Even the disease-causing organisms and pests that affected them earlier may not be present in the new habitat. Their uncontrolled growth can affect the native species and may also alter the ecosystem.
Surge in global trade and tourism is considered the main reason for the menace called invasive plants. While some of these plants find a way to a new region accidentally (like use of contaminated seeds), some others are introduced as ornamental plants that got invasive later.
In the U.S. only, around 2 million acres of national park land is very badly infested with invasive plants. According to statistics, 7 million acres of these parks have such plants.
Invasive plant infestation is a grave problem and the said figures are only a small fraction of what can be seen in private, state and federal lands. Apart from being a menace to the land owners, invasive plant infestation is a threat to the whole public in general, as its impact is both ecological and economical.
How to Eliminate Invasive Plants?
Weeding is a common task that most gardeners are familiar with. Some plants spread fast and cover large areas. They may grow again even if you try to eradicate them. These plants can be generally termed invasive. Most of us have a basic idea about some invasive plants, there are many who are unaware about these weeds.
So, it is always better to know more about such plants in your region. Nowadays, you may find various authentic websites that can provide you with this data. Once you identify those plants, start getting rid of them. Here too, you must know the specific method of eradicating a particular invasive plant. Such methods may vary from one plant to another.
As mentioned earlier, eradication of invasive plants is better done at an early stage, before they spread. Start the work with proper guidance from concerned authorities of the county's agricultural department. Removal of these plants can be done manually or with help of chemicals. Even biological control is sometimes found to be effective for some plants.
You may also suffocate plants. If you have enough time to wait, then try UV-stabilized plastic sheets on them. Get these sheets and spread them above the area where the weeds grow. Secure these sheets by keeping stones over them. The sheets must cover the entire area and some extra distance of 4 to 5 feet around the edges of the infested area.
Go for clear or black sheets. Keep the sheets intact for a year or two. Each plant beneath the sheets will be affected due to it. If you want to grow something in this soil (after removing the sheets), start with a cover crop. This is suitable for small plants that grow at ground level. Use mulch to smother invasive plants.
Flooding and Burning are also among the methods used to destroy these aggressive plants. Plants covered with water for a particular time period (vary with plant species) get destroyed. But this method can be adopted only if the area to be covered can be flooded, till the plants are completely immersed. This is not applicable for aquatic weed control.
Another method, used for invasive plants, is setting them on fire. This method is risky and should be done very carefully, after taking permission from concerned authorities. Ensure to check the local laws regarding permit to burn plants. Better to opt for prescribed burn or fire (controlled fire) with the help of professionals.
Chemical control consists of various methods that use chemicals. In this case too, you must have knowledge about the right method and chemical for a particular plant. While some of these chemicals affect each and every plant in the area, where it is applied, others are more specific. The most commonly used herbicides are glyphosate and triclopyr.
Various factors like presence of other plants, animals or water bodies and weather, are taken into consideration while using herbicides. Make sure to check the local laws with regard to application of such chemicals.
Another method is to tie the stems together and cut them (above the tied part), before applying chemicals on the cut part. This can be done with a brush or sprayer. You may also cut the stems at ground level and apply the herbicide on the cut part as well as the root crown.
In some cases, the bark of the tree trunk is cut in the form of a ring and herbicide is applied on the exposed part. Such cut must have at least six inches width and must be within 15 to 25 inches from the bottom of the tree. Even the root collar can be cut and exposed for this purpose. Apply herbicide generously, but ensure that the chemical does not spill.
As per this method, the natural predators, pests and disease-causing organisms of specific plants are used for their termination. Being non-native, most of these aggressive plants do not face a threat (in their new habitat) from herbivores and pests that are usually found in their natural habitat.
Introducing such animals (grazing ones, like sheep and cattle), pests and other disease-causing organisms in their new habitat may prove beneficial to eradicate these plants. This method can be adopted only if it is safe for the native species. So, identifying the control organism is not an easy task and requires study.
This method can be adopted only with the permission of concerned authorities. It is a time-consuming project, as biological control of invasive plants may take several years to show noticeable results. Again, effectiveness cannot be guaranteed. Biological control is usually preferred for very large infestations.
Plants like, garlic mustard, tansy, Canada thistle, wild parsnip, sweet clover, hill mustard, can be cut or mowed down. The plants will not be able to make food without leaves and they will eventually die. Do this before the flowering season or before the seeds are formed. So, contact the concerned authorities and fix the correct timing for this task.
You may or may not apply herbicide on the exposed part of the trunk. Early spring is the best time for trying this method. Even cultural control can be practiced by growing and preserving native plants that are resistant to invasive species.
In general, manual and chemical methods are commonly used for herbaceous annuals or biennials, woody trees, vines or shrubs and herbaceous perennials. One of the commonly found invasive plant, dog-strangling vine is generally pulled out if the plants are young and are found in small numbers. In case of a bad infestation, chemical methods are used.
Manitoba maple and Norway maple can be controlled similarly. Bigger trees can be cut down. Garlic mustard plants are pulled out or cut down numerous times during the growing season. While multiflora rose is treated chemically, purple loosestrife can be controlled through manual, chemical or biological methods.
Pulling out with the root system is preferred for small infestation, stray plants as well as young plants, whereas chemicals are applied, if they are spread over large areas. In case of a very bad infestation certain types of beetles (like Galerucella pusilla) or weevils (Hylobius transversovittatus) are used for biological control.
They may either burn them or use for composting (thorough processing to avoid spread of seeds). Choose the right method, as per the factors like, extent of infestation, type of plant and its growth stage, presence of other plant or animal life and water bodies in the vicinity, feasibility of the control method and its expenses, weather condition, etc.
So, specific plants have specific control methods that have to done in the correct manner at the right time. Commonly found invasive plants in one region may not be seen in another area. So, contact the authorities and act as per their instructions.
So, it is better to be aware about the commonly found invasive plant species in your area. Listed here are some of the reasons why you should eliminate invasive plants.
✦ We all know that these plants are aggressive, spread rapidly and cover the nearby areas, within a short period. This may affect other plants that grow around them. One fine morning, you may realize that most of the plants that were growing around the invasive ones have vanished.
✦ Some of these plants produce millions of seeds (as in case of Purple loosestrife) that are carried by wind for long distances. This results in rapid spread not only in your place, but also in your neighbor's land, roadsides, etc. Introducing such plants in your place may result in a public nuisance, unless you take care of the problem, at an early stage.
The native plants have other threats like predators, pests and diseases, which the invasive ones may not have at that time. Gradually, the native species may get extinct and the invasive ones may take over. In fact, after habitat loss, invasive plant infestation is found to be the cause of extinction of various plant species.
✦ With a single species of plant taking over a whole area, there is no biodiversity. Even the animals, birds and insects that once lived in the area may leave, due to shortage of food and even shelter. Some of the invasive plants increase the fire frequency and intensity and make it difficult for the native plants to survive.
✦ Unchecked spread of invasive plant species limits the use of land. Whether it be for forage, agriculture or recreation, they can be a real nuisance. It has been noted by experts that these plants alter the nature of soil and availability of nutrients and water. Even the type of microbes in soil and their mode of action change with spread of these plants.
✦ Growth of certain invasive species may also change the flow and quality of water. Some of them grow so dense that the undergrowth die, naturally, with no sunlight. Plants like salt cedar absorb so much water that in large numbers, they can consume a major chunk of water in streams and lakes, near which they are planted as windbreaks.
These were some of the common problems associated with invasive plant infestation. Another issue is the cost of getting rid of these plants. As invasive plants spread and cover large areas, it becomes become more and more difficult and expensive to remove them. So, early intervention is always preferred.