Integrated Vegetation Management
This sections will discuss concepts of integrated vegetation management, and then discuss control options for some high priority invasive plants.
Integrated vegetation management (IVM) is a common sense approach to managing vegetation that achieves the desired outcome using the plants biology to identify effective, safe, and efficient methods of control. IVM uses five general methods of control: prevention, physical, biological, cultural, and chemical. Below is a description of each of these methods.
Prevention: Includes approaches such as using certified weed free materials, and cleaning equipment to prevent movement of seeds of weeds. Prevention measures should always be part of an IVM plan.
Physical: Includes mowing, grading, and hand pulling.
Biological: Using biological organisms such as insects, grazers, and pathogens to control to control a weed population. Grazers may be appropriate on some utility rights of way, but may be problematic in areas where vehicular traffic is present. Insects and pathogens can be effective, however they require large populations of the weed. In Alaska, there are no weeds with both a high enough population, and an approved biocontrol agent. Biological control is not discussed with the weed species highlighted in this section.Biological control with insects or diseases requires extensive preparation.
Cultural: Actions that promote desirable vegetation are considered cultural methods for controlling weeds. Examples of cultural methods includes revegetation of bare ground with plants that will outcompete weeds, and activities such as mowing that promote the growth of desirable grasses while eliminating the weeds. Revegetation is key to effective cultural control. For strategies to revegetate refer to the Alaska Division of Agriculture, Plant Materials Center publication “A Revegetation Manual for Alaska” (http://dnr.alaska.gov/ag/RevegManual.pdf).
Chemical: Herbicides are used to control a variety of weeds, and is sometimes the most efficient method of control when eliminating a weed infestation is desired. In Alaska, all right-of-way applications must be made by a certified pesticide applicator. The University of Alaska Fairbanks, Cooperative Extension Service provides courses and proctors tests for certified pesticide applicators in Alaska. In some cases a permit may be necessary. Contact the Alaska Department of Environmental Conservation for information on when a permit is necessary. This course identifies herbicides that will work with the highlighted priority weeds. We do not present an exhaustive list of chemicals or products. Many products may work just as well, particularly different brand names with the same active ingredient.
Timing chemical applications is critical because the chemical used may only be effective at certain life stages of the plant. Life stages of plants that are pertinent to chemical applications include:Insert picture “Plant life stages”
Product labels provide detailed instructions on how to apply the chemical, and what the maximum amount you can apply per year. Labels list a range of application rates. Generally speaking if you haven’t controlled the plant in the area you are working in we recommend using the higher rate, and if you desire to use a lower rate do so on a small portion of the infestation so that you can monitor the effectiveness. Treatment methods covered include ground, spot treatments. After treatment with a chemical the plants absorb the toxin which is distributed throughout the plant. The distribution of these chemicals throughout the plant is critical to success of the control effort. Treated plants must remain undisturbed for up to two weeks to successful.
When weed seed is suspected to contaminate soil in the surrounding area of the targeted infestation it may be prudent to treat the soil with an herbicide that has residual soil activity. The residual soil activity of the chemical will kill seedlings that sprout later in the season, and in some cases in future years. Aminopyralid and clopyralid are examples of herbicides that have residual soil activity. Care should be taken though with the use of persistent chemicals with residual activity. If fill material is moved from the site it may contain the herbicide, and disrupt revegetation efforts in the area it is moved to. Additionally plans for future revegetation should be considered to avoid the effects of soil persistent chemicals on sensitive species.
After treatment of weeds with herbicides it is imperative to monitor for effective control, and to avoid developing herbicide resistance in a species. If some of the plants are not affected by an herbicide they may be resistant to the chemical mode of action chosen. If those resistant plants go to seed their offspring may also be resistant. Control those unaffected plants with another method or chemical with a different mode of action. Planning ahead for resistance management by mixing two chemicals with different modes of action, or budgeting the time to implement mechanical or other control measures will help with overall control effectiveness.
Always Read the Label
All herbicides have detailed instructions on how to apply the chemical to various sites, and species of plants. Labels are considered legal documents for the use of these chemicals. Always refer to the label for the appropriate way to apply that product.
Species Specific Control measures
Bird Vetch, Vicia cracca
Bird vetch is a perennial plant that is prevalent around the communities of Fairbanks, Palmer, and Anchorage. While bird vetch is less prevalent elsewhere in Alaska it is showing up, and should be considered a priority for control when found. Bird vetch spreads by seeds and underground rhizomes. As bird vetch grows it climbs and smothers woody vegetation, fences, and signs.
Be aware there are some native plants that look similar to bird vetch. Marsh pea and beach pea look similar, and climb although they do not grow as aggressively as bird vetch. You can easily identify that the species is marsh pea or beach pea because they have a winged stem while bird vetch has an angled stem.
Mowing: Bird vetch should be mowed before flowering. Mowing mature plants will spread seed and contaminate equipment. Mowing will not kill bird vetch, but will delay flowering and seed set. Mowing multiple times throughout the season will favor grasses and reduce the amount of bird vetch present.
Grading: Grading will spread root fragments replanting them where the grader pushes the roots.
Herbicide: Chemical control of bird vetch is most effective early in the growing season when leaves of the plant are obvious and before plants form flowers. Apply the maximum label rate of an herbicide containing clopyralid, triclopyr, or 2,4-D as the primary active ingredient. Only 2,4-D may be used in areas managed as lawns or with ornamental plantings. Triclopyr is excellent at controlling woody vegetation presenting an opportunity to control bird vetch while controlling woody vegetation. Do not pull or mow bird vetch for at least two weeks after herbicide application. Herbicides are most effective when allowed to translocate to the plants roots. Management with the mentioned herbicides will damage other broadleaf plants, but will not damage grasses.
Creeping thistle, Cirsium arvense
Creeping thistle is a perennial with extensive underground rhizomes: also know as Canada thistle. It is widespread in Anchorage and hainse but rare elsewhere in Alaska. If found report infestations so information can be forwarded to the Division of Agriculture.
Manual: Not effective unless digging an individual plant or seedling that is in the early stages of development.
Mowing: Mow when the plants begin to bolt (shoots elongate and begin to form a flower), but before flowering; this will keep seeds from spreading and reduce seed production.
Grading: Creeping thistle spreads readily from root fragments; grading will spread thistle.
Herbicides: Chemical control of creeping thistle is effective at multiple times of the year, depending on the active ingredient used. Products containing 2,4-D with dicamba, aminopyralid, or clopyralid as the primary active ingredients are effective in early summer or fall. Applications of these products in the fall are enhanced by mowing midsummer to force plants into the rosette stage. Midsummer mowing also may reduce seed production. Products containing glyphosate are most effective when used at the pre-bud or bud stages(shoots elongating and beginning to form flowers), or in the fall after midsummer mowing.
Giant hogweed, Heracleum mantegazzianum
Giant hogweed has only been found once, in Kake, Alaska. If giant hogweed is found, report the location immediately. Giant hogweed looks similar to the native Heracleum sp., commonly called cow parsnip or pushke, and is distinguished by size and leaf form. Giant hogweed can reach 10-15 feet in height, with flowers that are up to 2 ½ feet across, and deeply divided leaves 3 to 5 feet wide. In contrast, cow parsnip or pushke is 4-6 feet tall with flowers up to 1 foot across, and lobed leaves up to 2 feet wide.
Caution: Giant hogweed has toxic sap that can cause photosensitivity and chemical burns on skin. Do not allow any part of the plant or sap from cut plants to come into contact with skin. Always wear appropriate personal protective equipment: long sleeves, long pants, closed-toe shoes, gloves and safety glasses.
Manual: Digging plants up is effective if done before flowers produce seed, and if all the roots are removed. Dispose of flowers in plastic bags to prevent the spread of seeds.
Mowing: When mowed, giant hogweed will resprout from the main root crown. Long-term repetitive mowing is necessary to prevent flowering and starve the roots of nutrients.
Herbicides: Control with herbicides is effective for management. Herbicide control in Alaska is not documented. However, the Pacific Northwest Weed Management Handbook (http://pnwhandbooks.org/weed/) recommends products containing the active ingredients glyphosate or imazapic.
Knotweeds - Japanese, Giant, Himalayan, and Bohemian, Fallopia and Persicaria spp.
Introduced as garden ornamentals, Japanese, giant, Himalayan, and Bohemian knotweeds are often found on roadsides and disturbed areas in Southeast Alaska. Knotweeds also grow on stream banks, lake shores, and beach fringes. Plants will grow to 10 feet tall and smother vegetation around them. Knotweed spreads by stems and roots. Southcentral Alaska has some ornamental plantings. If found outside of cultivation, report these knotweeds.
Infested areas should be avoided, and any dirt or fill material from infested areas should be disposed of in a contained area where it will not be allowed to grow. For disposal recommendations contact your local Cooperative Extension Service office.
Manual: Not effective
Mowing: Do not mow knotweeds or allow brush-cutting activities in infested areas. Mowing or cutting knotweeds will encourage stem growth and may spread plant fragments to new areas. If brush cutting must occur, it is best performed during winter months when the knotweed has died back to its roots.
Grading: Knotweeds spread by root and stem fragments. Grading will spread knotweed to new areas.
Herbicide: Currently, the control of knotweeds is best achieved through chemical methods. Effective active ingredients for knotweed control are triclopyr, glyphosate, and imazapyr. These active ingredients are sold under many trade names, some labeled for use around water. Knotweeds are best treated when actively growing from the bud stage or beyond. Imazapyr can be used just before a killing frost. Stem injection of knotweeds with Aquamaster is possible, but sometimes adjacent vegetation can be injured from root uptake of injected glyphosate.
Orange hawkweed, Hieracium aurantiacum
Orange hawkweed is a perennial with unmistakable bold orange flowers that make identification easy. No other wild aster plants in Alaska have red-orange flowers. Typically, where there is one plant and flower there are many. Avoid areas with orange hawkweed present and not actively controlled.
Manual: Not effective
Mowing: Orange hawkweed is not controlled by mowing. If mowing or brush cutting is needed for an area where hawkweed is present and not actively controlled, mow early in the season before plants flower. To prevent spread seeds and contaminating equipment, do not mow mature plants.
Grading: Orange hawkweed spreads by below-ground rhizomes and aboveground stolons. Grading will move viable these viable plant parts, and spread the infestation.
Herbicides: Application of herbicides to actively growing orange hawkweed plants from the early season rosette stage through bud stage is more effective than late season applications to the rosettes. Herbicides effective on orange hawkweed include products containing aminopyralid, clopyralid, and 2,4-D with dicamba. Use the maximum label rate. A compatible surfactant will help control by breaking up the water tension that will otherwise keep the herbicide on the plants hairs instead of contact the plant.
Perennial sowthistle, Sonchus arvensis
Perennial sowthistle resembles a tall, gangly dandelion and is most easily identified in August when in flower. Sowthistle is prevalent in Juneau, Anchorage, and Fairbanks, and is found in smaller numbers in other areas of Alaska.
Manual: Hand pulling or digging sowthistle is not effective except for small infestations, and all roots must be removed. Plants will regenerate from root fragments.
Mowing: Complete mowing activities before flowering to prevent equipment from spreading seed. Mowing multiple times in the summer season will control, but not eradicate, perennial sowthistle.
Grading: Grading will spread root fragments to new areas.
Herbicides: Control of perennial sowthistle is effective at multiple times of the year, depending on the active ingredient used. Products containing aminopyralid, and clopyralid as the primary active ingredients are effective in the early summer or fall. Products containing glyphosate or 2,4-D with dicamba are most effective when used while the plant is bolding (shoots elongating and beginning to form flowers) or in the fall. Applications of any of these products in the fall are enhanced by mowing mid summer, which may also prevent seed production.
Reed canarygrass, Phalaris arundinacea
Reed canarygrass was introduced as a forage crop and for erosion control to much of Southeast Alaska and the road system-connected portions of the northern and central regions of Alaska. Reed canarygrass spreads by roots and seeds, becoming a problem when it invades stream banks and wetlands. Control work should focus on keeping reed canarygrass out of areas near streams and wetlands.
Manual: Hand pulling or digging reed canarygrass is not effective unless done for a small infestation and all roots are removed.
Weed barriers: Use of tarps and weed barriers for control has mixed results. Control is increased by laying barriers 2 feet beyond the infestation and controlling the edges manually or with chemicals.
Mowing: Reed canarygrass seed production may be reduced or eliminated if the plant is mowed at least twice during the growing season. Mowing will not eradicate an infestation. To prevent spreading seeds and contaminating equipment, do not mow mature plants.
Grading: Grading will spread root fragments to new areas.
Herbicides: Chemical control of reed canarygrass is effective in spring and fall on actively growing plants. Late-season applications are enhanced by mowing mid summer, which starves roots of carbohydrates. Use the maximum label rate for products containing imazapyr or glyphosate. Take care to avoid spraying desirable vegetation, as products listed are not selective. The Examples provided are formulations approved for sue when contact with water is expected.
Spotted knapweed, Centaurea stoebe
Rare in Alaska, spotted knapweed should be reported whenever found to help with eradication efforts. Knapweed is usually found near pullouts, and areas where equipment or vehicles were staged or parked. If found, avoid the area completely.
Manual: Small infestations of spotted knapweed are effectively controlled with hand pulling prior to seed set. Knapweed should be pulled twice each growing season until eradicated.
Mowing: Spotted knapweed can be mowed from the bud stage to early flowering stage. To prevent spreading seeds, and contaminating equipment, do not mow mature plants. Mowing will not eradicate the infestation unless seed production is prevented every year until all plants are gone.
Grading: Seeds remain viable in the soil for several years and grading will move them to new areas.
Herbicides: Herbicide products with active ingredients such as 2,4-D, clopyralid, glyphosate, and aminopyralid will control knapweed. Most chemical controls are best applied to rosettes in the fall or early spring using maximum label rates.
White sweetclover, Melilotus albus
Prevalent on road systems in in some gravel pits sweetclover invades glacial floodplains, burned areas and trails. When present in high densities, it inhibits establishment of willow.
Manual: Hand pulling is possible, but is labor intensive. Pulling after mowing, or pulling plants that are not controlled by herbicide treatments, will aid in eradication efforts.
Mowing: Mow 1 inch from the ground before maturity, or the beginning of flowering. Repeated mowing will reduce but not eliminate, seed production. When mowing is combined with revegetation efforts, eradication may be achieved.
Grading; Early spring grading of infested roadsides can kill first-year sweetclover plants, but grading will spread seed. If possible, start at the end of the infested section of right of way and work toward the center of the infested section.
Herbicides: Chlorsulfuron provides the most thorough control. To avoid selection for resistant populations, rotate repeated applications with different modes of action or consider tank mixing two products. make application in spring or summer to seedlings or plants in early bud to flower stage. Use chlorsulfuron, triclopyr, 2,4-D, or aminopyralid.
Woody vegetation
Safety along a right of way is the main issue when determining which woody vegetation should be removed. Woody vegetation reduces sight distance, attracts animals, and grows to heights that could damage power lines during wind storms. All woody vegetation that endangers the public should be removed as soon as possible. A thorough understanding of the species to be controlled, and consideration of proper timing is important with any control method to reduce damage, minimize visual impact, and be cost effective.
Mechanical: In many cases, mowing most of the existing vegetation is effective: it may be necessary to chop or hand cut large trees and mow smaller brush. This removal should be performed in coordination with other target species control methods.Attention should be paid to the development stage of target species and removal should be performed well before plant mature and set seed to eliminate seed spread. Removal of woody vegetation prior to chemical control methods may be necessary to ensure good coverage of target species.
Herbicides: Where mechanical removal is not practical herbicides may be applied. Generally, the best control of woody vegetation occurs when most of the sap is not flowing up the tree or after the plant is fully leafed. Broadcast applications are effective for controlling brush and trees along roadsides.
The above chart documents the effectiveness of herbicides that work for woody vegetation and selected invasive weeds on Alaska rights-of-way. The chart can be used to plan effective management of weeds and woody vegetation in the same application.
E = Excellent (90+ percent control)
G = Good (75-90 percent control)
F = Fair (some suppression)
P = Poor (no control)