You should set your priorities with the following in mind:
Prevention: Preventing an invasive plant species from arriving on your site or preventing the spread of an invasive plant species are the most effective management measures that can be taken. Prevention measures range from raising awareness, to ensuring that good site hygiene practices are employed for the movement of materials into, out of and around the site. Prevention measures include:
- Cordoning off the invasive species;
- Preventing illegal dumping of site waste;
- Specifying that topsoil must be free of the seeds and rhizomes of key invasive plant species;
- Making sure that no nesting birds or other protected species are present;
- Ensuring vehicles coming onto your site are free of seeds and rhizomes;
- Limiting movement of people and / or machinery in infested area;
- Designating staff and machinery to the task for the duration of the works; and
- Ensuring anyone undertaking control measures is suitably qualified.
Note: If your prevention efforts failed, you should spend some time trying to find out why and look for any ways to improve your prevention plan with the lessons learned.
Containment: In general, once an invasive plant species is identified on your site, you should aim to contain its spread in the first instance. This is usually done by cordoning off stands of the plants (including the relevant buffer zones) to stop people and machinery entering these areas. The measures used for containment are very similar to the measures used in prevention.
Treatment and eradication: There are many effective ways of treating and/or eradicating invasive plant species, including chemical treatment, removal by hand/ or machinery.
Where to start?
You should develop an invasive species management plan for your site/area. This should clearly document your goals, what action is needed, over what timescale and the resources needed to achieve your goals.
In setting up your plan, your priorities will be determined by a number of factors. These will vary on a case-by-case basis but may include one or more of the following:
- What you want to achieve (e.g. prevention, containment, treatment, eradication etc.);
- What species you want to target and in what order;
- What options are open to you to manage the infestation;
- How the species are getting on to your site;
- What resources (financial, equipment, human, etc.) are available to tackle the problem; and
- How much time you have/ need for management actions.
Ideally your management plan should aim to prevent invasive plant species from entering the site, contain them, and control or eradicate them if possible.
Key site types
- Construction sites: Generally speaking, it is important to deal with invasive species on construction sites due to the potential for further spread both onsite and offsite during construction works through the movement of seed, root or plant material which would be in breach of legislation; due to health and safety concerns for staff working on the site due to the presence of species such as Giant hogweed and structural concerns due to species such as Japanese knotweed which is known to damage hard structures. In addition the presence of an invasive species, such as Japanese knotweed, may affect your ability to obtain a mortgage or any prospective buyers to obtain a mortgage. The Royal Institute of Chartered Surveyors (RICS) guidance to surveyors for Japanese knotweed provides addition information on this subject.
- Nature conservation areas: In these areas invasive plant species pose a threat to our native species which they may outcompete. If you are managing an invasive species on or near a protected site (e.g. SAC, SPA, or ASSI) you should liaise with NPWS/NIEA before undertaking any action. You may require specific licences to proceed and may also need to carry out an Appropriate Assessment.
- Privately owned properties: Private landowners often find themselves with invasive plant species either on their land or encroaching onto their land. It is important to remember that you do not have the right to manage species on other people’s land without their permission. Some landowners may not want herbicides used on their lands e.g. organic farmers. Where possible, you should always aim to work with your neighbours.
- Public areas: The proximity of the invasive species to the areas used by the general public will be the main concern in this instance. In general it is best to target stands that may be disturbed by people first, to help reduce the chances of spread. In particular, giant hogweed should also be prioritised due the Health and Safety risks associated with the plant. You should also consider erecting signage to notify members of the public.
- Sites on or near river/lake systems: Watercourses are very effective in acting to spread/ disperse invasive plant species. Therefore it is best to tackle stands of invasive plants in these areas first to try to reduce spread and contain growth both on your site. Often the presence of invasive species on watercourses is not an isolated issue just for your site, therefore it may be necessary to work with others to tackle the problem. When working in or near water extra care should be taken to ensure the herbicide selected is approved for use in or near water.
It is recommended that you develop a management plan to suit your needs. If you already have a template or outline plan that you work with then it’s best to keep using this but ensure that it covers all aspects and legislative requirements.
Identify how the species got to your site
When managing a site for invasive plant species, it is important to know how they got there in the first place, or, if you intend to keep them off your site, it is important to identify all entry routes if it is possible to do so. Key considerations include if they are being spread naturally to your site from somewhere else (e.g. seeds or viable plant parts being washed on to your site by a local watercourse) or what human activity has brought them to your site. It may be necessary to speak to other land owners around your site to try to identify where the species may be coming from.
How do I determine what control method is best for my site?
Once you have documented the distribution of the invasive species on the site, there are a number of issues that will determine the action you can take to control them. These include (in alphabetical order):
- Chemical treatments (all species): Many chemical (herbicide) treatments are best used on more than one occasion during the growing season. For example for a large stand of Japanese knotweed a spray in year one many be required close to the beginning, in the middle and at the end of the growing season. Similarly for plants, such as Giant hogweed and Himalayan balsam, which spread by seed an early season spray will be required prior to the seed head forming which is followed up by a monthly check for any late germinating seeds throughout the growing season. The exact timing of when a particular herbicide is used will be dependent on a number of factors including the target plant(s), if your site is near water, the prevailing weather conditions and your chosen herbicide. It is essential that you read the Pesticide Product Label each and every time before use and that you check if the product is licensed for your intended use. It is also essential that you follow all Health and Safety precautions as stipulated on the label.
- Invasive species located close to rivers/ watercourses: Invasive plant species are commonly found in close proximity to watercourses. It is important to know the characteristics of the watercourse and to plan your actions accordingly. It is also important to know if your site is at the lower end of a much bigger problem upstream. If this is the case, you should work with the riparian owners upstream, or, if there is a group active in the management of invasive species in your area, you should seek to engage with them. It is important to be aware that near water only a select number of herbicides are approved for use.
- Legislative issues: Invasive plant species can provide shelter for nesting birds. It is important to be aware that birds are protected by law. It is therefore important to ensure that any works carried out do not disturb birds, in particular nesting birds. Other protected species may also be present, such as badgers; therefore you may be required to time your actions to ensure that these species are not disturbed during sensitive periods in their lifecycle. You may be required to obtain a license to undertake control works which may have an impact on a protected species. Speak to your local NPWS ranger or NIEA Wildlife Officer for advice in this regard.
- Species that set seed: Ideally it is best to prevent plants from setting seed, therefore plants should be controlled prior to the seed head / pods forming with monthly checks undertaken throughout the growing season for any late germinating seeds. This is particularly of relevance to invasive plant species such as giant hogweed or Himalayan balsam.
What resources do you need?
The level of management that can be undertaken may be limited by the resources (e.g. funding and/ or human resources) you have. Therefore it is important to identify all of the resources that will be needed to complete the planned works in the planned timescales.
You should aim to resource the works outlined in your entire management plan. If you are unsure about whether you will have enough resources to complete your management plan, you should set the plan up in phases. In this instance, you should identify options to further resource your plan at appropriate times.
In some cases, it may be necessary to ‘dedicate’ resources for the duration to ensure that works can be undertaken in as short a time as possible. This is particularly true on development sites or when managing small infestations on domestic properties.
Resourcing for community groups
On sites that are managed by community groups, resourcing your plan may be difficult, as these groups often rely on external funding. In these cases, the group’s desire to achieve their goals and their ability to access suitable funding pots are important.