National Invasive Species Awareness Week, which concludes today, is a national event to raise awareness about invasive species, the threats that they pose, and what can be done to prevent their spread. It is sponsored by the North American Invasive Species Management Association (NAISMA), which supports local, state, tribal, federal, regional, and national organizations to raise awareness of local invasive species concerns to elected officials, agency leadership, and the public.
The term “invasive” is used for non-native species of plants and animals that grow and reproduce rapidly, displace native species, and cause major disturbance to the areas in which they are present. However, invasive species also include non-native pathogens. Invasive species can be found on land or in water. Once they become established in areas outside their normal habitat range, they are capable of causing severe damage, including harming the economy, the environment, or human health.
This week, we’ve explored:
- a brief history of the arrival of invasive species,
- how invasive species spread,
- why they are harmful,
- types of invasive species (animals, insects, pathogens, and plants),
- how invading species are now being detected, and
- ongoing research efforts about invasive species.
Today, we’ll conclude this week-long series of articles about invasive species by exploring various methods employed to control or eradicate invasive species.
The most economical and safest way to manage invasive species is by prevention. Early detection and rapid response of invasive species is much more effective than trying to control a widespread infestation.
Once invasive species are discovered, a variety of methods are used for their control and management. Those include:
- biological,
- chemical,
- cultural,
- manual, and
- mechanical.
You can also use a combination of control methods for an integrated approach using Integrated Pest Management (IPM). The IPM approach does not refer to a specific management technique, rather it uses a multi-strategic approach with compatible techniques and methods to maintain pest populations below levels that will cause significant economic and environmental damage.
Special Collections, USDA National Agricultural Library. https://www.nal.usda.gov/exhibits/speccoll/items/show/323
Biological control is the intentional manipulation of biocontrol agents by humans for the purpose of reducing the population of a targeted invasive species. Agents selected and typically used are the natural enemies of the targeted species and may involve different organisms, such as insects, mites, nematodes, and pathogens. In North America, most biological control agents of invasive plants are plant-feeding insects, of which beetles, flies, and moths are among the most commonly used. Biological control agents also include imported fish, and other organisms that eat or infect the targeted species. Further, biological control may involve the release of genetically modified organisms.
Genetic biocontrol can be defined as the release of organisms with genetic methods designed to disrupt the reproduction of invasive populations. Different approaches of genetic biocontrol for invasive species include:
- sterile insect technique,
- YY males (trojan Y chromosome),
- trojan female technique, and
- gene drive.
Sterile insect technique produces large numbers of sterile individuals that are then distributed within a target population in order to suppress reproduction. YY males (trojan Y chromosome) reverses the sex of a captive population of males via use of sex hormones to produce genetically all-YY males whose progeny are then released into a target wild population where they increase in the population over time at the expense of females until females are eventually eliminated, causing the population to collapse. Trojan female technique involves the steady release of modified females that carry mitochondrial DNA (mtDNA) mutations that cause reductions to male, but not female, fertility, and, over time, causes the population to collapse. Gene drive is gene editing technology to introduce desired genetic traits (such as genes designed to reduce populations by skewing sex ratios) into a captive population that, when they are released, will be inherited by the targeted wild population. (SOURCE: Teem John L., Alphey Luke, Descamps Sarah, Edgington Matt P., Edwards Owain, Gemmell Neil, Harvey-Samuel Tim, Melnick Rachel L., Oh Kevin P., Piaggio Antoinette J., Saah J. Royden, Schill Dan, Thomas Paul, Smith Trevor, Roberts Andrew, Genetic Biocontrol for Invasive Species, Frontiers in Bioengineering and Biotechnology, 25 May 2020, Volume 8, https://doi.org/10.3389/fbioe.2020.00452)
The aim of biological control is not to eradicate the targeted invasive species, but to control it in a way that it becomes manageable. In other words, the method uses nature’s own mechanisms to help ensure equilibrium within the population of the invading species.
Biological control involves much research and testing to make sure the prey targets only the invasive species intended. Successful examples include:
- Canada Thistle
- Common Reed and Common Reed
- Dalmatian Toadflax
- Emerald Ash Borer and Emerald Ash Borer
- Eurasian Watermilfoil
- Garlic Mustard and Garlic Mustard
- Hemlock Woolly Adelgid
- Houndstongue
- Hydrilla and Hydrilla
- Japanese Knotweed and Japanese Knotweed
- Knapweeds and Knapweeds
- Knotweeds
- Kudzu
- Leafy Spurge
- Mile-a-Minute Weed and Mile-a-Minute Weed and Mile-a-Minute Weed
- Multiflora Rose
- Purple Loosestrife and Purple Loosestrife and Purple Loosestrife
- Scotch Broom and Scotch Broom
- Spotted Knapweed
- Spotted-Wing Drosophila and Spotted-Wing Drosohila
- Swallow-wort
- Tree-of-Heaven and Tree-of-Heaven and Tree-of-Heaven
- Water Chestnut
Chemical control includes the use of herbicides, fungicides, and insecticides. Although chemical use can be very effective, they can be dangerous to other species or to the ecosystem in general. Pesticides must always be applied in accordance with the label. Please refer to How to Read a Pesticide Product Label Infographic.
(Click on image below to enlarge)
A systemic herbicide is applied to and absorbed by the leaves or other portions of a plant so that it is translocated throughout the plant, including the roots. This generally results in the death of the entire plant, rather than just the portions directly treated with the herbicide. Contrastingly, a contact herbicide is a chemical that kills only the portion of the plant to which it is applied. Herbicides of this type do not kill the roots of a plant, but may be effective in controlling annual weeds or seedlings that do not have a well-developed root system.
Most of the commonly known invasive plants can be treated using only two herbicides: glyphosate and triclopyr. Glyphosate (the active ingredient in Roundup™ and Rodeo™) is non-selective, meaning it kills everything it contacts. Triclopyr (the active ingredient in Brush-BGone™ and Garlon™) is selective and does not injure monocots (grasses, orchids, lilies, etc.).
Herbicides are applied by one of the following methods:
- foliar mist,
- basal bark treatment, and
- cut-stem treatment.
Foliar mist (or “spraying”) is one of the most common techniques of herbicide application. This technique uses a mist blower or sprayer to apply a low concentration of herbicide onto the surface of living leaves where it is absorbed into the plant. This technique is best used when the foliage of the plant is relatively accessible, and wherever the target invasive species has effectively become a monoculture with a high density of stems. Conversely, individual invasive plants may be easily targeted by foliar application with a small handheld spray bottle. Large infestations will likely require a backpack sprayer or a sprayer mounted on an all-terrain vehicle that can travel across the treatment site. Spraying works best when plants are actively growing, the mist completely wets the leaves, and the spraying is conducted on a day with little wind and no rain in the forecast.
https://www.aces.edu/blog/topics/forestry-wildlife/basal-bark-herbicide-treatment-for-invasive-plants-in-pastures-natural-areas-forests/
Basal bark treatment involves applying a low volume of herbicide solution sprayed at the base of the stem of a woody plant. This is a common technique used on small- or medium-sized shrubs and trees where overhead foliage is not easily accessible. The herbicide solution includes a surfactant or an oil carrier that allows for the herbicide to be absorbed through the bark into the plant. This technique can be used during the growing season and well into the fall or early winter. Basal bark treatment is best for small- and medium-sized stems.
Cut-stem treatment involves cutting the woody plant stem completely or partially and applying a more concentrated herbicide solution to the freshly exposed wood. The herbicide solution is painted on the cut stump using a brush or sponge, or it is injected using a special tool. Herbicides should be applied to the exposed wood immediately following cutting so to avoid dry-out before treatment. A colored dye is often added to the herbicide solution to track which stems have been treated. Cut-stem treatments are most effective when applied in late summer and fall and they are best for large stems.
Successful examples of chemical control of invasive species include:
Cultural control measures are aimed at changing human behavior to address the issue of spreading invasives — using opportunities to educate people about practices to increase awareness about how to prevent the spread of invasives. Cultural practices include mulching, soil solarization with plastic film, thermal weed control (e.g., flaming, hot water, and steam), prescribed burning, water manipulation, and prescribed grazing using cattle, goats, horses, and sheep.
Successful examples of cultural control of invasive species include:
- Cultural Control Strategies
- Earth-Kind Gardening Series Cultural Control Practices
- Manual, Mechanical, and Cultural Control Methods and Tools
Manual control involves physical activities such as hand-pulling, digging, flooding, de-watering, dredging, mulching, manual destruction or removal of nests, egg masses, or other life stages, or shading to control invasive plants. Methods generally include the removal or destruction of an invasive species by hand. Manual control is often labor-intensive, costly, and may only provide temporary relief.
Successful examples of manual control of invasive species include:
Mechanical control techniques include mowing, hoeing, tilling, girdling, chopping, and constructing barriers using tools or machines to “harvest” invasive plants by removing and collecting them, and transporting elsewhere and allowing them to decompose in place. Mechanical treatments complement chemical control and, especially when combined with chemical control, can be very effective and efficient in reducing the presence of invasive species.
Successful examples of mechanical control of invasive species include:
- Manual and Mechanical Control Techniques
- Manual, Mechanical, and Cultural Control Methods and Tools
- Mechanical Control Methods
- Mechanical Control of Terrestrial Invasive Plants
- What is Mechanical Control?
Integrated Pest Management (IPM) is an ecosystem-based strategy and a process for planning and managing the land that focuses on long-term prevention of invasive species or their damage through a combination of techniques. A key principle is that it is necessary to take action only when infestations warrant it, not as a routine measure. This might even require changing your activities on your own property or, if on public lands, changing the activities of visitors, such as restricting the use of recreational vehicles, to prevent disturbance that often leads to invasive plant invasion. Within an IPM framework, pesticides are used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism. Pesticides are then selected and applied in a manner that minimizes risks to human health, beneficial and nontarget organisms, and the environment.
The principles of IPM include:
- identify invasive species, their hosts, and beneficial organisms also present within the treatment area before taking action,
- establish monitoring guidelines for each invasive species,
- evaluate and implement control tactics, and
- monitor, evaluate, and document the results.
Successful examples of an IPM approach to the control of invasive species include:
- A Framework of Response and Integrated Pest Management
- Emerging control strategies for integrated pest management of invasive carps
- Integrated Pest Management for Woody Invasive Plants
- Risk Assessment
I hope this series of posts over this past week has helped you to learn more about invasive species and that they will inspire you to join efforts to help reduce their impacts. Thank you!
Curious By Nature 