For Vermont, Biocontrol is Best Control Available

What follows is the Vermont experience with biocontrols as a Purple Loosestrife control. The notes below are excerpted from "The 2000 Purple Loosestrife Control Program Annual Report". Their program has existed since 1996.

Biological control works by using a plant's natural enemies against it. In 1992, five insect species that feed on purple loosestrife in Europe were approved and introduced as biological control agents in North America. Years of rigorous testing proved these insects to be host-specific to purple loosestrife and not feed on agricultural crops.

In 1996, Vermont became one of 34 States using biocontrols. They did so with the guidance of Bernd Blossey of Cornell University, and some thoughtful information-gathering.

Traditional controls comparison demonstrates a biocontrol is the better alternative than no action, or traditional controls. A comparison matrix in the Vermont study compares control methods in terms of

1. effectiveness (poor, moderate, or good),
2. risk to native plants (none, low, moderate, or high risk),
3. and costs (inexpensive, moderate, or expensive).

Using these three criteria, biocontrol is the best tool we have at this time.

Chemical control - is good in the short term, but needs reapplication over time. Herbicides are not species specific and few can be used near water. They are expensive in terms of money, time and risk to native ecosystems.

Water manipulation - is mostly poor because it spreads seed and plant fragments. This method is a high risk to native plants that cannot tolerate the extent of flooding that purple loosestrife can. Water manipulation is expensive in terms of money and native species damage.

Replacement with native vegetation - has a moderate effectiveness if areas are drawn down and have invasive seed in the seed bank. This method has no impact on existing native plants. It is an inexpensive method, IF native seed is available.

Cutting and mowing - results in poor control after and during flowering due to the mechanical methods ability to spread the plant and seeds. If done before flowering, moderate success is possible.

Hand removal - is effective in small, newly established stands; but it is difficult to remove all plant parts with certainty. In established stands, hand removal is virtually impossible.

Biological control - is considered effective, although it sometimes takes years to see the results; and possibly does not eradicate the plant completely. It does offer a long term and self-sustaining solution. Biocontrols are known to reduce purple loosestrife populations to less than 5% of the original size.

Biocontrol release by Bailey Elementary students with MNDOT.

Use and Results of a Biocontrol

The States of New York, Illinois, Minnesota, and Michigan have had highly effective results with biocontrols. Their experiences were shared with Vermont. The State of Vermont used a Minnesota Department of Natural Resources 1997 publication, Biological Control of Purple Loosestrife - a Rearing Guide for Galerucella spp. The Vermont rearing effort began in April 2000 with the collection of host purple loosestrife rearing plants and with beetles from Cornell University. To date, more than 141,000 beetles have been released in carefully selected infestations. This year 300 root-boring weevils (Hylobius transversovittatus) were also introduced for a double whammy to purple loosestrife control. Monitoring of the 20 sites is done through GPS recording and photographs.

Although effects of biological controls often take three to four years to produce visible results, 2001 has seen some dramatic results of flourishing beetle populations. The decrease of purple loosestrife growth rate, height, number of flower buds and inflorescenses is significant. Native cattail populations have already begun to rebound, increasing in cover by 197% since 1999. Monitoring of the program is critical and has begun to yield important data. Unfortunately, site development has eliminated 4 of the original sites. However, as Vermont improves its ability to rear the beetles, successful release sites will continue to increase.