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College of Agriculture & Natural Resources

Invasives

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Emerald Ash Borer

What is an invasive species?
An invasive species is any non-native organism whose introduction can cause harm to the environment, human health or economic interests.

How do invasive species get here?
Invasive species are introduced through many means. Intentional introductions have often been for agricultural or ornamental purposes. Accidental introductions are usually the result of contaminated freight or movement of contaminated wood products, plants, or food products. Once introduced, some of these species escape their enclosures or cultivation and can become established as viable populations.

Are all exotic species invasive?
No, actually only a small percent of introduced species ever become invasive. However, it is nearly impossible to predict which species will become invasive and new species are being introduced every day. Some species are present for many years before they exhibit invasive characteristics. Many invasive species go through a "lag phase" in which their populations grow slowly until they reach a size large enough for the population to explode and/or become adapted to the local environment and become invasive.

What type of harm does an invasive species do?
Since invasive species are in a new environment, they are free of their former natural predators, parasites, or competitors, they often develop large population sizes very rapidly. These high populations can out-compete, displace or kill native species or can reduce wildlife food and habitat. Some also have the potential to disrupt vital ecosystem functions, such as water flow, nutrient cycling, or soil decomposition. Other invasive species cause massive amounts of economic damage to the agricultural business by destroying crops and contaminating produce. Some invasive species can cause direct harm to humans or domestic animals.

Why don't our native plants have resistance to these exotic pests?
Plants developed resistance to pests through their interaction with the pest over many generations. The plants that were resistant survived to pass their survival characteristics on to the next generation. As a result, the plant species develops a set of effective defenses that allows the species to survive. When a new pest is introduced, the defenses of the plant are not prepared to counter the attacks of the new pest; therefore significant losses are often experienced.

What type of damage do these species cause?
Pests can damage plants in many different ways. They cause direct damage, such as tunneling by wood boring insects often leading to the death of the plant. And indirect damage, where the injury inflicted by the pest weakens the plant and renders it susceptible to other stress factors.

What can I do to fight these exotic species?
Invasive organisms can easily be transported on living plants or fresh products such as fruit. Many pests can be found in recently killed plant material including firewood, lumber, and wooden packing material. Avoiding the long range movement of these materials is a simple way to slow the spread of pests. Buying only certified pest-free nursery stock is also a good idea.

By knowing what to look for and rapidly identifying any new introductions, we may be able to minimize the impact of new invaders. Control of small infestations is more effective and economical than trying to control a well-established, rapidly spreading infestation.

Link: Invasive and Exotic Species of North America

Adapted from Invasive.org's Frequently Asked Questions
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IET Departmentof the College of Agriculture and Natural Resources. © 2014.