Tom's Blog

Thursday, September 18, 2014

Buckthorn eradication: results of a five year study

Because of buckthorn's importance, there have been many earlier posts from Tom's Blog. A list of these posts, with URLs, can be found at this link.
Buckthorn is probably the most difficult shrub to get rid of in prairie and savanna restoration (it’s at the top of IPAW’s list). Because of its strong allelopathic nature, if unchecked it can form extensive monocultures.

Removal of buckthorn requires the use of an herbicide, either as a basal bark or cut stem application. Although these treatments are very effective, they do not eradicate an infestation for two reasons:
  •  There is almost always an extensive seed bank. This is fairly easy to control, and only persists for several years.
  • There are numerous dormant root masses capable of sending up new shoots, and these are a much more difficult problem. Experience has shown that these viable structures can remain alive for at least 15 years, perhaps longer, even if any new shoots they form are mowed or top-killed by annual fire.

What I am reporting here are the results of a long-term study I carried out at Pleasant Valley Conservancy. The area used was a small part of a much larger bur oak savanna which was first cleared of buckthorn in the 1999-2000 period. The initial fairly large-diameter shrubs were killed by basal bark treatment with Garlon 4 in oil. After the shrubs had died (which took about two years) they were removed when the savanna was restored. Since then, the site has been burned annually.

Despite annual burns, new buckthorn shoots kept appearing every year. Each shoot was part of an extensive underground root mass. Five years ago I decided to see how long it would take to get rid of them. I think I have finally succeeded.

Starting in 2010 I canvassed the site carefully and sprayed with Garlon each buckthorn shoot, counting as I proceeded. In the three early years, when there were lots of shoots, I returned over and over again at 2-3 week intervals. At the end of the season, I made sure that there were no live buckthorn shoots left.

The table shows the results. I should emphasize that the effectiveness of my spraying is not in question. Thus, a shoot found in 2012 is not one that had been sprayed in 2011 and not killed. My conclusion is that in this small area there were many dormant root masses, but not all of them left dormancy the same year.

Buckthorn shoots sprayed in study area
Year total
not recorded

Another conclusion is that it is possible to eradicate a site of buckthorn, but the site must be revisited in multiple years.

One might ask what effect this multiple spraying might have on the natural flora. That’s a lot of Garlon! I should emphasize that I was careful with my spraying, making sure that nearby “good” plants were not treated.  The table below is the species check list I made this year, when no spraying had been done. The diversity is satisfyingly high! Note the presence of Gentiana alba, a State Threatened species. There are actually two separate patches of this species, one of which has numerous stems, and both patches flowered.

Latin name
Common name
Actaea rubra
Red baneberry
Agrimonia gryposepala
Tall agrimony
Allium cernuum
Nodding wild onion
Amorpha canescens
Andropogon gerardii
Big bluestem
Anemone virginiana
Woodland thimbleweed
Asclepias syriaca
Common milkweed
Asclepias verticillata
Whorled milkweed
Aster ericoides
Heath aster
Aster novae-angliae
New England aster
Aster sagittifolius
Arrow-leaved aster
Campanula americana
Tall bellflower
Desmodium glutinosum
Pointed tick-trefoil
Desmodium illinoense
Illinois tick-trefoil
Elymus hystrix
Bottlebrush grass
Eupatorium altissimum
Tall boneset
Eupatorium purpureum
Purple joe-pye weed
Gentiana alba
Cream gentian
Gentianella quinquefolia
Stiff gentian
Heliopsis helianthoides
Ox-eye sunflower
Hieracium kalmii
Canada hawkweed
Lactuca canadensis
Tall lettuce
Monarda fistulosa
Wild bergamot
Ratibida pinnata
Yellow coneflower
Rudbeckia hirta
Black-eyed Susan
Schizachyrium scoparium
Little bluestem
Silphium integrifolium
Silphium terebinthinaceum
Prairie dock
Solidago rigida
Stiff goldenrod
Solidago speciosa
Showy goldenrod
Sorghastrum nutans
Indian grass
Sporobolus heterolepis
Prairie dropseed
Toxicodendron radicans
Poison ivy
Tradescantia ohiensis
Common spiderwort
Verbena stricta
Hoary vervain
Zizia aurea
Golden Alexander


Post a Comment

Subscribe to Post Comments [Atom]

<< Home