In 2008, the University of Arkansas and the Arkansas State Plant Board — with the help of a coalition of agencies, including the Nature Conservancy and the U.S. Army Corps of Engineers — released a guide, Top 10 Invasive Species of Concern in Arkansas. The publication lists 10 alien species that have or will affect Arkansas ecosystems.  

Top 10 invasive species

1. Cogongrass:
   This weed first entered the U.S. through an Alabama port in 1900, and is now prevalent in states from South Carolina to Texas. It spreads through rhizome fragments in soil or on farming equipment. Hurricane Katrina greatly contributed to cogongrass's movement into interior states because of the presence of rhizome fragments on emergency equipment that traveled inland after the storm. The weed can grow 5 to 6 feet tall and form large colonies. It can be treated with herbicide but often requires multiple treatments.
2. Tropical soda apple :
   This shrub is native to South America and was introduced into the U.S. through the stomach of cattle. It was declared a noxious weed in Arkansas in 2007. The tropical soda apple can grow up to 6 feet tall and wide and carries yellow fruits that look like small watermelons. It most commonly invades open fields and pastures but can also grow in open forest areas. The shrub forms dense areas of growth and leaves the land unusable for humans or wildlife.
3. Sudden oak death:
   This microorganism appears to be fungus-like. It was identified in Europe in 1993. In 2000, the disease was discovered in California and has more recently been found in the eastern U.S. It has spread in large part due to the nursery plant trade and contaminated soil. The disease affects at least 90 species of trees and woody ornamental plants. Oaks usually die within months or years later. Trunk cankers and leaf spots are stress signs displayed by oaks. Control of the disease depends on detection and the removal of infected plants.
4. Bacteria leaf streak of rice:
   This disease was originally identified in Asia, Africa and Australia. It affects only leaf blades and forms streaks on the blade surface that eventually join to form yellow or brown sections. Warm, wet conditions as well as excessive nitrogen encourage the disease. Local spreading is often due to irrigation water or farming techniques. Over larger regions, the disease is spread through seeds or parts of an infected plant. Overall, it can be controlled 
   
5. Hydrellia wirthi:
   This fly is only about 5 millimeters long and is known to attack rice seedlings. Its impact is quite visible — the fly can stunt the seedling's growth or kill it completely. While the damage can be easily identified, identification of the actual fly requires a specialist.
   
6. Hydrilla:
   Originally, it was thought that this aquatic weed was not capable of living as far north as Arkansas. But in 2001, it was discovered in Lake Ouachita and is now found in waters across the state. It grows at or just below the surface of the water. Hydrilla can form large mats that can grow up to 10 meters deep. It is spread through boats and plant fragments. Control programs largely focus on the larvae of a tiny fly that feed on this aquatic weed. This method has been effective in several Arkansas lakes.
   
7. Sirex wood wasp:
   In 2004, this insect was identified in New York. The wasp affects pine stands of the same age or those already undergoing stresses. It could affect most North American pines. Global pine populations, including loblolly pine, have been significantly affected. Both silvicultural and biological controls have been applied. Improving overall tree health has helped increase resistance, while parasites may also prove to be an effective treatment against the wasp.
8. Old world bollworm:
   This insect is found throughout Europe and Asia. It affects flowers, ornamental plants and also crops, such as tomatoes, corn and cotton. Accurate identification is important because the bollworm looks extremely similar to the native corn earworm through its life stages. While the insect has not yet been identified in Arkansas, it would likely be spread through the transportation of ornamental plants from Europe. Surveys are ongoing to detect the bollworm if it is introduced.
9. Channeled apple snail:
   This snail is native to South American lakes and swamps and was first found in the southern U.S. in 2000. It mainly threatens rice fields and wetlands. It can tolerate very cold temperatures and survive dry periods by burying into the soil. The snail lays clusters of eggs every two to three weeks. These clusters have a light pink color and are always located above the water's surface. The snail was introduced by the aquarium trade, and there are no chemicals that can selectively treat for this organism.
10. Rice nematode:
    Rice nematodes cause Ufra disease, which is primarily associated with deep-water rice and found in Africa and Asia. This disease can result in complete yield losses. The nematode itself is not visible, but the disease's symptoms can be seen on panicles. If infected early, the panicles will remain in the leaf sheath. If infected later, the panicles will be distorted and likely sterile. The nematode can remain viable in leftover plant debris for six months and contaminate developing seedlings and plants.

Source:
Top Ten Invasive Species of Concern in Arkansas (PDF | 1.1. MB)