Emerald ash borer (EAB), Agrilus planipennis Fairmaire, is a non-native beetle that was discovered in southeastern Michigan  in 2002. The larvae feed on the inner bark of ash trees, disrupting the tree’s ability to transport water and nutrients and kills all native ash trees (Fraxinus spp.). Emerald ash borer is now found in 48 states and several Canadian provinces.

EAB was discovered in Tompkins County for the first time in 2018, including on the Cornell campus and within Cornell Botanic Gardens. We are actively managing EAB in ash tree collections within the F. R. Newman Arboretum through the use of systemic pesticides. Within our natural areas, ash trees make up 5-30 percent of the mature tree canopy. While selected ash trees are also being treated with pesticides, over 1,700 trees that posed a safety risk to developed infrastructure were removed between 2019-2023.

Conserving Ash

Cornell Botanic Gardens is also working on conserving white (Fraxinus americana), green (F. pennsylvanica), and black (F. nigra) ash through propagating lingering ash. A lingering ash is a mature, native, untreated ash tree, typically 4 inches or more in diameter at breast height (about 4.5 feet above the ground), that remains healthy for at least two years after at least 95% of nearby mature ash trees have died from emerald ash borer infestation.

Propagating lingering ash involves collecting scion (e.g. twig samples) from these trees, propagating green ash rootstock, and then grafting the rootstock to the scion through a specialized grafting process known as hot callus grafting. Once grafted, the trees are grown in our nursery facility for two years before being planted out in field sites known as conservation banks. The goal of the project is to plant 50 – 60 genotypes (e.g. genetically different individuals) with five replicates each (e.g. five clones) for a total of 250 trees for all three ash species. These trees will be protected from EAB with pesticide applications.  

When the conservation bank trees are large enough, scion will be collected from each and grown on following the process above, until these new trees are large enough to be tested for resistance in a research planting. Testing for resistance, formally called a bioassay, will involve discontinuing pesticide treatments to allow EAB to naturally attack the trees. Staff will then collect data on tree health (e.g. canopy size and condition, stem growth, etc.) to quantify the level of a tree's resistance to EAB.  The analysis will also quantify and compare tree health levels of known non-resistant individuals, known as susceptible controls, that were included in the research planting.   

Surviving lingering ash trees and/or crosses of surviving trees will then be converted into a seed orchard, which will generate seed and eventually ash tree seedlings to ultimately restore green, white, and black ash to our forests.

What  can you do?

Individuals can assist in ash conservation by helping identify lingering ash, particularly black and green ash, using the TreeSnap app. Tag trees you find in your community, on your property, or out in the wild using TreeSnap. Scientists will use the data you collect to locate trees for further evaluation and potential scion collection.