Potato Y potyvirus
Photo by Univ of Idaho

There are numerous ways in which invasive species can be transported.

Mile-a-minute weed first became established in the U.S. in the late 1930’s and slowly began to spread. Natural causes tend to be the primary methods of spreading. Birds eat the fruit and carry the seed for long distances before depositing the seeds along with their feces. Waterways also play a significant role in spreading the seeds. This weed produces vines that tend to hang over waterways. As the seeds ripen and fall, they may float for a week and be carried over long distances downstream. Over shorter distances, ants may be involved in distributing mile-a-minute seeds.

Another example of natural causes spreading an invasive species is that of wind. This is especially important when considering plant diseases. Fungi produce spores that can be carried by the wind and quickly and widely distributed. An Internet interactive model has been developed that predicts the potential for infestation of tobacco by the wind distributed plant pathogen, Tobacco Blue Mold. This type of information immediately available can literally save a farmer’s crop.

Female Gypsy moths cannot fly, so human involvement greatly increases the rate at which this pest expands its range. The females lay their egg masses on just about anything, cars, recreational vehicles, and even lawn furniture. If this egg mass is carried into an uninfested area before the eggs hatch, a new infestation is started. It is estimated that the Gypsy moth invades an additional 15,600 square miles each year (three times the area of Connecticut).

Giant Salvina, a water fern from southeastern Brazil, is a tremendous threat to waterways. Under optimal conditions, it can double its numbers within a week. This weed has been illegally sold for use in residential ponds from Florida to California and currently is known to infest waterways in Alabama, Arizona, California, Florida, Hawaii, Louisiana, Mississippi, and Texas. Once established in a lake the weed can easily be caught on boats and boat trailers then moved from one lake to another.

Cattle are a major source of transporting Tropical Soda Apple seeds. If cattle eat Tropical Soda Apple fruit growing in one field then are moved to another field the seeds will then be deposited in manure in the new the location. This can rapidly spread this weed when cattle are sold from and infested region and transported across state lines, if proper holding and shipping procedures are not followed.