As many Madisonians know, the Emerald Ash Borer (EAB) was confirmed on the north side of Madison in November 2013. By April 2015, EAB was found in other areas of Madison, including areas neighboring the Arboretum’s west side.
Arboretum staff and volunteers continue to monitor the property for signs of the insect. Although ash trees are not widespread in the Arboretum, there are some in the woodland communities as well as in the Longenecker Horticultural Garden (LHG). EAB is fatal to untreated ash trees, so treatment or removal are the two management options for urban or high-value trees. Ash trees in the Arboretum woodlands will be removed near trails and roadways for public safety, as infected forest trees would become a hazard to visitors when they die. Otherwise, ash trees in natural areas will be left untreated, in part to document the impact of EAB on trees here and watch for signs of potential resistance.
In LHG, EAB will be allowed to infest most of the ash specimens as a way to test resistance. These trees will be closely monitored and removed when necessary for public safety.
There are two trees in LHG of historic and conservation value, and they were recently treated against EAB. The first is the white ash (Fraxinus americana) cultivar ‘Autumn Purple,’ originally selected for its outstanding fall color and propagated by William Longenecker from a wild tree growing on the UW–Madison campus. The tree was planted in 1955. It was so prized by Longenecker that he requested some of his ashes be spread below the tree upon his death, as did his wife Sarah. The second is a blue ash (Fraxinus quadrangulata), the rarest of Wisconsin’s four native ash species. Wisconsin is at the northern edge of the species range, and the blue ash only occurs naturally in the southeastern part of the state. The LHG’s blue ash was selected from a tree growing in Waukesha County and added to the collection in 1960.
With a mission to conserve and restore native habitats, the Arboretum wanted to choose a treatment that would be effective against EAB with as little harmful impact on other living organisms as possible. After an extensive review of existing research, Arboretum staff decided to use the botanical insecticide TreeAzin for the two trees in LHG, hiring a local tree care company to assess the trees and manage the treatment. TreeAzin, a product from BioForest Technologies, Inc., is derived from an extract of the neem tree seed, and is listed with the Organic Review Materials Institute. Among insecticides, it seems to have the least impact on birds, earthworms, pollinators, and other non-target animal life, as well as water. The treatment method – injecting the chemical into the tree, rather than spraying it or drenching the soil – also minimizes impact beyond the target insect.
Representatives from Tree Health Management, LLC, and BioForest Technologies, Inc., held a public treatment demonstration at the Arboretum on June 2, 2015, to discuss TreeAzin, tree assessment and care, and the insecticide application. Paul Bolan, VP of BioForest Technologies, did the injection treatment. The Arboretum welcomed the opportunity to present information about an alternative approach to treating ash trees over the more common injections of TREE-äge (emamectin benzoate) or chemical soil drenches; the latter having the greatest residual impact while being less effective than injections. TreeAzin is less potent than TREE-äge, and will require more applications, but we decided the potentially lower environmental impact, and the opportunity to diversify treatment options, was worth the tradeoff.
Homeowners with ash trees on their property will need to decide which option—treatment or removal—is best for them. We highly recommend that people have their ash trees assessed by a licensed arborist to help make an informed decision. If you remove an ash tree from your landscape there are many considerations, from site conditions to biodiversity, in choosing a replacement tree. Our tree replacement list can help you decide what to plant in its place if you would like a tree species that is native to Wisconsin.