Tom's Blog

Friday, May 27, 2011

Story of a small buckthorn area

We've been working for over 10 years to eradicate buckthorn in some of our savanna areas. It is hard now to realize how dense the buckthorn was when we started. Generally, you could not see past the first line of buckthorn plants into the interior of a unit. Knocking the buckthorn back, by basal bark and cut-and-treat, got rid of these large thickets, but due to seed bank and presence of dormant root masses, there was plenty of new growth. How to eradicate permanently?

This is the story of a single area where I am now convinced that I have successfully eradicated buckthorn. The area is Unit 19A, a long, narrow unit on top of the dolomite, where buckthorn had been well established. In the winter of 1998 the buckthorn had been basal barked (Garlon 4), which effectively killed the large stems. In the spring of 1999 no shoots came up next to the treated stems.

However, during the summer small shoots sprang up throughout the unit. They were effectively killed (1999 or 2000) by basal bark treatment, using a sponge-type applicator.

Unfortunately, by this time our attention had been turned to complete clearing of the south-facing slope and the ridge-top savannas, so this area was neglected (overlooked).

By 2006 the buckthorn was back in full force, and I decided to use this as a test area, small enough to deal with, but large enough so that there was plenty of buckthorn.

In early August 2006 the whole buckthorn area was removed using a Stihl brush cutter. All cut stems were removed, and any stems missed with the Stihl were hand cut. Because the density was so high, the cut stems were not treated with herbicide. Rather, the cut plants were allowed to resprout, which they did with a vengeance.

Then in late Sept 2006 these resprouts were foliar sprayed, using fosamine (Krenite; a woody plant herbicide). (One patch was left unsprayed as a control.) At the time of spraying, the buckthorn resprouts were about 6-12 inches tall.

Observations showed that these resprouts were NOT from underground root masses. Rather, each resprout was from the first lateral bud below the cut stem. (See photo to left) Thus, cutting each stem eliminated apical dominance, permitting lateral buds to become activated.

At the time of spraying, the buckthorn stem density was about 75 sprouts were square meter! (See photo below.)

Observations made the following late summer of 2007 showed that the foliar spraying had greatly delayed buckthorn growth but had not eliminated it. Lots of shoots 2-4 feet tall. There was, however, lots of native vegetation becoming established, including zig zag goldenrod, arrow-leaf aster, purple Joe Pye weed, bottle brush grass, and white snakeroot. (The buckthorn control area that had not be sprayed in 2006 was then treated with Garlon 3A (foliar).

At this point, the very dense buckthorn patch had been eliminated, although there were scattered viable buckthorn stems throughout the unit. For the next two years (2008 and 2009), these stems were sprayed with foliar Garlon 3A in early October, at a time when most native vegetation had senesced. Then in mid-summer 2010 all remaining viable buckthorn stems were treated with Garlon 4 basal bark, using the sponge stick technique. Since by this time, viable buckthorn stems were quite scattered, the sponge technique was quite easy to carry out. Observations a few weeks after treatment showed that all treated buckthorn stems had died.

During the three years that the remaining buckthorn plants were being eliminated, the native vegetation was proliferating. Presumably because the buckthorn stem density was low, buckthorn allelopathy was not being exhibited.

Last November, Unit 19A was burned when we burned the north woods. Since no viable buckthorn stems were visible, the burn may not have had any effect on the buckthorn, but it probably greatly stimulated the growth of native vegetation this spring.

Returning to this area now, I was unable to find any living buckthorns, but very lush native vegetation. The whole Unit looks very good.

Because this unit is adjacent to the main trail along the ridge, it is very easy to monitor for buckthorn resurgence. We'll be keeping an eye on it, but I am very encouraged. This may be the first site at Pleasant Valley Conservancy where buckthorn has been definitvely eradicated. Lots of work, but worth it!


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