The Essentials: What you need to understand aerial spraying in forestry

Dr. Robert Wagner

Comments from Robert G. Wagner, Professor and head of Forestry and Natural Resources, Purdue University, and formerly Henry W. Saunders Distinguished Professor, School of Forest Resources, University of Maine.

Fields of expertise: Academic and research leadership, industry/university partnerships, silviculture, forest management, forest regeneration, vegetation ecology and management. Robert Wagner CV

Forest managers must be able to determine which tree species make up future forest

In order to successfully manage forests to achieve ecological or economic goals for the people of Maine, foresters must be able to promote the kinds of tree species needed to achieve specific forest management goals. This is a core principle that determines whether forestry is a viable business or public enterprise or whether it is a total failure. Decades of research from around the world (Wagner et al. 2006) have clearly shown that effectively managing vegetation is vital to the success of forest regeneration. Indeed, one of the longest running studies in the world, the Austin Pond study in northern Maine, has clearly demonstrated the important role that herbicides play in providing for successful conifer regeneration over many decades (Olson et al. 2012, Bataineh et al. 2013). The inability to use herbicides, especially glyphosate, will lead to forest regeneration failures in many places that will have negative repercussions for many decades to come.

Herbicides are vital for preventing the spread of invasive exotic plants in Maine’s forests

Invasive plant species are threatening native tree regeneration in forests across the United States. A number of invasive plant species are increasing in abundance across Maine’s forests every year. The Maine Natural Areas Program has identified 52 plants species that are severely invasive, and 31 species considered to be very invasive. Herbicides, especially glyphosate, are highly effective, and in most cases, the only effective and affordable tool for combating the spread of invasive exotic plants in Maine’s forests. Loss of this safe and effective tool will severely reduce the ability of forest managers to help stop the spread of invasive exotic plants.

Photo by Lonnie S. Jandreau. Forester, Prentiss & Carlisle

Herbicides are important tools for providing critical habitat for snowshoe hare and Canada lynx

Research has shown that snowshoe hare, a primary prey species of Canada lynx and other major forest carnivores, prefer habitats with high densities of young conifer regeneration. These conditions were provided in abundance following the salvage cutting and subsequent herbicide spraying following the spruce budworm outbreak of the 1970s. The increases in snowshoe hare populations were followed by substantial increases in Canada lynx populations (Simons-Legaard et al. 2013) and produced the largest lynx populations in the lower 48 states. Reduction in the use of harvesting that produces large forest openings and herbicide treatment in recent decades is associated with a projected decline in lynx habitat in the coming decades. Herbicides, particularly glyphosate, are important tools used by professional foresters to create the young, conifer-dominated habitats that are needed to promote Canada lynx and other major forest carnivores in Maine’s forests.

Reducing abundance of diseased beech in Maine’s forests

The abundance of American beech has increased substantially across the Northeastern U.S. forests over the past three decades (Bose et al. 2017). Beech has been shown to competitively exclude more desirable tree species such as sugar maple and yellow birch. Since beech across Maine is also universally infected with the invasive beech-bark disease, reducing its spread in portions of Maine forests is important to providing desirable wildlife habitat and healthier forest stands. Glyphosate has been shown to be one of the most effective herbicides in controlling beech (Nelson and Wagner 2011) and is the only affordable approach to addressing the beech problem. The loss of glyphosate will prevent forest managers from reducing the dominance and spread of diseased beech in many circumstances. Read American Beech — A Tree in Trouble

Increased carbon sequestration comes from a larger wood products pool

The important role of forests in sequestering carbon comes not just from carbon in trees and vegetation itself, but also in the carbon that can be sequestered synergistically in wood products, the use of wood energy, as well as from the forested landscape (Lippke et al. 2011, Cameron et al. 2013, Oliver et al. 2016). Therefore, long-term enhancements in carbon sequestration in Maine’s forests should also consider the ability of the forest to contribute to the long-term wood products pool. The Austin Pond study in northern Maine has clearly demonstrated the crucial role that herbicides can play in producing commercially viable forests that will be able to contribute to the wood products pools of the future (Olson et al. 2012, Bataineh et al. 2013). The loss of herbicides, therefore, could reduce the overall ability of Maine’s forest to sequester carbon by reducing the successful regeneration of commercially viable tree species and thereby reducing the abundance of forest species and stand conditions that can make a greater contribution to the long-term wood products pool, not to mention the associated gains in the state’s economy.

MFPC answers frequently asked questions

What does the EPA say about glyphosate?

When it comes to safety assessments, glyphosate is among the most extensively tested pesticides on the market. Evaluations spanning more than 40 years, and the overwhelming conclusion of experts and regulators worldwide, support the safety of glyphosate and that glyphosate does not cause cancer.

When it comes to safety assessments, glyphosate is among the most extensively tested pesticides on the market. Evaluations spanning more than 40 years, and the overwhelming conclusion of experts and regulators worldwide, support the safety of glyphosate and that glyphosate does not cause cancer. Regulatory authorities routinely review all approved pesticide products. Most recently, in January 2020, the U.S. EPA published its Interim Registration Review Decision on glyphosate and stated EPA scientists performed an independent evaluation of available data for glyphosate and found:

  • No risks of concern to human health from current uses of glyphosate. Glyphosate products used according to label directions do not result in risks to children or adults.
  • No indication that children are more sensitive to glyphosate. After evaluating numerous studies from a variety of sources, the Agency found no indication that children are more sensitive to glyphosate from in utero or post-natal exposure. As part of the human health risk assessment, the Agency evaluated all populations, including infants, children and women of child-bearing age, and found no risks of concern from ingesting food with glyphosate residues. EPA also found no risks of concern for children entering or playing on residential areas treated with glyphosate.
  • No evidence that glyphosate causes cancer in humans. The Agency concluded that glyphosate is not likely to be carcinogenic to humans. EPA considered a significantly more extensive and relevant dataset than the International Agency on the Research for Cancer (IARC). EPA’s database includes studies submitted to support registration of glyphosate and studies EPA identified in the open literature.
  • EPA considered a significantly more extensive and relevant dataset than the International Agency on the Research for Cancer (IARC). EPA’s database includes studies submitted to support registration of glyphosate and studies EPA identified in the open literature. For instance, IARC only considered eight animal carcinogenicity studies while EPA used 15 acceptable carcinogenicity studies. EPA does not agree with IARC’s conclusion that glyphosate is “probably carcinogenic to humans.”
  • EPA’s cancer classification is consistent with other international expert panels and regulatory authorities, including the Canadian Pest Management Regulatory Agency, Australian Pesticide and Veterinary Medicines Authority, European Food Safety Authority, European Chemicals Agency, German Federal Institute for Occupational Safety and Health, New Zealand Environmental Protection Authority, and the Food Safety Commission of Japan and the Joint Food and Agriculture Organization/World Health Organization (FAO/WHO) Meeting on Pesticide Residues (JMPR).
  • For more information, read the Revised Glyphosate Issue Paper: Evaluation of Carcinogenic Potential “EPA has thoroughly evaluated potential human health risk associated with exposure to glyphosate and determined that there are no risks to human health from the current registered uses of glyphosate and that glyphosate is not likely to be carcinogenic to humans.”
  • No indication that glyphosate is an endocrine disruptor. Glyphosate has undergone Tier I screening under EPA’s Endocrine Disruptor Screening Program. Based on all available information, EPA concluded, using a weight-of-evidence approach, that the existing data do not indicate that glyphosate has the potential to interact with the estrogen, androgen or thyroid signaling pathways. The screening program did not indicate the need for additional testing for glyphosate. All registered glyphosate uses have value for weed control in agriculture and non-agricultural land management.
  • In addition, The National Pesticide Information Center reports that “in humans, glyphosate does not easily pass through the skin. Glyphosate that is absorbed or ingested will pass through the body relatively quickly. The vast majority of glyphosate leaves the body in urine and feces without being changed into another chemical.
  • Also it’s important to keep in mind that most studies have focused on agriculture, not forestry where trees would be treated perhaps one or twice in 40-to 80 years.

What did Canada’s in-depth research conclude about glyphosate? Health Canada’s Pest Management Regulatory Agency (PMRA)recently conducted an in-depth analysis of the latest scientific data on assessed the potential human health risk of glyphosate from drinking water, food, occupational and bystander exposure, as well as the environmental risk to non-target organisms and sale and use in Canada in 2017 and concluded:

  • Glyphosate is not genotoxic and is unlikely to pose a human cancer risk.
             o Dietary (food and drinking water) exposure associated with the use of glyphosate is not expected                 to pose a risk of concern to human health.
            o  Occupational and residential risks associated with the use of glyphosate are not of concern,                           provided that updated label instructions are followed.
  • The environmental assessment concluded that spray buffer zones are necessary to mitigate potential risks to non-target species (for example, vegetation near treated areas, aquatic invertebrates and fish) from spray drift.
  • When used according to revised label directions, glyphosate products are not expected to pose risks of concern to the environment.
  • All registered glyphosate uses have value for weed control in agriculture and non-agricultural land management. Read more.