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Why No-Spray Buffer Zones Help Ease Environmental Concerns in Invasive Tree Management

WESTMINISTER, Colorado. November 10, 2023— Invasive conifers are to New Zealand ecosystems what waterhemp is to U.S. soybean farmers. Trees such as lodgewood pine are weeds that quickly outcompete local flora. This has led New Zealand to launch The National Wilding Conifer Management Programme to manage the problem.

An article in the journal Invasive Plant Science and Management shows how scientists are dealing with the invasive conifers.  

One way to manage these infestations is to aerially apply a herbicide mixture of triclopyr, dicamba, picloram, and aminopyralid that’s locally known as TDPA. However, concerns have mounted that TDPA rates used to control invasive conifers may cause environmental problems by persisting in the forest floor, soil and water.

So, scientists studied persistence of all herbicides in cast needles, forest floor (including litter) and soil following aerial application at three New Zealand sites. They collected water from a local stream at two sites and across all sites in cast needles following spraying.

Scientists found all herbicides persisted in dead tree needles overlaying the soil for up to two years. However, just triclopyr accumulated in the soil, and it declined to below detection levels within one year.

Scientists also detected all herbicides in stream water on the day of spray application at one site and during a rainfall event one month later. However, sites where a 30-meter (32.82 yards) no-spray buffer zone did not exceed New Zealand environmental and drinking water standards.

“The studies showed that forest litter retains most of the herbicide mixture,” says the Chair of the Wilding Pine Network, an independent body of community groups and trusts involved in invasive conifer control. “They also found maintaining no-spray buffer zones of 30 meters (32.82 yards) near riparian areas is critical in protection waterways from herbicide run-off.”

About Invasive Plant Science and Management

Invasive Plant Science and Management is a journal of the Weed Science Society of America, a nonprofit scientific society focused on weeds and their impact on the environment. The publication presents peer-reviewed original research related to all aspects of weed science, including the biology, ecology, physiology, management and control of weeds. To learn more, visit www.wssa.net.