A wilt disease (Verticillium albo-atrum), discovered in SE Pennsylvania, has been causing unprecedented wilt and mortality of invasive tree-of-heaven (Ailanthus altissima) and could be considered a potential bio-control agent.
The most common approach is to identify and release insects or diseases known to affect the specified interfering plant. Biological control measures reduce interfering plant populations to manageable levels rather than eradicating them completely. After the initial biological control agent introduction it may take years before their populations are present in large enough numbers to control targeted plants. Biological controls can provide long-term, inexpensive solutions to many interfering plant problems. However, few biological control measures are known for interfering plants.
To find appropriate biological controls researchers search a plant's native range to identify pests that limit its spread. The key to successful biocontrol is finding the insect or disease that will thrive after introduction, controlling only the targeted interfering plant species. The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) is responsible for controlling introductions of species brought into the United States for biological control of plants.
Grazing by domestic livestock and white-tailed deer is a form of biological control. Livestock and deer grazing on palatable interfering vegetation can control some species. This form of control rarely results in eradication. Most livestock species are preferential grazers. This means they select the most palatable species first. Deer in particular will tend to browse the most desired tree species from a woodlot and can actually shift species composition towards less desirable interfering plants. Using goats to control interfering plant species in woodlots has met with some success. Cornell University and Penn State cooperated on several studies using "Goats in the Woods". The studies showed how to manage herd stocking levels; how to assess success potential; and how to sustain forest and herd health.