Weeding out invasive species with classical biological control

Dr. Gadi V. P. Reddy, chemical ecologist and entomologist at the University of Guam, has just received a $33,000 grant from USDA-APHIS to control the insidious weed Mikania micrantha.

The mile-a-minute vine is an invasive weed in Guam and other islands in the Pacific. Mikania's native range is the tropical and subtropical areas of North, Central, and South America. This prolific weed is on the top 10 list of important weeds of Pacific island countries and territories due to its aggressive climbing abilities, which allow it to strangle young establishing plants. This can negatively impact agriculture and agro-forestry plants greatly affecting plant biodiversity in the areas it colonizes. Estimates have the infestation of mikania in Guam around 2,581 acres.

Reddy, with Dr. Christy Leppanen and their team at the Western Pacific Tropical Research Center's Chemical Ecology and Entomology Laboratory, have been investigating a proven biological agent to control the spread of the mile-a-minute vine in Guam and on Saipan. Although Puccinia spegazzinii sounds like an appetizing menu item, it is a rust fungus that has been used in various places around the world, including the Pacific islands of Papua New Guinea and Fiji, to contain the spread of mikania. Working in collaboration with Secretariat of the Pacific Community, Reddy's team has received a permit to release the strain of P. spegazzinii that was released in Fiji and Papua New Guinea for the same purpose.

"The rust is highly damaging to the leaves, petioles and stems of M. micrantha, causing cankers and often resulting in death of the plant. Tests have shown that Puccinia spegazzinii is completely host specific and will not cause damage to any other plants or humans,” said Reddy.

One of the greatest advantages of using classical biological control is that it eliminates the need to use toxic chemicals such as herbicides that may contaminate ground water, rivers or the ocean through runoff. Aside from the environmental damage herbicides may cause, they have proven ineffective in containing the spread of mikania.

Live spores of P. spegazzinii will be cultivated in Guam for release into the field. Reddy fully expects the fungus to thrive in the hot humid conditions on the island and reduce the severity of the mile-a-minute infestation. The rust fungus will also be released in the Commonwealth of the Northern Mariana Islands.

Protecting the region's natural environment from the devastating effects of invasive species is an important part of the work carried out by Reddy and his team.