HERBACEOUS FORBS

CONTROL OPTIONS

GENERAL GUIDANCE FOR HERBACEOUS FORBS

Use pesticides wisely: always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations. Notice: mention of a trade name does not constitute the endorsement of the product by authors, agencies or organizations involved in the production of this publication.

Chemical
Foliar. This method is effective on infestations where mechanical control is not practical or desired. Glyphosate (e.g., Accord®, Rodeo® and other products) is a non-selective systemic herbicide that is absorbed by the plant and carried to the roots, killing the entire plant. It is important to avoid contact of spray with desirable plants. Treatments should be done either in early spring when most other non-target vegetation is dormant or mid to late summer and fall when plant growth slows and resources are being sent to the roots. Refer to manufacturer’s label for specific information and restrictions regarding use. In general, a 1-2% solution of glyphosate mixed with water and a non-ionic surfactant (seek manufacturer’s recommendations) is used. Spray should be applied such that it thoroughly covers most of the leaves but not to the point that it is dripping off the leaves.

Manual
Generally speaking, most herbaceous plants can be pulled by hand as long as the entire plant including the roots is removed to prevent regrowth. This is almost always recommended for individual plants

Mechanical
While repeated mowing can be effective for control of some herbaceous forbs, it may not be practical for others. Mowing often needs to be conducted repeatedly and for many years to eradicate plants with significant root systems. It may be more practical and effective to use chemical methods or a combination of mowing and herbicides for difficult species.

BEEFSTEAK PLANT

See General Guidance.

CANADA THISTLE

See General Guidance.

Management of Canada thistle can be achieved through cutting, mowing, controlled burning, and chemical means, depending on the level of infestation and the type of area being managed. Due to its perennial nature, entire plants must be killed in order to prevent regrowth from rootstock. Hand-cutting of individual plants or mowing of larger infestations prior to seed set will help reduce spread, but will need to be done repeatedly to exhaust root reserves. Controlled burns have been used but require training and expertise not provided here. Other sources of information should be consulted. In natural areas where Canada thistle is interspersed with desirable native plants, targeted spot application of a systemic herbicide will be needed.

CHINESE LESPEDEZA

See General Guidance.

Mechanical and chemical methods are the most effective options currently available for Chinese lespedeza. Hand pulling is not recommended due to lespedeza’s extensive perennial root system that will resprout from the root crown. Mowing plants in the flower bud stage for two or three consecutive years may reduce the vigor of lespedeza stands and control further spread. Plants should be cut as low to the ground as possible. Impacts to adjacent native plants should be minimized as much as possible during any treatments. Since root reserves increase up to the flower bud stage, all herbicide treatments should be completed in early to mid summer. The addition of a non-ionic surfactant at a concentration of 0.5% will improve the effectiveness of foliar treatments. A 2% solution of glyphosate (Accord® for upland and wet areas or Rodeo® for wet sites only) mixed with water is effective during the vegetative stage prior to branching or during flowering. Treatments should cover the leaves and stems of plants just to the point of runoff but should not be dripping off the leaves.

COMMON DAYLILY

See General Guidance.

DAME’S ROCKET

See General Guidance.

EUROPEAN STINGING NETTLE

See General Guidance.

FIG BUTTERCUP

See General Guidance.

In order to have the greatest negative impact to fig buttercup and the least impact to desirable native wildflower species, herbicide should be applied in late winter-early spring, generally February through March. Start applications prior to flowering and up until about 50 percent of the plants are in flower, around April 1, then stop. After that, control success declines and many more native wildflowers have emerged that could be killed by spray. Native amphibians would also be emerging and could be harmed. Apply a 1.5-2% rate of a 53.8% active ingredient glyphosate isopropylamine salt (e.g., Rodeo® which is labeled for use in wetland areas), mixed with water and a non-ionic surfactant to foliage, avoiding application to anything but the celandine. The full effect on the plant may take 1-2 weeks and retreatment will likely be needed for many years to fully eradicate it. Applications can be made during the winter season as long as the temperature is above about 65° F and no rain is anticipated for 12-24 hours. To minimize impacts to sensitive-skinned frogs and salamanders, some experts recommend applying herbicide in March and then switching to manual methods.

For small infestations, fig buttercup may be pulled up by hand or dug up using a hand trowel or shovel. It is very important to remove all bulblets and tubers. Due to the abundant tiny bulblets and tubers, all material must be bagged up, removed from the site and disposed properly in a landfill or incinerator. A major consideration when manually removing invasive plants like this is the disturbance to the soil which can encourage the target invasive as well provide openings for invasion by other exotic species. For these reasons, manual and mechanical removal is probably inappropriate for larger infestations in high quality natural areas.

GARLIC MUSTARD

Because the seeds of garlic mustard can remain viable in the soil for five years or more, effective management requires a long-term commitment. The goal is to prevent seed production until the stored seed is exhausted. Hand removal of plants is possible for light infestations and when desirable native species co-occur. Care must be taken to remove the plant with its entire root system because new plants can sprout from root fragments. This is best achieved when the soil is moist, by grasping low and firmly on the plant and tugging gently until the main root loosens from the soil and the entire plant pulls out. Pulled plants should be removed from site if at all possible, especially if flowers are present.

Mechanical
For larger infestations of garlic mustard, or when hand-pulling is not practical, flowering stems can be cut at ground level or within several inches of the ground, to prevent seed production. If stems are cut too high, the plant may produce additional flowers at leaf axils. Once seedpods are present, but before the seeds have matured or scattered, the stalks can be clipped, bagged and removed from the site to help prevent continued buildup of seed stores. This can be done through much of the summer.

Chemical
For very heavy infestations, where the risk to desirable plant species is minimal, application of the systemic herbicide glyphosate (e.g., Roundup®) is also effective. Herbicide may be applied at any time of year, including winter (to kill overwintering rosettes), as long as the temperature is above 65°F and rain is not expected for 8-12 hours, to allow for drying. Extreme care must be taken to avoid contact of glyphosate with desirable plants as the product is non-selective and will kill almost any plant it contacts. Spray shields may be used to better direct herbicide and limit non-intentional drift.

Fire
Fire has been used to control garlic mustard in some large natural settings but, because burning opens the understory, it can encourage germination of stored seeds and promote growth of emerging garlic mustard seedlings. For this reason, burns must be conducted for three to five consecutive years. Regardless of the control method employed, annual monitoring is necessary for a period of at least five years to ensure that seed stores of garlic mustard have been exhausted.

GROUND IVY

See General Guidance.

JAPANESE KNOTWEED

See General Guidance.

NODDING STAR-OF-BETHLEHEM

See General Guidance.

PURPLE LOOSESTRIFE

See General Guidance.

Small infestations of young purple loosestrife plants may be pulled by hand, preferably before seed set. For older plants, spot treating with a glyphosate type herbicide (e.g., Rodeo® for wetlands, Accord® for uplands) is recommended. Herbicides are often most effective when applied late in the season when plants are preparing for dormancy but an additional application in mid-summer would help to reduce the amount of seed produced. While herbicides and hand removal may be useful for controlling individual plants or small populations, biological control is seen as the most likely candidate for effective long term control of large infestations of purple loosestrife. As of 1997, three insect species from Europe have been approved by the U.S. Department of Agriculture for use as biological control agents. Two leaf-feeding beetles (Galerucella calmariensis and Galerucella pusilla) offer the most promise and have been widely used with good control results throughout much of the northern U.S. Although occasional feeding on other plants has been observed it has been light and non-destructive and the beetles have not shown successful reproduction on any native plant species other than purple loosestrife.

SPOTTED KNAPWEED

See General Guidance.

Biological control
Biological control is available and used primarily in the western and Southeastern U.S. for control for large infestations. However, because it has not been used in the mid-Atlantic to date and non-target effects are not well studied or understood, it is not recommended by the author at this time.

Manual
Small infestations of spotted knapweed can be controlled by persistent hand-pulling done prior to seed set. Gloves should be worn because of the possibility of skin irritation and potential carcinogenicity of chemicals in knapweed. Because spotted knapweed can regrow from the base, care must be taken to remove the entire crown and taproot. Plants can also be dug out using a spade. In areas with more than about 10 plants per square meter, repeated spot-burning (see below) by trained individuals is more effective and efficient. For detailed information see McGowan-Stinski in the References section.

Burning
Swath or spot-burning methods developed by The Nature Conservancy, Michigan Chapter, have been used very successfully. Generally, this method involves using a six-wheeled Polaris® ATV that has a rear bed retrofitted with a propane-based weed burner. The torches are set 1½-2 ft. above the ground and burn the knapweed at very high flame temperatures around 2,000°F. For detailed information see McGowan-Stinski in the References section.

Mechanical
Mechanical removal of spotted knapweed involves the use of a Weed Popper®. This tool consists of a row of spikes at the end of a spring-loaded pedal. The user inserts the spikes into the ground at the base of the plant, steps on the square foot pad on the top of the pedal and pushes down lightly (the same movement as when using a shovel). In one motion, the spikes move forward and up, thus uprooting the plant, and a plate moves forward that pushes the plant off of the spikes.

When removing knapweed mechanically, individuals generally spread out in a line and walk through an area to ensure complete coverage. For detailed information see McGowan-Stinski in the References section.

 

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Last updated:11-Nov-2010