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Common buckthorn, Rhamnus cathartica, fills the understory of this hardwood forest. Buckthorn retains its green leaves longer than most other woody plants. |
Anyone who’s tried to manage invasive common buckthorn (Rhamnus cathartica) knows it’s a battle. Pull it out and seedlings take its place. Cut it and it grows back, especially if the cut stump isn’t treated with herbicide. Buckthorn baggies or other covers for cut stumps are an option, but not a practical one for large, dense infestations. The search for insects that target buckthorn hasn’t succeeded yet, either.
Although these difficulties are frustrating, researchers at
the University of Minnesota haven’t given up. Just the opposite: They are
leading several investigations of potential solutions. Their studies
of biodiversity, fungi, goats and other possible buckthorn remedies are shedding light on what works, what doesn’t and what to try
next. Here are summaries of some of their
efforts.
Using biodiversity to control buckthorn
The University’s “Cover It Up!” studies investigate the use
of plants to suppress regrowth of common buckthorn after it is removed. Two
phases are completed and a third is in progress, all asking questions about
which plants are best at outcompeting buckthorn, how best to plant them, and
how managing fire and deer browsing affects the success of using plants to
control buckthorn.
The researchers were surprised by one of their findings: Most
buckthorn seeds remain viable in the soil for only 1-2 years, not the commonly
thought 6 years. That means seedlings will be abundant for the first year or
two after buckthorn is removed but should taper after that, assuming new seeds
aren’t introduced.
Phase 3 of the project is underway. When it’s done,
researchers hope to offer buckthorn solutions that are both affordable and
practical. For more information, see the Cover
It Up! project page.
Can fungi help?
In some parts of Minnesota and Wisconsin, buckthorn is dying,
possibly from canker rot, root rot and other fungal diseases. Researchers are
trying to identify the fungi infecting the trees and how they may be used to
manage buckthorn stands. Employing fungi would reduce the use of herbicides, an
important benefit when working near water or other places where protection of
other resources is paramount. The project began in January 2023 and will continue
for another two years. See the project
website for more information and updates.
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| Orange growths of crown rust on common buckthorn. |
What about goats?
A study to evaluate the effectiveness of goat grazing on
buckthorn ended in 2021. Researchers found that although goats can control
buckthorn, the benefit is temporary. Buckthorn can rebound after grazing unless
other control measures follow.
Grazing goats are also at risk of eating snails or slugs
that are intermediate hosts for the brainworm Parastronguloides tenuis,
which can cause fatal neurological disease. Co-grazing waterfowl with goats has
been suggested to reduce that risk, so the study also examined the effect of waterfowl
on the abundance of snails or slugs. In a 2022
paper published in EcoHealth, the researchers found that where goats grazed
alone, the abundance of snails and slugs increased, but where ducks and geese
were included with goats, the increase didn’t occur. They also found that
waterfowl didn’t affect the overall diversity of the snails and slugs, which is
important to protect populations of native gastropods.
The researchers point out that while waterfowl can lower the
numbers of snails and slugs and therefore reduce the risk to goats of acquiring
brainworms, more study is needed to learn if this also reduces the incidence of
the disease.
More challenges of goat grazing are discussed in this paper
and several others linked at the project
website.
