Posted: April 6, 2020

Brushpiles is the opinion page of Forest Leaves. It’s a place for you to write in and share your reactions and thoughts. The following piece was excerpted from an article in the PA Forest Stewards newsletter by Mike and Laura Jackson, PA Forest Stewards, in response to questions received about glyphosate after the article by Jonathan Kays appeared in the Winter 2020 issue.

Like many forest landowners, we are dealing with a lot of invasive plant species: Japanese vine honeysuckle, Japanese barberry, Japanese stiltgrass, Autumn olive, privet, and multiflora rose are the big ones. We didn't use much herbicide at first, preferring to cut, dig, and pull our way out of the invasive plant jungle. We finally conceded that we were losing the battle and knew that more drastic action had to be taken. We attended workshops and did a lot of research to learn more about herbicides and the correct way to apply them. The weapon of choice for foliar sprays and cut stump treatment was most often glyphosate (found in Roundup®) with added surfactant. A surfactant is a chemical that helps the herbicide adhere to the leaf.

Although herbicides go through extensive testing in order to be approved for use, testing on amphibians was often lacking. This was - and still is - a real concern, so we spent many hours doing literature searches to find out what is known about the impacts of herbicides on amphibians.

We found that biologists have been studying amphibian impacts for about 20 years, but it's still controversial whether forestry applications of herbicides can be lethal to amphibians. While Round-up® does break down relatively quickly compared to many other herbicides, the problem for tadpoles is that Roundup®, even though it strongly binds to soil, is highly soluble in water(1). In some cases, sublethal doses created other behavioral and morphological issues in tadpoles.

Rodeo® is a glyphosate-based product that is approved to control emergent aquatic vegetation because it lacks the surfactant found in Roundup®. Although we learned that proper applications of Rodeo® do not kill fish, we also learned that amphibians were not used in studies that assessed the safety of Rodeo®(2).

Researchers also found that herbicides can produce sublethal effects on wildlife, affecting their fitness. Amphibians are the most threatened group of vertebrates on our planet due to habitat loss and sensitivity to chemical pollution. Some researchers hypothesize that the spread of the chytrid fungus, which is deadly to frogs, may occur because herbicides have affected the frogs' ability to with-stand the fungal attack(3).

A forest landowner's decision to use herbicide can have far-reaching effects on unintended targets. Ultimately, we decided to use glyphosate, but on a very controlled basis. We only use herbicides when:

  • There is no wind
  • Rain is not predicted for at least 24 hours
  • The treatment site is far from water with a lot of vegetative buffer
  • We can treat individual plants very selectively so very little, if any, herbicide hits the ground

To be fair, much of the laboratory glyphosate research methods have been criticized because doses of herbicide were higher in lab studies than what might be found in forestry applications when the recommended dosages and practices were followed(4). We hope this information will help other forest landowners make informed decisions about using herbicides.


References:

1 https://www.biology.pitt.edu/sites/default/files/facilities-images/Relyea%20286.pdf
2 https://bioone.org/journals/journal-of-herpetology/volume-51/issue-3/16-092/
Rodeo-Herbicide-Negatively-Affects-Blanchards-Cricket-Frogs-Acris-blanchardi-Survival/10.1670/16-092.full

3 https://www.unboundmedicine.com/medline/citation/28679726/
Chronic_exposure_to_a_glyphosate-based_herbicide_makes_toad_larvae_more_toxic.2017

4 https://www.ncasi.org/wp-content/uploads/2019/02/tb970.pdf

Center for Private Forests

Address

416 Forest Resources Building
University Park, PA 16802

Center for Private Forests

Address

416 Forest Resources Building
University Park, PA 16802