margins, followed by leaves that are pinately divided.
• Flowers are pink to purple followed by dark seeds.
• Spreads by seed by wind, water, and animals.
• Found in canyon grasslands, rangelands, and forests.
• Also found in gravel pits, highway, and railroad corridors.
• Seeds remain viable in soils up to 12 years.
• Tolerates high elevation environments.
• Plants overwinter as rosettes, set to bolt in April.

Impacts:

• Crupina is responsible for loss of forage value.
• Hay shipped with crupina in it will speed up the spread.
• Deer and elk populations can decline as well as associated hunting.
• Increased erosion will affect water quality.
• Crupina will likely replace native communities after disturbances.

Management:
As usual prevention of crupina is an important strategy. Washing off construction equipment before moving to a new site is helpful. Avoid importing soils from infested areas to new projects. Apparently a mix of manual, mechanical, biological, thermal, cultural, and chemical tools must be integrated on a site by site basis.

Scentless Chamomile, Matricaria maritime

Scentless Chamomile, Matricaria maritime

(Borrowed from "Weed Identification in Alberta" by AAAF and Telus.

Background:
This annual to short-lived perennial spreads by seed. Scentless chamomile is often confused with ox-eye daisy when flowering. A closer look gives an easy distinction of finely divided leaves. This European scentless herb is considered an agricultural weed in Alberta. It has been seen as far south as Central Wisconsin along highways adjacent to pasture land. Canada is warning us of its aggressive movement.

Characteristics:

• Flower is similar to that of Oxeye daisy, Chrysanthemum leucanthemum
• Leaves are similar to common pineapple weed
• Lacks odor of pineapple weed
• Common to disturbed sites
• Somewhat bushy growth appearance.

Impacts:

• This plant diminishes forage quality.
• Potentially will reduce diversity.
• Could out compete native grasses and forbs.
• Has no wildlife value.

Management:
Spot-spraying will eradicate small populations.

Buffelgrass, Pennisetum ciliare

Buffelgrass, Pennisetum ciliare

Background:
Introduced from Africa to this continent as a forage grass in the early 1900's The grass was purposefully planted from Arizona to Florida. It is now well established in the Sonoran Desert region both north and south of the border. Buffelgrass is still planted in some areas. It already dominates some highway rights-of-way. Currently the Arizona DOT is working with its neighbors to the South in a partnership effort to map and control existing buffelgrass infestations. Recurrent fires would decimate desertscrub communities that are not adapted to fire. Only desert grasslands have tolerance of such fires. Mexico is warning us of its grave ecosystem impacts.

Characteristics:

• Perennial warm season grass/
• Deep rooted and can form sods.
• Tolerates sand and clay soils.
• Reproduces from seeds and rhizomes (blading will spread)
• 1-4' in height
• Forms dense stands.

Impacts:

• Highways hold moisture and attract grass movement.
• Threatens desert tortoise habitat.
• Displaces native plant community.
• Serve as standing fuel for wildfires when green or dormant.

Management:
Planting of this grass should no longer be an option in vegetation management. Mapping the locations of buffelgrass infestations will be key to long term management success. Spot-spraying appears to be the best maintenance tool at this time.

Partnerships with adjacent landowners will be needed for lasting control.

There are many others like: Japanese Knotweed, Pragmites, Ailanthus, Scotch broom, houndstongue, common tansy, Dyer's woad, reed canary grass, wild parsnip, Medusahead, Bermudagrass, teasle, Japanese stiltgrass, Johnsongrass, Dame's Rocket, Russian olive, Mile-a-Minute weed, and purple loosestrife. The following are the problem plants with huge economic and environmental costs, most often mentioned in the 2004 Weeds Across Borders II, a North American conference. And do not forget Kudzu! The continually adapting erosion control vine of the South was recently found on a roadside near Portland, Oregon. Invasive plants have the ability to increase their current range. Never be off guard.